<?php

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

final class AI_Narration_Audio {
	private const SESSION_LIFETIME = 3600;
	private const OPENAI_ENDPOINT  = 'https://api.openai.com/v1/audio/speech';

	private AI_Narration_Content $content;
	private AI_Narration_Cache $cache;

	public function __construct( AI_Narration_Content $content, AI_Narration_Cache $cache ) {
		$this->content = $content;
		$this->cache   = $cache;

		add_action( 'wp_ajax_ai_narration_session', array( $this, 'create_session' ) );
		add_action( 'wp_ajax_nopriv_ai_narration_session', array( $this, 'create_session' ) );
		add_action( 'wp_ajax_ai_narration_voice_preview', array( $this, 'serve_voice_preview' ) );
	}

	public function create_bootstrap_token( int $post_id ): string {
		$post = get_post( $post_id );
		if ( ! $post instanceof WP_Post ) {
			return '';
		}

		$message = $post_id . '|' . $post->post_modified_gmt;
		return hash_hmac( 'sha256', $message, wp_salt( 'nonce' ) );
	}

	public function create_session(): void {
		$reference = $this->new_reference();
		$this->require_same_origin( $reference );

		// This public playback endpoint uses the signed article bootstrap token below rather than a user nonce.
		// phpcs:disable WordPress.Security.NonceVerification.Missing
		$post_id   = isset( $_POST['post_id'] ) ? absint( $_POST['post_id'] ) : 0;
		$bootstrap = isset( $_POST['bootstrap'] ) ? sanitize_text_field( wp_unslash( $_POST['bootstrap'] ) ) : '';
		// phpcs:enable WordPress.Security.NonceVerification.Missing

		if ( ! $post_id || ! hash_equals( $this->create_bootstrap_token( $post_id ), $bootstrap ) ) {
			$this->send_error( 'invalid_article', $reference, 403 );
		}

		$settings = AI_Narration_Admin::get_settings();
		$profile_id = 'a';
		if ( ! $this->content->is_eligible( $post_id, $settings ) ) {
			$this->send_error( 'unavailable', $reference, 403 );
		}
		$cache_manifest = $this->cache->get_available_manifest( $post_id );
		if ( null === $cache_manifest ) {
			$this->send_error( 'audio_unavailable', $reference, 404 );
		}

		try {
			$prepared = $this->content->prepare( $post_id );
		} catch ( RuntimeException $exception ) {
			$this->log( $reference, 'content_prepare_failed', array( 'post' => $post_id, 'detail' => $exception->getMessage() ) );
			$this->send_error( 'article_unavailable', $reference, 422 );
		}
		$ip_hash = $this->ip_hash();

		$session_id = bin2hex( random_bytes( 12 ) );
		$expires    = time() + self::SESSION_LIFETIME;
		$session_chunk_count = count( $cache_manifest['chunks'] );
		$payload    = array(
			'v'      => 1,
			'post'   => $post_id,
			'hash'   => $prepared['hash'],
			'chunks' => $session_chunk_count,
			'exp'    => $expires,
			'sid'    => $session_id,
			'ip'     => $ip_hash,
			'profile' => $profile_id,
		);

		$token = $this->sign_payload( $payload );
		wp_send_json_success(
			array(
				'session'    => $token,
				'chunks'     => $session_chunk_count,
				'cache'      => $cache_manifest['chunks'],
				'words'      => $prepared['words'],
				'expires'    => $expires,
				'reference' => strtoupper( substr( $session_id, 0, 10 ) ),
			),
			200
		);
	}


	public function serve_voice_preview(): void {
		$reference = $this->new_reference();

		if ( ! current_user_can( 'manage_options' ) ) {
			$this->send_error( 'preview_forbidden', $reference, 403 );
		}

		$nonce = isset( $_POST['nonce'] ) ? sanitize_text_field( wp_unslash( $_POST['nonce'] ) ) : '';
		if ( ! wp_verify_nonce( $nonce, 'ai_narration_voice_preview' ) ) {
			$this->send_error( 'preview_expired', $reference, 403 );
		}

		$this->require_same_origin( $reference );

		if ( ! AI_Narration_Admin::has_api_key() ) {
			$this->send_error( 'openai_key_missing', $reference, 400 );
		}

		$user_id = get_current_user_id();
		$bucket = 'voice-preview-hour-' . $user_id;
		if ( ! $this->consume_limit( $bucket, 30, HOUR_IN_SECONDS ) ) {
			$this->send_error( 'preview_rate_limited', $reference, 429 );
		}

		$model = isset( $_POST['model'] ) ? sanitize_text_field( wp_unslash( $_POST['model'] ) ) : '';
		$voice = isset( $_POST['voice'] ) ? sanitize_text_field( wp_unslash( $_POST['voice'] ) ) : '';
		$model = sanitize_key( $model );
		$voice = sanitize_key( $voice );
		if ( ! array_key_exists( $model, AI_Narration_Admin::models() ) || ! array_key_exists( $voice, AI_Narration_Admin::voices() ) ) {
			$this->send_error( 'invalid_preview_selection', $reference, 400 );
		}

		$instructions = isset( $_POST['instructions'] ) ? sanitize_textarea_field( wp_unslash( $_POST['instructions'] ) ) : '';
		$instructions = $this->limit_string( $instructions, 4096 );

		$preview_settings = array(
			'model'            => $model,
			'voice'            => $voice,
			'instructions'     => $instructions,
			'read_h2_headings' => ! empty( $_POST['read_h2_headings'] ),
		);
		$post_id = isset( $_POST['post_id'] ) ? absint( $_POST['post_id'] ) : 0;
		if ( $post_id > 0 ) {
			try {
				$prepared = $this->content->prepare( $post_id, $preview_settings );
				$preview_text = $this->preview_excerpt( (string) $prepared['text'] );
			} catch ( RuntimeException $exception ) {
				$this->log( $reference, 'article_preview_failed', array( 'post' => $post_id, 'detail' => $exception->getMessage() ) );
				$this->send_error( 'preview_article_unavailable', $reference, 422 );
			}
		} else {
			$preview_text = __( 'Welcome to AI Narration. This is a short preview of the selected voice, pacing and speaking style.', 'ai-narration' );
		}
		$mime = 'audio/aac';
		$filename = 'voice-preview.aac';
		$audio = $this->request_openai_audio( $preview_text, 0, 0, $reference, $preview_settings, 'voice_preview' );
		if ( 0 === $post_id ) {
			AI_Narration_Admin::mark_voice_previewed();
		}

		nocache_headers();
		header( 'Cache-Control: no-store, no-cache, must-revalidate, private, max-age=0' );
		header( 'Pragma: no-cache' );
		header( 'Expires: 0' );
		header( 'Content-Type: ' . $mime );
		header( 'Content-Disposition: inline; filename="' . $filename . '"' );
		header( 'X-Content-Type-Options: nosniff' );
		header( 'X-AI-Narration-Reference: ' . $reference );
		echo $audio; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Binary preview-audio response.
		wp_die( '', '', array( 'response' => 200 ) );
	}

	private function limit_string( string $text, int $limit ): string {
		if ( function_exists( 'mb_substr' ) ) {
			return mb_substr( $text, 0, $limit, 'UTF-8' );
		}
		return substr( $text, 0, $limit );
	}

	private function limit_utf8_bytes( string $text, int $limit ): string {
		if ( strlen( $text ) <= $limit ) {
			return $text;
		}
		$candidate = substr( $text, 0, $limit );
		while ( '' !== $candidate && 1 !== preg_match( '//u', $candidate ) ) {
			$candidate = substr( $candidate, 0, -1 );
		}
		return $candidate;
	}

	private function preview_excerpt( string $text ): string {
		$text = trim( $text );
		$limit = 1100;
		$length = function_exists( 'mb_strlen' ) ? mb_strlen( $text, 'UTF-8' ) : strlen( $text );
		if ( $length <= $limit ) {
			return $text;
		}

		$excerpt = function_exists( 'mb_substr' ) ? mb_substr( $text, 0, $limit, 'UTF-8' ) : substr( $text, 0, $limit );
		$sentence_end = -1;
		foreach ( array( '.', '!', '?' ) as $punctuation ) {
			$position = function_exists( 'mb_strrpos' ) ? mb_strrpos( $excerpt, $punctuation, 0, 'UTF-8' ) : strrpos( $excerpt, $punctuation );
			if ( false !== $position ) {
				$sentence_end = max( $sentence_end, (int) $position );
			}
		}

		if ( $sentence_end >= 500 ) {
			$excerpt = function_exists( 'mb_substr' ) ? mb_substr( $excerpt, 0, $sentence_end + 1, 'UTF-8' ) : substr( $excerpt, 0, $sentence_end + 1 );
		}

		return trim( $excerpt );
	}

	/**
	 * @param array<string,mixed>|null $settings_override Validated settings for an administrator preview.
	 */
	private function request_openai_audio( string $text, int $post_id, int $index, string $reference, ?array $settings_override = null, string $source = 'article', string $profile_id = 'a' ): string {
		$settings = is_array( $settings_override ) ? $settings_override : AI_Narration_Admin::get_settings();
		if ( ! is_array( $settings_override ) ) {
			$settings = $this->article_profile_settings( $settings, $profile_id );
		}
		$model    = isset( $settings['model'] ) && array_key_exists( $settings['model'], AI_Narration_Admin::models() ) ? (string) $settings['model'] : 'gpt-4o-mini-tts';
		$voice    = isset( $settings['voice'] ) && array_key_exists( $settings['voice'], AI_Narration_Admin::voices() ) ? (string) $settings['voice'] : 'cedar';

		$body = array(
			'model'           => $model,
			'input'           => $text,
			'voice'           => $voice,
			'response_format' => 'aac',
		);

		$instructions = trim( (string) $settings['instructions'] );
		if ( str_starts_with( $model, 'gpt-4o-mini-tts' ) && '' !== $instructions ) {
			$body['instructions'] = $instructions;
		}

		$response = wp_remote_post(
			self::OPENAI_ENDPOINT,
			array(
				'timeout'             => 60,
				'redirection'         => 0,
				'sslverify'           => true,
				'limit_response_size' => 8 * MB_IN_BYTES,
				'headers'             => array(
					'Authorization' => 'Bearer ' . AI_Narration_Admin::get_api_key(),
					'Content-Type'  => 'application/json',
					'Accept'        => 'audio/aac',
				),
				'body'                => wp_json_encode( $body ),
				'data_format'         => 'body',
			)
		);

		if ( is_wp_error( $response ) ) {
			$this->log(
				$reference,
				'openai_transport_error',
				array(
					'source' => $source,
					'post'  => $post_id,
					'chunk' => $index,
					'code'  => $response->get_error_code(),
				)
			);
			$this->send_error( 'openai_transport', $reference, 502 );
		}

		$status     = (int) wp_remote_retrieve_response_code( $response );
		$response_body = (string) wp_remote_retrieve_body( $response );
		$request_id = sanitize_text_field( (string) wp_remote_retrieve_header( $response, 'x-request-id' ) );

		if ( 200 !== $status || '' === $response_body || str_starts_with( ltrim( $response_body ), '{' ) ) {
			$error_code = '';
			$decoded    = json_decode( $response_body, true );
			if ( is_array( $decoded ) && isset( $decoded['error']['code'] ) ) {
				$error_code = sanitize_key( (string) $decoded['error']['code'] );
			} elseif ( is_array( $decoded ) && isset( $decoded['error']['type'] ) ) {
				$error_code = sanitize_key( (string) $decoded['error']['type'] );
			}

			$this->log(
				$reference,
				'openai_http_error',
				array(
					'source'            => $source,
					'post'              => $post_id,
					'chunk'             => $index,
					'http_status'       => $status,
					'openai_code'       => $error_code,
					'openai_request_id' => $request_id,
				)
			);

			if ( 401 === $status || 403 === $status ) {
				$this->send_error( 'openai_auth', $reference, 502 );
			}
			if ( 429 === $status ) {
				$this->send_error( 'openai_rate_limit', $reference, 503 );
			}
			$this->send_error( 'openai_error', $reference, 502 );
		}

		return $response_body;
	}

	/**
	 * Apply an article profile's voice and instructions to the established
	 * OpenAI on-demand settings shape without changing its shared model.
	 *
	 * @param array<string,mixed> $settings Saved narration settings.
	 * @return array<string,mixed>
	 */
	private function article_profile_settings( array $settings, string $profile_id ): array {
		return $settings;
	}

	private function require_same_origin( string $reference ): void {
		$source = '';
		if ( isset( $_SERVER['HTTP_ORIGIN'] ) ) {
			$source = esc_url_raw( wp_unslash( $_SERVER['HTTP_ORIGIN'] ) );
		} elseif ( isset( $_SERVER['HTTP_REFERER'] ) ) {
			$source = esc_url_raw( wp_unslash( $_SERVER['HTTP_REFERER'] ) );
		}

		$source_host = strtolower( (string) wp_parse_url( $source, PHP_URL_HOST ) );
		$home_host   = strtolower( (string) wp_parse_url( home_url( '/' ), PHP_URL_HOST ) );
		if ( '' === $source_host || '' === $home_host || ! hash_equals( $home_host, $source_host ) ) {
			$this->send_error( 'origin_rejected', $reference, 403 );
		}
	}

	/**
	 * @return array<string,mixed>|null
	 */
	private function verify_payload( string $token ): ?array {
		$parts = explode( '.', $token, 2 );
		if ( 2 !== count( $parts ) ) {
			return null;
		}

		$expected = hash_hmac( 'sha256', $parts[0], wp_salt( 'auth' ) );
		if ( ! hash_equals( $expected, $parts[1] ) ) {
			return null;
		}

		$json = $this->base64url_decode( $parts[0] );
		if ( false === $json ) {
			return null;
		}

		$payload = json_decode( $json, true );
		return is_array( $payload ) ? $payload : null;
	}

	/**
	 * @param array<string,mixed> $payload Session payload.
	 */
	private function sign_payload( array $payload ): string {
		$encoded   = $this->base64url_encode( (string) wp_json_encode( $payload ) );
		$signature = hash_hmac( 'sha256', $encoded, wp_salt( 'auth' ) );
		return $encoded . '.' . $signature;
	}

	private function base64url_encode( string $value ): string {
		return rtrim( strtr( base64_encode( $value ), '+/', '-_' ), '=' );
	}

	/**
	 * @return string|false
	 */
	private function base64url_decode( string $value ) {
		$padding = strlen( $value ) % 4;
		if ( $padding ) {
			$value .= str_repeat( '=', 4 - $padding );
		}
		return base64_decode( strtr( $value, '-_', '+/' ), true );
	}

	private function consume_limit( string $bucket, int $limit, int $ttl ): bool {
		$key     = 'ai_narration_' . hash( 'sha256', $bucket );
		$current = (int) get_transient( $key );
		if ( $current >= $limit ) {
			return false;
		}
		set_transient( $key, $current + 1, $ttl );
		return true;
	}

	/**
	 * Count a narration chunk once per signed session. Native media engines can
	 * retry the same URL (including Safari byte-range probes), so those retries
	 * must not exhaust the broader visitor limit. The separate per-chunk limit
	 * still caps the number of billable generation attempts.
	 *
	 * @param array<string,mixed> $payload Verified session payload.
	 */
	private function consume_audio_limit_once( array $payload, int $index, string $limit_scope, int $audio_limit ): bool {
		$session_id = isset( $payload['sid'] ) ? sanitize_key( (string) $payload['sid'] ) : '';
		$dedupe_key = 'audio-counted-' . $session_id . '-' . $index;
		$transient  = 'ai_narration_' . hash( 'sha256', $dedupe_key );

		if ( '' !== $session_id && false !== get_transient( $transient ) ) {
			return true;
		}

		if ( ! $this->consume_limit( 'audio-10m-' . $limit_scope, $audio_limit, 10 * MINUTE_IN_SECONDS ) ) {
			return false;
		}

		if ( '' !== $session_id ) {
			set_transient( $transient, 1, self::SESSION_LIFETIME );
		}

		return true;
	}

	private function ip_hash(): string {
		$ip = isset( $_SERVER['REMOTE_ADDR'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REMOTE_ADDR'] ) ) : 'unknown';
		return hash_hmac( 'sha256', $ip, wp_salt( 'auth' ) );
	}

	private function new_reference(): string {
		try {
			return strtoupper( substr( bin2hex( random_bytes( 8 ) ), 0, 10 ) );
		} catch ( Exception $exception ) {
			return strtoupper( substr( wp_generate_password( 10, false, false ), 0, 10 ) );
		}
	}

	private function send_error( string $code, string $reference, int $status ): void {
		wp_send_json_error(
			array(
				'code'      => sanitize_key( $code ),
				'reference' => sanitize_text_field( $reference ),
			),
			$status
		);
	}

	/**
	 * @param array<string,mixed> $context Non-sensitive diagnostic context.
	 */
	private function log( string $reference, string $event, array $context = array() ): void {
		$parts = array( '[AI Narration]', 'reference=' . sanitize_text_field( $reference ), 'event=' . sanitize_key( $event ) );
		foreach ( $context as $key => $value ) {
			$value   = is_scalar( $value ) ? (string) $value : wp_json_encode( $value );
			$value   = preg_replace( '/[\r\n]+/', ' ', (string) $value );
			$parts[] = sanitize_key( (string) $key ) . '=' . substr( (string) $value, 0, 180 );
		}
		// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log -- Deliberate non-sensitive operational logging.
		error_log( implode( ' ', $parts ) );
	}
}