#!/usr/bin/env node
import { existsSync } from 'node:fs';
import { readdir, readFile, rename, writeFile } from 'node:fs/promises';
import { basename, dirname, relative, resolve } from 'node:path';
import { fileURLToPath } from 'node:url';

const EXCLUDED_DIRECTORIES = new Set(['.git', '.hg', '.svn', 'node_modules', 'vendor', 'dist', 'target', '__pycache__']);
const utf8Decoder = new TextDecoder('utf-8', { fatal: true, ignoreBOM: true });
const argumentsList = process.argv.slice(2);
const applyChanges = argumentsList.at(-1) === '--apply';

if (applyChanges) {
	argumentsList.pop();
}

if (argumentsList.length !== 2 || argumentsList[0] === '') {
	console.error('Usage: node replace-text.mjs <old> <new> [--apply]');
	process.exit(1);
}

const [oldText, newText] = argumentsList;
if (newText.includes('/') || newText.includes('\\')) {
	console.error('The new value cannot contain a path separator.');
	process.exit(1);
}

const rootDirectory = resolve(process.cwd());
const scriptPath = resolve(fileURLToPath(import.meta.url));
const textChanges = new Map();
const pathChanges = new Map();

await scanDirectory(rootDirectory);
const sortedPathChanges = validatePathChanges(pathChanges);

for (const file of textChanges.keys()) {
	console.log(`${applyChanges ? 'Updating' : 'Would update'} ${displayPath(file)}`);
}

for (const [source, target] of sortedPathChanges) {
	console.log(`${applyChanges ? 'Renaming' : 'Would rename'} ${displayPath(source)} to ${displayPath(target)}`);
}

if (!applyChanges) {
	console.log('\nDry run only. Re-run with --apply to write the changes.');
	process.exit(0);
}

for (const [file, contents] of textChanges) {
	await writeFile(file, contents);
}

for (const [source, target] of sortedPathChanges) {
	await rename(source, target);
}

console.log(`Replaced text in ${textChanges.size} file(s) and renamed ${pathChanges.size} path(s).`);

/**
 * Scans a directory tree for text and path replacements.
 *
 * @param {string} directory
 * @returns {Promise<void>}
 */
async function scanDirectory(directory) {
	let entries;

	try {
		entries = await readdir(directory, { withFileTypes: true });
	} catch {
		console.error(`Unable to read directory: ${displayPath(directory)}.`);
		process.exit(1);
	}

	for (const entry of entries) {
		const path = resolve(directory, entry.name);
		if (path === scriptPath || entry.isSymbolicLink()) {
			continue;
		}

		collectPathChange(path, oldText, newText, pathChanges);

		if (entry.isDirectory()) {
			if (!EXCLUDED_DIRECTORIES.has(entry.name)) {
				await scanDirectory(path);
			}
			continue;
		}

		if (entry.isFile()) {
			await collectTextChange(path, oldText, newText, textChanges);
		}
	}
}

/**
 * Records a rename when a file or directory basename contains the old text.
 *
 * @param {string} path
 * @param {string} oldValue
 * @param {string} newValue
 * @param {Map<string, string>} changes
 */
function collectPathChange(path, oldValue, newValue, changes) {
	if (basename(path).includes(oldValue)) {
		changes.set(path, resolve(dirname(path), basename(path).replaceAll(oldValue, newValue)));
	}
}

/**
 * Records a replacement when a file is text and contains the old text.
 *
 * @param {string} path
 * @param {string} oldValue
 * @param {string} newValue
 * @param {Map<string, string>} changes
 * @returns {Promise<void>}
 */
async function collectTextChange(path, oldValue, newValue, changes) {
	let contents;

	try {
		contents = await readFile(path);
	} catch {
		console.error(`Unable to read file: ${displayPath(path)}.`);
		process.exit(1);
	}

	if (contents.includes(0) || !contents.includes(oldValue)) {
		return;
	}

	const text = decodeUtf8(contents);
	if (text === null) {
		console.warn(`Skipped non-UTF-8 file: ${displayPath(path)}.`);
		return;
	}

	changes.set(path, text.replaceAll(oldValue, newValue));
}

/**
 * Decodes a buffer as strict UTF-8, preserving any BOM.
 *
 * @param {Buffer} contents
 * @returns {string|null} Decoded text, or null when the bytes are not valid UTF-8.
 */
function decodeUtf8(contents) {
	try {
		return utf8Decoder.decode(contents);
	} catch (error) {
		if (error instanceof TypeError) {
			return null;
		}
		throw error;
	}
}

/**
 * Validates path targets and orders renames from deepest to shallowest.
 *
 * @param {Map<string, string>} changes
 * @returns {[string, string][]}
 */
function validatePathChanges(changes) {
	const targets = [...changes.values()];
	if (new Set(targets).size !== targets.length) {
		console.error('The replacement would create duplicate paths.');
		process.exit(1);
	}

	for (const [source, target] of changes) {

		// Case-insensitive filesystems (NTFS, APFS) resolve a case-only target to the source itself.
		const isCaseOnlyRename = source.toLowerCase() === target.toLowerCase();
		if (existsSync(target) && !changes.has(target) && !isCaseOnlyRename) {
			console.error(`Target path already exists: ${displayPath(target)}.`);
			process.exit(1);
		}
	}

	return [...changes].sort(([left], [right]) => right.length - left.length);
}

/**
 * Formats an absolute path relative to the scanned directory.
 *
 * @param {string} path
 * @returns {string}
 */
function displayPath(path) {
	return relative(rootDirectory, path) || '.';
}