<?php
/**
 * F13 — multilingual awareness.
 *
 * Oorank published one `llms.txt` for the whole site with no idea that half
 * of it was in another language. For an answer engine that is worse than
 * publishing nothing: a single mixed-language index gives it no signal about
 * which version of a page to quote to whom, and the duplicate-in-translation
 * entries look like near-duplicate content.
 *
 * This is a thin read-only adapter over whichever translation plugin is
 * active. It never writes, never assumes one is present, and holds no state:
 * on a monolingual site `active()` is false and every caller behaves exactly
 * as it did before.
 *
 * WPML and Polylang are supported because they are the two the competition
 * documents; both expose a stable public API, so neither is reached into.
 *
 * @package Oorank
 */

defined( 'ABSPATH' ) || exit;

/**
 * Language detection across WPML and Polylang.
 */
class Oorank_Multilingual {

	/**
	 * Whether a translation plugin is active with more than one language.
	 *
	 * @return bool
	 */
	public static function active() {
		return count( self::languages() ) > 1;
	}

	/**
	 * Active languages as code => display name.
	 *
	 * @return array<string, string>
	 */
	public static function languages() {
		static $cache = null;

		if ( null !== $cache ) {
			return $cache;
		}

		$languages = array();

		if ( function_exists( 'pll_languages_list' ) ) {
			$slugs = pll_languages_list( array( 'fields' => 'slug' ) );
			$names = pll_languages_list( array( 'fields' => 'name' ) );
			foreach ( (array) $slugs as $index => $slug ) {
				$languages[ (string) $slug ] = isset( $names[ $index ] ) ? (string) $names[ $index ] : (string) $slug;
			}
		}

		if ( empty( $languages ) && has_filter( 'wpml_active_languages' ) ) {
			// WPML's own read API; the prefix rule is about hooks we own.
			$active = apply_filters( 'wpml_active_languages', null, array( 'skip_missing' => 0 ) ); // phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound -- Third-party API.
			foreach ( (array) $active as $code => $entry ) {
				$languages[ (string) $code ] = isset( $entry['translated_name'] ) ? (string) $entry['translated_name'] : (string) $code;
			}
		}

		/**
		 * Filter the language list Oorank groups content by.
		 *
		 * Supply this to support a translation plugin Oorank does not know.
		 *
		 * @param array $languages Code => display name.
		 */
		$cache = apply_filters( 'oorank_languages', $languages );

		return $cache;
	}

	/**
	 * The language code a post belongs to.
	 *
	 * @param WP_Post|int $post Post or ID.
	 * @return string Code, or '' when unknown or monolingual.
	 */
	public static function post_language( $post ) {
		$post_id = ( $post instanceof WP_Post ) ? $post->ID : absint( $post );
		if ( ! $post_id ) {
			return '';
		}

		if ( function_exists( 'pll_get_post_language' ) ) {
			return (string) pll_get_post_language( $post_id, 'slug' );
		}

		if ( has_filter( 'wpml_post_language_details' ) ) {
			$details = apply_filters( 'wpml_post_language_details', null, $post_id ); // phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound -- Third-party API.
			if ( is_array( $details ) && ! empty( $details['language_code'] ) ) {
				return (string) $details['language_code'];
			}
		}

		return '';
	}

	/**
	 * Whether a code is one of the site's languages.
	 *
	 * @param string $code Language code.
	 * @return bool
	 */
	public static function is_language( $code ) {
		return '' !== $code && isset( self::languages()[ $code ] );
	}

	/**
	 * Display name for a code, falling back to the code itself.
	 *
	 * @param string $code Language code.
	 * @return string
	 */
	public static function label( $code ) {
		$languages = self::languages();

		return isset( $languages[ $code ] ) ? $languages[ $code ] : $code;
	}

	/**
	 * The URL of a language's own llms.txt.
	 *
	 * @param string $code    Language code.
	 * @param string $variant index|full.
	 * @return string
	 */
	public static function endpoint( $code, $variant = 'index' ) {
		$file = ( 'full' === $variant ) ? 'llms-full.txt' : 'llms.txt';

		if ( get_option( 'permalink_structure' ) ) {
			return home_url( '/' . $code . '/' . $file );
		}

		return add_query_arg( 'oorank_lang', $code, home_url( '/' . $file ) );
	}
}