<?php
/**
 * Checks the Google tags on the site's pages (F-GOOGLE-01 to 03).
 *
 * @package ForensixDigital
 */

declare(strict_types=1);

namespace ForensixDigital\Apps\Google;

defined( 'ABSPATH' ) || exit;

use ForensixDigital\Services\Http\Http;
use ForensixDigital\Services\Scan\Fetcher;

/**
 * Fetches the front page, a post and a page the way a visitor sees them, then explains in plain
 * words what is wrong: a tag that is missing on a page, loaded twice, set to another property,
 * or held back by a consent tool. The addresses of tags that belong to other plugins are
 * remembered, so Forensix Digital never prints the same tag a second time.
 */
final class GoogleCheck {

	public const OPTION = 'forensix_google_check';

	private const BUDGET = 18;

	/**
	 * Gateway for outbound requests.
	 *
	 * @var Http
	 */
	private Http $http;

	/**
	 * Creates the check.
	 *
	 * @param Http $http Outbound gateway.
	 */
	public function __construct( Http $http ) {
		$this->http = $http;
	}

	/**
	 * Runs the check and keeps the outcome.
	 *
	 * @param array<string, mixed> $values Saved Google settings.
	 * @return array{time: int, results: array<int, array<string, string>>, foreign: array{ga4: array<int, string>, gtm: array<int, string>, verification: array<int, string>}}
	 */
	public function run( array $values ): array {
		$fetcher = new Fetcher( $this->http );
		$home    = home_url( '/' );
		$mode    = $fetcher->probe( $home );
		$pages   = array();
		$failed  = array();

		if ( null === $mode ) {
			$failed[] = $home;
		} else {
			$fetcher = new Fetcher( $this->http, $mode );
			$started = microtime( true );
			foreach ( self::addresses() as $label => $url ) {
				if ( microtime( true ) - $started > self::BUDGET ) {
					break;
				}
				$response = $fetcher->fetch( $url );
				if ( 200 === $response['status'] && '' !== $response['body'] ) {
					$pages[ $label ] = $response['body'];
				} else {
					$failed[] = $url;
				}
			}
		}

		$outcome = self::evaluate( $pages, $values, $failed );
		update_option( self::OPTION, $outcome, false );
		return $outcome;
	}

	/**
	 * The last stored outcome, or null before the first check.
	 *
	 * @return array<string, mixed>|null
	 */
	public static function last(): ?array {
		$saved = get_option( self::OPTION, null );
		return is_array( $saved ) ? $saved : null;
	}

	/**
	 * Tag codes that other plugins or the theme already print, from the last check.
	 *
	 * @return array{ga4: array<int, string>, gtm: array<int, string>, verification: array<int, string>}
	 */
	public static function foreign(): array {
		$last = self::last();
		$seen = is_array( $last ) && isset( $last['foreign'] ) && is_array( $last['foreign'] ) ? $last['foreign'] : array();
		return array(
			'ga4'          => array_values( array_map( 'strval', (array) ( $seen['ga4'] ?? array() ) ) ),
			'gtm'          => array_values( array_map( 'strval', (array) ( $seen['gtm'] ?? array() ) ) ),
			'verification' => array_values( array_map( 'strval', (array) ( $seen['verification'] ?? array() ) ) ),
		);
	}

	/**
	 * The pages to look at: the front page, the newest post and the newest page.
	 *
	 * @return array<string, string>
	 */
	private static function addresses(): array {
		$urls = array( __( 'Front page', 'forensix-digital' ) => home_url( '/' ) );
		foreach (
			array(
				'post' => __( 'A post', 'forensix-digital' ),
				'page' => __( 'A page', 'forensix-digital' ),
			) as $type => $label
		) {
			$ids = get_posts(
				array(
					'post_type'      => $type,
					'post_status'    => 'publish',
					'posts_per_page' => 1,
					'fields'         => 'ids',
					'no_found_rows'  => true,
				)
			);
			if ( array() !== $ids && (int) get_option( 'page_on_front' ) !== (int) $ids[0] ) {
				$urls[ $label ] = (string) get_permalink( (int) $ids[0] );
			}
		}
		return $urls;
	}

	/**
	 * Turns the fetched pages into plain statements.
	 *
	 * @param array<string, string> $pages  Page label => HTML.
	 * @param array<string, mixed>  $values Saved Google settings.
	 * @param array<int, string>    $failed Addresses that could not be read.
	 * @return array{time: int, results: array<int, array<string, string>>, foreign: array{ga4: array<int, string>, gtm: array<int, string>, verification: array<int, string>}}
	 */
	public static function evaluate( array $pages, array $values, array $failed = array() ): array {
		$results = array();
		$foreign = array(
			'ga4'          => array(),
			'gtm'          => array(),
			'verification' => array(),
		);
		$add     = static function ( string $level, string $code, string $message ) use ( &$results ): void {
			$row = array(
				'level'   => $level,
				'code'    => $code,
				'message' => $message,
			);
			if ( ! in_array( $row, $results, true ) ) {
				$results[] = $row;
			}
		};

		foreach ( $failed as $url ) {
			/* translators: %s: page address. */
			$add( 'problem', 'unreachable', sprintf( __( 'This page could not be read for the check: %s', 'forensix-digital' ), $url ) );
		}

		$verification = (string) ( $values['verification'] ?? '' );
		$ga4          = (string) ( $values['ga4_id'] ?? '' );
		$gtm          = (string) ( $values['gtm_id'] ?? '' );
		$tools        = array();

		foreach ( $pages as $label => $html ) {
			$page  = TagDetector::inspect( $html );
			$tools = array_merge( $tools, $page['consent_tools'] );

			$count = static function ( string $kind, string $id ) use ( $page ): int {
				return (int) ( $page['ours'][ $kind ][ $id ] ?? 0 ) + (int) ( $page['other'][ $kind ][ $id ] ?? 0 );
			};

			if ( '' !== $verification && array_key_first( $pages ) === $label ) {
				$codes = array_merge( $page['ours']['verification'], $page['other']['verification'] );
				if ( ! in_array( $verification, $codes, true ) ) {
					$add( 'problem', 'verification_missing', __( 'The Search Console verification tag is not on your front page. If you just saved it, empty the cache of your caching plugin and check again.', 'forensix-digital' ) );
				}
			}

			$foreign['verification'] = array_merge( $foreign['verification'], $page['other']['verification'] );
			foreach ( array_keys( $page['other']['ga4'] ) as $id ) {
				$foreign['ga4'][] = $id;
			}
			foreach ( array_keys( $page['other']['gtm'] ) as $id ) {
				$foreign['gtm'][] = $id;
			}

			foreach ( array(
				'ga4' => $ga4,
				'gtm' => $gtm,
			) as $kind => $id ) {
				if ( '' === $id ) {
					continue;
				}
				$found = $count( $kind, $id );
				if ( 0 === $found ) {
					/* translators: 1: page, 2: tag code. */
					$add( 'problem', 'tag_missing', sprintf( __( '%1$s: the tag %2$s is not on this page.', 'forensix-digital' ), $label, $id ) );
				} elseif ( $found > 1 ) {
					/* translators: 1: page, 2: tag code, 3: how many times. */
					$add( 'problem', 'duplicate_tag', sprintf( __( '%1$s: the tag %2$s is loaded %3$d times, so visits are counted more than once. Another plugin or your theme probably adds it too.', 'forensix-digital' ), $label, $id, $found ) );
				}
				foreach ( array_merge( array_keys( $page['other'][ $kind ] ), array_keys( $page['ours'][ $kind ] ) ) as $seen ) {
					if ( $seen !== $id ) {
						/* translators: 1: page, 2: tag code found, 3: tag code set here. */
						$add( 'warning', 'other_property', sprintf( __( '%1$s: this page also loads %2$s, which is not the code set here (%3$s). Make sure both belong to you and that this is intended.', 'forensix-digital' ), $label, $seen, $id ) );
					}
				}
			}

			if ( '' === $ga4 && '' === $gtm ) {
				foreach ( array_keys( $page['other']['ga4'] ) as $id ) {
					/* translators: %s: tag code. */
					$add( 'ok', 'found_elsewhere', sprintf( __( 'A Google Analytics tag (%s) is added by another plugin or your theme. Forensix Digital adds nothing, so nothing is counted twice.', 'forensix-digital' ), $id ) );
				}
				foreach ( array_keys( $page['other']['gtm'] ) as $id ) {
					/* translators: %s: container code. */
					$add( 'ok', 'found_elsewhere', sprintf( __( 'A Google Tag Manager container (%s) is added by another plugin or your theme. Forensix Digital adds nothing.', 'forensix-digital' ), $id ) );
				}
			}

			$gtm_here = array_merge( $page['ours']['gtm'], $page['other']['gtm'] );
			$ga4_here = array_merge( $page['ours']['ga4'], $page['other']['ga4'] );
			if ( array() !== $gtm_here && array() !== $ga4_here ) {
				/* translators: %s: page. */
				$add( 'warning', 'ga4_and_gtm', sprintf( __( '%s: Tag Manager and a direct Analytics tag are both loaded. If your container also sends Analytics data, every visit is counted twice.', 'forensix-digital' ), $label ) );
			}
			if ( array() !== array_merge( $page['ours']['universal'], $page['other']['universal'] ) ) {
				/* translators: %s: page. */
				$add( 'warning', 'universal_analytics', sprintf( __( '%s: an old Universal Analytics code (UA-…) is still loaded. Google stopped collecting data with it, so it can be removed.', 'forensix-digital' ), $label ) );
			}
		}

		$tools = array_values( array_unique( $tools ) );
		if ( array() !== $tools ) {
			/* translators: %s: names of consent tools. */
			$add( 'ok', 'consent_tool', sprintf( __( 'A consent tool is active (%s). Google tags may load only after a visitor accepts, so test in a private window and accept cookies first.', 'forensix-digital' ), implode( ', ', $tools ) ) );
		}
		$configured = '' !== $verification || '' !== $ga4 || '' !== $gtm;
		if ( array() !== $pages && ! $configured && array() === $results ) {
			$add( 'ok', 'nothing', __( 'No Google tags were found on your pages, and none are set up here yet.', 'forensix-digital' ) );
		}
		$trouble = array_filter( $results, static fn( array $row ): bool => 'ok' !== $row['level'] );
		if ( array() !== $pages && $configured && array() === $trouble ) {
			$add( 'ok', 'all_good', __( 'Everything you set up here is on your pages exactly once.', 'forensix-digital' ) );
		}

		return array(
			'time'    => time(),
			'results' => $results,
			'foreign' => array(
				'ga4'          => array_values( array_unique( $foreign['ga4'] ) ),
				'gtm'          => array_values( array_unique( $foreign['gtm'] ) ),
				'verification' => array_values( array_unique( $foreign['verification'] ) ),
			),
		);
	}
}