<?php
/**
 * Firebase Cloud Messaging (FCM) Integration — HTTP v2 API
 *
 * Handles push notifications to mobile devices via FCM using
 * service account credentials and OAuth2 access tokens.
 */
class TWP_FCM {

    private $project_id;
    private $service_account;
    private $fcm_url_template = 'https://fcm.googleapis.com/v1/projects/%s/messages:send';

    /**
     * Constructor
     */
    public function __construct() {
        $this->project_id = get_option('twp_fcm_project_id', '');
        $sa_json = get_option('twp_fcm_service_account_json', '');
        if (!empty($sa_json)) {
            $this->service_account = json_decode($sa_json, true);
        }
    }

    /**
     * Send push notification to user's devices
     */
    public function send_notification($user_id, $title, $body, $data = array(), $data_only = false) {
        if (empty($this->project_id) || empty($this->service_account)) {
            error_log('TWP FCM: Project ID or service account not configured');
            return false;
        }

        // Get user's FCM tokens
        $tokens = $this->get_user_tokens($user_id);

        if (empty($tokens)) {
            error_log("TWP FCM: No tokens found for user $user_id");
            return false;
        }

        $success_count = 0;
        $failed_tokens = array();

        foreach ($tokens as $token) {
            $result = $this->send_to_token($token, $title, $body, $data, $data_only);

            if ($result['success']) {
                $success_count++;
            } else {
                $failed_tokens[] = $token;

                // If token is invalid, remove it from database
                if ($result['error'] === 'invalid_token') {
                    $this->remove_invalid_token($token);
                }
            }
        }

        error_log("TWP FCM: Sent notification to $success_count/" . count($tokens) . " devices for user $user_id");

        return $success_count > 0;
    }

    /**
     * Send notification to specific token via FCM HTTP v2 API
     */
    private function send_to_token($token, $title, $body, $data = array(), $data_only = false) {
        $access_token = $this->get_access_token();
        if (!$access_token) {
            return array('success' => false, 'error' => 'auth_failed');
        }

        // FCM v2 requires all data values to be strings
        $string_data = array();
        foreach ($data as $key => $value) {
            $string_data[$key] = is_string($value) ? $value : (string)$value;
        }
        $string_data['title'] = $title;
        $string_data['body'] = $body;
        $string_data['timestamp'] = (string)time();

        // Build the v2 message payload
        $message = array(
            'token' => $token,
            'data' => $string_data,
            'android' => array(
                'priority' => 'high',
            ),
        );

        if (!$data_only) {
            $message['notification'] = array(
                'title' => $title,
                'body' => $body,
            );
            $message['android']['notification'] = array(
                'sound' => 'default',
                'click_action' => 'FLUTTER_NOTIFICATION_CLICK',
            );
        }

        $payload = array('message' => $message);

        $url = sprintf($this->fcm_url_template, $this->project_id);

        $headers = array(
            'Authorization: Bearer ' . $access_token,
            'Content-Type: application/json'
        );

        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($payload));

        $response = curl_exec($ch);
        $http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        if ($http_code !== 200) {
            error_log("TWP FCM: Failed to send notification. HTTP $http_code: $response");

            $response_data = json_decode($response, true);
            $error_code = isset($response_data['error']['details'][0]['errorCode'])
                ? $response_data['error']['details'][0]['errorCode'] : '';
            $error_status = isset($response_data['error']['status'])
                ? $response_data['error']['status'] : '';

            if (in_array($error_code, array('UNREGISTERED', 'INVALID_ARGUMENT')) ||
                $error_status === 'NOT_FOUND') {
                return array('success' => false, 'error' => 'invalid_token');
            }

            return array('success' => false, 'error' => 'http_error');
        }

        return array('success' => true);
    }

    /**
     * Get OAuth2 access token from service account credentials.
     * Caches the token in a transient until near expiry.
     */
    private function get_access_token() {
        $cached = get_transient('twp_fcm_access_token');
        if ($cached) {
            return $cached;
        }

        if (empty($this->service_account)) {
            error_log('TWP FCM: Service account not configured');
            return false;
        }

        $jwt = $this->create_jwt();
        if (!$jwt) {
            return false;
        }

        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $this->service_account['token_uri']);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query(array(
            'grant_type' => 'urn:ietf:params:oauth:grant-type:jwt-bearer',
            'assertion' => $jwt,
        )));

        $response = curl_exec($ch);
        $http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
        curl_close($ch);

        if ($http_code !== 200) {
            error_log("TWP FCM: Failed to get access token. HTTP $http_code: $response");
            return false;
        }

        $token_data = json_decode($response, true);
        $access_token = $token_data['access_token'];
        $expires_in = isset($token_data['expires_in']) ? (int)$token_data['expires_in'] : 3600;

        // Cache token for 5 minutes less than actual expiry
        set_transient('twp_fcm_access_token', $access_token, max(60, $expires_in - 300));

        return $access_token;
    }

    /**
     * Create a signed JWT for the service account OAuth2 flow
     */
    private function create_jwt() {
        $sa = $this->service_account;

        if (empty($sa['client_email']) || empty($sa['private_key']) || empty($sa['token_uri'])) {
            error_log('TWP FCM: Service account JSON missing required fields');
            return false;
        }

        $now = time();
        $header = array('alg' => 'RS256', 'typ' => 'JWT');
        $claims = array(
            'iss' => $sa['client_email'],
            'scope' => 'https://www.googleapis.com/auth/firebase.messaging',
            'aud' => $sa['token_uri'],
            'iat' => $now,
            'exp' => $now + 3600,
        );

        $segments = array(
            $this->base64url_encode(json_encode($header)),
            $this->base64url_encode(json_encode($claims)),
        );

        $signing_input = implode('.', $segments);

        $private_key = openssl_pkey_get_private($sa['private_key']);
        if (!$private_key) {
            error_log('TWP FCM: Failed to parse service account private key');
            return false;
        }

        $signature = '';
        if (!openssl_sign($signing_input, $signature, $private_key, OPENSSL_ALGO_SHA256)) {
            error_log('TWP FCM: Failed to sign JWT');
            return false;
        }

        $segments[] = $this->base64url_encode($signature);

        return implode('.', $segments);
    }

    /**
     * Base64url encode (RFC 4648)
     */
    private function base64url_encode($data) {
        return rtrim(strtr(base64_encode($data), '+/', '-_'), '=');
    }

    /**
     * Get all active FCM tokens for a user
     */
    private function get_user_tokens($user_id) {
        global $wpdb;
        $table = $wpdb->prefix . 'twp_mobile_sessions';

        return $wpdb->get_col($wpdb->prepare(
            "SELECT fcm_token FROM $table
             WHERE user_id = %d
             AND is_active = 1
             AND fcm_token IS NOT NULL
             AND fcm_token != ''
             AND expires_at > NOW()",
            $user_id
        ));
    }

    /**
     * Remove invalid FCM token from database
     */
    private function remove_invalid_token($token) {
        global $wpdb;
        $table = $wpdb->prefix . 'twp_mobile_sessions';

        $wpdb->update(
            $table,
            array('fcm_token' => null),
            array('fcm_token' => $token),
            array('%s'),
            array('%s')
        );

        error_log("TWP FCM: Removed invalid token from database");
    }

    /**
     * Send incoming call notification
     */
    public function notify_incoming_call($user_id, $from_number, $queue_name, $call_sid) {
        $title = 'Incoming Call';
        $body = "Call from $from_number in $queue_name queue";

        $data = array(
            'type' => 'incoming_call',
            'call_sid' => $call_sid,
            'from_number' => $from_number,
            'queue_name' => $queue_name
        );

        return $this->send_notification($user_id, $title, $body, $data, true);
    }

    /**
     * Send queue timeout notification
     */
    public function notify_queue_timeout($user_id, $queue_name, $waiting_count) {
        $title = 'Queue Alert';
        $body = "$queue_name has $waiting_count waiting call" . ($waiting_count > 1 ? 's' : '');

        $data = array(
            'type' => 'queue_timeout',
            'queue_name' => $queue_name,
            'waiting_count' => $waiting_count
        );

        return $this->send_notification($user_id, $title, $body, $data);
    }

    /**
     * Send agent status change notification
     */
    public function notify_status_change($user_id, $old_status, $new_status) {
        $title = 'Status Changed';
        $body = "Your status changed from $old_status to $new_status";

        $data = array(
            'type' => 'status_change',
            'old_status' => $old_status,
            'new_status' => $new_status
        );

        return $this->send_notification($user_id, $title, $body, $data);
    }

    /**
     * Test notification (for settings page)
     */
    public function send_test_notification($user_id) {
        $title = 'Test Notification';
        $body = 'This is a test notification from Twilio WordPress Plugin';

        $data = array(
            'type' => 'test',
            'test' => 'true'
        );

        return $this->send_notification($user_id, $title, $body, $data);
    }
}