<?php
/**
 * Value transforms for migrating WebCalendar 1.9.x data.
 *
 * @package WebCalendar\WP\Migration
 */

declare(strict_types=1);

namespace WebCalendar\WP\Migration;

defined( 'ABSPATH' ) || exit;

use DateTimeImmutable;
use DateTimeZone;

/**
 * Pure transforms derived from the Phase 0 verification of how 1.9.x stores
 * data (see legacy-migration-plan.md):
 *
 * - Timed values (event start, task due, mod timestamps) are stored in GMT
 *   and must be rebased to the site timezone using the offset AT THAT DATE.
 * - All-day (cal_time=0 + cal_duration=1440) and untimed (cal_time=-1) events
 *   store literal local dates and must not be shifted; both map to the
 *   plugin's single all-day representation (cal_time = -1).
 * - repeats.cal_end stays in GMT (the plugin stores UNTIL in UTC as well).
 * - Repeat exception dates are literal local dates: never touched.
 * - Pre-1.9 repeats rows may carry only the Sunday-first cal_days mask,
 *   which core ignores, so it is converted to a cal_byday list here.
 *
 * Consumed by the migration wizard (next step of Phase 2); currently
 * exercised via tests only, hence the dead-code suppressions.
 *
 * @psalm-suppress UnusedClass
 * @psalm-suppress PossiblyUnusedMethod
 */
final class LegacyTransformer {

	private const CAL_DAYS_ORDER = array( 'SU', 'MO', 'TU', 'WE', 'TH', 'FR', 'SA' );

	/**
	 * Converts a GMT-stored date/time integer pair to site-timezone wall clock.
	 *
	 * @return array{0: int, 1: int} Rebased [YYYYMMDD, HHMMSS].
	 */
	public static function rebase_to_site_time( int $date, int $time, DateTimeZone $site_tz ): array {
		$gmt = DateTimeImmutable::createFromFormat(
			'Ymd His',
			sprintf( '%08d %06d', $date, $time ),
			new DateTimeZone( 'UTC' )
		);
		if ( false === $gmt ) {
			return array( $date, $time );
		}
		$local = $gmt->setTimezone( $site_tz );
		return array( (int) $local->format( 'Ymd' ), (int) $local->format( 'His' ) );
	}

	/**
	 * Whether a legacy entry row is all-day or untimed (literal dates, no rebase).
	 *
	 * Heuristic per Phase 0: untimed rows store cal_time = -1; all-day rows
	 * store cal_time = 0 with cal_duration = 1440. A genuinely timed midnight
	 * event has cal_time = 0 with a different duration.
	 *
	 * @param array<string, string|null> $row Legacy webcal_entry row.
	 */
	public static function is_all_day( array $row ): bool {
		$time     = (int) ( $row['cal_time'] ?? -1 );
		$duration = (int) ( $row['cal_duration'] ?? 0 );
		return -1 === $time || ( 0 === $time && 1440 === $duration );
	}

	/**
	 * Applies the timezone/all-day rules to a legacy webcal_entry row.
	 *
	 * @param array<string, string|null> $row Legacy webcal_entry row.
	 * @return array<string, string|null> Row with rebased date/time values.
	 */
	public static function transform_entry_times( array $row, DateTimeZone $site_tz ): array {
		if ( self::is_all_day( $row ) ) {
			// Literal dates stay; collapse both legacy encodings to the
			// plugin's all-day representation.
			$row['cal_time'] = '-1';
			return $row;
		}

		list( $date, $time ) = self::rebase_to_site_time( (int) $row['cal_date'], (int) $row['cal_time'], $site_tz );
		$row['cal_date']     = (string) $date;
		$row['cal_time']     = (string) $time;

		if ( isset( $row['cal_due_date'], $row['cal_due_time'] ) && (int) $row['cal_due_time'] >= 0 ) {
			list( $due_date, $due_time ) = self::rebase_to_site_time( (int) $row['cal_due_date'], (int) $row['cal_due_time'], $site_tz );
			$row['cal_due_date']         = (string) $due_date;
			$row['cal_due_time']         = (string) $due_time;
		}

		if ( isset( $row['cal_mod_date'], $row['cal_mod_time'] ) ) {
			list( $mod_date, $mod_time ) = self::rebase_to_site_time( (int) $row['cal_mod_date'], (int) $row['cal_mod_time'], $site_tz );
			$row['cal_mod_date']         = (string) $mod_date;
			$row['cal_mod_time']         = (string) $mod_time;
		}

		return $row;
	}

	/**
	 * Converts the pre-1.9 Sunday-first cal_days mask ('ynynynn') to a
	 * cal_byday list ('SU,TU,TH'), mirroring legacy's own upgrade logic.
	 * All-yes and all-no masks mean "no day selection" and yield ''.
	 */
	public static function cal_days_to_byday( string $mask ): string {
		if ( 'yyyyyyy' === $mask || 'nnnnnnn' === $mask || 7 !== strlen( $mask ) ) {
			return '';
		}
		$days = array();
		foreach ( self::CAL_DAYS_ORDER as $i => $abbrev ) {
			if ( 'y' === $mask[ $i ] ) {
				$days[] = $abbrev;
			}
		}
		return implode( ',', $days );
	}

	/**
	 * Maps repeat type names retired by legacy's own upgrades onto their
	 * modern equivalents (dumps from never-upgraded databases carry them).
	 */
	public static function normalize_repeat_type( string $type ): string {
		return 'monthlyByDayR' === $type ? 'monthlyByDay' : $type;
	}

	/**
	 * Keep only valid RFC 5545 BYDAY tokens from a legacy cal_byday value.
	 *
	 * Legacy dumps occasionally carry junk in this field (e.g. "TH,-17"), which
	 * builds an unparseable RRULE (`BYDAY=TH,-17`) that then 500s the calendar
	 * feed. Each token must be an optional ±ordinal followed by a weekday
	 * (SU/MO/TU/WE/TH/FR/SA); anything else is dropped.
	 *
	 * @param string $byday Comma-separated legacy BYDAY value.
	 * @return string Sanitized comma-separated BYDAY value ('' if none valid).
	 */
	public static function sanitize_byday( string $byday ): string {
		$valid = array();
		foreach ( explode( ',', $byday ) as $token ) {
			$token = trim( $token );
			if ( '' !== $token && 1 === preg_match( '/^[+-]?[0-9]{0,2}(SU|MO|TU|WE|TH|FR|SA)$/', $token ) ) {
				$valid[] = $token;
			}
		}
		return implode( ',', $valid );
	}

	/**
	 * Keep only integer tokens from a legacy cal_bysetpos value.
	 *
	 * @param string $bysetpos Comma-separated legacy BYSETPOS value.
	 * @return string Sanitized comma-separated integer list ('' if none valid).
	 */
	public static function sanitize_bysetpos( string $bysetpos ): string {
		$valid = array();
		foreach ( explode( ',', $bysetpos ) as $token ) {
			$token = trim( $token );
			if ( '' !== $token && 1 === preg_match( '/^-?[0-9]+$/', $token ) ) {
				$valid[] = $token;
			}
		}
		return implode( ',', $valid );
	}

	/**
	 * Deterministic UID matching legacy's own iCal-export format, so that a
	 * calendar previously imported from a legacy .ics export UID-matches
	 * instead of duplicating.
	 *
	 * Mirrors generate_uid() in legacy includes/xcal.php: server URL without
	 * scheme, ':' to '-', '-<login>-<10-digit id>' appended, runs of '/' and
	 * '-' collapsed to a single '-'.
	 */
	public static function legacy_uid( int $legacy_id, string $server_url, string $login ): string {
		$uid  = '' !== $server_url ? $server_url : 'UNCONFIGURED-WEBCALENDAR';
		$uid  = str_replace( array( 'http://', 'https://' ), '', $uid );
		$uid  = str_replace( ':', '-', $uid );
		$uid .= sprintf( '-%s-%010d', $login, $legacy_id );
		return (string) preg_replace( '/[\/-]+/', '-', $uid );
	}
}