<?php
/**
 * Yoast SEO target keyword source.
 *
 * @package Postlinkly
 * @since   1.0.0
 */

declare(strict_types=1);

namespace Postlinkly\Keywords\Sources;

/**
 * Reads the focus keyword set by Yoast SEO for a post.
 *
 * Yoast stores the primary focus keyword in `_yoast_wpseo_focuskw` and
 * additional keyphrases (Premium) in `_yoast_wpseo_focuskw_multi_terms`.
 * Both are post-meta keys on the post itself.
 *
 * Availability is determined by checking for the Yoast main class
 * `WPSEO_Options`, which is present whenever Yoast Free or Premium is
 * active.
 *
 * @since 1.0.0
 */
final class YoastSource implements KeywordSourceInterface {

	/**
	 * Source identifier.
	 */
	public const SOURCE_ID = 'yoast';

	/**
	 * Returns the unique identifier for this source.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	public function get_id(): string {
		return self::SOURCE_ID;
	}

	/**
	 * Returns the human-readable label for this source.
	 *
	 * @since 1.0.0
	 *
	 * @return string
	 */
	public function get_label(): string {
		return __( 'Yoast SEO', 'postlinkly' );
	}

	/**
	 * Whether the Yoast SEO plugin is active.
	 *
	 * @since 1.0.0
	 *
	 * @return bool
	 */
	public function is_available(): bool {
		return class_exists( 'WPSEO_Options', false );
	}

	/**
	 * Returns Yoast focus keyphrase keywords for a post.
	 *
	 * @since 1.0.0
	 *
	 * @param int    $post_id   Post identifier (terms not supported by Yoast meta).
	 * @param string $post_type Item type. Default `post`.
	 *
	 * @return array<int, string>
	 */
	public function get_keywords_for( int $post_id, string $post_type = 'post' ): array {
		if ( $post_id <= 0 || 'post' !== $post_type || ! function_exists( 'get_post_meta' ) ) {
			return array();
		}

		$out = array();

		// Primary focus keyword.
		$primary = get_post_meta( $post_id, '_yoast_wpseo_focuskw', true );
		if ( is_string( $primary ) && '' !== trim( $primary ) ) {
			$out[] = trim( $primary );
		}

		// Additional keyphrases (Yoast Premium stores a serialised array).
		$multi_raw = get_post_meta( $post_id, '_yoast_wpseo_focuskw_multi_terms', true );
		if ( is_string( $multi_raw ) && '' !== $multi_raw ) {
			$multi = maybe_unserialize( $multi_raw );
			if ( is_array( $multi ) ) {
				foreach ( $multi as $item ) {
					if ( is_array( $item ) && isset( $item['keyword'] ) ) {
						$kw = trim( (string) $item['keyword'] );
					} elseif ( is_string( $item ) ) {
						$kw = trim( $item );
					} else {
						continue;
					}
					if ( '' !== $kw && ! in_array( $kw, $out, true ) ) {
						$out[] = $kw;
					}
				}
			}
		}

		return $out;
	}
}