<?php
/**
 * Context Service
 *
 * Centralized service for managing conversation context across
 * all generation paths. Provides a single source of truth for
 * chat history, plan, and per-post configuration.
 *
 * @package WP_Agentic_Writer
 */

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

/**
 * Class WP_Agentic_Writer_Context_Service
 *
 * Single source of truth for conversation context.
 *
 * Storage Layer Rules:
 * - Conversation messages → wpaw_conversations table (authoritative)
 * - Article outline/plan → post_meta._wpaw_plan (authoritative)
 * - Per-post config → post_meta._wpaw_post_config (authoritative)
 * - Legacy _wpaw_chat_history → migrated to session table on read
 */
class WP_Agentic_Writer_Context_Service {

	/**
	 * Singleton instance.
	 *
	 * @var WP_Agentic_Writer_Context_Service
	 */
	private static $instance = null;

	/**
	 * Get singleton instance.
	 *
	 * @return WP_Agentic_Writer_Context_Service
	 */
	public static function get_instance() {
		if ( null === self::$instance ) {
			self::$instance = new self();
		}
		return self::$instance;
	}

	/**
	 * Constructor.
	 */
	private function __construct() {
		// Private constructor for singleton.
	}

	/**
	 * Get conversation context for a session.
	 *
	 * @param string $session_id Session ID.
	 * @param int    $post_id    Post ID (optional).
	 * @return array Context data.
	 */
	public function get_context( $session_id, $post_id = 0 ) {
		$manager = WP_Agentic_Writer_Conversation_Manager::get_instance();
		$session = $manager->get_session( $session_id );
		$effective_session_id = $session_id;

		// Migrate legacy history on read if no session exists but post has legacy data.
		if ( ! $session && $post_id > 0 ) {
			$legacy_history = get_post_meta( $post_id, '_wpaw_chat_history', true );
			$is_migrated = get_post_meta( $post_id, '_wpaw_chat_history_migrated', true );

			if ( ! empty( $legacy_history ) && empty( $is_migrated ) ) {
				$migrated_session_id = $this->migrate_legacy_chat_history( $post_id, $session_id );
				// Use the session_id returned from migration (may be newly created)
				$effective_session_id = is_string( $migrated_session_id ) ? $migrated_session_id : $session_id;
				$session = $manager->get_session( $effective_session_id );
			}
		}

		if ( ! $session ) {
			return $this->get_empty_context( $effective_session_id, $post_id );
		}

		// If post_id is provided, get post-specific data
		$post_data = array();
		if ( $post_id > 0 ) {
			$post_data = $this->get_post_context( $post_id );
		}

		return array(
			'session_id'   => $effective_session_id,
			'post_id'      => $post_id,
			'messages'    => $session['messages'] ?? array(),
			'context'     => $session['context'] ?? array(),
			'plan'        => $post_data['plan'] ?? null,
			'post_config' => $post_data['post_config'] ?? $this->get_default_post_config(),
			'title'        => $session['title'] ?? '',
			'focus_keyword' => $session['focus_keyword'] ?? '',
			'status'      => $session['status'] ?? 'active',
		);
	}

	/**
	 * Get empty context structure.
	 *
	 * @param string $session_id Session ID.
	 * @param int    $post_id    Post ID.
	 * @return array Empty context.
	 */
	private function get_empty_context( $session_id, $post_id ) {
		return array(
			'session_id'   => $session_id,
			'post_id'      => $post_id,
			'messages'     => array(),
			'context'      => array(),
			'plan'         => null,
			'post_config' => $this->get_default_post_config(),
			'title'        => '',
			'focus_keyword' => '',
			'status'       => 'active',
		);
	}

	/**
	 * Get post-specific context (plan, config).
	 *
	 * @param int $post_id Post ID.
	 * @return array Post context.
	 */
	public function get_post_context( $post_id ) {
		$plan = get_post_meta( $post_id, '_wpaw_plan', true );
		if ( ! is_array( $plan ) ) {
			$plan = null;
		}

		$post_config = get_post_meta( $post_id, '_wpaw_post_config', true );
		if ( ! is_array( $post_config ) ) {
			$post_config = $this->get_default_post_config();
		}

		return array(
			'plan' => $plan,
			'post_config' => $post_config,
		);
	}

	/**
	 * Save messages to session.
	 *
	 * @param string $session_id Session ID.
	 * @param array  $messages   Messages array.
	 * @return bool Success.
	 */
	public function save_messages( $session_id, $messages ) {
		$manager = WP_Agentic_Writer_Conversation_Manager::get_instance();
		return $manager->update_messages( $session_id, $messages );
	}

	/**
	 * Add a message to the session.
	 *
	 * @param string $session_id Session ID.
	 * @param array  $message   Message data.
	 * @return bool Success.
	 */
	public function add_message( $session_id, $message ) {
		$manager = WP_Agentic_Writer_Conversation_Manager::get_instance();
		$session = $manager->get_session( $session_id );

		if ( ! $session ) {
			return false;
		}

		$messages = $session['messages'] ?? array();
		$messages[] = $message;

		return $manager->update_messages( $session_id, $messages );
	}

	/**
	 * Save plan to post meta.
	 *
	 * @param int   $post_id Post ID.
	 * @param array $plan    Plan data.
	 * @return bool Success.
	 */
	public function save_plan( $post_id, $plan ) {
		if ( $post_id <= 0 ) {
			return false;
		}

		return update_post_meta( $post_id, '_wpaw_plan', $plan ) !== false;
	}

	/**
	 * Get plan from post meta.
	 *
	 * @param int $post_id Post ID.
	 * @return array|null Plan or null.
	 */
	public function get_plan( $post_id ) {
		if ( $post_id <= 0 ) {
			return null;
		}

		$plan = get_post_meta( $post_id, '_wpaw_plan', true );
		return is_array( $plan ) ? $plan : null;
	}

	/**
	 * Save post config to post meta.
	 *
	 * @param int   $post_id     Post ID.
	 * @param array $post_config Post config.
	 * @return bool Success.
	 */
	public function save_post_config( $post_id, $post_config ) {
		if ( $post_id <= 0 ) {
			return false;
		}

		return update_post_meta( $post_id, '_wpaw_post_config', $post_config ) !== false;
	}

	/**
	 * Get post config from post meta.
	 *
	 * @param int $post_id Post ID.
	 * @return array Post config.
	 */
	public function get_post_config( $post_id ) {
		if ( $post_id <= 0 ) {
			return $this->get_default_post_config();
		}

		$config = get_post_meta( $post_id, '_wpaw_post_config', true );
		return is_array( $config ) ? wp_parse_args( $config, $this->get_default_post_config() ) : $this->get_default_post_config();
	}

	/**
	 * Get default post config.
	 *
	 * @return array Default config.
	 */
	public function get_default_post_config() {
		$settings = get_option( 'wp_agentic_writer_settings', array() );

		return array(
			'article_length' => 'medium',
			'language' => 'auto',
			'tone' => '',
			'audience' => '',
			'experience_level' => 'general',
			'include_images' => true,
			'web_search' => false,
			'default_mode' => 'writing',
			'seo_focus_keyword' => '',
			'seo_secondary_keywords' => '',
			'seo_meta_description' => '',
			'seo_enabled' => false,
		);
	}

	/**
	 * Migrate legacy chat history from post meta to session.
	 *
	 * @param int    $post_id    Post ID.
	 * @param string $session_id Optional session ID to use. If not provided and no
	 *                           session exists, creates a new one.
	 * @return string|false Session ID used for migration, or false on failure.
	 */
	public function migrate_legacy_chat_history( $post_id, $session_id = '' ) {
		if ( $post_id <= 0 ) {
			return false;
		}

		$legacy_history = get_post_meta( $post_id, '_wpaw_chat_history', true );
		if ( empty( $legacy_history ) || ! is_array( $legacy_history ) ) {
			return $session_id ?: true; // Nothing to migrate, return existing or true
		}

		$manager = WP_Agentic_Writer_Conversation_Manager::get_instance();

		// Try to find existing session for this post if no session_id provided
		$sessions = array();
		if ( empty( $session_id ) ) {
			$sessions = $manager->get_sessions_for_post( $post_id );
		}

		if ( ! empty( $sessions ) ) {
			// Append to existing session
			$session = $sessions[0];
			$existing_messages = $session['messages'] ?? array();

			// Merge legacy messages (avoid duplicates based on content hash)
			$existing_hashes = array();
			foreach ( $existing_messages as $msg ) {
				$existing_hashes[] = $this->get_message_hash( $msg );
			}

			foreach ( $legacy_history as $msg ) {
				$hash = $this->get_message_hash( $msg );
				if ( ! in_array( $hash, $existing_hashes, true ) ) {
					$existing_messages[] = $msg;
				}
			}

			$manager->update_messages( $session['session_id'], $existing_messages );
			$migrated_session_id = $session['session_id'];
		} else {
			// Create new session with legacy messages
			$new_session_id = $manager->create_session( array(
				'post_id'  => $post_id,
				'messages' => $legacy_history,
				'title'    => 'Migrated from legacy',
			) );
			$migrated_session_id = is_string( $new_session_id ) ? $new_session_id : ( ! empty( $session_id ) ? $session_id : '' );
		}

		// Delete legacy meta after successful migration and mark as migrated.
		delete_post_meta( $post_id, '_wpaw_chat_history' );
		update_post_meta( $post_id, '_wpaw_chat_history_migrated', current_time( 'mysql' ) );

		return $migrated_session_id;
	}

	/**
	 * Get hash for message deduplication.
	 *
	 * @param array $message Message.
	 * @return string Hash.
	 */
	private function get_message_hash( $message ) {
		$content = $message['content'] ?? '';
		$role = $message['role'] ?? '';
		return md5( $role . ':' . $content );
	}

	/**
	 * Clear context for a session and post.
	 *
	 * @param string $session_id Session ID.
	 * @param int    $post_id    Post ID.
	 * @return bool Success.
	 */
	public function clear_context( $session_id, $post_id = 0 ) {
		$manager = WP_Agentic_Writer_Conversation_Manager::get_instance();

		// Clear specific session if provided
		if ( $session_id ) {
			$manager->update_messages( $session_id, array() );
		} elseif ( $post_id > 0 ) {
			// No session_id provided - clear all active sessions for this post
			$sessions = $manager->get_sessions_for_post( $post_id );
			foreach ( $sessions as $session ) {
				if ( ! empty( $session['session_id'] ) && 'active' === ( $session['status'] ?? '' ) ) {
					$manager->update_messages( $session['session_id'], array() );
				}
			}
		}

		// Clear post meta if post_id provided
		if ( $post_id > 0 ) {
			delete_post_meta( $post_id, '_wpaw_plan' );
			delete_post_meta( $post_id, '_wpaw_memory' );
			delete_post_meta( $post_id, '_wpaw_chat_history' );
			// Keep _wpaw_post_config as it's user settings
		}

		return true;
	}

	/**
	 * Get context summary for display.
	 *
	 * @param array $context Context data.
	 * @return string Human-readable summary.
	 */
	public function get_context_summary( $context ) {
		$parts = array();

		// Message count
		$msg_count = count( $context['messages'] ?? array() );
		$parts[] = sprintf( _n( '%d message', '%d messages', $msg_count, 'wp-agentic-writer' ), $msg_count );

		// Plan status
		if ( ! empty( $context['plan'] ) ) {
			$sections = count( $context['plan']['sections'] ?? array() );
			$parts[] = sprintf( _n( '%d section in plan', '%d sections in plan', $sections, 'wp-agentic-writer' ), $sections );
		} else {
			$parts[] = 'No plan';
		}

		// Focus keyword
		if ( ! empty( $context['focus_keyword'] ) ) {
			$parts[] = 'Focus: ' . $context['focus_keyword'];
		}

		return implode( ' | ', $parts );
	}

	/**
	 * Build context for AI prompt.
	 *
	 * @param array $context Context data.
	 * @param int   $max_messages Maximum messages to include.
	 * @return array Messages for AI.
	 */
	public function build_ai_context( $context, $max_messages = 20 ) {
		$messages = $context['messages'] ?? array();

		// Limit to most recent messages
		if ( count( $messages ) > $max_messages ) {
			$messages = array_slice( $messages, -$max_messages );
		}

		// Add context summary if available
		$context_summary = array(
			'role' => 'system',
			'content' => 'Current context: ' . $this->get_context_summary( $context ),
		);

		return array_merge( array( $context_summary ), $messages );
	}
}