<?php

/**
 * Creates blocker-resistant copies of plugin admin assets.
 *
 * @package    AdUnblocker
 * @subpackage AdUnblocker/admin
 */
class AdUnblocker_Admin_Assets
{
	const OPTION_NAME = 'daau_admin_asset_bundle';
	const BUNDLE_OWNER = 'admin';
	const MARKER_FILE = '.daau-admin-assets';
	const MARKER_CONTENT = 'adunblocker';

	private static $instances = array();

	private $version;
	private $state;

	private function __construct($version)
	{
		$this->version = sanitize_text_field((string) $version);
	}

	/**
	 * Returns the shared manager for this plugin.
	 *
	 * @param string $plugin_name Plugin identifier.
	 * @param string $version Plugin version.
	 * @return AdUnblocker_Admin_Assets
	 */
	public static function instance($plugin_name, $version)
	{
		$key = sanitize_key($plugin_name);
		if (! isset(self::$instances[$key])) {
			self::$instances[$key] = new self($version);
		}

		return self::$instances[$key];
	}

	/**
	 * Returns an opaque public URL for an admin asset.
	 *
	 * The original URL is returned when the source cannot be copied, allowing
	 * WordPress to retain its normal asset-loading behaviour on read-only hosts.
	 *
	 * @param string $logical_name Internal asset identifier.
	 * @param string $source_path Absolute source file path.
	 * @param string $fallback_url Original plugin asset URL.
	 * @return string
	 */
	public function get_asset_url($logical_name, $source_path, $fallback_url)
	{
		$logical_name = sanitize_key($logical_name);
		$source_path = (string) $source_path;
		$extension = strtolower(pathinfo($source_path, PATHINFO_EXTENSION));

		if (
			'' === $logical_name ||
			! in_array($extension, array('css', 'js'), true) ||
			! is_file($source_path) ||
			! is_readable($source_path)
		) {
			return $fallback_url;
		}

		$state = $this->get_state();
		if (! $this->ensure_bundle_directory($state['key'])) {
			return $fallback_url;
		}

		$signature = hash_file('sha256', $source_path);
		if (! is_string($signature) || '' === $signature) {
			return $fallback_url;
		}

		$entry = isset($state['files'][$logical_name]) && is_array($state['files'][$logical_name])
			? $state['files'][$logical_name]
			: array();
		$file_name = isset($entry['file']) ? sanitize_file_name((string) $entry['file']) : '';
		$target_path = $this->get_bundle_path($state['key'], $file_name);
		$is_current = (
			isset($entry['signature']) &&
			hash_equals((string) $entry['signature'], $signature) &&
			$this->is_safe_asset_file_name($file_name, $extension) &&
			is_file($target_path)
		);

		if (! $is_current) {
			$new_file_name = $this->generate_available_file_name($state['key'], $extension);
			if ('' === $new_file_name) {
				return $fallback_url;
			}

			$new_target_path = $this->get_bundle_path($state['key'], $new_file_name);
			if (! $this->copy_atomically($source_path, $new_target_path)) {
				return $fallback_url;
			}

			$old_file_name = $file_name;
			$state['files'][$logical_name] = array(
				'file' => $new_file_name,
				'signature' => $signature,
			);
			$this->state = $state;
			$this->persist_state($state);

			if ($this->is_safe_asset_file_name($old_file_name, $extension)) {
				$old_target_path = AdUnblocker_Asset_Cache::get_path($state['key'], $old_file_name);
				if ($old_target_path !== $new_target_path && is_file($old_target_path)) {
					AdUnblocker_Asset_Cache::delete_file($state['key'], self::BUNDLE_OWNER, $old_file_name);
				}
			}

			$file_name = $new_file_name;
			AdUnblocker_Asset_Cache::delete_legacy_marked_bundle(
				$state['key'],
				self::MARKER_FILE,
				self::MARKER_CONTENT
			);
		}

		$asset_url = AdUnblocker_Asset_Cache::get_url($state['key'], $file_name);

		return '' !== $asset_url ? $asset_url : $fallback_url;
	}

	/**
	 * Removes the generated admin bundle during plugin deactivation.
	 *
	 * @return void
	 */
	public static function clear_bundle()
	{
		$state = get_option(self::OPTION_NAME, array());
		$key = isset($state['key']) ? sanitize_file_name((string) $state['key']) : '';

		AdUnblocker_Asset_Cache::delete_bundle($key, self::BUNDLE_OWNER);
		AdUnblocker_Asset_Cache::delete_legacy_marked_bundle(
			$key,
			self::MARKER_FILE,
			self::MARKER_CONTENT
		);
		delete_option(self::OPTION_NAME);
		self::$instances = array();
	}

	private function get_state()
	{
		if (is_array($this->state)) {
			return $this->state;
		}

		$state = get_option(self::OPTION_NAME, array());
		$is_valid = (
			is_array($state) &&
			isset($state['key'], $state['version'], $state['files']) &&
			$this->is_safe_bundle_key($state['key']) &&
			is_array($state['files'])
		);

		if ($is_valid && (string) $state['version'] === $this->version) {
			$this->state = $state;
			return $this->state;
		}

		if ($is_valid) {
			AdUnblocker_Asset_Cache::delete_bundle($state['key'], self::BUNDLE_OWNER);
			AdUnblocker_Asset_Cache::delete_legacy_marked_bundle(
				$state['key'],
				self::MARKER_FILE,
				self::MARKER_CONTENT
			);
		}

		$this->state = array(
			'key' => $this->generate_available_bundle_key(),
			'version' => $this->version,
			'files' => array(),
		);
		$this->persist_state($this->state);

		return $this->state;
	}

	private function persist_state($state)
	{
		if (false === get_option(self::OPTION_NAME, false)) {
			return add_option(self::OPTION_NAME, $state, '', 'no');
		}

		return update_option(self::OPTION_NAME, $state, false);
	}

	private function ensure_bundle_directory($key)
	{
		return AdUnblocker_Asset_Cache::ensure_bundle($key, self::BUNDLE_OWNER);
	}

	private function copy_atomically($source_path, $target_path)
	{
		$file_name = wp_basename($target_path);
		$bundle_key = wp_basename(dirname($target_path));

		return AdUnblocker_Asset_Cache::copy(
			$bundle_key,
			self::BUNDLE_OWNER,
			$file_name,
			$source_path
		);
	}

	private function generate_available_bundle_key()
	{
		for ($attempt = 0; $attempt < 10; $attempt++) {
			$key = $this->generate_opaque_name(16);
			if (! file_exists(AdUnblocker_Asset_Cache::get_path($key))) {
				return $key;
			}
		}

		return '';
	}

	private function generate_available_file_name($key, $extension)
	{
		for ($attempt = 0; $attempt < 10; $attempt++) {
			$file_name = $this->generate_opaque_name(16) . '.' . $extension;
			if (! file_exists(AdUnblocker_Asset_Cache::get_path($key, $file_name))) {
				return $file_name;
			}
		}

		return '';
	}

	private function generate_opaque_name($length)
	{
		$characters = 'cefghijklmnpqruvwxyz';
		$name = '';
		$max_index = strlen($characters) - 1;

		for ($index = 0; $index < $length; $index++) {
			$name .= $characters[random_int(0, $max_index)];
		}

		return $name;
	}

	private function get_bundle_path($key, $file_name = '')
	{
		return AdUnblocker_Asset_Cache::get_path($key, $file_name);
	}

	private function is_safe_bundle_key($key)
	{
		return is_string($key) && 1 === preg_match('/^[cefghijklmnpqruvwxyz]{16}$/', $key);
	}

	private function is_safe_asset_file_name($file_name, $extension)
	{
		return is_string($file_name) && 1 === preg_match(
			'/^[cefghijklmnpqruvwxyz]{16}\.' . preg_quote($extension, '/') . '$/',
			$file_name
		);
	}

}