<?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 = [],
    ) {
        $context_service = WP_Agentic_Writer_Context_Service::get_instance();
        $saved_context = !empty($session_id)
            ? $context_service->get_context($session_id, $post_id)
            : [];

        $session_context = $saved_context["context"] ?? [];
        $messages = $saved_context["messages"] ?? [];

        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,
            $post_id,
        );

        // Check MEMANTO status for audit (lightweight: just checks is_active, no recall).
        $memanto_active = WP_Agentic_Writer_Memanto_Client::get_instance()->is_active();

        return [
            "system_context" => "",
            "working_context" => $working_context,
            "active_content" => $this->get_active_content($request_params),
            "research_context" => $this->build_research_context(
                $session_context,
                $request_params,
                $token_policy["max_research_snippets"],
            ),
            "audit" => [
                "included_recent_messages" => count($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,
                "memanto_active" => $memanto_active,
            ],
        ];
    }

    /**
     * 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 = [],
    ) {
        $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 [
                "message" => null,
                "audit" => $package["audit"],
            ];
        }

        return [
            "message" => [
                "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"]
                : [];

        return [
            "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 [];
    }

    /**
     * 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 = [];

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

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

            $prepared[] = [
                "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"] ?? [];

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

        return is_array($config) ? $config : [];
    }

    /**
     * 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.
     * @param int    $post_id         Post ID.
     * @return string Context text.
     */
    private function build_working_context(
        $task,
        $session_context,
        $recent_messages,
        $plan,
        $post_config,
        $request_params,
        $post_id = 0,
    ) {
        $sections = [];
        $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);

        // MEMANTO persistent memory injection.
        $memanto_context = $this->build_memanto_context(
            $post_id,
            $request_params["latestUserMessage"] ?? "",
        );
        if ("" !== $memanto_context) {
            $sections[] = $memanto_context;
        }

        $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)) {
            $lines = [];
            foreach ($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 = [];
        $keys = [
            "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 "";
        }

        $lines = [];
        if (!empty($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 "";
        }

        $lines = [];
        foreach (array_slice($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 = [
            "activeContent",
            "blockContent",
            "selectedText",
            "sectionContent",
            "articleContent",
        ];

        $lines = [];
        foreach ($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 "";
        }

        $items = [];
        if (
            !empty($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);
        $lines = [];
        foreach ($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);
    }

    /**
     * Build MEMANTO persistent memory context section.
     *
     * Calls recall_for_context() via the MEMANTO Context Enhancer
     * and formats the returned memories into a prompt-ready section.
     * Returns empty string when MEMANTO is inactive or no memories found.
     *
     * @param int    $post_id        Post ID.
     * @param string $current_message User's current message for semantic search.
     * @return string Formatted memory section or empty string.
     */
    private function build_memanto_context($post_id, $current_message = "")
    {
        // Guard: skip entirely if MEMANTO is not active.
        $memanto = WP_Agentic_Writer_Memanto_Context_Enhancer::get_instance();
        $memories = $memanto->recall_for_context(
            $post_id,
            get_current_user_id(),
            $current_message,
        );

        if (empty($memories) || !is_array($memories)) {
            return "";
        }

        $lines = [];
        foreach ($memories as $memory) {
            $type = ucfirst($memory["type"] ?? "memory");
            $content = trim((string) ($memory["content"] ?? ""));
            if ("" === $content) {
                continue;
            }
            $title = !empty($memory["title"])
                ? " [" . trim($memory["title"]) . "]"
                : "";
            $lines[] = "- ({$type}){$title} {$content}";
        }

        if (empty($lines)) {
            return "";
        }

        return "PERSISTENT MEMORY (from MEMANTO)\n" .
            "The following are memories recalled from prior sessions and interactions. " .
            "Use them to maintain continuity, respect user preferences, and avoid repeating past mistakes.\n" .
            implode("\n", $lines);
    }

    /**
     * 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);
    }
}