<?php
/**
 * Short tracked links for messages.
 *
 * @package Rahkar\WP
 */

declare( strict_types = 1 );

namespace Rahkar\WP\Notifications;

use Rahkar\WP\Database\Schema;
use Rahkar\WP\Support\Events;
use Rahkar\WP\Support\Logger;
use Rahkar\WP\Support\Manifest;

defined( 'ABSPATH' ) || exit;

/**
 * Turns a long link — a cart recovery URL with its UTM tags — into
 * `example.com/r/k7Qx2aPm` for one recipient and one message.
 *
 * The long URL stays in this site's database and nowhere else. The SMS carries
 * eight characters instead of a hundred and fifty, which on a Persian message
 * is one or two fewer billed parts, and a link a customer recognises as the
 * shop's own.
 *
 * The redirect itself, the click record, the attribution cookie and the coupon
 * that rides along live in the `tracked_links` module ({@see \Rahkar\WP\Modules\TrackedLinks\Redirector}).
 * This class is the part other modules call; when the module is off it returns
 * the long URL unchanged, so a message never loses its link.
 */
final class TrackedLinks {

	/**
	 * Path segment the short links live under.
	 */
	public const PATH = 'r';

	/**
	 * Default lifetime, in days. Matches the attribution cookie.
	 */
	public const TTL_DAYS = 7;

	/**
	 * Days an expired link is kept, so a late click still lands somewhere sensible
	 * and the dashboard can still read the row.
	 */
	public const KEEP_DAYS = 30;

	/**
	 * Destination kinds the contract knows (EVENTS-v1.md §9, `link.created`).
	 */
	public const TARGETS = [ 'cart', 'checkout', 'product', 'review', 'home', 'page' ];

	private const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';

	/**
	 * Is the module on?
	 */
	public static function enabled(): bool {
		return Manifest::isEnabled( 'tracked_links' );
	}

	/**
	 * A short link for one message, or the long URL when it cannot be made.
	 *
	 * @param string                $url       Destination on this site, UTM tags included.
	 * @param string                $module    Module slug, e.g. `abandoned_cart`.
	 * @param string                $target    One of {@see self::TARGETS}.
	 * @param array<string, mixed>  $options   Optional: `flow`, `step` (slug, e.g. `reminder1`), `phone`,
	 *                                         `message_id` (UUID), `coupon_code`, `product_id`, `ttl_days`.
	 * @param array<string, string> $context   Ids the link is about, e.g. `cart_id`.
	 */
	public static function create( string $url, string $module, string $target, array $options = [], array $context = [] ): string {
		if ( ! self::enabled() || '' === $url ) {
			return $url;
		}

		// Same host as the shop, or no short link: the redirect must never be an
		// open redirect, and a link elsewhere is not the shop's to shorten.
		$host = wp_parse_url( home_url(), PHP_URL_HOST );

		if ( ! is_string( $host ) || wp_parse_url( $url, PHP_URL_HOST ) !== $host ) {
			Logger::warning( 'links', 'Refused to shorten a link to another host.', [ 'module' => $module ] );

			return $url;
		}

		$target    = in_array( $target, self::TARGETS, true ) ? $target : 'page';
		$phone     = PhoneNumber::parse( (string) ( $options['phone'] ?? '' ) );
		$messageId = (string) ( $options['message_id'] ?? '' );
		$coupon    = (string) ( $options['coupon_code'] ?? '' );
		$productId = (int) ( $options['product_id'] ?? 0 );
		$flow      = sanitize_key( (string) ( $options['flow'] ?? '' ) );
		$step      = sanitize_key( (string) ( $options['step'] ?? '' ) );
		$ttl       = max( 1, (int) ( $options['ttl_days'] ?? self::TTL_DAYS ) );
		$expires   = time() + ( $ttl * DAY_IN_SECONDS );
		$token     = self::insert( $url, $module, $flow, $step, $target, $productId, $coupon, $phone, $messageId, $expires );

		if ( null === $token ) {
			return $url;
		}

		if ( Events::listening() ) {
			$data = [
				'token'       => $token,
				'module'      => sanitize_key( $module ),
				'flow'        => '' === $flow ? null : $flow,
				'step'        => '' === $step ? null : $step,
				'message_id'  => 1 === preg_match( '/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/', $messageId ) ? $messageId : null,
				'target'      => $target,
				'product_id'  => $productId > 0 ? (string) $productId : null,
				'coupon_code' => '' === $coupon ? null : $coupon,
				'expires_at'  => gmdate( 'Y-m-d\TH:i:s\Z', $expires ),
				'phone'       => null === $phone ? null : $phone->canonical(),
			];

			$context = Message::context( $context );

			if ( [] !== $context ) {
				$data['context'] = $context;
			}

			Events::emit( 'link.created', $data );
		}

		return self::url( $token );
	}

	/**
	 * The public address of a token.
	 *
	 * @param string $token Link token.
	 */
	public static function url( string $token ): string {
		return home_url( '/' . self::PATH . '/' . $token );
	}

	/**
	 * Store a link under a fresh token.
	 *
	 * @param string           $url       Destination.
	 * @param string           $module    Module slug.
	 * @param string           $flow      Flow slug.
	 * @param string           $step      Step slug.
	 * @param string           $target    Destination kind.
	 * @param int              $productId Product, or 0.
	 * @param string           $coupon    Coupon to apply, or empty.
	 * @param PhoneNumber|null $phone     Recipient.
	 * @param string           $messageId Message carrying the link.
	 * @param int              $expires   Expiry timestamp.
	 *
	 * @return string|null The token, or null when the row could not be written.
	 */
	private static function insert( string $url, string $module, string $flow, string $step, string $target, int $productId, string $coupon, ?PhoneNumber $phone, string $messageId, int $expires ): ?string {
		global $wpdb;

		$table = Schema::table( 'links' );

		// 62^8 tokens: guessing one is not a strategy. A collision is retried
		// rather than assumed impossible.
		for ( $try = 0; $try < 3; $try++ ) {
			$token = self::token();

			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Own table; the unique key decides.
			$written = $wpdb->query(
				$wpdb->prepare(
					'INSERT IGNORE INTO %i (token, module, flow, step, target, destination, product_id, coupon_code, phone_hash, message_id, created_at, expires_at) VALUES (%s, %s, %s, %s, %s, %s, %d, %s, %s, %s, %s, %s)',
					$table,
					$token,
					sanitize_key( $module ),
					$flow,
					$step,
					$target,
					$url,
					$productId,
					$coupon,
					null === $phone ? '' : SiteKey::phoneHash( $phone->canonical() ),
					substr( $messageId, 0, 36 ),
					gmdate( 'Y-m-d H:i:s' ),
					gmdate( 'Y-m-d H:i:s', $expires )
				)
			);

			if ( 1 === $written ) {
				self::maybePurge();

				return $token;
			}
		}

		Logger::error( 'links', 'Could not store a short link.', [ 'module' => $module ] );

		return null;
	}

	/**
	 * Eight random characters from the 62-letter alphabet.
	 */
	private static function token(): string {
		$token = '';

		for ( $i = 0; $i < 8; $i++ ) {
			$token .= self::ALPHABET[ random_int( 0, 61 ) ];
		}

		return $token;
	}

	/**
	 * Now and then, drop links long past their expiry.
	 *
	 * Trimmed as links are made rather than by a job of its own: a store that
	 * sends nothing never grows the table.
	 */
	private static function maybePurge(): void {
		if ( 1 !== wp_rand( 1, 100 ) ) {
			return;
		}

		global $wpdb;

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Own table, bounded delete.
		$wpdb->query(
			$wpdb->prepare(
				'DELETE FROM %i WHERE expires_at < %s LIMIT 1000',
				Schema::table( 'links' ),
				gmdate( 'Y-m-d H:i:s', time() - ( self::KEEP_DAYS * DAY_IN_SECONDS ) )
			)
		);
	}
}