/**
 * Regex pattern for markdown todo checkboxes (for toggling).
 */
const TODO_PATTERN = /^(\s*[-*+]\s+\[)([xX ]?)(\].*)$/;

/**
 * Toggle the checkbox state at the specified line number.
 * Returns the modified content.
 */
export function toggleTodo(content: string, lineNumber: number): string {
	const lines = content.split('\n');

	if (lineNumber < 0 || lineNumber >= lines.length) {
		return content;
	}

	const line = lines[lineNumber];
	if (line === undefined) {
		return content;
	}

	const match = line.match(TODO_PATTERN);
	if (!match) {
		return content;
	}

	const checkboxContent = match[2];
	const isChecked = checkboxContent === 'x' || checkboxContent === 'X';
	const newCheckbox = isChecked ? ' ' : 'x';

	lines[lineNumber] = `${match[1]}${newCheckbox}${match[3]}`;
	return lines.join('\n');
}

/**
 * Remove the line at the specified line number.
 * Returns the modified content.
 */
export function removeTodoLine(content: string, lineNumber: number): string {
	const lines = content.split('\n');

	if (lineNumber < 0 || lineNumber >= lines.length) {
		return content;
	}

	lines.splice(lineNumber, 1);
	return lines.join('\n');
}

/**
 * Insert a todo line at the end of the content.
 * Handles files with/without trailing newlines.
 */
export function insertTodoAtEnd(content: string, todoLine: string): string {
	if (!content) {
		return todoLine;
	}

	// If content ends with newline(s), append directly
	if (content.endsWith('\n')) {
		return content + todoLine;
	}

	// Otherwise add a newline before the todo
	return content + '\n' + todoLine;
}

/**
 * Move a todo (and its children) from one position to another within the same content.
 * @param content - The file content
 * @param todoLineNumber - Line number of the todo to move
 * @param childLineNumbers - Line numbers of child todos (must be consecutive after todoLineNumber)
 * @param targetLineNumber - Line number to insert before (0-based). Lines are inserted at this position.
 */
export function moveTodoWithChildren(
	content: string,
	todoLineNumber: number,
	childLineNumbers: number[],
	targetLineNumber: number
): string {
	const lines = content.split('\n');
	const allLineNumbers = [todoLineNumber, ...childLineNumbers].sort((a, b) => a - b);

	// Extract the lines to move
	const movedLines = allLineNumbers.map((ln) => lines[ln]!);

	// If moving to same position, no-op
	if (targetLineNumber === todoLineNumber) {
		return content;
	}

	// Remove lines from original positions (in reverse to preserve indices)
	for (let i = allLineNumbers.length - 1; i >= 0; i--) {
		lines.splice(allLineNumbers[i]!, 1);
	}

	// Adjust target position for removed lines
	let adjustedTarget = targetLineNumber;
	for (const ln of allLineNumbers) {
		if (ln < targetLineNumber) {
			adjustedTarget--;
		}
	}

	// Insert at adjusted target
	lines.splice(adjustedTarget, 0, ...movedLines);

	return lines.join('\n');
}

/**
 * Move a todo (and its children) under a heading within the same file.
 * Inserts at the end of the heading's section.
 * @param content - The file content
 * @param todoLineNumber - Line number of the todo to move
 * @param childLineNumbers - Line numbers of child todos
 * @param headingLineNumber - Line number of the target heading
 * @param nextHeadingLineNumber - Optional line number of the next heading (section boundary)
 */
export function moveTodoUnderHeadingInFile(
	content: string,
	todoLineNumber: number,
	childLineNumbers: number[],
	headingLineNumber: number,
	nextHeadingLineNumber?: number
): string {
	// Determine insert position: end of section (before next heading) or after heading
	let targetLineNumber: number;
	if (nextHeadingLineNumber !== undefined) {
		targetLineNumber = nextHeadingLineNumber;
	} else {
		// No next heading — insert at end of file
		const lines = content.split('\n');
		targetLineNumber = lines.length;
	}

	return moveTodoWithChildren(content, todoLineNumber, childLineNumbers, targetLineNumber);
}

/**
 * Adjust indentation of todo lines by a delta (positive = indent, negative = outdent).
 * Each level is 2 spaces. Will not outdent past zero.
 */
export function indentTodoLines(todoLines: string[], indentDelta: number): string[] {
	if (indentDelta === 0) return [...todoLines];

	const indent = '  '; // 2 spaces per level

	return todoLines.map((line) => {
		if (indentDelta > 0) {
			return indent.repeat(indentDelta) + line;
		} else {
			// Outdent: remove leading spaces
			let result = line;
			for (let i = 0; i < Math.abs(indentDelta); i++) {
				if (result.startsWith(indent)) {
					result = result.slice(indent.length);
				} else if (result.startsWith('\t')) {
					result = result.slice(1);
				}
			}
			return result;
		}
	});
}

/**
 * Insert a todo line under a specific heading.
 * @param content - The file content
 * @param headingLineNumber - The line number of the heading (0-based)
 * @param todoLine - The todo line to insert
 * @param nextHeadingLineNumber - Optional line number of the next heading (for section boundary)
 * @param addBlankLine - Whether to add a blank line between the heading and the todo
 */
export function insertTodoUnderHeading(
	content: string,
	headingLineNumber: number,
	todoLine: string,
	nextHeadingLineNumber?: number,
	addBlankLine = false
): string {
	const lines = content.split('\n');

	// Determine where to insert
	let insertPosition: number;

	if (nextHeadingLineNumber !== undefined) {
		insertPosition = nextHeadingLineNumber;
	} else {
		insertPosition = headingLineNumber + 1;
	}

	if (addBlankLine) {
		// Check if there's already a blank line at the insert position
		const lineAfterHeading = lines[headingLineNumber + 1];
		const alreadyHasBlank = lineAfterHeading !== undefined && lineAfterHeading.trim() === '';

		if (alreadyHasBlank) {
			// Insert after the existing blank line
			lines.splice(headingLineNumber + 2, 0, todoLine);
		} else {
			// Insert blank line + todo
			lines.splice(insertPosition, 0, '', todoLine);
		}
	} else {
		lines.splice(insertPosition, 0, todoLine);
	}

	return lines.join('\n');
}