<?php
/**
 * Resolves the right Stemmer for the current site locale.
 *
 * @package Postlinkly
 * @since   1.0.0
 */

declare(strict_types=1);

namespace Postlinkly\Text;

use Postlinkly\Text\Stemmers\NullStemmer;
use Postlinkly\Text\Stemmers\SnowballStemmer;

/**
 * Resolves the right Stemmer implementation for a given locale.
 *
 * Maps WordPress locale strings (e.g. `en_US`, `pt_BR`) to a Stemmer
 * instance. Locales without a registered stemmer fall back to the
 * NullStemmer, which gives case-insensitive matching but no morphological
 * reduction.
 *
 * Resolution is cached per locale for the lifetime of the request so
 * repeated calls don't reconstruct stemmer instances.
 *
 * Site owners can override the locale-to-stemmer mapping via the
 * `postlinkly_stemmer_for_locale` filter, which makes adding a custom
 * stemmer for an unsupported language possible without forking the plugin.
 *
 * @since 1.0.0
 */
final class StemmerLoader {

	/**
	 * Cached stemmer instances keyed by normalised locale.
	 *
	 * @var array<string, Stemmer>
	 */
	private array $cache = array();

	/**
	 * Returns the Stemmer for the current WordPress locale.
	 *
	 * Reads `get_locale()` at call time rather than caching across locale
	 * changes (multilingual sites swap locale per request).
	 *
	 * @since 1.0.0
	 *
	 * @return Stemmer Stemmer for the current locale, or NullStemmer if unsupported.
	 */
	public function for_current_locale(): Stemmer {
		$locale = function_exists( 'get_locale' ) ? get_locale() : 'en_US';
		return $this->for_locale( $locale );
	}

	/**
	 * Returns the Stemmer for a specific locale.
	 *
	 * @since 1.0.0
	 *
	 * @param string $locale WordPress locale string (e.g. `en_US`, `pt_BR`)
	 *                       or a bare language code (`en`, `pt`).
	 *
	 * @return Stemmer Stemmer for the locale, or NullStemmer if unsupported.
	 */
	public function for_locale( string $locale ): Stemmer {
		$language = self::extract_language_code( $locale );

		if ( isset( $this->cache[ $language ] ) ) {
			return $this->cache[ $language ];
		}

		$stemmer = $this->build_stemmer( $language );

		/**
		 * Filters the Stemmer instance used for a given language code.
		 *
		 * Use this to register a custom Stemmer for a language Postlinkly
		 * does not support out of the box.
		 *
		 * @since 1.0.0
		 *
		 * @param Stemmer $stemmer  Default Stemmer (may be NullStemmer for unsupported langs).
		 * @param string  $language Two-letter language code.
		 */
		$stemmer = apply_filters( 'postlinkly_stemmer_for_locale', $stemmer, $language );

		$this->cache[ $language ] = $stemmer;
		return $stemmer;
	}

	/**
	 * Returns the list of language codes with a real (non-Null) Stemmer.
	 *
	 * Useful for surfacing "supported languages" lists in admin UI.
	 *
	 * @since 1.0.0
	 *
	 * @return array<int, string> Sorted list of supported language codes.
	 */
	public static function supported_language_codes(): array {
		return array(
			'ca',
			'da',
			'de',
			'en',
			'es',
			'fi',
			'fr',
			'it',
			'nl',
			'no',
			'pt',
			'ro',
			'ru',
			'sv',
		);
	}

	/**
	 * Builds the Stemmer for a language code, without filtering or caching.
	 *
	 * @since 1.0.0
	 *
	 * @param string $language Two-letter language code.
	 *
	 * @return Stemmer
	 */
	private function build_stemmer( string $language ): Stemmer {
		switch ( $language ) {
			case 'ca':
				return SnowballStemmer::catalan();
			case 'da':
				return SnowballStemmer::danish();
			case 'de':
				return SnowballStemmer::german();
			case 'en':
				return SnowballStemmer::english();
			case 'es':
				return SnowballStemmer::spanish();
			case 'fi':
				return SnowballStemmer::finnish();
			case 'fr':
				return SnowballStemmer::french();
			case 'it':
				return SnowballStemmer::italian();
			case 'nl':
				return SnowballStemmer::dutch();
			case 'no':
				return SnowballStemmer::norwegian();
			case 'pt':
				return SnowballStemmer::portuguese();
			case 'ro':
				return SnowballStemmer::romanian();
			case 'ru':
				return SnowballStemmer::russian();
			case 'sv':
				return SnowballStemmer::swedish();
			default:
				return new NullStemmer( $language );
		}
	}

	/**
	 * Normalises a locale string to its two-letter language code.
	 *
	 * `en_US` → `en`, `pt-BR` → `pt`, `en` → `en`. Returns `und` for empty input.
	 *
	 * @since 1.0.0
	 *
	 * @param string $locale Locale string.
	 *
	 * @return string Normalised language code.
	 */
	private static function extract_language_code( string $locale ): string {
		$locale = strtolower( trim( $locale ) );
		if ( '' === $locale ) {
			return 'und';
		}
		// Split on either underscore or hyphen.
		$parts = preg_split( '/[_-]/', $locale, 2 );
		if ( false === $parts || array() === $parts ) {
			return 'und';
		}
		return $parts[0];
	}
}