<?php
/**
 * Conversation memory using transients.
 *
 * @package Aivexa
 */

declare(strict_types=1);

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

/**
 * Conversation memory manager.
 */
class Aivexa_Memory {

	private const TRANSIENT_PREFIX = 'aivexa_conv_';
	private const TTL              = DAY_IN_SECONDS;

	/**
	 * Create a new conversation.
	 *
	 * @return string Conversation ID.
	 */
	public function create_conversation(): string {
		try {
			$conversation_id = bin2hex( random_bytes( 16 ) );
		} catch ( Exception $exception ) {
			unset( $exception );
			$conversation_id = md5( wp_generate_uuid4() . wp_rand() );
		}

		$this->save_conversation(
			$conversation_id,
			array(
				'id'         => $conversation_id,
				'created_at' => time(),
				'updated_at' => time(),
				'session'    => Aivexa_Security::get_session_token(),
				'messages'   => array(),
				'response_ids' => array(),
			)
		);

		$this->increment_conversation_count();

		return $conversation_id;
	}

	/**
	 * Get conversation by ID.
	 *
	 * @param string $conversation_id Conversation ID.
	 * @return array<string, mixed>|null
	 */
	public function get_conversation( string $conversation_id ): ?array {
		if ( '' === $conversation_id ) {
			return null;
		}

		$data = get_transient( self::TRANSIENT_PREFIX . $conversation_id );
		if ( ! is_array( $data ) ) {
			return null;
		}

		if ( ! $this->can_access_conversation( $data ) ) {
			return null;
		}

		return $data;
	}

	/**
	 * Append a message.
	 *
	 * @param string               $conversation_id Conversation ID.
	 * @param array<string, mixed> $message         Message.
	 */
	public function append_message( string $conversation_id, array $message ): void {
		$conversation = $this->get_conversation( $conversation_id );
		if ( null === $conversation ) {
			return;
		}

		$conversation['messages'][] = $message;
		$conversation['updated_at']   = time();

		$max = (int) Aivexa_Settings::get( 'max_conversation_messages', 20 );
		if ( count( $conversation['messages'] ) > $max ) {
			$conversation['messages'] = array_slice( $conversation['messages'], -$max );
		}

		$this->save_conversation( $conversation_id, $conversation );
	}

	/**
	 * Store OpenAI response ID for multi-turn continuity.
	 *
	 * @param string $conversation_id Conversation ID.
	 * @param string $response_id     Response ID.
	 */
	public function append_response_id( string $conversation_id, string $response_id ): void {
		$conversation = $this->get_conversation( $conversation_id );
		if ( null === $conversation ) {
			return;
		}

		$conversation['response_ids'][] = sanitize_text_field( $response_id );
		$conversation['updated_at']     = time();
		$this->save_conversation( $conversation_id, $conversation );
	}

	/**
	 * Get latest response ID.
	 *
	 * @param string $conversation_id Conversation ID.
	 */
	public function get_latest_response_id( string $conversation_id ): string {
		$conversation = $this->get_conversation( $conversation_id );
		if ( null === $conversation || empty( $conversation['response_ids'] ) ) {
			return '';
		}

		$ids = $conversation['response_ids'];
		return (string) end( $ids );
	}

	/**
	 * Clear conversation.
	 *
	 * @param string $conversation_id Conversation ID.
	 */
	public function clear_conversation( string $conversation_id ): bool {
		$conversation = $this->get_conversation( $conversation_id );
		if ( null === $conversation ) {
			return false;
		}

		delete_transient( self::TRANSIENT_PREFIX . $conversation_id );
		return true;
	}

	/**
	 * Save conversation.
	 *
	 * @param string               $conversation_id Conversation ID.
	 * @param array<string, mixed> $conversation    Conversation data.
	 */
	private function save_conversation( string $conversation_id, array $conversation ): void {
		set_transient( self::TRANSIENT_PREFIX . $conversation_id, $conversation, self::TTL );
	}

	/**
	 * Verify session ownership.
	 *
	 * @param array<string, mixed> $conversation Conversation.
	 */
	private function can_access_conversation( array $conversation ): bool {
		if ( current_user_can( 'manage_options' ) ) {
			return true;
		}

		$session = isset( $conversation['session'] ) ? (string) $conversation['session'] : '';
		return $session === Aivexa_Security::get_session_token();
	}

	/**
	 * Increment stats counter.
	 */
	private function increment_conversation_count(): void {
		$stats = get_option( 'aivexa_stats', array() );
		if ( ! is_array( $stats ) ) {
			$stats = array();
		}

		$stats['total_conversations'] = isset( $stats['total_conversations'] ) ? (int) $stats['total_conversations'] + 1 : 1;
		update_option( 'aivexa_stats', $stats, false );
	}

	/**
	 * Get conversations associated with a session token.
	 *
	 * @param string $session Session token.
	 * @return array<string, array<string, mixed>>
	 */
	public function get_conversations_for_session( string $session ): array {
		global $wpdb;

		if ( '' === $session || ! $wpdb instanceof wpdb ) {
			return array();
		}

		$like  = $wpdb->esc_like( '_transient_' . self::TRANSIENT_PREFIX ) . '%';
		$rows  = $wpdb->get_results( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
			$wpdb->prepare(
				"SELECT option_name, option_value FROM {$wpdb->options} WHERE option_name LIKE %s",
				$like
			)
		);
		$items = array();

		if ( ! is_array( $rows ) ) {
			return $items;
		}

		foreach ( $rows as $row ) {
			if ( ! isset( $row->option_name, $row->option_value ) ) {
				continue;
			}

			$data = maybe_unserialize( $row->option_value );
			if ( ! is_array( $data ) ) {
				continue;
			}

			if ( (string) ( $data['session'] ?? '' ) !== $session ) {
				continue;
			}

			$conversation_id = str_replace( '_transient_' . self::TRANSIENT_PREFIX, '', (string) $row->option_name );
			$items[ $conversation_id ] = $data;
		}

		return $items;
	}
}