<?php
/**
 * Machine-translates a post's SEO fields into another language and saves them.
 */

declare( strict_types = 1 );

namespace AddBlack\Lang\Translation;

defined( 'ABSPATH' ) || exit;

use AddBlack\Lang\MachineTranslation\Provider;
use AddBlack\Lang\MachineTranslation\Translator;
use WP_Error;

final class MetaTranslator {

	public function __construct(
		private readonly SeoFields $fields,
		private readonly Translator $translator,
		private readonly PostTranslations $posts,
		private readonly SyncGuard $sync
	) {}

	/** @return array<string, string> Non-empty translatable values: field => text. */
	public function collect( int $post_id ): array {
		$out = array();
		foreach ( $this->fields->translatable() as $field ) {
			$text = $this->fields->read( $post_id, $field );
			if ( '' !== trim( $text ) ) {
				$out[ $field ] = $text;
			}
		}
		return $out;
	}

	/**
	 * The source post's SEO texts in $to. Nothing is saved.
	 *
	 * @return array<string, string>|WP_Error field => translated text.
	 */
	public function translate_values( int $source_id, string $to, ?Provider $provider = null ): array|WP_Error {
		$values = $this->collect( $source_id );
		if ( ! $values ) {
			return array();
		}
		$from = $this->posts->language_of( $source_id );
		if ( $from === $to ) {
			return new WP_Error( 'blocklingo_same_lang', __( 'Source and target are in the same language.', 'blocklingo' ) );
		}
		$post  = get_post( $source_id );
		$type  = $post ? get_post_type_object( $post->post_type ) : null;
		$hints = array();
		foreach ( array_keys( $values ) as $field ) {
			$hints[ $field ] = SeoFields::hint( $field );
		}
		$summary = $post ? ( $post->post_excerpt ? $post->post_excerpt : wp_trim_words( $post->post_content, 120 ) ) : '';
		$result  = $this->translator->translate_strings(
			$values,
			array_fill_keys( array_keys( $values ), 'text' ),
			$from,
			$to,
			$provider,
			array(
				'hints'   => $hints,
				'context' => array(
					'title'   => $post ? $post->post_title : '',
					'type'    => $type ? (string) $type->labels->singular_name : '',
					'outline' => $post ? $post->post_title . "\n" . wp_strip_all_tags( strip_shortcodes( $summary ) ) : '',
				),
			)
		);
		return is_wp_error( $result ) ? $result : array_map( 'strval', $result );
	}

	/**
	 * Save field => text values on a post, without triggering sync.
	 *
	 * @param array<string, string> $values
	 */
	public function apply( int $post_id, array $values ): void {
		$this->sync->paused(
			function () use ( $post_id, $values ): void {
				foreach ( $values as $field => $text ) {
					$this->fields->write( $post_id, (string) $field, (string) $text );
				}
			}
		);
	}

	/**
	 * Translate the source's SEO texts into the target post's language and save them.
	 *
	 * @return array<string, string>|WP_Error
	 */
	public function translate( int $source_id, int $target_id, ?Provider $provider = null ): array|WP_Error {
		$values = $this->translate_values( $source_id, $this->posts->language_of( $target_id ), $provider );
		if ( ! is_wp_error( $values ) ) {
			$this->apply( $target_id, $values );
		}
		return $values;
	}

	/** Remove canonical-style fields from a freshly copied translation. */
	public function clear_per_language( int $post_id ): void {
		foreach ( $this->fields->per_language() as $field ) {
			$this->fields->remove( $post_id, $field );
		}
	}
}