<?php
/**
 * Page weight, request count, blocking scripts and lazy loading (F-PERF-01, F-PERF-03).
 *
 * @package ForensixDigital
 */

declare(strict_types=1);

namespace ForensixDigital\Apps\Perf;

defined( 'ABSPATH' ) || exit;

use ForensixDigital\Services\Findings\Observation;
use ForensixDigital\Services\Findings\Priority;
use ForensixDigital\Services\Scan\Check;
use ForensixDigital\Services\Scan\ParsedPage;
use ForensixDigital\Services\Scan\Reference;
use ForensixDigital\Services\Sources\Source;

/**
 * What the server-side fetch can say about speed without a browser: how large the page code is,
 * how many script and style files it asks for, which scripts stop the page from showing until
 * they are loaded, and whether images are loaded lazily where that helps. All are suggestions,
 * and none of them is a timing.
 */
final class PageWeightCheck implements Check {

	public const ID = 'perf.page_weight';

	public const HTML_LIMIT = 300000;

	public const FILE_LIMIT = 40;

	public const PER_PAGE = 10;

	/**
	 * Check id.
	 */
	public function id(): string {
		return self::ID;
	}

	/**
	 * The check looks only at the page itself.
	 *
	 * @param ParsedPage $page Parsed page.
	 * @return string[]
	 */
	public function targets( ParsedPage $page ): array {
		return array();
	}

	/**
	 * Problems on this page.
	 *
	 * @param ParsedPage $page    Parsed page.
	 * @param array      $results Not used.
	 * @phpstan-param array<string, \ForensixDigital\Services\Scan\TargetResult> $results
	 * @return array<int, array{observation: Observation, context: string}>
	 */
	public function inspect( ParsedPage $page, array $results ): array {
		$hits   = array();
		$counts = array();
		foreach ( $page->facts->perf as $fact ) {
			if ( 'html_bytes' === $fact[0] ) {
				if ( (int) $fact[1] > self::HTML_LIMIT ) {
					$hits[] = $this->hit( 'perf.page_size', Priority::LOW, __( 'The page code is very large', 'forensix-digital' ), $page->url, Source::TEMPLATE, '', (int) round( (int) $fact[1] / 1000 ) . ' KB', array( 'kilobytes' => (int) round( (int) $fact[1] / 1000 ) ) );
				}
				continue;
			}
			$counts[ $fact[0] ] = ( $counts[ $fact[0] ] ?? 0 ) + 1;
			if ( $counts[ $fact[0] ] > self::PER_PAGE ) {
				continue;
			}
			if ( 'blocking_script' === $fact[0] ) {
				$hits[] = $this->hit( 'perf.render_blocking', Priority::LOW, __( 'A script stops the page from showing until it has loaded', 'forensix-digital' ), $fact[1], $fact[2], $fact[3], $fact[1] );
			} elseif ( 'lazy_missing' === $fact[0] ) {
				$hits[] = $this->hit( 'perf.lazy_missing', Priority::LOW, __( 'An image further down the page is not loaded lazily', 'forensix-digital' ), $fact[1], $fact[2], $fact[3], $fact[1] );
			} elseif ( 'lazy_first' === $fact[0] ) {
				$hits[] = $this->hit( 'perf.lazy_first', Priority::MEDIUM, __( 'The first image on the page is loaded lazily', 'forensix-digital' ), $fact[1], $fact[2], $fact[3], $fact[1] );
			}
		}
		$files = array();
		foreach ( $page->references as $reference ) {
			if ( in_array( $reference->kind, array( Reference::SCRIPT, Reference::STYLE ), true ) ) {
				$files[ $reference->url ] = true;
			}
		}
		if ( count( $files ) > self::FILE_LIMIT ) {
			$hits[] = $this->hit( 'perf.many_files', Priority::LOW, __( 'The page asks for many script and style files', 'forensix-digital' ), $page->url, Source::TEMPLATE, '', (string) count( $files ), array( 'files' => count( $files ) ) );
		}
		return $hits;
	}

	/**
	 * One suggestion.
	 *
	 * @param string $check_id    Finding id.
	 * @param string $severity    Priority level.
	 * @param string $title       Title.
	 * @param string $target      Page or file the finding is about.
	 * @param string $source_type Source type.
	 * @param string $source_ref  Source reference.
	 * @param string $context     Shown beside the finding.
	 * @param array  $details     Extra facts.
	 * @phpstan-param array<string, mixed> $details
	 * @return array{observation: Observation, context: string}
	 */
	private function hit( string $check_id, string $severity, string $title, string $target, string $source_type, string $source_ref, string $context, array $details = array() ): array {
		return array(
			'observation' => new Observation( $check_id, $severity, Priority::SUGGESTION, $title, $target, $source_type, $source_ref, '', $details ),
			'context'     => $context,
		);
	}
}