<?php
/**
 * AKSRT Credits Service
 *
 * 积分系统核心：余额读取、加减、日志写入。
 *
 * 数据存储：
 *   - 余额：user_meta key = 'aksrt_credits'  (int)
 *   - 流水：表 {prefix}aksrt_credit_log
 *
 * 并发安全：
 *   - 所有加减操作通过 user_meta 直读 + DB 更新，
 *     使用 wp_cache 失效 + 短事务，避免高并发下的丢失。
 *   - 同一用户短时间多次扣减时仍可能出现少量不一致，
 *     可通过 P5 阶段的 token 唯一性兜底（同一资源不会被重复扣费）。
 *
 * @package AKSRT
 */

defined('ABSPATH') || exit;

class AKSRT_Credits {

    /** user_meta 键名 */
    const META_KEY = 'aksrt_credits';

    /**
     * 取用户余额。
     */
    public static function balance(int $user_id): int {
        if ($user_id <= 0) return 0;
        $val = get_user_meta($user_id, self::META_KEY, true);
        return is_numeric($val) ? (int) $val : 0;
    }

    /**
     * 增加积分。
     *
     * @param int    $user_id
     * @param int    $delta   必须 > 0
     * @param string $reason  例 register/signin/comment/invite/admin
     * @param array  $ref     ['type' => 'post|comment|user|invite', 'id' => int]
     * @return int|WP_Error 新余额或错误
     */
    public static function add(int $user_id, int $delta, string $reason, array $ref = [], string $remark = '') {
        if ($user_id <= 0) return new WP_Error('aksrt_credits_user', __('用户无效', 'aksrt'));
        if ($delta <= 0)   return new WP_Error('aksrt_credits_delta', __('增加积分必须为正数', 'aksrt'));

        $new_balance = self::atomic_update($user_id, $delta, false);
        if ($new_balance === null) {
            return new WP_Error('aksrt_credits_db', __('积分写入失败', 'aksrt'));
        }
        self::log($user_id, $delta, $new_balance, $reason, $ref, $remark);

        do_action('aksrt_credits_added', $user_id, $delta, $reason, $new_balance);
        return $new_balance;
    }

    /**
     * 扣减积分。
     *
     * @return int|WP_Error 新余额或错误
     */
    public static function deduct(int $user_id, int $cost, string $reason, array $ref = [], string $remark = '') {
        if ($user_id <= 0) return new WP_Error('aksrt_credits_user', __('用户无效', 'aksrt'));
        if ($cost < 0)     return new WP_Error('aksrt_credits_delta', __('扣减积分必须为非负数', 'aksrt'));
        if ($cost === 0) {
            return self::balance($user_id);
        }

        $new_balance = self::atomic_update($user_id, $cost, true);
        if ($new_balance === null) {
            $current = self::balance($user_id);
            return new WP_Error('aksrt_credits_insufficient', __('积分不足', 'aksrt'), [
                'balance' => $current,
                'cost'    => $cost,
            ]);
        }

        self::log($user_id, -$cost, $new_balance, $reason, $ref, $remark);

        do_action('aksrt_credits_deducted', $user_id, $cost, $reason, $new_balance);
        return $new_balance;
    }

    /**
     * 原子加减：用单条 SQL UPDATE 修改 user_meta，避免 read-modify-write 竞态。
     *
     * @param int  $user_id
     * @param int  $abs_delta 绝对值
     * @param bool $is_deduct true=扣减（带余额检查），false=增加
     * @return int|null 新余额；失败（余额不足或 DB 错误）返回 null
     */
    private static function atomic_update(int $user_id, int $abs_delta, bool $is_deduct): ?int {
        global $wpdb;

        // 确保 meta 行存在（首次扣费可能没有 row）
        $existing = get_user_meta($user_id, self::META_KEY, true);
        if ($existing === '' || $existing === false || $existing === null) {
            update_user_meta($user_id, self::META_KEY, 0);
        }

        $meta_key = self::META_KEY;

        if ($is_deduct) {
            // 扣减：仅当 meta_value >= cost 时才更新
            $sql = $wpdb->prepare(
                "UPDATE {$wpdb->usermeta}
                 SET meta_value = CAST(meta_value AS SIGNED) - %d
                 WHERE user_id = %d
                   AND meta_key = %s
                   AND CAST(meta_value AS SIGNED) >= %d",
                $abs_delta,
                $user_id,
                $meta_key,
                $abs_delta
            );
        } else {
            $sql = $wpdb->prepare(
                "UPDATE {$wpdb->usermeta}
                 SET meta_value = CAST(meta_value AS SIGNED) + %d
                 WHERE user_id = %d
                   AND meta_key = %s",
                $abs_delta,
                $user_id,
                $meta_key
            );
        }

        $affected = $wpdb->query($sql);
        if ($affected === false || $affected === 0) {
            return null;
        }

        // 失效 user meta cache，下次 get_user_meta 会重读
        wp_cache_delete($user_id, 'user_meta');

        $new = (int) get_user_meta($user_id, self::META_KEY, true);
        return $new;
    }

    /**
     * 写一条流水。
     *
     * @param int    $user_id
     * @param int    $delta         本次变动（正/负/0）
     * @param int    $balance_after 操作后余额
     * @param string $reason
     * @param array  $ref
     */
    public static function log(int $user_id, int $delta, int $balance_after, string $reason, array $ref = [], string $remark = ''): void {
        global $wpdb;

        $table = AKSRT_DB_Migrator::table('credit_log');
        if (!$table) return;

        $ref_type = isset($ref['type']) ? sanitize_key((string) $ref['type']) : null;
        $ref_id   = isset($ref['id']) ? (int) $ref['id'] : null;

        $wpdb->insert(
            $table,
            [
                'user_id'       => $user_id,
                'delta'         => $delta,
                'balance_after' => $balance_after,
                'reason'        => substr($reason, 0, 64),
                'remark'        => $remark !== '' ? substr($remark, 0, 255) : null,
                'ref_type'      => $ref_type,
                'ref_id'        => $ref_id,
                'ip'            => self::client_ip(),
                'ua'            => self::client_ua(),
                'created_at'    => current_time('mysql', true),
            ],
            ['%d', '%d', '%d', '%s', '%s', '%s', '%d', '%s', '%s', '%s']
        );
    }

    /**
     * 取流水（管理员页面用）。
     *
     * @param array $args { user_id, reason, page, per_page, date_from, date_to }
     * @return array { items, total, page, per_page }
     */
    public static function get_log(array $args = []): array {
        global $wpdb;

        $table = AKSRT_DB_Migrator::table('credit_log');
        if (!$table) {
            return ['items' => [], 'total' => 0, 'page' => 1, 'per_page' => 20];
        }

        $page     = max(1, (int) ($args['page'] ?? 1));
        $per_page = min(100, max(1, (int) ($args['per_page'] ?? 20)));
        $offset   = ($page - 1) * $per_page;

        $where = ['1=1'];
        $params = [];

        if (!empty($args['user_id'])) {
            $where[] = 'user_id = %d';
            $params[] = (int) $args['user_id'];
        }
        if (!empty($args['reason'])) {
            $where[] = 'reason = %s';
            $params[] = sanitize_key((string) $args['reason']);
        }
        if (!empty($args['date_from'])) {
            $where[] = 'created_at >= %s';
            $params[] = (string) $args['date_from'];
        }
        if (!empty($args['date_to'])) {
            $where[] = 'created_at <= %s';
            $params[] = (string) $args['date_to'];
        }

        $where_sql = implode(' AND ', $where);

        // total
        $count_sql = "SELECT COUNT(*) FROM {$table} WHERE {$where_sql}";
        $total = (int) ($params
            ? $wpdb->get_var($wpdb->prepare($count_sql, $params))
            : $wpdb->get_var($count_sql));

        // items
        $items_sql = "SELECT * FROM {$table} WHERE {$where_sql} ORDER BY created_at DESC, id DESC LIMIT %d OFFSET %d";
        $items_params = array_merge($params, [$per_page, $offset]);
        $items = $wpdb->get_results($wpdb->prepare($items_sql, $items_params), ARRAY_A);
        if (!is_array($items)) $items = [];

        // user 名字预填
        $uid_set = array_unique(array_map(fn($r) => (int) $r['user_id'], $items));
        $names = [];
        foreach ($uid_set as $uid) {
            $u = get_userdata($uid);
            if ($u) $names[$uid] = $u->display_name;
        }
        foreach ($items as &$row) {
            $row['user_display_name'] = $names[(int) $row['user_id']] ?? '#' . $row['user_id'];
            $row['delta'] = (int) $row['delta'];
            $row['balance_after'] = (int) $row['balance_after'];
        }

        return [
            'items'    => $items,
            'total'    => $total,
            'page'     => $page,
            'per_page' => $per_page,
        ];
    }

    /**
     * 查询用户余额列表（管理员）。
     *
     * @param array $args { search, page, per_page }
     * @return array
     */
    public static function list_users(array $args = []): array {
        $page     = max(1, (int) ($args['page'] ?? 1));
        $per_page = min(100, max(1, (int) ($args['per_page'] ?? 20)));

        $q = [
            'number'  => $per_page,
            'paged'   => $page,
            'orderby' => 'registered',
            'order'   => 'DESC',
        ];
        if (!empty($args['search'])) {
            $q['search'] = '*' . esc_attr((string) $args['search']) . '*';
            $q['search_columns'] = ['user_login', 'user_email', 'display_name', 'user_nicename'];
        }
        $user_query = new WP_User_Query($q);
        $users = $user_query->get_results();
        $items = [];
        foreach ($users as $u) {
            $items[] = [
                'id'           => (int) $u->ID,
                'login'        => $u->user_login,
                'email'        => $u->user_email,
                'display_name' => $u->display_name,
                'balance'      => self::balance((int) $u->ID),
                'registered'   => $u->user_registered,
            ];
        }
        return [
            'items'    => $items,
            'total'    => (int) $user_query->get_total(),
            'page'     => $page,
            'per_page' => $per_page,
        ];
    }

    // ---------- 工具方法 ----------

    private static function client_ip(): string {
        if (function_exists('aksrt_get_client_ip')) {
            return (string) aksrt_get_client_ip();
        }
        if (!empty($_SERVER['REMOTE_ADDR'])) {
            return (string) $_SERVER['REMOTE_ADDR'];
        }
        return '';
    }

    private static function client_ua(): string {
        $ua = isset($_SERVER['HTTP_USER_AGENT']) ? (string) $_SERVER['HTTP_USER_AGENT'] : '';
        return substr($ua, 0, 255);
    }
}