AyuGramDesktop/Telegram/SourceFiles/iv/editor/iv_editor_state.cpp

/*
This file is part of Telegram Desktop,
the official desktop application for the Telegram messaging service.

For license and copyright information please follow this link:
https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
*/
#include "iv/editor/iv_editor_state.h"

#include <algorithm>
#include <utility>

namespace Iv::Editor {
namespace {

using Block = RichPage::Block;
using BlockContainerKind = State::BlockContainerKind;
using BlockContainerPath = State::BlockContainerPath;
using BlockKind = RichPage::BlockKind;
using BlockPath = State::BlockPath;
using FieldMode = State::FieldMode;
using InsertBlockType = State::InsertBlockType;
using InsertionAnchor = State::InsertionAnchor;
using LeafKind = State::LeafKind;
using LeafPath = State::LeafPath;
using ListItem = RichPage::ListItem;
using ListKind = RichPage::ListKind;
using PreparedBlockContainerKind = Markdown::PreparedEditBlockContainerKind;
using PreparedEditLeafKind = Markdown::PreparedEditLeafKind;
using PreparedEditSelectionKind = Markdown::PreparedEditSelectionKind;
using PreparedBlockContainerPath = Markdown::PreparedEditBlockContainerPath;
using PreparedBlockContainerStep = Markdown::PreparedEditBlockContainerStep;
using PreparedEditSelection = Markdown::PreparedEditSelection;
using RemovalKind = State::RemovalKind;
using RemovalTarget = State::RemovalTarget;
using RichText = RichPage::RichText;
using TableCell = RichPage::TableCell;
using TaskState = RichPage::TaskState;
using TextNodeDescriptor = State::TextNodeDescriptor;

[[nodiscard]] BlockContainerPath BlockChildrenContainer(BlockPath path) {
	auto result = std::move(path.container);
	result.steps.push_back({
		.kind = BlockContainerKind::BlockChildren,
		.blockIndex = path.index,
	});
	return result;
}

[[nodiscard]] BlockContainerPath ListItemChildrenContainer(
		BlockPath path,
		int itemIndex) {
	auto result = std::move(path.container);
	result.steps.push_back({
		.kind = BlockContainerKind::ListItemChildren,
		.blockIndex = path.index,
		.listItemIndex = itemIndex,
	});
	return result;
}

[[nodiscard]] PreparedBlockContainerPath ToPreparedBlockContainerPath(
		const BlockContainerPath &path) {
	auto result = PreparedBlockContainerPath();
	result.steps.reserve(path.steps.size());
	for (const auto &step : path.steps) {
		auto converted = PreparedBlockContainerStep();
		converted.blockIndex = step.blockIndex;
		converted.listItemIndex = step.listItemIndex;
		switch (step.kind) {
		case BlockContainerKind::Root:
			continue;
		case BlockContainerKind::BlockChildren:
			converted.kind = PreparedBlockContainerKind::BlockChildren;
			break;
		case BlockContainerKind::ListItemChildren:
			converted.kind = PreparedBlockContainerKind::ListItemChildren;
			break;
		}
		result.steps.push_back(converted);
	}
	return result;
}

[[nodiscard]] bool ContainerHasPrefix(
		const BlockContainerPath &path,
		const BlockContainerPath &prefix) {
	if (path.steps.size() < prefix.steps.size()) {
		return false;
	}
	return std::equal(
		prefix.steps.begin(),
		prefix.steps.end(),
		path.steps.begin());
}

[[nodiscard]] bool IndexInRange(int index, int from, int till) {
	return (index >= from) && (index < till);
}

[[nodiscard]] std::optional<int> BlockIndexInContainer(
		const LeafPath &leaf,
		const BlockContainerPath &container) {
	if (leaf.block.container == container) {
		return leaf.block.index;
	}
	if (!ContainerHasPrefix(leaf.block.container, container)
		|| leaf.block.container.steps.size() <= container.steps.size()) {
		return std::nullopt;
	}
	const auto &step = leaf.block.container.steps[container.steps.size()];
	return (step.kind == BlockContainerKind::BlockChildren
			|| step.kind == BlockContainerKind::ListItemChildren)
		? std::make_optional(step.blockIndex)
		: std::nullopt;
}

[[nodiscard]] std::optional<int> ListItemIndexForLeaf(
		const LeafPath &leaf,
		const BlockPath &block) {
	if (leaf.block == block && leaf.kind == LeafKind::ListItemText) {
		return leaf.listItemIndex;
	}
	if (!ContainerHasPrefix(leaf.block.container, block.container)
		|| leaf.block.container.steps.size() <= block.container.steps.size()) {
		return std::nullopt;
	}
	const auto &step = leaf.block.container.steps[block.container.steps.size()];
	return (step.kind == BlockContainerKind::ListItemChildren
			&& step.blockIndex == block.index)
		? std::make_optional(step.listItemIndex)
		: std::nullopt;
}

[[nodiscard]] std::optional<int> TableRowIndexForLeaf(
		const LeafPath &leaf,
		const BlockPath &block) {
	if (!(leaf.block == block)) {
		return std::nullopt;
	}
	if (leaf.kind == LeafKind::BlockText) {
		return -1;
	}
	return (leaf.kind == LeafKind::TableCellText)
		? std::make_optional(leaf.tableRowIndex)
		: std::nullopt;
}

[[nodiscard]] std::optional<int> TableCellIndexForLeaf(
		const LeafPath &leaf,
		const BlockPath &block,
		int rowIndex) {
	return (leaf.block == block
			&& leaf.kind == LeafKind::TableCellText
			&& leaf.tableRowIndex == rowIndex)
		? std::make_optional(leaf.tableCellIndex)
		: std::nullopt;
}

[[nodiscard]] bool BlockCanOwnChildContainer(const Block &block) {
	return (block.kind == BlockKind::Quote)
		|| (block.kind == BlockKind::Details);
}

[[nodiscard]] bool BlockSupportsBlockText(const Block &block) {
	switch (block.kind) {
	case BlockKind::Heading:
	case BlockKind::Paragraph:
	case BlockKind::Footer:
	case BlockKind::Code:
	case BlockKind::Quote:
	case BlockKind::Table:
	case BlockKind::Details:
		return true;
	default:
		return false;
	}
}

[[nodiscard]] bool BlockSupportsBlockCaption(const Block &block) {
	switch (block.kind) {
	case BlockKind::Quote:
	case BlockKind::Photo:
	case BlockKind::Video:
	case BlockKind::Audio:
	case BlockKind::Map:
		return true;
	default:
		return false;
	}
}

[[nodiscard]] bool StringIsEmpty(const QString &text) {
	return text.trimmed().isEmpty();
}

[[nodiscard]] bool CanEditBlocks(const std::vector<Block> &blocks);

[[nodiscard]] bool CanEditBlock(const Block &block) {
	switch (block.kind) {
	case BlockKind::Heading:
	case BlockKind::Paragraph:
	case BlockKind::Footer:
	case BlockKind::Code:
	case BlockKind::Divider:
	case BlockKind::Anchor:
	case BlockKind::GroupedMedia:
	case BlockKind::Photo:
	case BlockKind::Video:
	case BlockKind::Audio:
	case BlockKind::Math:
	case BlockKind::Table:
	case BlockKind::Map:
		return true;
	case BlockKind::Quote:
	case BlockKind::Details:
		return CanEditBlocks(block.blocks);
	case BlockKind::List:
		return ranges::all_of(block.listItems, [](const ListItem &item) {
			return CanEditBlocks(item.blocks);
		});
	case BlockKind::Unsupported:
	case BlockKind::Thinking:
	case BlockKind::AuthorDate:
	case BlockKind::Embed:
	case BlockKind::EmbedPost:
	case BlockKind::Channel:
	case BlockKind::RelatedArticles:
		return false;
	}
	return false;
}

[[nodiscard]] bool CanEditBlocks(const std::vector<Block> &blocks) {
	return ranges::all_of(blocks, &CanEditBlock);
}

} // namespace

State::State()
: State(std::make_shared<RichPage>(), nullptr) {
}

State::State(
	std::shared_ptr<RichPage> richPage,
	std::shared_ptr<Markdown::MediaRuntime> mediaRuntime)
: _richPage(richPage ? std::move(richPage) : std::make_shared<RichPage>())
, _mediaRuntime(std::move(mediaRuntime)) {
	if (_richPage->blocks.empty()) {
		_richPage->blocks.push_back(MakeParagraphBlock());
	}
	rebuild();
}

const RichPage &State::richPage() const {
	return *_richPage;
}

const Markdown::MarkdownArticleContent &State::prepared() const {
	return _prepared;
}

const std::vector<TextNodeDescriptor> &State::textNodes() const {
	return _textNodes;
}

int State::textOrdinalForLeaf(
		const Markdown::PreparedEditLeafSource &source) const {
	const auto leaf = convertLeafPath(source);
	return leaf ? textNodeOrdinal(*leaf) : -1;
}

int State::textNodeCount() const {
	return int(_textNodes.size());
}

int State::activeTextOrdinal() const {
	return _activeTextOrdinal;
}

bool State::setActiveTextByOrdinal(int ordinal) {
	if (ordinal < 0 || ordinal >= textNodeCount()) {
		return false;
	}
	_activeTextOrdinal = ordinal;
	return true;
}

TextWithEntities State::activeText() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return TextWithEntities();
	}
	if (const auto current = richText(descriptor->leaf)) {
		return StripEditModeWrapperEntities(current->text);
	}
	if (const auto current = rawText(descriptor->leaf)) {
		return MakeText(*current);
	}
	return TextWithEntities();
}

void State::applyActiveText(TextWithEntities text) {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return;
	}
	if (auto current = richText(descriptor->leaf)) {
		current->text = std::move(text);
		rebuild();
		return;
	}
	if (auto current = rawText(descriptor->leaf)) {
		*current = std::move(text.text);
		rebuild();
	}
}

FieldMode State::activeFieldMode() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	return descriptor ? descriptor->mode : FieldMode::Rich;
}

QString State::activeRawText() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return QString();
	}
	if (const auto current = rawText(descriptor->leaf)) {
		return *current;
	}
	if (const auto current = richText(descriptor->leaf)) {
		return StripEditModeWrapperEntities(current->text).text;
	}
	return QString();
}

QString State::activePlaceholderText() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return QString();
	}
	const auto owner = block(descriptor->leaf.block);
	if (!owner) {
		return QString();
	}
	switch (descriptor->leaf.kind) {
	case LeafKind::BlockText:
		switch (owner->kind) {
		case BlockKind::Paragraph:
		case BlockKind::Footer:
		case BlockKind::Code:
		case BlockKind::Quote:
			return u"Text"_q;
		case BlockKind::Heading:
		case BlockKind::Details:
			return u"Header"_q;
		default:
			return QString();
		}
	case LeafKind::BlockCaption:
		switch (owner->kind) {
		case BlockKind::Quote:
		case BlockKind::Photo:
		case BlockKind::Video:
		case BlockKind::Audio:
		case BlockKind::Map:
			return u"Caption"_q;
		default:
			return QString();
		}
	case LeafKind::ListItemText:
		return u"Text"_q;
	case LeafKind::TableCellText:
		return u"Cell"_q;
	case LeafKind::MathFormula:
		return u"x^2 + y^2"_q;
	}
	return QString();
}

void State::applyActiveRawText(QString text) {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return;
	}
	if (auto current = rawText(descriptor->leaf)) {
		*current = std::move(text);
		rebuild();
		return;
	}
	if (auto current = richText(descriptor->leaf)) {
		current->text = MakeText(std::move(text));
		rebuild();
	}
}

std::optional<QString> State::codeBlockLanguage(int ordinal) const {
	const auto descriptor = textNode(ordinal);
	if (!descriptor || descriptor->leaf.kind != LeafKind::BlockText) {
		return std::nullopt;
	}
	const auto owner = block(descriptor->leaf.block);
	return (owner && owner->kind == BlockKind::Code)
		? std::make_optional(owner->language)
		: std::nullopt;
}

bool State::setCodeBlockLanguage(int ordinal, QString language) {
	const auto descriptor = textNode(ordinal);
	if (!descriptor || descriptor->leaf.kind != LeafKind::BlockText) {
		return false;
	}
	auto owner = block(descriptor->leaf.block);
	if (!owner || owner->kind != BlockKind::Code) {
		return false;
	}
	owner->language = std::move(language).trimmed();
	rebuild();
	return true;
}

bool State::toggleTaskState(
		const Markdown::PreparedEditListItemSource &source) {
	const auto blockPath = convertBlockPath(source.block);
	if (!blockPath) {
		return false;
	}
	auto item = listItem(*blockPath, source.listItemIndex);
	if (!item || item->taskState == TaskState::None) {
		return false;
	}
	item->taskState = (item->taskState == TaskState::Unchecked)
		? TaskState::Checked
		: TaskState::Unchecked;
	rebuild();
	return true;
}

bool State::toggleDetailsOpen(
		const Markdown::PreparedEditBlockSource &source) {
	const auto path = convertBlockPath(source);
	if (!path) {
		return false;
	}
	auto owner = block(*path);
	if (!owner || owner->kind != BlockKind::Details) {
		return false;
	}
	owner->open = !owner->open;
	rebuild();
	return true;
}

int State::activeTextLength() const {
	return activeRawText().size();
}

std::optional<int> State::previousEditableOrdinal() const {
	return adjacentEditableOrdinal(false);
}

std::optional<int> State::nextEditableOrdinal() const {
	return adjacentEditableOrdinal(true);
}

State::BoundaryTarget State::activeBoundaryTarget(bool forward) const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return {};
	}
	auto elements = std::vector<BoundaryElement>();
	collectBoundaryElements(
		_richPage->blocks,
		BlockContainerPath(),
		&elements);
	auto current = -1;
	for (auto i = 0, count = int(elements.size()); i != count; ++i) {
		const auto &element = elements[i];
		if (element.kind == BoundaryElement::Kind::Text
			&& element.textOrdinal == _activeTextOrdinal) {
			current = i;
			break;
		}
	}
	if (current < 0) {
		return {};
	}
	const auto adjacentIndex = current + (forward ? 1 : -1);
	if (adjacentIndex < 0 || adjacentIndex >= int(elements.size())) {
		return {};
	}
	const auto &adjacent = elements[adjacentIndex];
	if (adjacent.kind == BoundaryElement::Kind::Text) {
		return { .textOrdinal = adjacent.textOrdinal };
	}
	return {
		.textOrdinal = -1,
		.structuralSelection = preparedSelectionForBlock(adjacent.block),
	};
}

bool State::isActiveTopLevelParagraph() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor || !descriptor->leaf.block.container.steps.empty()) {
		return false;
	}
	const auto owner = block(descriptor->leaf.block);
	return owner && owner->kind == BlockKind::Paragraph;
}

bool State::activeLeafUsesQuoteCaptionColor() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor || descriptor->leaf.kind != LeafKind::BlockCaption) {
		return false;
	}
	const auto owner = block(descriptor->leaf.block);
	return owner && owner->kind == BlockKind::Quote && !owner->pullquote;
}

bool State::activeLeafUsesQuotePlaceholderColor() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return false;
	}
	const auto &leaf = descriptor->leaf;
	const auto owner = block(leaf.block);
	if (owner
		&& owner->kind == BlockKind::Quote
		&& !owner->pullquote
		&& (leaf.kind == LeafKind::BlockText
			|| leaf.kind == LeafKind::BlockCaption)) {
		return true;
	}
	auto container = leaf.block.container;
	while (!container.steps.empty()) {
		const auto step = container.steps.back();
		container.steps.pop_back();
		if (step.kind != BlockContainerKind::BlockChildren) {
			continue;
		}
		const auto ancestor = block({
			.container = container,
			.index = step.blockIndex,
		});
		if (ancestor
			&& ancestor->kind == BlockKind::Quote
			&& !ancestor->pullquote) {
			return true;
		}
	}
	return false;
}

bool State::activeOwnerIsEmpty() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	return descriptor && removalTargetIsEmpty(descriptor->removalTarget);
}

std::optional<int> State::removeActiveOwnerAndSelectAdjacent(bool forward) {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor || !removalTargetIsEmpty(descriptor->removalTarget)) {
		return std::nullopt;
	}
	const auto target = descriptor->removalTarget;
	auto first = _activeTextOrdinal;
	auto last = _activeTextOrdinal;
	while (first > 0 && _textNodes[first - 1].removalTarget == target) {
		--first;
	}
	while (last + 1 < textNodeCount()
		&& _textNodes[last + 1].removalTarget == target) {
		++last;
	}
	auto adjacent = std::optional<LeafPath>();
	if (forward) {
		for (auto i = last + 1, count = textNodeCount(); i != count; ++i) {
			if (!(_textNodes[i].removalTarget == target)) {
				adjacent = _textNodes[i].leaf;
				break;
			}
		}
	} else {
		for (auto i = first; i != 0; --i) {
			if (!(_textNodes[i - 1].removalTarget == target)) {
				adjacent = _textNodes[i - 1].leaf;
				break;
			}
		}
	}
	if (!removeTarget(target)) {
		return std::nullopt;
	}
	rebuild();
	if (adjacent && (!forward || target.kind == RemovalKind::TableCell)) {
		const auto ordinal = textNodeOrdinal(*adjacent);
		if (setActiveTextByOrdinal(ordinal)) {
			return _activeTextOrdinal;
		}
	}
	if (!textNodeCount()) {
		return std::nullopt;
	}
	const auto fallback = forward
		? std::min(first, textNodeCount() - 1)
		: std::max(std::min(first - 1, textNodeCount() - 1), 0);
	if (!setActiveTextByOrdinal(fallback)) {
		ensureActiveTextOrdinal();
	}
	return _activeTextOrdinal;
}

std::optional<int> State::removeStructuralSelection(
		const Markdown::PreparedEditSelection &selection,
		bool forward) {
	const auto activate = [&](const LeafPath &leaf) -> std::optional<int> {
		const auto ordinal = textNodeOrdinal(leaf);
		if (setActiveTextByOrdinal(ordinal)) {
			return _activeTextOrdinal;
		}
		return std::nullopt;
	};
	const auto finish = [&](
			auto postMutationFocus,
			std::optional<LeafPath> plannedFocus) -> std::optional<int> {
		rebuild();
		if (const auto focus = postMutationFocus()) {
			if (const auto ordinal = activate(*focus)) {
				return ordinal;
			}
		}
		if (plannedFocus) {
			if (const auto ordinal = activate(*plannedFocus)) {
				return ordinal;
			}
		}
		ensureActiveTextOrdinal();
		return (_activeTextOrdinal >= 0)
			? std::make_optional(_activeTextOrdinal)
			: std::nullopt;
	};
	const auto leafForContainerOwner = [&](
			const BlockContainerPath &container) -> std::optional<LeafPath> {
		if (container.steps.empty()) {
			return std::nullopt;
		}
		auto parent = container;
		const auto step = parent.steps.back();
		parent.steps.pop_back();
		const auto owner = BlockPath{
			.container = parent,
			.index = step.blockIndex,
		};
		if (step.kind == BlockContainerKind::BlockChildren) {
			for (const auto &descriptor : _textNodes) {
				if (leafBelongsToBlock(descriptor.leaf, owner)) {
					return descriptor.leaf;
				}
			}
		} else if (step.kind == BlockContainerKind::ListItemChildren) {
			for (const auto &descriptor : _textNodes) {
				const auto index = ListItemIndexForLeaf(
					descriptor.leaf,
					owner);
				if (index && *index == step.listItemIndex) {
					return descriptor.leaf;
				}
			}
		}
		return std::nullopt;
	};
	const auto leafNearBlockRange = [&](
			const StructuralBlockRange &range,
			bool forward) -> std::optional<LeafPath> {
		if (forward) {
			for (const auto &descriptor : _textNodes) {
				const auto index = BlockIndexInContainer(
					descriptor.leaf,
					range.container);
				if (index && *index >= range.from) {
					return descriptor.leaf;
				}
			}
		} else {
			for (auto i = textNodeCount(); i != 0; --i) {
				const auto &leaf = _textNodes[i - 1].leaf;
				const auto index = BlockIndexInContainer(leaf, range.container);
				if (index && *index < range.from) {
					return leaf;
				}
			}
		}
		return leafForContainerOwner(range.container);
	};
	const auto leafOutsideBlock = [&](
			const BlockPath &path,
			bool forward) -> std::optional<LeafPath> {
		if (forward) {
			for (const auto &descriptor : _textNodes) {
				const auto index = BlockIndexInContainer(
					descriptor.leaf,
					path.container);
				if (index && *index > path.index) {
					return descriptor.leaf;
				}
			}
		} else {
			for (auto i = textNodeCount(); i != 0; --i) {
				const auto &leaf = _textNodes[i - 1].leaf;
				const auto index = BlockIndexInContainer(leaf, path.container);
				if (index && *index < path.index) {
					return leaf;
				}
			}
		}
		return std::nullopt;
	};
	const auto leafNearListItemRange = [&](
			const StructuralListItemRange &range,
			bool forward) -> std::optional<LeafPath> {
		if (forward) {
			for (const auto &descriptor : _textNodes) {
				const auto index = ListItemIndexForLeaf(
					descriptor.leaf,
					range.block);
				if (index && *index >= range.from) {
					return descriptor.leaf;
				}
			}
		} else {
			for (auto i = textNodeCount(); i != 0; --i) {
				const auto &leaf = _textNodes[i - 1].leaf;
				const auto index = ListItemIndexForLeaf(leaf, range.block);
				if (index && *index < range.from) {
					return leaf;
				}
			}
		}
		return leafOutsideBlock(range.block, forward);
	};
	const auto tableTitleLeaf = [&](
			const BlockPath &path) -> std::optional<LeafPath> {
		auto leaf = LeafPath{
			.kind = LeafKind::BlockText,
			.block = path,
		};
		return (textNodeOrdinal(leaf) >= 0)
			? std::make_optional(leaf)
			: std::nullopt;
	};
	const auto leafNearTableRows = [&](
			const StructuralTableRowRange &range,
			bool forward) -> std::optional<LeafPath> {
		const auto cellInDirection = [&](
				bool direction) -> std::optional<LeafPath> {
			if (direction) {
				for (const auto &descriptor : _textNodes) {
					const auto &leaf = descriptor.leaf;
					if (leaf.block == range.block
						&& leaf.kind == LeafKind::TableCellText
						&& leaf.tableRowIndex >= range.from) {
						return leaf;
					}
				}
			} else {
				for (auto i = textNodeCount(); i != 0; --i) {
					const auto &leaf = _textNodes[i - 1].leaf;
					if (leaf.block == range.block
						&& leaf.kind == LeafKind::TableCellText
						&& leaf.tableRowIndex < range.from) {
						return leaf;
					}
				}
			}
			return std::nullopt;
		};
		if (const auto leaf = cellInDirection(forward)) {
			return leaf;
		}
		if (const auto leaf = cellInDirection(!forward)) {
			return leaf;
		}
		if (const auto leaf = tableTitleLeaf(range.block)) {
			return leaf;
		}
		return leafOutsideBlock(range.block, forward);
	};
	const auto leafNearTableCells = [&](
			const StructuralTableCellRange &range,
			bool forward) -> std::optional<LeafPath> {
		if (const auto leaf = firstSelectedLeaf(range)) {
			return leaf;
		}
		return adjacentLeafOutsideRange(range, forward);
	};
	const auto focusForRemovedBlock = [&](
			const BlockPath &path,
			bool forward) {
		return leafNearBlockRange(StructuralBlockRange{
			.container = path.container,
			.from = path.index,
			.till = path.index + 1,
		}, forward);
	};
	switch (selection.kind) {
	case PreparedEditSelectionKind::Blocks: {
		const auto range = validateBlockRange(selection.blocks);
		if (!range) {
			return std::nullopt;
		}
		const auto plannedFocus = plannedFocusForRange(*range, forward);
		const auto blocks = blockContainer(range->container);
		if (!blocks) {
			return std::nullopt;
		}
		blocks->erase(
			blocks->begin() + range->from,
			blocks->begin() + range->till);
		return finish([&] {
			return leafNearBlockRange(*range, forward);
		}, plannedFocus);
	}
	case PreparedEditSelectionKind::ListItems: {
		const auto range = validateListItemRange(selection.listItems);
		if (!range) {
			return std::nullopt;
		}
		const auto plannedFocus = plannedFocusForRange(*range, forward);
		const auto owner = block(range->block);
		if (!owner || owner->kind != BlockKind::List) {
			return std::nullopt;
		}
		owner->listItems.erase(
			owner->listItems.begin() + range->from,
			owner->listItems.begin() + range->till);
		if (owner->listItems.empty()) {
			const auto removed = range->block;
			if (!removeTarget({
					.kind = RemovalKind::Block,
					.block = removed,
				})) {
				return std::nullopt;
			}
			return finish([&] {
				return focusForRemovedBlock(removed, forward);
			}, plannedFocus);
		}
		return finish([&] {
			return leafNearListItemRange(*range, forward);
		}, plannedFocus);
	}
	case PreparedEditSelectionKind::TableRows: {
		const auto range = validateTableRowRange(selection.tableRows);
		if (!range) {
			return std::nullopt;
		}
		const auto plannedFocus = plannedFocusForRange(*range, forward);
		const auto owner = block(range->block);
		if (!owner || owner->kind != BlockKind::Table) {
			return std::nullopt;
		}
		owner->tableRows.erase(
			owner->tableRows.begin() + range->from,
			owner->tableRows.begin() + range->till);
		if (owner->tableRows.empty() && RichTextIsEmpty(owner->text)) {
			const auto removed = range->block;
			if (!removeTarget({
					.kind = RemovalKind::Block,
					.block = removed,
				})) {
				return std::nullopt;
			}
			return finish([&] {
				return focusForRemovedBlock(removed, forward);
			}, plannedFocus);
		}
		return finish([&] {
			return leafNearTableRows(*range, forward);
		}, plannedFocus);
	}
	case PreparedEditSelectionKind::TableCells: {
		const auto range = validateTableCellRange(selection.tableCells);
		if (!range) {
			return std::nullopt;
		}
		const auto plannedFocus = plannedFocusForRange(*range, forward);
		const auto owner = block(range->block);
		if (!owner
			|| owner->kind != BlockKind::Table
			|| range->tableRowIndex >= int(owner->tableRows.size())) {
			return std::nullopt;
		}
		auto &row = owner->tableRows[range->tableRowIndex];
		if (range->till > int(row.cells.size())) {
			return std::nullopt;
		}
		for (auto i = range->from; i != range->till; ++i) {
			row.cells[i].text = RichText();
		}
		return finish([&] {
			return leafNearTableCells(*range, forward);
		}, plannedFocus);
	}
	case PreparedEditSelectionKind::None:
		return std::nullopt;
	}
	return std::nullopt;
}

std::optional<State::BlockContainerPath> State::convertBlockContainerPath(
		const Markdown::PreparedEditBlockContainerPath &path) const {
	auto result = BlockContainerPath();
	result.steps.reserve(path.steps.size());
	const auto *blocks = &_richPage->blocks;
	for (const auto &step : path.steps) {
		if (step.blockIndex < 0 || step.blockIndex >= int(blocks->size())) {
			return std::nullopt;
		}
		const auto &parent = (*blocks)[step.blockIndex];
		auto converted = BlockContainerStep();
		converted.blockIndex = step.blockIndex;
		converted.listItemIndex = step.listItemIndex;
		switch (step.kind) {
		case PreparedBlockContainerKind::Root:
			return std::nullopt;
		case PreparedBlockContainerKind::BlockChildren:
			if (!BlockCanOwnChildContainer(parent)) {
				return std::nullopt;
			}
			converted.kind = BlockContainerKind::BlockChildren;
			blocks = &parent.blocks;
			break;
		case PreparedBlockContainerKind::ListItemChildren:
			if (parent.kind != BlockKind::List
				|| step.listItemIndex < 0
				|| step.listItemIndex >= int(parent.listItems.size())) {
				return std::nullopt;
			}
			converted.kind = BlockContainerKind::ListItemChildren;
			blocks = &parent.listItems[step.listItemIndex].blocks;
			break;
		}
		result.steps.push_back(converted);
	}
	return result;
}

std::optional<State::BlockPath> State::convertBlockPath(
		const Markdown::PreparedEditBlockPath &path) const {
	if (path.index < 0) {
		return std::nullopt;
	}
	const auto container = convertBlockContainerPath(path.container);
	if (!container) {
		return std::nullopt;
	}
	const auto blocks = blockContainer(*container);
	if (!blocks || path.index >= int(blocks->size())) {
		return std::nullopt;
	}
	return BlockPath{
		.container = *container,
		.index = path.index,
	};
}

std::optional<State::BlockPath> State::convertBlockPath(
		const Markdown::PreparedEditBlockSource &source) const {
	return convertBlockPath(source.path);
}

std::optional<State::LeafPath> State::convertLeafPath(
		const Markdown::PreparedEditLeafSource &source) const {
	const auto blockPath = convertBlockPath(source.block);
	if (!blockPath) {
		return std::nullopt;
	}
	auto result = LeafPath();
	result.block = *blockPath;
	switch (source.kind) {
	case PreparedEditLeafKind::BlockText:
		result.kind = LeafKind::BlockText;
		break;
	case PreparedEditLeafKind::BlockCaption:
		result.kind = LeafKind::BlockCaption;
		break;
	case PreparedEditLeafKind::ListItemText:
		if (source.listItemIndex < 0) {
			return std::nullopt;
		}
		result.kind = LeafKind::ListItemText;
		result.listItemIndex = source.listItemIndex;
		break;
	case PreparedEditLeafKind::TableCellText:
		if (source.tableRowIndex < 0 || source.tableCellIndex < 0) {
			return std::nullopt;
		}
		result.kind = LeafKind::TableCellText;
		result.tableRowIndex = source.tableRowIndex;
		result.tableCellIndex = source.tableCellIndex;
		break;
	case PreparedEditLeafKind::MathFormula:
		result.kind = LeafKind::MathFormula;
		break;
	}
	const auto owner = block(result.block);
	if (!owner) {
		return std::nullopt;
	}
	switch (result.kind) {
	case LeafKind::BlockText:
		if (!BlockSupportsBlockText(*owner)) {
			return std::nullopt;
		}
		break;
	case LeafKind::BlockCaption:
		if (!BlockSupportsBlockCaption(*owner)) {
			return std::nullopt;
		}
		break;
	case LeafKind::ListItemText:
		if (owner->kind != BlockKind::List
			|| !listItem(result.block, result.listItemIndex)) {
			return std::nullopt;
		}
		break;
	case LeafKind::TableCellText:
		if (owner->kind != BlockKind::Table
			|| !tableCell(
				result.block,
				result.tableRowIndex,
				result.tableCellIndex)) {
			return std::nullopt;
		}
		break;
	case LeafKind::MathFormula:
		if (owner->kind != BlockKind::Math) {
			return std::nullopt;
		}
		break;
	}
	return result;
}

std::optional<State::StructuralBlockRange> State::validateBlockRange(
		const Markdown::PreparedEditBlockRange &range) const {
	if (range.empty()) {
		return std::nullopt;
	}
	const auto container = convertBlockContainerPath(range.container);
	if (!container) {
		return std::nullopt;
	}
	const auto blocks = blockContainer(*container);
	if (!blocks
		|| range.from < 0
		|| range.till > int(blocks->size())) {
		return std::nullopt;
	}
	for (auto i = range.from; i != range.till; ++i) {
		if (!CanEditBlock((*blocks)[i])) {
			return std::nullopt;
		}
	}
	return StructuralBlockRange{
		.container = *container,
		.from = range.from,
		.till = range.till,
	};
}

std::optional<State::StructuralListItemRange> State::validateListItemRange(
		const Markdown::PreparedEditListItemRange &range) const {
	if (range.empty()) {
		return std::nullopt;
	}
	const auto path = convertBlockPath(range.block);
	if (!path) {
		return std::nullopt;
	}
	const auto owner = block(*path);
	if (!owner
		|| owner->kind != BlockKind::List
		|| range.from < 0
		|| range.till > int(owner->listItems.size())) {
		return std::nullopt;
	}
	for (auto i = range.from; i != range.till; ++i) {
		if (!CanEditBlocks(owner->listItems[i].blocks)) {
			return std::nullopt;
		}
	}
	return StructuralListItemRange{
		.block = *path,
		.from = range.from,
		.till = range.till,
	};
}

std::optional<State::StructuralTableRowRange> State::validateTableRowRange(
		const Markdown::PreparedEditTableRowRange &range) const {
	if (range.empty()) {
		return std::nullopt;
	}
	const auto path = convertBlockPath(range.block);
	if (!path) {
		return std::nullopt;
	}
	const auto owner = block(*path);
	if (!owner
		|| owner->kind != BlockKind::Table
		|| range.from < 0
		|| range.till > int(owner->tableRows.size())) {
		return std::nullopt;
	}
	return StructuralTableRowRange{
		.block = *path,
		.from = range.from,
		.till = range.till,
	};
}

std::optional<State::StructuralTableCellRange> State::validateTableCellRange(
		const Markdown::PreparedEditTableCellRange &range) const {
	if (range.empty()) {
		return std::nullopt;
	}
	const auto path = convertBlockPath(range.block);
	if (!path) {
		return std::nullopt;
	}
	const auto owner = block(*path);
	if (!owner
		|| owner->kind != BlockKind::Table
		|| range.tableRowIndex < 0
		|| range.tableRowIndex >= int(owner->tableRows.size())) {
		return std::nullopt;
	}
	const auto &row = owner->tableRows[range.tableRowIndex];
	if (range.from < 0 || range.till > int(row.cells.size())) {
		return std::nullopt;
	}
	return StructuralTableCellRange{
		.block = *path,
		.tableRowIndex = range.tableRowIndex,
		.from = range.from,
		.till = range.till,
	};
}

bool State::leafWillBeRemoved(
		const LeafPath &path,
		const StructuralBlockRange &range) const {
	const auto index = BlockIndexInContainer(path, range.container);
	return index && IndexInRange(*index, range.from, range.till);
}

bool State::leafWillBeRemoved(
		const LeafPath &path,
		const StructuralListItemRange &range) const {
	const auto index = ListItemIndexForLeaf(path, range.block);
	return index && IndexInRange(*index, range.from, range.till);
}

bool State::leafWillBeRemoved(
		const LeafPath &path,
		const StructuralTableRowRange &range) const {
	const auto index = TableRowIndexForLeaf(path, range.block);
	return index && IndexInRange(*index, range.from, range.till);
}

bool State::leafWillBeRemoved(
		const LeafPath &,
		const StructuralTableCellRange &) const {
	return false;
}

bool State::leafBelongsToBlock(
		const LeafPath &leaf,
		const BlockPath &path) const {
	const auto &owner = leaf.block;
	if (owner == path) {
		return true;
	}
	if (!ContainerHasPrefix(owner.container, path.container)) {
		return false;
	}
	if (owner.container.steps.size() <= path.container.steps.size()) {
		return false;
	}
	const auto &step = owner.container.steps[path.container.steps.size()];
	return step.blockIndex == path.index
		&& (step.kind == BlockContainerKind::BlockChildren
			|| step.kind == BlockContainerKind::ListItemChildren);
}

std::optional<State::LeafPath> State::firstSelectedLeaf(
		const StructuralTableCellRange &range) const {
	for (const auto &descriptor : _textNodes) {
		const auto &leaf = descriptor.leaf;
		if (leaf.block == range.block
			&& leaf.kind == LeafKind::TableCellText
			&& leaf.tableRowIndex == range.tableRowIndex
			&& IndexInRange(leaf.tableCellIndex, range.from, range.till)) {
			return leaf;
		}
	}
	return std::nullopt;
}

std::optional<State::LeafPath> State::adjacentLeafOutsideRange(
		const StructuralBlockRange &range,
		bool forward) const {
	if (forward) {
		for (const auto &descriptor : _textNodes) {
			const auto index = BlockIndexInContainer(
				descriptor.leaf,
				range.container);
			if (index && *index >= range.till) {
				return descriptor.leaf;
			}
		}
	} else {
		for (auto i = textNodeCount(); i != 0; --i) {
			const auto &leaf = _textNodes[i - 1].leaf;
			const auto index = BlockIndexInContainer(leaf, range.container);
			if (index && *index < range.from) {
				return leaf;
			}
		}
	}
	return std::nullopt;
}

std::optional<State::LeafPath> State::adjacentLeafOutsideRange(
		const StructuralListItemRange &range,
		bool forward) const {
	if (forward) {
		for (const auto &descriptor : _textNodes) {
			const auto index = ListItemIndexForLeaf(
				descriptor.leaf,
				range.block);
			if (index && *index >= range.till) {
				return descriptor.leaf;
			}
		}
	} else {
		for (auto i = textNodeCount(); i != 0; --i) {
			const auto &leaf = _textNodes[i - 1].leaf;
			const auto index = ListItemIndexForLeaf(leaf, range.block);
			if (index && *index < range.from) {
				return leaf;
			}
		}
	}
	return std::nullopt;
}

std::optional<State::LeafPath> State::adjacentLeafOutsideRange(
		const StructuralTableRowRange &range,
		bool forward) const {
	if (forward) {
		for (const auto &descriptor : _textNodes) {
			const auto index = TableRowIndexForLeaf(
				descriptor.leaf,
				range.block);
			if (index && *index >= range.till) {
				return descriptor.leaf;
			}
		}
	} else {
		for (auto i = textNodeCount(); i != 0; --i) {
			const auto &leaf = _textNodes[i - 1].leaf;
			const auto index = TableRowIndexForLeaf(leaf, range.block);
			if (index && *index < range.from) {
				return leaf;
			}
		}
	}
	return std::nullopt;
}

std::optional<State::LeafPath> State::adjacentLeafOutsideRange(
		const StructuralTableCellRange &range,
		bool forward) const {
	if (forward) {
		for (const auto &descriptor : _textNodes) {
			const auto index = TableCellIndexForLeaf(
				descriptor.leaf,
				range.block,
				range.tableRowIndex);
			if (index && *index >= range.till) {
				return descriptor.leaf;
			}
		}
	} else {
		for (auto i = textNodeCount(); i != 0; --i) {
			const auto &leaf = _textNodes[i - 1].leaf;
			const auto index = TableCellIndexForLeaf(
				leaf,
				range.block,
				range.tableRowIndex);
			if (index && *index < range.from) {
				return leaf;
			}
		}
	}
	return std::nullopt;
}

std::optional<State::LeafPath> State::fallbackFocusLeaf() const {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (descriptor) {
		return descriptor->leaf;
	}
	return !_textNodes.empty()
		? std::make_optional(_textNodes.front().leaf)
		: std::nullopt;
}

std::optional<State::LeafPath> State::plannedFocusForRange(
		const StructuralBlockRange &range,
		bool forward) const {
	if (const auto adjacent = adjacentLeafOutsideRange(range, forward)) {
		return adjacent;
	}
	const auto descriptor = textNode(_activeTextOrdinal);
	if (descriptor && !leafWillBeRemoved(descriptor->leaf, range)) {
		return descriptor->leaf;
	}
	for (const auto &fallback : _textNodes) {
		if (!leafWillBeRemoved(fallback.leaf, range)) {
			return fallback.leaf;
		}
	}
	return fallbackFocusLeaf();
}

std::optional<State::LeafPath> State::plannedFocusForRange(
		const StructuralListItemRange &range,
		bool forward) const {
	if (const auto adjacent = adjacentLeafOutsideRange(range, forward)) {
		return adjacent;
	}
	const auto ownerRange = StructuralBlockRange{
		.container = range.block.container,
		.from = range.block.index,
		.till = range.block.index + 1,
	};
	if (const auto adjacent = adjacentLeafOutsideRange(ownerRange, forward)) {
		return adjacent;
	}
	const auto descriptor = textNode(_activeTextOrdinal);
	if (descriptor && !leafWillBeRemoved(descriptor->leaf, range)) {
		return descriptor->leaf;
	}
	for (const auto &fallback : _textNodes) {
		if (!leafWillBeRemoved(fallback.leaf, range)) {
			return fallback.leaf;
		}
	}
	return fallbackFocusLeaf();
}

std::optional<State::LeafPath> State::plannedFocusForRange(
		const StructuralTableRowRange &range,
		bool forward) const {
	if (const auto adjacent = adjacentLeafOutsideRange(range, forward)) {
		return adjacent;
	}
	const auto ownerRange = StructuralBlockRange{
		.container = range.block.container,
		.from = range.block.index,
		.till = range.block.index + 1,
	};
	if (const auto adjacent = adjacentLeafOutsideRange(ownerRange, forward)) {
		return adjacent;
	}
	const auto descriptor = textNode(_activeTextOrdinal);
	if (descriptor && !leafWillBeRemoved(descriptor->leaf, range)) {
		return descriptor->leaf;
	}
	for (const auto &fallback : _textNodes) {
		if (!leafWillBeRemoved(fallback.leaf, range)) {
			return fallback.leaf;
		}
	}
	return fallbackFocusLeaf();
}

std::optional<State::LeafPath> State::plannedFocusForRange(
		const StructuralTableCellRange &range,
		bool forward) const {
	if (const auto selected = firstSelectedLeaf(range)) {
		return selected;
	}
	if (const auto adjacent = adjacentLeafOutsideRange(range, forward)) {
		return adjacent;
	}
	return fallbackFocusLeaf();
}

State::InsertionAnchor State::resolveActiveInsertionTarget() const {
	auto result = InsertionAnchor{
		.container = BlockContainerPath(),
		.blockIndex = int(_richPage->blocks.size()) - 1,
	};
	if (const auto descriptor = textNode(_activeTextOrdinal)) {
		result = descriptor->insertionAnchor;
	}
	return blockContainer(result.container)
		? result
		: InsertionAnchor{
			.container = BlockContainerPath(),
			.blockIndex = int(_richPage->blocks.size()) - 1,
		};
}

std::optional<int> State::normalizeTextOnlyListItemForInsertion(
		const BlockContainerPath &container) {
	if (container.steps.empty()) {
		return std::nullopt;
	}
	const auto &step = container.steps.back();
	if (step.kind != BlockContainerKind::ListItemChildren) {
		return std::nullopt;
	}
	auto parent = container;
	parent.steps.pop_back();
	auto itemPath = BlockPath{
		.container = parent,
		.index = step.blockIndex,
	};
	auto item = listItem(itemPath, step.listItemIndex);
	if (!item || (item->anchorId.isEmpty() && RichTextIsEmpty(item->text))) {
		return std::nullopt;
	}
	auto paragraph = MakeParagraphBlock();
	paragraph.anchorId = std::move(item->anchorId);
	paragraph.text = std::move(item->text);
	item->anchorId.clear();
	item->text = RichText();
	if (!BlockIsEmpty(paragraph)) {
		item->blocks.insert(item->blocks.begin(), std::move(paragraph));
		return 0;
	}
	return -1;
}

std::optional<int> State::normalizeTextOnlyQuoteForInsertion(
		const BlockContainerPath &container) {
	if (container.steps.empty()) {
		return std::nullopt;
	}
	const auto &step = container.steps.back();
	if (step.kind != BlockContainerKind::BlockChildren) {
		return std::nullopt;
	}
	auto parent = container;
	parent.steps.pop_back();
	auto owner = block({
		.container = parent,
		.index = step.blockIndex,
	});
	if (!owner
		|| owner->kind != BlockKind::Quote
		|| owner->pullquote
		|| !owner->blocks.empty()) {
		return std::nullopt;
	}
	auto paragraph = MakeParagraphBlock();
	paragraph.text = std::move(owner->text);
	owner->text = RichText();
	if (!BlockIsEmpty(paragraph)) {
		owner->blocks.push_back(std::move(paragraph));
		return 0;
	}
	return -1;
}

bool State::shouldReplaceActiveTextOnlyBlock(
		const TextNodeDescriptor &descriptor,
		const std::vector<Block> &blocks) const {
	if (descriptor.leaf.kind != LeafKind::BlockText
		|| descriptor.removalTarget.kind != RemovalKind::Block) {
		return false;
	}
	const auto owner = block(descriptor.removalTarget.block);
	if (!owner || !BlockIsEmpty(*owner)) {
		return false;
	}
	if (owner->kind == BlockKind::Paragraph) {
		return true;
	}
	return owner->kind == BlockKind::Heading
		&& blocks.size() == 1
		&& blocks.front().kind == BlockKind::Heading;
}

std::optional<int> State::activateRebuiltLeaf(const LeafPath &path) {
	const auto ordinal = textNodeOrdinal(path);
	if (setActiveTextByOrdinal(ordinal)) {
		return _activeTextOrdinal;
	}
	ensureActiveTextOrdinal();
	return (_activeTextOrdinal >= 0)
		? std::make_optional(_activeTextOrdinal)
		: std::nullopt;
}

std::optional<State::LeafPath> State::reuseOrInsertParagraph(
		const BlockContainerPath &containerPath,
		int index) {
	const auto blocks = blockContainer(containerPath);
	if (!blocks) {
		return std::nullopt;
	}
	const auto insertAt = std::clamp(index, 0, int(blocks->size()));
	if (insertAt < int(blocks->size())
		&& (*blocks)[insertAt].kind == BlockKind::Paragraph) {
		return LeafPath{
			.kind = LeafKind::BlockText,
			.block = {
				.container = containerPath,
				.index = insertAt,
			},
		};
	}
	blocks->insert(blocks->begin() + insertAt, MakeParagraphBlock());
	return LeafPath{
		.kind = LeafKind::BlockText,
		.block = {
			.container = containerPath,
			.index = insertAt,
		},
	};
}

auto State::activeNonPullquoteQuote() const
-> std::optional<State::ActiveNonPullquoteQuote> {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return std::nullopt;
	}
	const auto direct = block(descriptor->leaf.block);
	if (direct && direct->kind == BlockKind::Quote) {
		return direct->pullquote
			? std::nullopt
			: std::make_optional(ActiveNonPullquoteQuote{
				.path = descriptor->leaf.block,
			});
	}
	auto container = descriptor->leaf.block.container;
	while (!container.steps.empty()) {
		const auto step = container.steps.back();
		container.steps.pop_back();
		if (step.kind != BlockContainerKind::BlockChildren) {
			continue;
		}
		const auto path = BlockPath{
			.container = container,
			.index = step.blockIndex,
		};
		const auto owner = block(path);
		if (!owner || owner->kind != BlockKind::Quote) {
			continue;
		}
		if (owner->pullquote) {
			return std::nullopt;
		}
		const auto body = BlockChildrenContainer(path);
		auto lastBodyLeaf = false;
		for (auto i = textNodeCount(); i != 0; --i) {
			const auto &candidate = _textNodes[i - 1].leaf;
			if (ContainerHasPrefix(candidate.block.container, body)) {
				lastBodyLeaf = (candidate == descriptor->leaf);
				break;
			}
		}
		return ActiveNonPullquoteQuote{
			.path = path,
			.activeLeafIsLastEditableBodyLeaf = lastBodyLeaf,
		};
	}
	return std::nullopt;
}

auto State::activeListItemSurface() const
-> std::optional<State::ActiveListItemSurface> {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return std::nullopt;
	}
	auto path = std::optional<BlockPath>();
	if (descriptor->leaf.kind == LeafKind::ListItemText) {
		path = descriptor->leaf.block;
	} else if (descriptor->leaf.kind == LeafKind::BlockText) {
		const auto owner = block(descriptor->leaf.block);
		if (!owner || owner->kind != BlockKind::Paragraph) {
			return std::nullopt;
		}
		const auto &container = descriptor->leaf.block.container;
		if (container.steps.empty()) {
			return std::nullopt;
		}
		const auto &step = container.steps.back();
		if (step.kind != BlockContainerKind::ListItemChildren) {
			return std::nullopt;
		}
		auto parent = container;
		parent.steps.pop_back();
		path = BlockPath{
			.container = parent,
			.index = step.blockIndex,
		};
	} else {
		return std::nullopt;
	}
	const auto owner = block(*path);
	if (!owner || owner->kind != BlockKind::List) {
		return std::nullopt;
	}
	const auto itemIndex = ListItemIndexForLeaf(descriptor->leaf, *path);
	if (!itemIndex) {
		return std::nullopt;
	}
	if (descriptor->leaf.kind == LeafKind::BlockText
		&& descriptor->leaf.block.container
			!= ListItemChildrenContainer(*path, *itemIndex)) {
		return std::nullopt;
	}
	return ActiveListItemSurface{
		.path = *path,
		.itemIndex = *itemIndex,
	};
}

auto State::normalizeActiveListItemSurface()
-> std::optional<State::ActiveListItemSurface> {
	const auto descriptor = textNode(_activeTextOrdinal);
	const auto surface = activeListItemSurface();
	if (!descriptor
		|| !surface
		|| descriptor->leaf.kind != LeafKind::ListItemText) {
		return surface;
	}
	const auto item = listItem(surface->path, surface->itemIndex);
	if (!item) {
		return std::nullopt;
	}
	auto paragraph = MakeParagraphBlock();
	paragraph.anchorId = std::move(item->anchorId);
	paragraph.text = std::move(item->text);
	item->anchorId.clear();
	item->text = RichText();
	item->blocks.insert(item->blocks.begin(), std::move(paragraph));
	return surface;
}

int State::ensureTrailingParagraphActive() {
	if (_richPage->blocks.empty()
		|| _richPage->blocks.back().kind != BlockKind::Paragraph) {
		_richPage->blocks.push_back(MakeParagraphBlock());
	}
	const auto path = BlockPath{
		.container = BlockContainerPath(),
		.index = int(_richPage->blocks.size()) - 1,
	};
	rebuild();
	const auto ordinal = textNodeOrdinal({
			.kind = LeafKind::BlockText,
			.block = path,
		});
	if (!setActiveTextByOrdinal(ordinal)) {
		ensureActiveTextOrdinal();
	}
	return _activeTextOrdinal;
}

std::optional<int> State::moveActiveQuoteDown() {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor) {
		return std::nullopt;
	}
	const auto quote = activeNonPullquoteQuote();
	if (!quote) {
		return std::nullopt;
	}
	auto target = std::optional<LeafPath>();
	if (descriptor->leaf.kind == LeafKind::BlockCaption
		&& descriptor->leaf.block == quote->path) {
		target = reuseOrInsertParagraph(
			quote->path.container,
			quote->path.index + 1);
	} else if (descriptor->leaf.kind == LeafKind::BlockText
		&& descriptor->leaf.block == quote->path) {
		const auto owner = block(quote->path);
		if (owner
			&& owner->kind == BlockKind::Quote
			&& owner->blocks.empty()) {
			target = LeafPath{
				.kind = LeafKind::BlockCaption,
				.block = quote->path,
			};
		}
	} else if (quote->activeLeafIsLastEditableBodyLeaf) {
		target = LeafPath{
			.kind = LeafKind::BlockCaption,
			.block = quote->path,
		};
	}
	if (!target) {
		return std::nullopt;
	}
	rebuild();
	return activateRebuiltLeaf(*target);
}

std::optional<int> State::handleActiveHeadingEnter() {
	const auto descriptor = textNode(_activeTextOrdinal);
	if (!descriptor || descriptor->leaf.kind != LeafKind::BlockText) {
		return std::nullopt;
	}
	const auto path = descriptor->leaf.block;
	const auto blocks = blockContainer(path.container);
	if (!blocks
		|| path.index < 0
		|| path.index >= int(blocks->size())
		|| (*blocks)[path.index].kind != BlockKind::Heading) {
		return std::nullopt;
	}
	const auto insertAt = path.index + 1;
	if (insertAt < 0 || insertAt > int(blocks->size())) {
		return std::nullopt;
	}
	blocks->insert(blocks->begin() + insertAt, MakeParagraphBlock());
	const auto target = LeafPath{
		.kind = LeafKind::BlockText,
		.block = {
			.container = path.container,
			.index = insertAt,
		},
	};
	rebuild();
	return activateRebuiltLeaf(target);
}

std::optional<int> State::handleActiveListEnter() {
	const auto surface = normalizeActiveListItemSurface();
	if (!surface) {
		return std::nullopt;
	}
	const auto owner = block(surface->path);
	const auto item = listItem(surface->path, surface->itemIndex);
	if (!owner || owner->kind != BlockKind::List || !item) {
		return std::nullopt;
	}
	auto target = std::optional<LeafPath>();
	const auto trailingEmpty = (surface->itemIndex + 1
			== int(owner->listItems.size()))
		&& (item->blocks.size() == 1)
		&& (item->blocks.front().kind == BlockKind::Paragraph)
		&& ListItemIsEmpty(*item);
	if (trailingEmpty) {
		owner->listItems.erase(owner->listItems.begin() + surface->itemIndex);
		if (owner->listItems.empty()) {
			const auto blocks = blockContainer(surface->path.container);
			if (!blocks
				|| surface->path.index < 0
				|| surface->path.index >= int(blocks->size())) {
				return std::nullopt;
			}
			blocks->erase(blocks->begin() + surface->path.index);
			target = reuseOrInsertParagraph(
				surface->path.container,
				surface->path.index);
		} else {
			target = reuseOrInsertParagraph(
				surface->path.container,
				surface->path.index + 1);
		}
	} else {
		owner->listItems.insert(
			owner->listItems.begin() + surface->itemIndex + 1,
			MakeParagraphListItem(item->taskState));
		target = LeafPath{
			.kind = LeafKind::BlockText,
			.block = {
				.container = ListItemChildrenContainer(
					surface->path,
					surface->itemIndex + 1),
				.index = 0,
			},
		};
	}
	if (!target) {
		return std::nullopt;
	}
	rebuild();
	return activateRebuiltLeaf(*target);
}

void State::insertHeading1AfterActive() {
	insertBlockAfterActive({
		.type = InsertBlockType::Heading,
		.headingLevel = 1,
	});
}

void State::insertBlockquoteAfterActive() {
	insertBlockAfterActive({
		.type = InsertBlockType::Blockquote,
	});
}

void State::insertBlockAfterActive(InsertAction action) {
	auto blocks = std::vector<Block>();
	blocks.push_back(makeBlock(action));
	insertBlocksAfterActive(std::move(blocks));
}

void State::insertPreparedBlockAfterActive(Block block) {
	auto blocks = std::vector<Block>();
	blocks.push_back(std::move(block));
	insertBlocksAfterActive(std::move(blocks));
}

void State::insertPreparedBlocksAfterActive(std::vector<Block> blocks) {
	insertBlocksAfterActive(std::move(blocks));
}

void State::insertBlocksAfterActive(std::vector<Block> blocks) {
	if (blocks.empty()) {
		return;
	}
	const auto descriptor = textNode(_activeTextOrdinal);
	if (descriptor && shouldReplaceActiveTextOnlyBlock(*descriptor, blocks)) {
		const auto path = descriptor->removalTarget.block;
		const auto container = blockContainer(path.container);
		if (container
			&& path.index >= 0
			&& path.index < int(container->size())) {
			const auto insertAt = path.index;
			const auto count = int(blocks.size());
			container->erase(container->begin() + insertAt);
			container->insert(
				container->begin() + insertAt,
				std::make_move_iterator(blocks.begin()),
				std::make_move_iterator(blocks.end()));
			rebuild();
			focusInsertedBlocks(path.container, insertAt, count);
			return;
		}
	}
	auto anchor = resolveActiveInsertionTarget();
	if (const auto normalized = normalizeTextOnlyListItemForInsertion(
			anchor.container)) {
		anchor.blockIndex = *normalized;
	} else if (const auto normalized = normalizeTextOnlyQuoteForInsertion(
			anchor.container)) {
		anchor.blockIndex = *normalized;
	}
	auto *container = blockContainer(anchor.container);
	if (!container) {
		anchor = InsertionAnchor{
			.container = BlockContainerPath(),
			.blockIndex = int(_richPage->blocks.size()) - 1,
		};
		container = &_richPage->blocks;
	}
	const auto insertAt = std::clamp(
		anchor.blockIndex + 1,
		0,
		int(container->size()));
	const auto count = int(blocks.size());
	container->insert(
		container->begin() + insertAt,
		std::make_move_iterator(blocks.begin()),
		std::make_move_iterator(blocks.end()));
	rebuild();
	focusInsertedBlocks(anchor.container, insertAt, count);
}

std::vector<Block> *State::blockContainer(const BlockContainerPath &path) {
	auto *blocks = &_richPage->blocks;
	for (const auto &step : path.steps) {
		if (step.blockIndex < 0 || step.blockIndex >= int(blocks->size())) {
			return nullptr;
		}
		auto &parent = (*blocks)[step.blockIndex];
		if (step.kind == BlockContainerKind::BlockChildren) {
			blocks = &parent.blocks;
		} else if (step.kind == BlockContainerKind::ListItemChildren) {
			if (step.listItemIndex < 0
				|| step.listItemIndex >= int(parent.listItems.size())) {
				return nullptr;
			}
			blocks = &parent.listItems[step.listItemIndex].blocks;
		} else {
			return nullptr;
		}
	}
	return blocks;
}

const std::vector<Block> *State::blockContainer(
		const BlockContainerPath &path) const {
	const auto *blocks = &_richPage->blocks;
	for (const auto &step : path.steps) {
		if (step.blockIndex < 0 || step.blockIndex >= int(blocks->size())) {
			return nullptr;
		}
		const auto &parent = (*blocks)[step.blockIndex];
		if (step.kind == BlockContainerKind::BlockChildren) {
			blocks = &parent.blocks;
		} else if (step.kind == BlockContainerKind::ListItemChildren) {
			if (step.listItemIndex < 0
				|| step.listItemIndex >= int(parent.listItems.size())) {
				return nullptr;
			}
			blocks = &parent.listItems[step.listItemIndex].blocks;
		} else {
			return nullptr;
		}
	}
	return blocks;
}

Block *State::block(const BlockPath &path) {
	const auto blocks = blockContainer(path.container);
	if (!blocks || path.index < 0 || path.index >= int(blocks->size())) {
		return nullptr;
	}
	return &(*blocks)[path.index];
}

const Block *State::block(const BlockPath &path) const {
	const auto blocks = blockContainer(path.container);
	if (!blocks || path.index < 0 || path.index >= int(blocks->size())) {
		return nullptr;
	}
	return &(*blocks)[path.index];
}

ListItem *State::listItem(const BlockPath &blockPath, int itemIndex) {
	const auto list = block(blockPath);
	if (!list
		|| itemIndex < 0
		|| itemIndex >= int(list->listItems.size())) {
		return nullptr;
	}
	return &list->listItems[itemIndex];
}

const ListItem *State::listItem(
		const BlockPath &blockPath,
		int itemIndex) const {
	const auto list = block(blockPath);
	if (!list
		|| itemIndex < 0
		|| itemIndex >= int(list->listItems.size())) {
		return nullptr;
	}
	return &list->listItems[itemIndex];
}

TableCell *State::tableCell(
		const BlockPath &blockPath,
		int rowIndex,
		int cellIndex) {
	const auto table = block(blockPath);
	if (!table
		|| rowIndex < 0
		|| rowIndex >= int(table->tableRows.size())) {
		return nullptr;
	}
	auto &row = table->tableRows[rowIndex];
	if (cellIndex < 0 || cellIndex >= int(row.cells.size())) {
		return nullptr;
	}
	return &row.cells[cellIndex];
}

const TableCell *State::tableCell(
		const BlockPath &blockPath,
		int rowIndex,
		int cellIndex) const {
	const auto table = block(blockPath);
	if (!table
		|| rowIndex < 0
		|| rowIndex >= int(table->tableRows.size())) {
		return nullptr;
	}
	const auto &row = table->tableRows[rowIndex];
	if (cellIndex < 0 || cellIndex >= int(row.cells.size())) {
		return nullptr;
	}
	return &row.cells[cellIndex];
}

RichText *State::richText(const LeafPath &path) {
	switch (path.kind) {
	case LeafKind::BlockText:
		if (const auto owner = block(path.block)) {
			return &owner->text;
		}
		return nullptr;
	case LeafKind::BlockCaption:
		if (const auto owner = block(path.block)) {
			return &owner->caption;
		}
		return nullptr;
	case LeafKind::ListItemText:
		if (const auto item = listItem(path.block, path.listItemIndex)) {
			return &item->text;
		}
		return nullptr;
	case LeafKind::TableCellText:
		if (const auto cell = tableCell(
				path.block,
				path.tableRowIndex,
				path.tableCellIndex)) {
			return &cell->text;
		}
		return nullptr;
	case LeafKind::MathFormula:
		return nullptr;
	}
	return nullptr;
}

const RichText *State::richText(const LeafPath &path) const {
	switch (path.kind) {
	case LeafKind::BlockText:
		if (const auto owner = block(path.block)) {
			return &owner->text;
		}
		return nullptr;
	case LeafKind::BlockCaption:
		if (const auto owner = block(path.block)) {
			return &owner->caption;
		}
		return nullptr;
	case LeafKind::ListItemText:
		if (const auto item = listItem(path.block, path.listItemIndex)) {
			return &item->text;
		}
		return nullptr;
	case LeafKind::TableCellText:
		if (const auto cell = tableCell(
				path.block,
				path.tableRowIndex,
				path.tableCellIndex)) {
			return &cell->text;
		}
		return nullptr;
	case LeafKind::MathFormula:
		return nullptr;
	}
	return nullptr;
}

QString *State::rawText(const LeafPath &path) {
	if (path.kind != LeafKind::MathFormula) {
		return nullptr;
	}
	const auto owner = block(path.block);
	return owner ? &owner->formula : nullptr;
}

const QString *State::rawText(const LeafPath &path) const {
	if (path.kind != LeafKind::MathFormula) {
		return nullptr;
	}
	const auto owner = block(path.block);
	return owner ? &owner->formula : nullptr;
}

const TextNodeDescriptor *State::textNode(int ordinal) const {
	return (ordinal >= 0 && ordinal < textNodeCount())
		? &_textNodes[ordinal]
		: nullptr;
}

int State::textNodeOrdinal(const LeafPath &path) const {
	for (auto i = 0, count = textNodeCount(); i != count; ++i) {
		if (_textNodes[i].leaf == path) {
			return i;
		}
	}
	return -1;
}

void State::rebuild() {
	rebuildTextNodes();
	ensureEditableNodes();
	ensureActiveTextOrdinal();
	_prepared = Markdown::TryPrepareNativeInstantView({
		.richPage = _richPage,
		.mediaRuntime = _mediaRuntime,
		.editMode = true,
	}).content;
}

void State::rebuildTextNodes() {
	_textNodes.clear();
	_textNodes.reserve(_richPage->blocks.size() * 3);
	rebuildTextNodes(_richPage->blocks, BlockContainerPath());
}

void State::rebuildTextNodes(
		const std::vector<Block> &blocks,
		const BlockContainerPath &container) {
	for (auto i = 0, count = int(blocks.size()); i != count; ++i) {
		const auto path = BlockPath{
			.container = container,
			.index = i,
		};
		const auto &block = blocks[i];
		switch (block.kind) {
		case BlockKind::Heading:
		case BlockKind::Paragraph:
		case BlockKind::Footer:
		case BlockKind::Code:
			appendBlockTextNode(path, LeafKind::BlockText);
			break;
		case BlockKind::Quote:
			if (block.blocks.empty()) {
				appendBlockTextNode(
					path,
					LeafKind::BlockText,
					FieldMode::Rich,
					!block.pullquote
						? std::make_optional(InsertionAnchor{
							.container = BlockChildrenContainer(path),
							.blockIndex = -1,
						})
						: std::nullopt);
			}
			rebuildTextNodes(block.blocks, BlockChildrenContainer(path));
			appendBlockTextNode(path, LeafKind::BlockCaption);
			break;
		case BlockKind::List:
			for (auto j = 0, itemCount = int(block.listItems.size());
					j != itemCount;
					++j) {
				const auto &item = block.listItems[j];
				if (!RichTextIsEmpty(item.text) || item.blocks.empty()) {
					appendListItemTextNode(path, j);
				}
				if (!item.blocks.empty()) {
					rebuildTextNodes(
						item.blocks,
						ListItemChildrenContainer(path, j));
				}
			}
			break;
		case BlockKind::Photo:
		case BlockKind::Video:
		case BlockKind::Audio:
		case BlockKind::Map:
			appendBlockTextNode(path, LeafKind::BlockCaption);
			break;
		case BlockKind::Math:
			appendBlockTextNode(path, LeafKind::MathFormula, FieldMode::Raw);
			break;
		case BlockKind::Table:
			if (!block.text.text.text.isEmpty()) {
				appendBlockTextNode(path, LeafKind::BlockText);
			}
			for (auto j = 0, rowCount = int(block.tableRows.size());
					j != rowCount;
					++j) {
				const auto &row = block.tableRows[j];
				for (auto k = 0, cellCount = int(row.cells.size());
						k != cellCount;
						++k) {
					appendTableCellTextNode(path, j, k);
				}
			}
			break;
		case BlockKind::Details:
			appendBlockTextNode(
				path,
				LeafKind::BlockText,
				FieldMode::Rich,
				InsertionAnchor{
					.container = BlockChildrenContainer(path),
					.blockIndex = -1,
				});
			rebuildTextNodes(block.blocks, BlockChildrenContainer(path));
			break;
		default:
			rebuildTextNodes(block.blocks, BlockChildrenContainer(path));
			break;
		}
	}
}

void State::appendBlockTextNode(
		const BlockPath &path,
		LeafKind kind,
		FieldMode mode,
		std::optional<InsertionAnchor> insertionAnchor) {
	_textNodes.push_back({
		.leaf = {
			.kind = kind,
			.block = path,
		},
		.insertionAnchor = insertionAnchor.value_or(InsertionAnchor{
			.container = path.container,
			.blockIndex = path.index,
		}),
		.removalTarget = {
			.kind = RemovalKind::Block,
			.block = path,
		},
		.mode = mode,
	});
}

void State::appendListItemTextNode(const BlockPath &path, int itemIndex) {
	_textNodes.push_back({
		.leaf = {
			.kind = LeafKind::ListItemText,
			.block = path,
			.listItemIndex = itemIndex,
		},
		.insertionAnchor = {
			.container = ListItemChildrenContainer(path, itemIndex),
			.blockIndex = -1,
		},
		.removalTarget = {
			.kind = RemovalKind::ListItem,
			.block = path,
			.listItemIndex = itemIndex,
		},
		.mode = FieldMode::Rich,
	});
}

void State::appendTableCellTextNode(
		const BlockPath &path,
		int rowIndex,
		int cellIndex) {
	_textNodes.push_back({
		.leaf = {
			.kind = LeafKind::TableCellText,
			.block = path,
			.tableRowIndex = rowIndex,
			.tableCellIndex = cellIndex,
		},
		.insertionAnchor = {
			.container = path.container,
			.blockIndex = path.index,
		},
		.removalTarget = {
			.kind = RemovalKind::TableCell,
			.block = path,
			.tableRowIndex = rowIndex,
			.tableCellIndex = cellIndex,
		},
		.mode = FieldMode::Rich,
	});
}

void State::ensureActiveTextOrdinal() {
	if (_textNodes.empty()) {
		_activeTextOrdinal = -1;
	} else if (_activeTextOrdinal < 0 || _activeTextOrdinal >= textNodeCount()) {
		_activeTextOrdinal = 0;
	}
}

void State::ensureEditableNodes() {
	if (!_textNodes.empty()) {
		return;
	}
	_richPage->blocks.push_back(MakeParagraphBlock());
	rebuildTextNodes();
}

void State::focusInsertedBlocks(
		const BlockContainerPath &container,
		int from,
		int count) {
	for (auto blockIndex = from; blockIndex != from + count; ++blockIndex) {
		const auto path = BlockPath{
			.container = container,
			.index = blockIndex,
		};
		for (auto i = 0, textCount = textNodeCount(); i != textCount; ++i) {
			if (descriptorBelongsToBlock(_textNodes[i], path)
				&& setActiveTextByOrdinal(i)) {
				return;
			}
		}
	}
	ensureActiveTextOrdinal();
}

std::optional<int> State::adjacentEditableOrdinal(bool forward) const {
	if (_activeTextOrdinal < 0) {
		return std::nullopt;
	}
	const auto ordinal = _activeTextOrdinal + (forward ? 1 : -1);
	return (ordinal >= 0 && ordinal < textNodeCount())
		? std::make_optional(ordinal)
		: std::nullopt;
}

void State::collectBoundaryElements(
		const std::vector<Block> &blocks,
		const BlockContainerPath &container,
		std::vector<BoundaryElement> *elements) const {
	for (auto i = 0, count = int(blocks.size()); i != count; ++i) {
		const auto path = BlockPath{
			.container = container,
			.index = i,
		};
		const auto &block = blocks[i];
		switch (block.kind) {
		case BlockKind::Heading:
		case BlockKind::Paragraph:
		case BlockKind::Footer:
		case BlockKind::Code:
			appendBoundaryTextElement({
				.kind = LeafKind::BlockText,
				.block = path,
			}, elements);
			break;
		case BlockKind::Quote:
			if (block.blocks.empty()) {
				appendBoundaryTextElement({
					.kind = LeafKind::BlockText,
					.block = path,
				}, elements);
			}
			appendBoundaryTextElement({
				.kind = LeafKind::BlockCaption,
				.block = path,
			}, elements);
			collectBoundaryElements(
				block.blocks,
				BlockChildrenContainer(path),
				elements);
			break;
		case BlockKind::List:
			for (auto j = 0, itemCount = int(block.listItems.size());
					j != itemCount;
					++j) {
				const auto &item = block.listItems[j];
				if (!RichTextIsEmpty(item.text) || item.blocks.empty()) {
					appendBoundaryTextElement({
						.kind = LeafKind::ListItemText,
						.block = path,
						.listItemIndex = j,
					}, elements);
				}
				if (!item.blocks.empty()) {
					collectBoundaryElements(
						item.blocks,
						ListItemChildrenContainer(path, j),
						elements);
				}
			}
			break;
		case BlockKind::Photo:
		case BlockKind::Video:
		case BlockKind::Audio:
		case BlockKind::Map:
			appendBoundaryTextElement({
				.kind = LeafKind::BlockCaption,
				.block = path,
			}, elements);
			break;
		case BlockKind::Math:
			appendBoundaryTextElement({
				.kind = LeafKind::MathFormula,
				.block = path,
			}, elements);
			break;
		case BlockKind::Table:
			if (!block.text.text.text.isEmpty()) {
				appendBoundaryTextElement({
					.kind = LeafKind::BlockText,
					.block = path,
				}, elements);
			}
			for (auto j = 0, rowCount = int(block.tableRows.size());
					j != rowCount;
					++j) {
				const auto &row = block.tableRows[j];
				for (auto k = 0, cellCount = int(row.cells.size());
						k != cellCount;
						++k) {
					appendBoundaryTextElement({
						.kind = LeafKind::TableCellText,
						.block = path,
						.tableRowIndex = j,
						.tableCellIndex = k,
					}, elements);
				}
			}
			break;
		case BlockKind::Details:
			appendBoundaryTextElement({
				.kind = LeafKind::BlockText,
				.block = path,
			}, elements);
			collectBoundaryElements(
				block.blocks,
				BlockChildrenContainer(path),
				elements);
			break;
		default: {
			const auto before = elements->size();
			if (!block.blocks.empty()) {
				collectBoundaryElements(
					block.blocks,
					BlockChildrenContainer(path),
					elements);
			}
			if (elements->size() == before) {
				appendBoundaryBlockElement(path, elements);
			}
		} break;
		}
	}
}

void State::appendBoundaryTextElement(
		LeafPath leaf,
		std::vector<BoundaryElement> *elements) const {
	const auto ordinal = textNodeOrdinal(leaf);
	if (ordinal >= 0) {
		elements->push_back({
			.kind = BoundaryElement::Kind::Text,
			.textOrdinal = ordinal,
		});
	}
}

void State::appendBoundaryBlockElement(
		const BlockPath &path,
		std::vector<BoundaryElement> *elements) const {
	const auto owner = block(path);
	if (owner && CanEditBlock(*owner)) {
		elements->push_back({
			.kind = BoundaryElement::Kind::Block,
			.block = path,
		});
	}
}

PreparedEditSelection State::preparedSelectionForBlock(
		const BlockPath &path) const {
	return {
		.kind = PreparedEditSelectionKind::Blocks,
		.blocks = {
			.container = ToPreparedBlockContainerPath(path.container),
			.from = path.index,
			.till = path.index + 1,
		},
	};
}

bool State::descriptorBelongsToBlock(
		const TextNodeDescriptor &descriptor,
		const BlockPath &path) const {
	return leafBelongsToBlock(descriptor.leaf, path);
}

bool State::removalTargetIsEmpty(const RemovalTarget &target) const {
	switch (target.kind) {
	case RemovalKind::Block:
		if (const auto owner = block(target.block)) {
			return BlockIsEmpty(*owner);
		}
		return false;
	case RemovalKind::ListItem:
		if (const auto item = listItem(target.block, target.listItemIndex)) {
			return ListItemIsEmpty(*item);
		}
		return false;
	case RemovalKind::TableCell:
		if (const auto cell = tableCell(
				target.block,
				target.tableRowIndex,
				target.tableCellIndex)) {
			return RichTextIsEmpty(cell->text);
		}
		return false;
	}
	return false;
}

bool State::removeTarget(const RemovalTarget &target) {
	switch (target.kind) {
	case RemovalKind::Block: {
		const auto blocks = blockContainer(target.block.container);
		if (!blocks
			|| target.block.index < 0
			|| target.block.index >= int(blocks->size())) {
			return false;
		}
		blocks->erase(blocks->begin() + target.block.index);
		return true;
	}
	case RemovalKind::ListItem: {
		const auto owner = block(target.block);
		if (!owner
			|| target.listItemIndex < 0
			|| target.listItemIndex >= int(owner->listItems.size())) {
			return false;
		}
		owner->listItems.erase(owner->listItems.begin() + target.listItemIndex);
		return true;
	}
	case RemovalKind::TableCell: {
		const auto cell = tableCell(
			target.block,
			target.tableRowIndex,
			target.tableCellIndex);
		if (!cell) {
			return false;
		}
		cell->text = RichText();
		return true;
	}
	}
	return false;
}

bool State::anchorIdExists(const QString &id) const {
	return anchorIdExists(_richPage->blocks, id);
}

bool State::anchorIdExists(
		const std::vector<Block> &blocks,
		const QString &id) const {
	for (const auto &block : blocks) {
		if (block.anchorId == id
			|| block.text.anchorId == id
			|| block.caption.anchorId == id) {
			return true;
		}
		if (anchorIdExists(block.blocks, id)) {
			return true;
		}
		for (const auto &item : block.listItems) {
			if (item.anchorId == id || item.text.anchorId == id) {
				return true;
			}
			if (anchorIdExists(item.blocks, id)) {
				return true;
			}
		}
		for (const auto &row : block.tableRows) {
			for (const auto &cell : row.cells) {
				if (cell.text.anchorId == id) {
					return true;
				}
			}
		}
	}
	return false;
}

QString State::nextAnchorId() const {
	for (auto i = 1;; ++i) {
		auto result = u"anchor-%1"_q.arg(i);
		if (!anchorIdExists(result)) {
			return result;
		}
	}
}

Block State::makeBlock(InsertAction action) const {
	switch (action.type) {
	case InsertBlockType::Heading:
		return MakeHeadingBlock(action.headingLevel);
	case InsertBlockType::Blockquote:
		return MakeQuoteBlock(false);
	case InsertBlockType::Code:
		return MakeCodeBlock();
	case InsertBlockType::Math:
		return MakeMathBlock();
	case InsertBlockType::Footer:
		return MakeFooterBlock();
	case InsertBlockType::Divider:
		return MakeDividerBlock();
	case InsertBlockType::Anchor:
		return MakeAnchorBlock(nextAnchorId());
	case InsertBlockType::OrderedList:
		return MakeListBlock(ListKind::Ordered);
	case InsertBlockType::BulletList:
		return MakeListBlock(ListKind::Bullet);
	case InsertBlockType::TaskList:
		return MakeListBlock(ListKind::Bullet, TaskState::Unchecked);
	case InsertBlockType::Pullquote:
		return MakeQuoteBlock(true);
	case InsertBlockType::Photo:
		return MakeMediaBlock(BlockKind::Photo);
	case InsertBlockType::Video:
		return MakeMediaBlock(BlockKind::Video);
	case InsertBlockType::Audio:
		return MakeMediaBlock(BlockKind::Audio);
	case InsertBlockType::Details:
		return MakeDetailsBlock();
	case InsertBlockType::Table:
		return MakeTableBlock();
	case InsertBlockType::Map:
		return MakeMapBlock(action.latitude, action.longitude);
	}
	return MakeParagraphBlock();
}

TextWithEntities State::MakeText(QString text) {
	auto result = TextWithEntities();
	result.text = std::move(text);
	return result;
}

Block State::MakeParagraphBlock() {
	auto block = Block();
	block.kind = BlockKind::Paragraph;
	return block;
}

Block State::MakeFooterBlock() {
	auto block = Block();
	block.kind = BlockKind::Footer;
	return block;
}

Block State::MakeHeadingBlock(int level) {
	auto block = Block();
	block.kind = BlockKind::Heading;
	block.headingLevel = std::clamp(level, 1, 6);
	return block;
}

Block State::MakeQuoteBlock(bool pullquote) {
	auto block = Block();
	block.kind = BlockKind::Quote;
	block.pullquote = pullquote;
	return block;
}

Block State::MakeCodeBlock() {
	auto block = Block();
	block.kind = BlockKind::Code;
	return block;
}

Block State::MakeMathBlock() {
	auto block = Block();
	block.kind = BlockKind::Math;
	return block;
}

Block State::MakeDividerBlock() {
	auto block = Block();
	block.kind = BlockKind::Divider;
	return block;
}

Block State::MakeAnchorBlock(QString anchorId) {
	auto block = Block();
	block.kind = BlockKind::Anchor;
	block.anchorId = std::move(anchorId);
	return block;
}

Block State::MakeListBlock(ListKind kind, TaskState taskState) {
	auto block = Block();
	block.kind = BlockKind::List;
	block.listKind = kind;
	block.listItems.reserve(3);
	for (auto i = 0; i != 3; ++i) {
		auto item = ListItem();
		item.taskState = taskState;
		block.listItems.push_back(std::move(item));
	}
	return block;
}

ListItem State::MakeParagraphListItem(TaskState taskState) {
	auto item = ListItem();
	item.taskState = taskState;
	item.blocks.push_back(MakeParagraphBlock());
	return item;
}

Block State::MakeDetailsBlock() {
	auto block = Block();
	block.kind = BlockKind::Details;
	block.blocks.push_back(MakeParagraphBlock());
	return block;
}

Block State::MakeTableBlock() {
	auto block = Block();
	block.kind = BlockKind::Table;
	block.tableRows.reserve(3);
	for (auto rowIndex = 0; rowIndex != 3; ++rowIndex) {
		auto row = RichPage::TableRow();
		row.cells.reserve(3);
		for (auto cellIndex = 0; cellIndex != 3; ++cellIndex) {
			auto cell = TableCell();
			cell.header = (rowIndex == 0);
			row.cells.push_back(std::move(cell));
		}
		block.tableRows.push_back(std::move(row));
	}
	return block;
}

Block State::MakeMediaBlock(BlockKind kind) {
	auto block = Block();
	block.kind = kind;
	return block;
}

Block State::MakeMapBlock(double latitude, double longitude) {
	auto block = Block();
	block.kind = BlockKind::Map;
	block.latitude = latitude;
	block.longitude = longitude;
	return block;
}

bool State::RichTextIsEmpty(const RichText &text) {
	return StringIsEmpty(text.text.text)
		&& text.anchorId.isEmpty()
		&& text.anchorIds.empty();
}

bool State::ListItemIsEmpty(const ListItem &item) {
	if (!RichTextIsEmpty(item.text) || !item.anchorId.isEmpty()) {
		return false;
	}
	for (const auto &block : item.blocks) {
		if (!BlockIsEmpty(block)) {
			return false;
		}
	}
	return true;
}

bool State::BlockIsEmpty(const Block &block) {
	if (!RichTextIsEmpty(block.text)
		|| !RichTextIsEmpty(block.caption)
		|| !StringIsEmpty(block.formula)
		|| !block.language.isEmpty()
		|| !block.anchorId.isEmpty()
		|| !block.url.isEmpty()
		|| !block.html.isEmpty()
		|| !block.author.isEmpty()
		|| !block.username.isEmpty()
		|| !block.channelTitle.isEmpty()
		|| !block.audioTitle.isEmpty()
		|| !block.audioPerformer.isEmpty()
		|| !block.audioFileName.isEmpty()
		|| block.photo
		|| block.document
		|| block.peer
		|| block.photoId
		|| block.documentId
		|| block.channelId
		|| block.accessHash
		|| block.latitude != 0.
		|| block.longitude != 0.
		|| !block.mediaItems.empty()) {
		return false;
	}
	for (const auto &child : block.blocks) {
		if (!BlockIsEmpty(child)) {
			return false;
		}
	}
	for (const auto &item : block.listItems) {
		if (!ListItemIsEmpty(item)) {
			return false;
		}
	}
	for (const auto &row : block.tableRows) {
		for (const auto &cell : row.cells) {
			if (!RichTextIsEmpty(cell.text)) {
				return false;
			}
		}
	}
	return true;
}

bool State::StripWrapperEntityInEditMode(EntityType type) {
	switch (type) {
	case EntityType::Url:
	case EntityType::Email:
	case EntityType::Hashtag:
	case EntityType::Cashtag:
	case EntityType::Mention:
	case EntityType::BotCommand:
	case EntityType::Phone:
	case EntityType::BankCard:
		return true;
	default:
		return false;
	}
}

TextWithEntities State::StripEditModeWrapperEntities(TextWithEntities text) {
	auto filtered = EntitiesInText();
	filtered.reserve(text.entities.size());
	for (const auto &entity : text.entities) {
		if (!StripWrapperEntityInEditMode(entity.type())) {
			filtered.push_back(entity);
		}
	}
	text.entities = std::move(filtered);
	return text;
}

bool CanEditRichPage(const RichPage &page) {
	return CanEditBlocks(page.blocks);
}

bool CanEditRichPage(const std::shared_ptr<const RichPage> &page) {
	return page && CanEditRichPage(*page);
}

} // namespace Iv::Editor