<?php

namespace RoosterLMS\Events;

use RoosterLMS\Content\CourseVisibility;
use RoosterLMS\Core\Clock;
use RoosterLMS\Domain\Services;
use RoosterLMS\Live\Ics;

defined( 'ABSPATH' ) || exit;

final class Feed {

	public const VAR = 'rooster_lms_events_ics';

	public const PATH = 'rooster-lms/events.ics';

	public const WINDOW_MONTHS = 12;

	public const MAX_EVENTS = 500;

	public const MAX_AGE = 900;

	public const PRODID = '-//Rooster LMS//Upcoming events//EN';

	private static bool $registered = false;

	public function register(): void {
		if ( self::$registered ) {
			return;
		}
		self::$registered = true;
		add_action( 'init', array( self::class, 'add_rewrite_rules' ), 4 );
		add_filter( 'query_vars', array( self::class, 'query_vars' ) );
		add_action( 'parse_request', array( self::class, 'parse_request' ), 0 );
	}

	public static function add_rewrite_rules(): void {
		add_rewrite_rule( '^rooster-lms/events\.ics$', 'index.php?' . self::VAR . '=1', 'top' );
	}

	public static function query_vars( $vars ) {
		if ( is_array( $vars ) ) {
			$vars[] = self::VAR;
		}
		return $vars;
	}

	public static function url( array $args = array() ): string {
		$args = array_filter( $args, static fn( $value ): bool => '' !== (string) $value && '0' !== (string) $value );
		$base = self::pretty() ? home_url( '/' . self::PATH ) : add_query_arg( self::VAR, '1', home_url( '/' ) );
		return array() === $args ? $base : add_query_arg( array_map( 'rawurlencode', array_map( 'strval', $args ) ), $base );
	}

	public static function course_url( int $course_id, CourseVisibility $visibility, int $user_id ): string {
		if ( $course_id <= 0 ) {
			return '';
		}
		if ( CourseVisibility::PUBLIC === $visibility ) {
			return self::url( array( 'course' => $course_id ) );
		}
		if ( $user_id <= 0 ) {
			return '';
		}
		return self::url(
			array(
				'course' => $course_id,
				'u'      => $user_id,
				't'      => FeedTokens::sign( $user_id, $course_id ),
			)
		);
	}

	public static function parse_request( $wp ): void {
		$vars = $wp instanceof \WP && is_array( $wp->query_vars ) ? $wp->query_vars : array();
		if ( empty( $vars[ self::VAR ] ) ) {
			return;
		}
		$arg      = static function ( string $key ): string {
			$raw = \RoosterLMS\UI\TableRequest::get( $key );
			return is_scalar( $raw ) ? sanitize_text_field( (string) $raw ) : '';
		};
		$etag     = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? trim( sanitize_text_field( wp_unslash( (string) $_SERVER['HTTP_IF_NONE_MATCH'] ) ) ) : '';
		$response = self::respond(
			array(
				'category'   => absint( $arg( 'category' ) ),
				'course'     => absint( $arg( 'course' ) ),
				'occurrence' => absint( $arg( 'occurrence' ) ),
				'u'          => absint( $arg( 'u' ) ),
				't'          => $arg( 't' ),
			),
			$etag
		);
		status_header( $response['status'] );
		foreach ( $response['headers'] as $name => $value ) {
			header( $name . ': ' . $value );
		}
		\RoosterLMS\Core\Output::body( $response['body'] );
		exit;
	}

	public static function respond( array $args, string $etag = '' ): array {
		$plain = array(
			'Content-Type'           => 'text/plain; charset=utf-8',
			'X-Content-Type-Options' => 'nosniff',
			'X-Robots-Tag'           => 'noindex, nofollow',
			'Cache-Control'          => 'no-store',
		);
		if ( ! FeedRate::hit() ) {
			return array(
				'status'  => 429,
				'headers' => $plain + array( 'Retry-After' => (string) FeedRate::WINDOW ),
				'body'    => "Too many requests.\n",
			);
		}
		$user = 0;
		$who  = EventRepository::GUEST;
		if ( (int) $args['u'] > 0 || '' !== (string) $args['t'] ) {
			if ( (int) $args['course'] <= 0 || ! FeedTokens::verify( (int) $args['u'], (int) $args['course'], (string) $args['t'] ) || ! get_userdata( (int) $args['u'] ) instanceof \WP_User ) {
				return array(
					'status'  => 404,
					'headers' => $plain,
					'body'    => "Not found.\n",
				);
			}
			$user = (int) $args['u'];
			$who  = EventRepository::FEED_USER;
		}
		$text    = self::calendar( (int) $args['category'], (int) $args['course'], (int) $args['occurrence'], $user, $who );
		$tag     = '"' . md5( $text ) . '"';
		$headers = array(
			'Content-Type'           => 'text/calendar; charset=utf-8',
			'Content-Disposition'    => 'inline; filename="' . ( (int) $args['occurrence'] > 0 ? 'event-' . (int) $args['occurrence'] : 'events' ) . '.ics"',
			'Cache-Control'          => ( $user > 0 ? 'private' : 'public' ) . ', max-age=' . self::MAX_AGE,
			'ETag'                   => $tag,
			'X-Content-Type-Options' => 'nosniff',
			'X-Robots-Tag'           => 'noindex, nofollow',
		);
		if ( '' !== $etag && in_array( $tag, array_map( 'trim', explode( ',', $etag ) ), true ) ) {
			return array(
				'status'  => 304,
				'headers' => $headers,
				'body'    => '',
			);
		}
		return array(
			'status'  => 200,
			'headers' => $headers,
			'body'    => $text,
		);
	}

	public static function calendar( int $term_id, int $course_id, int $occurrence, int $user_id, string $who ): string {
		$q      = new EventQuery( $term_id > 0 ? array( $term_id ) : array(), array(), '', '', 0, '', self::WINDOW_MONTHS, self::MAX_EVENTS, 1, false, $course_id, 0, $occurrence );
		$now    = new \DateTimeImmutable( '@' . Clock::timestamp() );
		$events = EventRepository::find( $q, $user_id, $now, $who, true, self::MAX_EVENTS, 0 );
		$posts  = EventPosts::of( $events );
		$name   = wp_specialchars_decode( (string) get_bloginfo( 'name' ), ENT_QUOTES );
		if ( $course_id > 0 && array() !== $events ) {
			$name = (string) ( $posts[ $events[0]->id() ]['course_title'] ?? $name );
		}
		$lines = array(
			'BEGIN:VCALENDAR',
			'VERSION:2.0',
			'PRODID:' . self::PRODID,
			'CALSCALE:GREGORIAN',
			'METHOD:PUBLISH',
			'X-WR-CALNAME:' . Ics::text( $name ),
			'REFRESH-INTERVAL;VALUE=DURATION:PT6H',
			'X-PUBLISHED-TTL:PT6H',
		);
		foreach ( $events as $e ) {
			$lines = array_merge( $lines, self::vevent( $e, $posts[ $e->id() ] ?? array() ) );
		}
		$lines[] = 'END:VCALENDAR';
		return implode( "\r\n", array_map( array( Ics::class, 'fold' ), $lines ) ) . "\r\n";
	}

	public static function vevent( Event $e, array $post ): array {
		$cancelled = $e->cancelled();
		$page      = CalendarLinks::assert_public( (string) ( $post['url'] ?? '' ) );
		$stamp     = '' !== $e->session->updated_at ? $e->session->updated_at : $e->occurrence->starts_at;
		$lines     = array(
			'BEGIN:VEVENT',
			'UID:' . History::uid( $e->id() ),
			'SEQUENCE:' . History::sequence( $e->id(), $cancelled ),
			'DTSTAMP:' . Ics::utc( $stamp ),
			'DTSTART:' . Ics::utc( $e->occurrence->starts_at ),
			'DTEND:' . Ics::utc( $e->occurrence->ends_at ),
			'SUMMARY:' . Ics::text( (string) ( $post['title'] ?? __( 'Live lesson', 'rooster-lms' ) ) ),
			'LOCATION:' . Ics::text( $e->location() ),
		);
		if ( '' !== $page ) {
			$lines[] = 'DESCRIPTION:' . Ics::text( $page );
			$lines[] = 'URL:' . Ics::uri( $page );
		}
		$lines[] = 'STATUS:' . ( $cancelled ? 'CANCELLED' : 'CONFIRMED' );
		$lines[] = 'END:VEVENT';
		return $lines;
	}

	public static function pretty(): bool {
		global $wp_rewrite;
		if ( ! $wp_rewrite instanceof \WP_Rewrite || ! $wp_rewrite->using_permalinks() ) {
			return false;
		}
		$rules = get_option( 'rewrite_rules' );
		$rule  = is_array( $rules ) ? ( $rules['^rooster-lms/events\.ics$'] ?? '' ) : '';
		return str_contains( (string) $rule, self::VAR . '=' );
	}
}