<?php
/**
 * Native lazy loading for pictures WordPress never saw; WordPress's own decisions always stand.
 *
 * @package AffStackDevImageManager
 */

namespace AffStackDev\ImageManager;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Lazy loading for pictures WordPress does not reach (Settings, Lazy-load pictures that WordPress does not reach):
 * loading="lazy" added on public pages, after the first pictures of the page.
 */
final class Lazy_Loading {
	/**
	 * Image sources WordPress's loading optimization saw in this request (its eager choices included).
	 *
	 * @var array
	 */
	private static array $core = array();
	private const SCRIPTED     = array( 'data-src', 'data-lazy-src', 'data-original', 'data-lazy-original', 'data-srcset', 'data-lazy-srcset' );

	/**
	 * Note a picture WordPress gave its own loading attributes (by its address), so the page pass leaves it.
	 *
	 * @param mixed $attrs   WordPress's loading attributes.
	 * @param mixed $tag     The tag (img or iframe).
	 * @param mixed $attr    The tag's attributes.
	 * @param mixed $context Where WordPress prints it.
	 * @return mixed The loading attributes, unchanged.
	 */
	public static function note( $attrs, $tag, $attr, $context ) {
		if ( 'img' === $tag && is_array( $attr ) && isset( $attr['src'] ) && is_string( $attr['src'] ) && '' !== $attr['src'] && count( self::$core ) < 4096 ) {
			self::$core[ html_entity_decode( $attr['src'], ENT_QUOTES | ENT_HTML5, 'UTF-8' ) ] = true;
		}
		return $attrs;
	}
	/**
	 * The same note for attributes another plugin decided before WordPress.
	 *
	 * @param mixed $value   The decided attributes, or false.
	 * @param mixed $tag     The tag.
	 * @param mixed $attr    The tag's attributes.
	 * @param mixed $context Where WordPress prints it.
	 * @return mixed The value, unchanged.
	 */
	public static function note_pre( $value, $tag, $attr, $context ) {
		if ( is_array( $value ) ) {
			self::note( $value, $tag, $attr, $context );
		}
		return $value;
	}
	/**
	 * Whether this request's page gets the pass: the setting is on, and it is a GET for a public page (not the admin,
	 * AJAX, cron, a feed, an embed, the Customizer preview, REST or AMP).
	 *
	 * @return bool True when it does.
	 */
	public static function enabled(): bool {
		if ( ! Settings::get()['lazy_loading'] || is_admin() || wp_doing_ajax() || wp_doing_cron() || is_feed() || is_embed() || is_customize_preview() || ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ) {
			return false;
		}
		if ( function_exists( 'amp_is_request' ) && amp_is_request() ) {
			return false;
		}
		return 'GET' === ( isset( $_SERVER['REQUEST_METHOD'] ) && is_string( $_SERVER['REQUEST_METHOD'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_METHOD'] ) ) : 'GET' );
	}
	/**
	 * The pass on the page's whole HTML when this request gets it, through WordPress's template enhancement output
	 * buffer (Hooks::PAGE_HTML), first of Image Manager's passes.
	 */
	public static function start_buffer(): void {
		if ( self::enabled() ) {
			add_filter( Hooks::PAGE_HTML, array( self::class, 'render' ), Hooks::PASS_LAZY );
		}
	}
	/**
	 * The buffered page after the pass; the page as it was when anything goes wrong.
	 *
	 * @param string $html The page.
	 * @return string The page.
	 */
	public static function render( string $html ): string {
		try {
			return self::lazy( $html );
		} catch ( \Throwable $e ) {
			return $html;
		} // A page is never broken by this optional attribute.
	}
	/**
	 * Whether the response is HTML (or has no content type yet).
	 *
	 * @return bool True when it is.
	 */
	private static function html_response(): bool {
		foreach ( headers_list() as  $header ) {
			if ( preg_match( '/^content-type:\s*([^;]+)/i', $header, $m ) ) {
				return in_array( strtolower( trim( $m[1] ) ), array( 'text/html', 'application/xhtml+xml' ), true );
			}
		}
		return true;
	}
	/**
	 * Bounded attribute-only pass. Unclear markup is left as it is.
	 *
	 * @param string $html The page.
	 * @return string The page with loading="lazy" on the pictures that get it.
	 */
	public static function lazy( string $html ): string {
		if ( '' === $html || strlen( $html ) > 2097152 || ! self::html_response() || ! class_exists( '\WP_HTML_Tag_Processor' ) ) {
			return $html;
		}
		$p = new \WP_HTML_Tag_Processor( $html );
		if ( ! method_exists( $p, 'set_attribute' ) || ! method_exists( $p, 'is_tag_closer' ) ) {
			return $html;
		}
		$threshold = max( 0, (int) wp_omit_loading_attr_threshold() );
		$seen      = 0;
		$changed   = 0;
		$n         = 0;
		$skip      = array(
			'HEADER'   => 0,
			'NOSCRIPT' => 0,
			'TEMPLATE' => 0,
		);
		while ( $n++ < 20000 && $p->next_tag( array( 'tag_closers' => 'visit' ) ) ) {
			$tag = $p->get_tag();
			if ( isset( $skip[ $tag ] ) ) {
				$skip[ $tag ] = $p->is_tag_closer() ? max( 0, $skip[ $tag ] - 1 ) : $skip[ $tag ] + 1;
				continue;
			}
			if ( 'IMG' !== $tag || $p->is_tag_closer() || $skip['NOSCRIPT'] || $skip['TEMPLATE'] ) {
				continue;
			}
			$src = $p->get_attribute( 'src' );
			if ( ! is_string( $src ) || '' === trim( $src ) || preg_match( '/^\s*(?:data|javascript|blob):/i', $src ) ) {
				continue;
			}
			// Every real picture counts toward the first ones on screen, in page order, whoever printed it.
			++$seen;
			if ( $skip['HEADER'] || $seen <= $threshold || null !== $p->get_attribute( 'loading' ) || 'high' === strtolower( (string) $p->get_attribute( 'fetchpriority' ) ) ) {
				continue;
			}
			if ( isset( self::$core[ html_entity_decode( $src, ENT_QUOTES | ENT_HTML5, 'UTF-8' ) ] ) ) {
				continue;
			}
			$width  = $p->get_attribute( 'width' );
			$height = $p->get_attribute( 'height' );
			if ( ! is_string( $width ) || ! is_string( $height ) || ! ctype_digit( trim( $width ) ) || ! ctype_digit( trim( $height ) ) ) {
				continue;
			}
			$scripted = false;
			foreach ( self::SCRIPTED as  $attr ) {
				if ( null !== $p->get_attribute( $attr ) ) {
					$scripted = true;
					break;
				}
			}
			if ( $scripted || $p->has_class( 'skip-lazy' ) ) {
				continue;
			}
			$p->set_attribute( 'loading', 'lazy' );
			++$changed;
		}
		return $changed ? $p->get_updated_html() : $html;
	}
}