<?php
/** Persistent discovery queue with bounded retries and atomic claims. */
namespace Accessibility_Audio_TTS\Admin;

use Accessibility_Audio_TTS\Core\Atomic_Options;

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

class Admin_Queue_Manager {
	const QUEUE_OPTION = 'accessibility_audio_tts_pending_queue';
	const RETRY_META = 'accessibility_audio_tts_queue_retry';
	const RETRY_AFTER_META = 'accessibility_audio_tts_queue_retry_after';
	const RETRY_STATE_META = 'accessibility_audio_tts_queue_retry_state';
	const MAX_ATTEMPTS = 3;

	/** Deferred/exhausted posts are filtered before LIMIT, so they cannot starve older posts. */
	public function auto_discover_pending_posts() {
		$types = get_option( 'accessibility_audio_tts_post_types', array( 'post' ) );
		if ( ! is_array( $types ) || empty( $types ) ) { return; }
		$query = new \WP_Query( array(
			'post_type' => $types, 'post_status' => 'publish', 'fields' => 'ids',
			'posts_per_page' => 20, 'orderby' => 'ID', 'order' => 'ASC',
			'no_found_rows' => true, 'update_post_term_cache' => false,
			'meta_query' => array(
				'relation' => 'AND',
				array( 'relation' => 'OR',
					array( 'key' => 'accessibility_audio_tts_generated', 'compare' => 'NOT EXISTS' ),
					array( 'key' => 'accessibility_audio_tts_generated', 'value' => array( '', '0' ), 'compare' => 'IN' ),
				),
				array( 'relation' => 'OR',
					array( 'key' => self::RETRY_STATE_META, 'compare' => 'NOT EXISTS' ),
					array( 'key' => self::RETRY_STATE_META, 'value' => array( 'permanent', 'exhausted' ), 'compare' => 'NOT IN' ),
				),
				array( 'relation' => 'OR',
					array( 'key' => self::RETRY_AFTER_META, 'compare' => 'NOT EXISTS' ),
					array( 'key' => self::RETRY_AFTER_META, 'value' => time(), 'compare' => '<=', 'type' => 'NUMERIC' ),
				),
			),
		) );
		$ids = array_map( 'intval', $query->posts );
		Atomic_Options::update( self::QUEUE_OPTION, static function ( $queue ) use ( $ids ) {
			return array_values( array_unique( array_merge( self::normalize_queue( $queue ), $ids ) ) );
		} );
	}

	private static function normalize_queue( $queue ) {
		return is_array( $queue ) ? array_values( array_filter( array_map( 'intval', $queue ), static function ( $id ) { return $id > 0; } ) ) : array();
	}

	public function get_pending_queue() { return self::normalize_queue( get_option( self::QUEUE_OPTION, array() ) ); }
	public function get_queue_size() { return count( $this->get_pending_queue() ); }
	public function get_next_post() { $queue = $this->get_pending_queue(); return $queue[0] ?? null; }

	/** Explicit retry re-enables a terminal job; automatic discovery never does. */
	public function add_to_queue( $post_id, $manual_retry = true ) {
		$post_id = absint( $post_id );
		if ( ! $post_id ) { return; }
		if ( $manual_retry ) { $this->clear_retry_state( $post_id ); }
		Atomic_Options::update( self::QUEUE_OPTION, static function ( $queue ) use ( $post_id ) {
			$queue = self::normalize_queue( $queue ); $queue[] = $post_id;
			return array_values( array_unique( $queue ) );
		} );
	}

	public function remove_from_queue( $post_id ) {
		$post_id = absint( $post_id );
		Atomic_Options::update( self::QUEUE_OPTION, static function ( $queue ) use ( $post_id ) {
			return array_values( array_diff( self::normalize_queue( $queue ), array( $post_id ) ) );
		} );
	}

	/** An exact-value CAS makes simultaneous workers claim distinct items. */
	public function process_next_and_remove() {
		$claimed = null;
		Atomic_Options::update( self::QUEUE_OPTION, static function ( $queue ) use ( &$claimed ) {
			$queue = self::normalize_queue( $queue ); $claimed = array_shift( $queue ); return $queue;
		} );
		return $claimed;
	}

	public function retry_is_due( $post_id ) {
		$state = get_post_meta( $post_id, self::RETRY_STATE_META, true );
		return ! in_array( $state, array( 'permanent', 'exhausted' ), true ) && (int) get_post_meta( $post_id, self::RETRY_AFTER_META, true ) <= time();
	}

	public function clear_retry_state( $post_id ) {
		foreach ( array( self::RETRY_META, self::RETRY_AFTER_META, self::RETRY_STATE_META ) as $key ) { delete_post_meta( $post_id, $key ); }
	}

	/** Unknown provider errors get finite backoff; only structurally invalid posts are permanent. */
	public function record_failure( $post_id, array $result, $permanent = false ) {
		$old = get_post_meta( $post_id, self::RETRY_META, true );
		$attempts = ( is_array( $old ) ? (int) ( $old['attempts'] ?? 0 ) : 0 ) + 1;
		$state = $permanent ? 'permanent' : ( $attempts >= self::MAX_ATTEMPTS ? 'exhausted' : 'deferred' );
		$after = 'deferred' === $state ? time() + min( HOUR_IN_SECONDS, 60 * ( 2 ** ( $attempts - 1 ) ) ) : 0;
		update_post_meta( $post_id, self::RETRY_META, array( 'attempts' => $attempts, 'state' => $state, 'retry_after' => $after, 'error' => sanitize_text_field( $result['error'] ?? 'Audio generation failed.' ) ) );
		update_post_meta( $post_id, self::RETRY_STATE_META, $state );
		update_post_meta( $post_id, self::RETRY_AFTER_META, $after );
		update_post_meta( $post_id, 'accessibility_audio_tts_generation_status', 'failed' );
	}
}