<?php
/**
 * Image SEO: every image gets meaningful alt text, either the one set in the media library or a sensible one
 * derived from the file name / page title. Alt text is read by search engines, screen readers and image search.
 */

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

class SXSEO_Images {

	public static function hook() {
		if ( ! sxseo_opt( 'auto_alt' ) ) {
			return;
		}
		add_filter( 'wp_get_attachment_image_attributes', array( __CLASS__, 'attrs' ), 20, 2 );
		add_filter( 'the_content', array( __CLASS__, 'content' ), 30 );
		add_filter( 'post_thumbnail_html', array( __CLASS__, 'thumb_html' ), 20, 5 );
	}

	/** "IMG_1234-web-final" -> "" ; "red-front-door" -> "Red front door". */
	public static function alt_from_filename( $name ) {
		$base = pathinfo( (string) $name, PATHINFO_FILENAME );
		$base = preg_replace( '/-\d+x\d+$/', '', $base );
		$base = trim( preg_replace( '/[\s_\-]+/', ' ', $base ) );
		if ( '' === $base || preg_match( '/^(img|dsc|dscn|image|photo|screenshot|pxl|whatsapp|untitled)?\s*[\d\s]*$/i', $base ) || preg_match( '/^[0-9a-f]{8,}$/i', $base ) ) {
			return '';
		}
		return ucfirst( $base );
	}

	public static function alt_for_attachment( $att_id, $fallback = '' ) {
		$alt = trim( (string) get_post_meta( $att_id, '_wp_attachment_image_alt', true ) );
		if ( '' !== $alt ) {
			return $alt;
		}
		$title = trim( (string) get_the_title( $att_id ) );
		$guess = self::alt_from_filename( $title ) ?: self::alt_from_filename( get_attached_file( $att_id ) );
		return $guess ?: $fallback;
	}

	public static function attrs( $attr, $attachment ) {
		if ( ! empty( $attr['alt'] ) ) {
			return $attr;
		}
		$parent = $attachment->post_parent ? get_the_title( $attachment->post_parent ) : get_the_title();
		$alt    = self::alt_for_attachment( $attachment->ID, (string) $parent );
		if ( $alt ) {
			$attr['alt'] = $alt;
		}
		return $attr;
	}

	public static function thumb_html( $html, $post_id ) {
		return self::fix_tags( $html, get_the_title( $post_id ) );
	}

	public static function content( $content ) {
		if ( is_admin() || ! in_the_loop() && ! is_singular() ) {
			return $content;
		}
		return self::fix_tags( $content, get_the_title() );
	}

	private static function fix_tags( $html, $fallback ) {
		if ( false === stripos( $html, '<img' ) ) {
			return $html;
		}
		return preg_replace_callback(
			'#<img\b[^>]*>#i',
			function ( $m ) use ( $fallback ) {
				$tag = $m[0];
				if ( preg_match( '#\balt=(["\'])(.*?)\1#is', $tag, $a ) && '' !== trim( $a[2] ) ) {
					return $tag;
				}
				$alt = '';
				if ( preg_match( '#wp-image-(\d+)#', $tag, $id ) ) {
					$alt = self::alt_for_attachment( (int) $id[1], $fallback );
				} elseif ( preg_match( '#\bsrc=["\']([^"\']+)["\']#i', $tag, $s ) ) {
					$alt = self::alt_from_filename( wp_parse_url( $s[1], PHP_URL_PATH ) ) ?: $fallback;
				}
				if ( '' === $alt ) {
					return $tag;
				}
				if ( preg_match( '#\balt=(["\'])\1#i', $tag ) ) {
					return preg_replace( '#\balt=(["\'])\1#i', 'alt="' . esc_attr( $alt ) . '"', $tag, 1 );
				}
				return preg_replace( '#<img\b#i', '<img alt="' . esc_attr( $alt ) . '"', $tag, 1 );
			},
			$html
		);
	}
}