import { Command, EditorView } from '@codemirror/view';

export interface ToggleCheckboxOptions {
	autoSort?: boolean;
}

export interface ChecklistItemBlock {
	lines: string[];
	isChecked: boolean;
	isTarget: boolean;
}

const CHECKLIST_REGEX = /^(\s*(?:[-*+]|\d+\.)\s+)\[([ xX])\]/;

/**
 * 判断单行文本是否符合 Markdown 任务列表语法（如 `- [ ] 待办`、`1. [x] 已完成`）
 */
export const isChecklistLine = (lineText: string): boolean => {
	return CHECKLIST_REGEX.test(lineText);
};

/**
 * 获取单行前置缩进空格数
 */
export const getLineIndent = (lineText: string): number => {
	const match = lineText.match(/^\s*/);
	return match ? match[0].length : 0;
};

/**
 * 对连续待办列表项执行重排（对标 Apple 备忘录自动沉底体验）
 * - 未勾选项保留在顶部
 * - 新勾选的项沉底至已完成列表末尾
 * - 取消勾选的项浮动至未完成列表末尾
 */
export const reorderChecklistItems = (
	items: ChecklistItemBlock[],
	targetChecked: boolean,
): ChecklistItemBlock[] => {
	const unchecked: ChecklistItemBlock[] = [];
	const checked: ChecklistItemBlock[] = [];
	let targetItem: ChecklistItemBlock | null = null;

	for (const item of items) {
		const isItemChecked = item.isTarget ? targetChecked : item.isChecked;
		const updatedItem: ChecklistItemBlock = {
			...item,
			isChecked: isItemChecked,
			lines: item.lines.map((l, idx) => {
				if (item.isTarget && idx === 0) {
					return l.replace(CHECKLIST_REGEX, (_match, prefix) => `${prefix}[${targetChecked ? 'x' : ' '}]`);
				}
				return l;
			}),
		};

		if (item.isTarget) {
			targetItem = updatedItem;
		} else if (isItemChecked) {
			checked.push(updatedItem);
		} else {
			unchecked.push(updatedItem);
		}
	}

	if (targetItem) {
		if (targetChecked) {
			// 勾选完成：沉底至已完成项的最末端
			checked.push(targetItem);
		} else {
			// 取消勾选：浮动至未完成项的最末端
			unchecked.push(targetItem);
		}
	}

	return [...unchecked, ...checked];
};

/**
 * 切换指定位置的复选框状态，并支持连续待办清单自动沉底
 */
const toggleCheckbox = (linePos: number, options: ToggleCheckboxOptions = { autoSort: true }): Command => (target: EditorView) => {
	const state = target.state;
	if (linePos >= state.doc.length) {
		return false;
	}

	const line = state.doc.lineAt(linePos);
	const checklistMatch = line.text.match(CHECKLIST_REGEX);

	// 非行首标准列表项，回退到就地匹配替换
	if (!checklistMatch) {
		const genericMatch = line.text.match(/\[([ xX])\]/);
		if (!genericMatch) {
			return false;
		}
		const isChecked = genericMatch[1].toLowerCase() === 'x';
		const checkboxPos = genericMatch.index! + line.from;
		target.dispatch({
			changes: [{ from: checkboxPos, to: checkboxPos + 3, insert: isChecked ? '[ ]' : '[x]' }],
		});
		return true;
	}

	const isCurrentlyChecked = checklistMatch[2].toLowerCase() === 'x';
	const newChecked = !isCurrentlyChecked;
	const shouldAutoSort = options.autoSort !== false;

	if (!shouldAutoSort) {
		const checkboxPos = checklistMatch[1].length + line.from;
		target.dispatch({
			changes: [{ from: checkboxPos, to: checkboxPos + 3, insert: newChecked ? '[x]' : '[ ]' }],
		});
		return true;
	}

	// 自动排序模式：查找同缩进层级的连续清单块
	const baseIndent = getLineIndent(line.text);
	let startLineNo = line.number;
	let endLineNo = line.number;

	// 向上探测列表起始行
	for (let i = line.number - 1; i >= 1; i--) {
		const prevLine = state.doc.line(i);
		if (!prevLine.text.trim()) break; // 空行阻断清单块
		const indent = getLineIndent(prevLine.text);
		if (isChecklistLine(prevLine.text) && indent === baseIndent) {
			startLineNo = i;
		} else if (indent > baseIndent) {
			continue;
		} else {
			break;
		}
	}

	// 向下探测列表结束行
	for (let i = line.number + 1; i <= state.doc.lines; i++) {
		const nextLine = state.doc.line(i);
		if (!nextLine.text.trim()) break; // 空行阻断清单块
		const indent = getLineIndent(nextLine.text);
		if (isChecklistLine(nextLine.text) && indent === baseIndent) {
			endLineNo = i;
		} else if (indent > baseIndent) {
			endLineNo = i;
		} else {
			break;
		}
	}

	// 将行聚合成项（包含可能的子缩进行）
	const items: ChecklistItemBlock[] = [];
	let currentItem: ChecklistItemBlock | null = null;

	for (let i = startLineNo; i <= endLineNo; i++) {
		const currentDocLine = state.doc.line(i);
		const indent = getLineIndent(currentDocLine.text);
		const isItemHeader = isChecklistLine(currentDocLine.text) && indent === baseIndent;

		if (isItemHeader) {
			if (currentItem) {
				items.push(currentItem);
			}
			const match = currentDocLine.text.match(CHECKLIST_REGEX);
			currentItem = {
				lines: [currentDocLine.text],
				isChecked: match ? match[2].toLowerCase() === 'x' : false,
				isTarget: i === line.number,
			};
		} else if (currentItem) {
			currentItem.lines.push(currentDocLine.text);
		}
	}
	if (currentItem) {
		items.push(currentItem);
	}

	// 单项列表直接就地切换，不触发重排
	if (items.length <= 1) {
		const checkboxPos = checklistMatch[1].length + line.from;
		target.dispatch({
			changes: [{ from: checkboxPos, to: checkboxPos + 3, insert: newChecked ? '[x]' : '[ ]' }],
		});
		return true;
	}

	const reordered = reorderChecklistItems(items, newChecked);
	const newContentLines: string[] = [];
	for (const item of reordered) {
		newContentLines.push(...item.lines);
	}

	const replaceFrom = state.doc.line(startLineNo).from;
	const replaceTo = state.doc.line(endLineNo).to;
	const newText = newContentLines.join('\n');

	target.dispatch({
		changes: [{ from: replaceFrom, to: replaceTo, insert: newText }],
	});
	return true;
};

export default toggleCheckbox;