<?php
/**
 * Context Builder
 *
 * Builds compact, backend-owned prompt context from saved sessions and posts.
 *
 * @package WP_Agentic_Writer
 */

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

/**
 * Class WP_Agentic_Writer_Context_Builder
 *
 * OpenRouter and other providers are stateless gateways. This class keeps
 * continuity in WordPress by selecting the relevant session/post context for
 * each request without resending the full browser history.
 */
class WP_Agentic_Writer_Context_Builder {

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

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

		return self::$instance;
	}

	/**
	 * Build a context package for a task.
	 *
	 * @param string $task           Task name.
	 * @param string $session_id     Session ID.
	 * @param int    $post_id        Post ID.
	 * @param array  $request_params Request params.
	 * @return array Context package.
	 */
	public function build_for_task( $task, $session_id, $post_id, $request_params = array() ) {
		$context_service = WP_Agentic_Writer_Context_Service::get_instance();
		$saved_context = ! empty( $session_id )
			? $context_service->get_context( $session_id, $post_id )
			: array();

		$session_context = $saved_context['context'] ?? array();
		$messages = $saved_context['messages'] ?? array();

		if ( empty( $messages ) ) {
			$messages = $this->get_request_messages( $request_params );
		}

		$token_policy = $this->get_token_policy( $session_context );
		$recent_messages = $this->prepare_recent_messages( $messages, $token_policy['max_recent_messages'] );
		$recent_messages = $this->remove_active_user_message( $recent_messages, $request_params['latestUserMessage'] ?? '' );
		$post_config = $this->resolve_post_config( $saved_context, $request_params );
		$plan = $this->resolve_plan( $saved_context, $request_params, $post_id );

		$working_context = $this->build_working_context(
			$task,
			$session_context,
			$recent_messages,
			$plan,
			$post_config,
			$request_params
		);

		return array(
			'system_context'   => '',
			'working_context'  => $working_context,
			'active_content'   => $this->get_active_content( $request_params ),
			'research_context' => $this->build_research_context( $session_context, $request_params, $token_policy['max_research_snippets'] ),
			'audit'            => array(
				'included_recent_messages' => count( $recent_messages ),
				'included_research_items'  => $this->count_research_items( $session_context, $request_params, $token_policy['max_research_snippets'] ),
				'estimated_input_tokens'   => $this->estimate_tokens( $working_context ),
				'used_full_history'        => false,
			),
		);
	}

	/**
	 * Build a system message that can be inserted after the primary system prompt.
	 *
	 * @param string $task           Task name.
	 * @param string $session_id     Session ID.
	 * @param int    $post_id        Post ID.
	 * @param array  $request_params Request params.
	 * @return array Context system message and audit metadata.
	 */
	public function build_system_message( $task, $session_id, $post_id, $request_params = array() ) {
		$package = $this->build_for_task( $task, $session_id, $post_id, $request_params );
		$content = trim(
			$package['working_context']
			. "\n"
			. $package['active_content']
			. "\n"
			. $package['research_context']
		);

		if ( '' === $content ) {
			return array(
				'message' => null,
				'audit'   => $package['audit'],
			);
		}

		return array(
			'message' => array(
				'role'    => 'system',
				'content' => $content,
			),
			'audit'   => $package['audit'],
		);
	}

	/**
	 * Get task token policy.
	 *
	 * @param array $session_context Session context.
	 * @return array Token policy.
	 */
	private function get_token_policy( $session_context ) {
		$policy = isset( $session_context['token_policy'] ) && is_array( $session_context['token_policy'] )
			? $session_context['token_policy']
			: array();

		return array(
			'max_recent_messages'   => max( 2, (int) ( $policy['max_recent_messages'] ?? 6 ) ),
			'max_summary_tokens'    => max( 200, (int) ( $policy['max_summary_tokens'] ?? 600 ) ),
			'max_research_snippets' => max( 0, (int) ( $policy['max_research_snippets'] ?? 5 ) ),
		);
	}

	/**
	 * Get messages from request fallback.
	 *
	 * @param array $request_params Request params.
	 * @return array Messages.
	 */
	private function get_request_messages( $request_params ) {
		if ( ! empty( $request_params['messages'] ) && is_array( $request_params['messages'] ) ) {
			return $request_params['messages'];
		}

		if ( ! empty( $request_params['chatHistory'] ) && is_array( $request_params['chatHistory'] ) ) {
			return $request_params['chatHistory'];
		}

		return array();
	}

	/**
	 * Prepare compact recent messages.
	 *
	 * @param array $messages     Messages.
	 * @param int   $max_messages Max messages.
	 * @return array Recent messages.
	 */
	private function prepare_recent_messages( $messages, $max_messages ) {
		$prepared = array();

		foreach ( (array) $messages as $message ) {
			$role = isset( $message['role'] ) ? (string) $message['role'] : '';
			if ( ! in_array( $role, array( 'user', 'assistant' ), true ) ) {
				continue;
			}

			$content = isset( $message['content'] ) ? trim( wp_strip_all_tags( (string) $message['content'] ) ) : '';
			if ( '' === $content ) {
				continue;
			}

			$prepared[] = array(
				'role'    => $role,
				'content' => $this->truncate_text( $content, 900 ),
			);
		}

		if ( count( $prepared ) > $max_messages ) {
			$prepared = array_slice( $prepared, -1 * $max_messages );
		}

		return $prepared;
	}

	/**
	 * Avoid echoing the active user turn inside the saved-context excerpt.
	 *
	 * @param array  $messages            Recent messages.
	 * @param string $active_user_message Active user message.
	 * @return array Messages without duplicate active turn.
	 */
	private function remove_active_user_message( $messages, $active_user_message ) {
		$active_user_message = trim( wp_strip_all_tags( (string) $active_user_message ) );
		if ( '' === $active_user_message || empty( $messages ) ) {
			return $messages;
		}

		for ( $i = count( $messages ) - 1; $i >= 0; $i-- ) {
			if ( 'user' !== ( $messages[ $i ]['role'] ?? '' ) ) {
				continue;
			}

			$content = trim( (string) ( $messages[ $i ]['content'] ?? '' ) );
			if ( $content === $active_user_message ) {
				array_splice( $messages, $i, 1 );
			}
			break;
		}

		return $messages;
	}

	/**
	 * Resolve post config.
	 *
	 * @param array $saved_context  Saved context package.
	 * @param array $request_params Request params.
	 * @return array Post config.
	 */
	private function resolve_post_config( $saved_context, $request_params ) {
		$config = $saved_context['post_config'] ?? array();

		if ( ! empty( $request_params['postConfig'] ) && is_array( $request_params['postConfig'] ) ) {
			$config = wp_parse_args( $request_params['postConfig'], $config );
		}

		return is_array( $config ) ? $config : array();
	}

	/**
	 * Resolve current plan.
	 *
	 * @param array $saved_context  Saved context package.
	 * @param array $request_params Request params.
	 * @param int   $post_id        Post ID.
	 * @return array|null Plan.
	 */
	private function resolve_plan( $saved_context, $request_params, $post_id ) {
		if ( ! empty( $saved_context['plan'] ) && is_array( $saved_context['plan'] ) ) {
			return $saved_context['plan'];
		}

		if ( ! empty( $request_params['plan'] ) && is_array( $request_params['plan'] ) ) {
			return $request_params['plan'];
		}

		if ( $post_id > 0 ) {
			$plan = get_post_meta( $post_id, '_wpaw_plan', true );
			if ( is_array( $plan ) ) {
				return $plan;
			}
		}

		return null;
	}

	/**
	 * Build compact working context.
	 *
	 * @param string $task            Task name.
	 * @param array  $session_context Session context.
	 * @param array  $recent_messages Recent messages.
	 * @param array  $plan            Current plan.
	 * @param array  $post_config     Post config.
	 * @param array  $request_params  Request params.
	 * @return string Context text.
	 */
	private function build_working_context( $task, $session_context, $recent_messages, $plan, $post_config, $request_params ) {
		$sections = array();
		$sections[] = "BACKEND CONTINUITY CONTEXT\nUse this compact WordPress-saved context as continuity. Do not assume OpenRouter remembers prior turns.";
		$sections[] = 'Current task: ' . sanitize_key( $task );

		$summary = $session_context['working_summary']['text'] ?? '';
		if ( '' !== trim( (string) $summary ) ) {
			$sections[] = "Working summary:\n" . $this->truncate_text( (string) $summary, 1600 );
		}

		$config_summary = $this->summarize_post_config( $post_config );
		if ( '' !== $config_summary ) {
			$sections[] = "Article configuration:\n" . $config_summary;
		}

		$plan_summary = $this->summarize_plan( $plan );
		if ( '' !== $plan_summary ) {
			$sections[] = "Current plan:\n" . $plan_summary;
		}

		$decision_summary = $this->summarize_context_items( $session_context, 'decisions', 'Decisions' );
		if ( '' !== $decision_summary ) {
			$sections[] = $decision_summary;
		}

		$rejection_summary = $this->summarize_context_items( $session_context, 'rejections', 'Rejected directions' );
		if ( '' !== $rejection_summary ) {
			$sections[] = $rejection_summary;
		}

		if ( ! empty( $request_params['context'] ) ) {
			$sections[] = "User supplied context:\n" . $this->truncate_text( (string) $request_params['context'], 1600 );
		}

		if ( ! empty( $recent_messages ) ) {
			$lines = array();
			foreach ( $recent_messages as $message ) {
				$lines[] = ucfirst( $message['role'] ) . ': ' . $message['content'];
			}
			$sections[] = "Recent saved conversation excerpts:\n" . implode( "\n", $lines );
		}

		return implode( "\n\n", array_filter( $sections ) );
	}

	/**
	 * Summarize post config.
	 *
	 * @param array $post_config Post config.
	 * @return string Summary.
	 */
	private function summarize_post_config( $post_config ) {
		$lines = array();
		$keys = array(
			'article_length'         => 'Article length',
			'language'               => 'Language',
			'tone'                   => 'Tone',
			'audience'               => 'Audience',
			'experience_level'       => 'Experience level',
			'seo_focus_keyword'      => 'SEO focus keyword',
			'seo_secondary_keywords' => 'SEO secondary keywords',
		);

		foreach ( $keys as $key => $label ) {
			if ( isset( $post_config[ $key ] ) && '' !== trim( (string) $post_config[ $key ] ) ) {
				$lines[] = '- ' . $label . ': ' . trim( (string) $post_config[ $key ] );
			}
		}

		if ( isset( $post_config['include_images'] ) ) {
			$lines[] = '- Include images: ' . ( $post_config['include_images'] ? 'yes' : 'no' );
		}

		if ( isset( $post_config['web_search'] ) ) {
			$lines[] = '- Web search: ' . ( $post_config['web_search'] ? 'yes' : 'no' );
		}

		return implode( "\n", $lines );
	}

	/**
	 * Summarize current plan.
	 *
	 * @param array|null $plan Plan.
	 * @return string Summary.
	 */
	private function summarize_plan( $plan ) {
		if ( empty( $plan ) || ! is_array( $plan ) ) {
			return '';
		}

		$lines = array();
		if ( ! empty( $plan['title'] ) ) {
			$lines[] = 'Title: ' . $plan['title'];
		}

		if ( ! empty( $plan['sections'] ) && is_array( $plan['sections'] ) ) {
			foreach ( $plan['sections'] as $index => $section ) {
				$heading = $section['heading'] ?? $section['title'] ?? '';
				if ( '' === trim( (string) $heading ) ) {
					continue;
				}
				$status = $section['status'] ?? 'pending';
				$lines[] = sprintf( '%d. [%s] %s', $index + 1, $status, $heading );
			}
		}

		return implode( "\n", $lines );
	}

	/**
	 * Summarize context array items.
	 *
	 * @param array  $session_context Session context.
	 * @param string $key             Context key.
	 * @param string $label           Label.
	 * @return string Summary.
	 */
	private function summarize_context_items( $session_context, $key, $label ) {
		if ( empty( $session_context[ $key ] ) || ! is_array( $session_context[ $key ] ) ) {
			return '';
		}

		$lines = array();
		foreach ( array_slice( $session_context[ $key ], -8 ) as $item ) {
			$summary = $item['summary'] ?? '';
			if ( '' === trim( (string) $summary ) ) {
				continue;
			}
			$target = ! empty( $item['target'] ) ? '[' . $item['target'] . '] ' : '';
			$lines[] = '- ' . $target . $summary;
		}

		return empty( $lines ) ? '' : $label . ":\n" . implode( "\n", $lines );
	}

	/**
	 * Get active content from request params.
	 *
	 * @param array $request_params Request params.
	 * @return string Active content context.
	 */
	private function get_active_content( $request_params ) {
		$candidates = array(
			'activeContent',
			'blockContent',
			'selectedText',
			'sectionContent',
			'articleContent',
		);

		$lines = array();
		foreach ( $candidates as $key ) {
			if ( ! empty( $request_params[ $key ] ) && is_string( $request_params[ $key ] ) ) {
				$lines[] = $key . ":\n" . $this->truncate_text( $request_params[ $key ], 2200 );
			}
		}

		return empty( $lines ) ? '' : "ACTIVE CONTENT SLICE\n" . implode( "\n\n", $lines );
	}

	/**
	 * Build research context.
	 *
	 * @param array $session_context Session context.
	 * @param array $request_params  Request params.
	 * @param int   $limit           Max snippets.
	 * @return string Research context.
	 */
	private function build_research_context( $session_context, $request_params, $limit ) {
		if ( $limit <= 0 ) {
			return '';
		}

		$items = array();
		if ( ! empty( $session_context['research_notes'] ) && is_array( $session_context['research_notes'] ) ) {
			$items = array_merge( $items, $session_context['research_notes'] );
		}
		if ( ! empty( $request_params['researchNotes'] ) && is_array( $request_params['researchNotes'] ) ) {
			$items = array_merge( $items, $request_params['researchNotes'] );
		}

		$items = array_slice( $items, -1 * $limit );
		$lines = array();
		foreach ( $items as $item ) {
			if ( ! is_array( $item ) ) {
				continue;
			}
			$title = $item['title'] ?? $item['source'] ?? 'Research note';
			$excerpt = $item['excerpt'] ?? $item['notes'] ?? '';
			if ( '' === trim( (string) $excerpt ) ) {
				continue;
			}
			$lines[] = '- ' . $title . ': ' . $this->truncate_text( (string) $excerpt, 700 );
		}

		return empty( $lines ) ? '' : "RELEVANT RESEARCH\n" . implode( "\n", $lines );
	}

	/**
	 * Count included research items.
	 *
	 * @param array $session_context Session context.
	 * @param array $request_params  Request params.
	 * @param int   $limit           Max snippets.
	 * @return int Count.
	 */
	private function count_research_items( $session_context, $request_params, $limit ) {
		if ( $limit <= 0 ) {
			return 0;
		}

		$count = 0;
		if ( ! empty( $session_context['research_notes'] ) && is_array( $session_context['research_notes'] ) ) {
			$count += count( $session_context['research_notes'] );
		}
		if ( ! empty( $request_params['researchNotes'] ) && is_array( $request_params['researchNotes'] ) ) {
			$count += count( $request_params['researchNotes'] );
		}

		return min( $limit, $count );
	}

	/**
	 * Truncate text safely.
	 *
	 * @param string $text  Text.
	 * @param int    $limit Character limit.
	 * @return string Truncated text.
	 */
	private function truncate_text( $text, $limit ) {
		$text = trim( (string) $text );
		if ( strlen( $text ) <= $limit ) {
			return $text;
		}

		return substr( $text, 0, $limit ) . '...';
	}

	/**
	 * Estimate tokens from character length.
	 *
	 * @param string $text Text.
	 * @return int Estimated tokens.
	 */
	private function estimate_tokens( $text ) {
		return (int) ceil( strlen( (string) $text ) / 4 );
	}
}