<?php
/**
 * AKSRT Private Message — 站内私信/会话系统
 *
 * 提供会话创建、消息发送、消息拉取、未读管理。
 * 存储：{prefix}aksrt_conversation + {prefix}aksrt_conversation_message
 *
 * @package AKSRT
 */

defined('ABSPATH') || exit;

class AKSRT_Private_Message {

    private static $instance = null;

    public static function get_instance(): self {
        if (null === self::$instance) self::$instance = new self();
        return self::$instance;
    }

    public function init(): void {
        add_action('wp_ajax_aksrt_pm_send', [$this, 'ajax_send']);
        add_action('wp_ajax_aksrt_pm_conversations', [$this, 'ajax_conversations']);
        add_action('wp_ajax_aksrt_pm_thread', [$this, 'ajax_thread']);
        add_action('wp_ajax_aksrt_pm_mark_read', [$this, 'ajax_mark_read']);
        add_action('wp_ajax_aksrt_pm_unread_count', [$this, 'ajax_unread_count']);
    }

    /* ------------------------------------------------------------------
     * Table name helpers
     * ----------------------------------------------------------------*/

    private function table_conv(): string {
        global $wpdb;
        return $wpdb->prefix . 'aksrt_conversation';
    }

    private function table_msg(): string {
        global $wpdb;
        return $wpdb->prefix . 'aksrt_conversation_message';
    }

    /* ------------------------------------------------------------------
     * Conversation CRUD
     * ----------------------------------------------------------------*/

    /**
     * Get or create a 1-to-1 conversation between two users.
     */
    public function get_or_create_conversation(int $user_a, int $user_b): int {
        global $wpdb;

        if ($user_a <= 0 || $user_b <= 0 || $user_a === $user_b) return 0;

        // Ensure consistent ordering
        $min_id = min($user_a, $user_b);
        $max_id = max($user_a, $user_b);

        $existing = $wpdb->get_var($wpdb->prepare(
            "SELECT id FROM {$this->table_conv()} WHERE user_a = %d AND user_b = %d",
            $min_id, $max_id
        ));

        if ($existing) return (int) $existing;

        $wpdb->insert($this->table_conv(), [
            'user_a'        => $min_id,
            'user_b'        => $max_id,
            'last_message'  => '',
            'last_message_at' => current_time('mysql'),
            'unread_a'      => 0,
            'unread_b'      => 0,
            'created_at'    => current_time('mysql'),
        ], ['%d', '%d', '%s', '%s', '%d', '%d', '%s']);

        return (int) $wpdb->insert_id;
    }

    /**
     * List conversations for a user (most recent first).
     *
     * @param int $user_id
     * @param int $limit
     * @return array
     */
    public function get_conversations(int $user_id, int $limit = 20): array {
        global $wpdb;

        if ($user_id <= 0) return [];

        $table_conv = $this->table_conv();
        $table_msg  = $this->table_msg();

        $rows = $wpdb->get_results($wpdb->prepare(
            "SELECT c.*,
                    CASE WHEN c.user_a = %d THEN c.unread_a ELSE c.unread_b END AS my_unread,
                    CASE WHEN c.user_a = %d THEN c.user_b ELSE c.user_a END AS other_user_id
             FROM {$table_conv} c
             WHERE c.user_a = %d OR c.user_b = %d
             ORDER BY c.last_message_at DESC
             LIMIT %d",
            $user_id, $user_id, $user_id, $user_id, $limit
        ), ARRAY_A);

        $conversations = [];
        foreach ((array) $rows as $row) {
            $other_id = (int) $row['other_user_id'];
            $other_user = get_userdata($other_id);
            $conversations[] = [
                'id'             => (int) $row['id'],
                'other_user_id'  => $other_id,
                'other_name'     => $other_user ? $other_user->display_name : __('用户', 'aksrt'),
                'other_avatar'   => $other_user ? get_avatar_url($other_id, ['size' => 48]) : '',
                'last_message'   => $row['last_message'] ?? '',
                'last_message_at' => $row['last_message_at'] ?? '',
                'unread'         => (int) $row['my_unread'],
            ];
        }

        return $conversations;
    }

    /* ------------------------------------------------------------------
     * Message CRUD
     * ----------------------------------------------------------------*/

    /**
     * Send a message in a conversation.
     *
     * @param int    $conversation_id
     * @param int    $sender_id
     * @param string $content
     * @return array{success: bool, message_id?: int, message: string}
     */
    public function send(int $conversation_id, int $sender_id, string $content): array {
        global $wpdb;

        if ($conversation_id <= 0 || $sender_id <= 0) {
            return ['success' => false, 'message' => __('参数无效', 'aksrt')];
        }

        $content = sanitize_textarea_field($content);
        if ($content === '') {
            return ['success' => false, 'message' => __('消息不能为空', 'aksrt')];
        }

        // Verify user is a participant
        $conv = $wpdb->get_row($wpdb->prepare(
            "SELECT * FROM {$this->table_conv()} WHERE id = %d",
            $conversation_id
        ), ARRAY_A);

        if (!$conv) {
            return ['success' => false, 'message' => __('会话不存在', 'aksrt')];
        }

        if ((int) $conv['user_a'] !== $sender_id && (int) $conv['user_b'] !== $sender_id) {
            return ['success' => false, 'message' => __('无权操作', 'aksrt')];
        }

        $now = current_time('mysql');

        // Insert message
        $wpdb->insert($this->table_msg(), [
            'conversation_id' => $conversation_id,
            'sender_id'       => $sender_id,
            'content'         => $content,
            'created_at'      => $now,
        ], ['%d', '%d', '%s', '%s']);

        $message_id = (int) $wpdb->insert_id;

        if (!$message_id) {
            return ['success' => false, 'message' => __('发送失败', 'aksrt')];
        }

        // Update conversation metadata
        $is_a = (int) $conv['user_a'] === $sender_id;
        $unread_field = $is_a ? 'unread_b' : 'unread_a';

        $wpdb->update($this->table_conv(), [
            'last_message'    => mb_substr($content, 0, 200),
            'last_message_at' => $now,
            $unread_field     => (int) $conv[$unread_field] + 1,
        ], ['id' => $conversation_id]);

        // Create notification for the recipient
        $recipient_id = $is_a ? (int) $conv['user_b'] : (int) $conv['user_a'];
        if (class_exists('AKSRT_Message')) {
            $sender_name = '';
            $sender_user = get_userdata($sender_id);
            if ($sender_user) {
                $sender_name = $sender_user->display_name;
            }
            AKSRT_Message::get_instance()->send(
                $recipient_id,
                'conversation',
                mb_substr($content, 0, 100),
                [
                    'title'      => sprintf(__('%s 发来私信', 'aksrt'), $sender_name),
                    'target_url' => add_query_arg(['msg_type' => 'conversation']),
                ]
            );
        }

        do_action('aksrt_private_message_sent', $conversation_id, $sender_id, $recipient_id, $message_id);

        return ['success' => true, 'message_id' => $message_id, 'message' => __('已发送', 'aksrt')];
    }

    /**
     * Get messages in a conversation (paginated, newest first).
     *
     * @param int $conversation_id
     * @param int $user_id         Must be a participant.
     * @param int $page
     * @param int $per_page
     * @return array
     */
    public function get_thread(int $conversation_id, int $user_id, int $page = 1, int $per_page = 30): array {
        global $wpdb;

        if ($conversation_id <= 0 || $user_id <= 0) return ['messages' => [], 'total' => 0];

        // Verify participation
        $conv = $wpdb->get_row($wpdb->prepare(
            "SELECT * FROM {$this->table_conv()} WHERE id = %d",
            $conversation_id
        ), ARRAY_A);

        if (!$conv || ((int) $conv['user_a'] !== $user_id && (int) $conv['user_b'] !== $user_id)) {
            return ['messages' => [], 'total' => 0];
        }

        $offset = max(0, ($page - 1) * $per_page);

        $total = (int) $wpdb->get_var($wpdb->prepare(
            "SELECT COUNT(*) FROM {$this->table_msg()} WHERE conversation_id = %d",
            $conversation_id
        ));

        $rows = $wpdb->get_results($wpdb->prepare(
            "SELECT * FROM {$this->table_msg()}
             WHERE conversation_id = %d
             ORDER BY created_at DESC
             LIMIT %d OFFSET %d",
            $conversation_id, $per_page, $offset
        ), ARRAY_A);

        $messages = [];
        foreach ((array) $rows as $row) {
            $sender = get_userdata((int) $row['sender_id']);
            $messages[] = [
                'id'         => (int) $row['id'],
                'sender_id'  => (int) $row['sender_id'],
                'sender_name' => $sender ? $sender->display_name : __('用户', 'aksrt'),
                'sender_avatar' => $sender ? get_avatar_url((int) $row['sender_id'], ['size' => 32]) : '',
                'content'    => $row['content'] ?? '',
                'is_mine'    => (int) $row['sender_id'] === $user_id,
                'created_at' => $row['created_at'] ?? '',
            ];
        }

        // Mark as read for this user
        $this->mark_conversation_read($conversation_id, $user_id);

        return [
            'messages' => $messages,
            'total'    => $total,
            'page'     => $page,
            'pages'    => max(1, (int) ceil($total / $per_page)),
        ];
    }

    /**
     * Mark all messages in a conversation as read for a user.
     */
    public function mark_conversation_read(int $conversation_id, int $user_id): void {
        global $wpdb;

        $conv = $wpdb->get_row($wpdb->prepare(
            "SELECT * FROM {$this->table_conv()} WHERE id = %d",
            $conversation_id
        ), ARRAY_A);

        if (!$conv) return;

        $is_a = (int) $conv['user_a'] === $user_id;
        $field = $is_a ? 'unread_a' : 'unread_b';

        $wpdb->update($this->table_conv(), [$field => 0], ['id' => $conversation_id]);
    }

    /**
     * Get total unread conversation count for a user.
     */
    public function get_unread_count(int $user_id): int {
        global $wpdb;

        if ($user_id <= 0) return 0;

        $count = $wpdb->get_var($wpdb->prepare(
            "SELECT SUM(CASE WHEN user_a = %d THEN unread_a ELSE unread_b END)
             FROM {$this->table_conv()}
             WHERE user_a = %d OR user_b = %d",
            $user_id, $user_id, $user_id
        ));

        return max(0, (int) $count);
    }

    /* ------------------------------------------------------------------
     * AJAX Handlers
     * ----------------------------------------------------------------*/

    public function ajax_send(): void {
        check_ajax_referer('aksrt_pm', '_nonce');

        $user_id = get_current_user_id();
        if ($user_id <= 0) wp_send_json_error(['message' => __('请先登录', 'aksrt')]);

        $recipient_id = (int) ($_POST['recipient_id'] ?? 0);
        $content = sanitize_textarea_field((string) ($_POST['content'] ?? ''));

        if ($recipient_id <= 0) wp_send_json_error(['message' => __('收件人无效', 'aksrt')]);

        $conv_id = $this->get_or_create_conversation($user_id, $recipient_id);
        if (!$conv_id) wp_send_json_error(['message' => __('无法创建会话', 'aksrt')]);

        $result = $this->send($conv_id, $user_id, $content);

        if ($result['success']) {
            wp_send_json_success($result);
        }
        wp_send_json_error($result);
    }

    public function ajax_conversations(): void {
        check_ajax_referer('aksrt_pm', '_nonce');

        $user_id = get_current_user_id();
        if ($user_id <= 0) wp_send_json_error(['message' => __('请先登录', 'aksrt')]);

        $limit = max(1, min(50, (int) ($_GET['limit'] ?? 20)));
        $conversations = $this->get_conversations($user_id, $limit);

        wp_send_json_success(['conversations' => $conversations]);
    }

    public function ajax_thread(): void {
        check_ajax_referer('aksrt_pm', '_nonce');

        $user_id = get_current_user_id();
        if ($user_id <= 0) wp_send_json_error(['message' => __('请先登录', 'aksrt')]);

        $conv_id = (int) ($_GET['conversation_id'] ?? 0);
        $page = max(1, (int) ($_GET['page'] ?? 1));

        $result = $this->get_thread($conv_id, $user_id, $page);
        wp_send_json_success($result);
    }

    public function ajax_mark_read(): void {
        check_ajax_referer('aksrt_pm', '_nonce');

        $user_id = get_current_user_id();
        if ($user_id <= 0) wp_send_json_error(['message' => __('请先登录', 'aksrt')]);

        $conv_id = (int) ($_POST['conversation_id'] ?? 0);
        $this->mark_conversation_read($conv_id, $user_id);

        wp_send_json_success(['unread' => $this->get_unread_count($user_id)]);
    }

    public function ajax_unread_count(): void {
        check_ajax_referer('aksrt_pm', '_nonce');

        $user_id = get_current_user_id();
        if ($user_id <= 0) wp_send_json_error(['message' => __('请先登录', 'aksrt')]);

        wp_send_json_success(['unread' => $this->get_unread_count($user_id)]);
    }
}