<?php

use Reservair\Logger\Logger;

class RsvGoogleCalendarService {

    public function is_google_connected(): bool {
        return (bool) get_option('rsv_google_access_token');
    }

    private function get_client_id(): string {
        return (string) get_option('rsv_google_client_id', '');
    }

    private function get_client_secret(): string {
        return (string) ($this->get_secret('rsv_google_client_secret') ?? '');
    }

    public function get_calendar_id(): string {
        return (string) get_option('rsv_google_calendar_id', 'primary');
    }

    public function is_webhook_registered(): bool {
        return (bool) get_option('rsv_google_webhook_channel_id');
    }

    // -------------------------------------------------------------------------
    // Encrypted option storage for secrets (tokens, client secret)
    // -------------------------------------------------------------------------

    /** Decrypt a secret stored in wp_options; null if unset or undecryptable. */
    private function get_secret(string $option): ?string {
        $stored = get_option($option);
        if (!is_string($stored) || $stored === '') {
            return null;
        }
        return RsvCrypto::decrypt($stored);
    }

    /** Store a secret in wp_options, encrypted at rest. */
    private function set_secret(string $option, string $value): void {
        update_option($option, RsvCrypto::encrypt($value));
    }

    /** Persist the OAuth client secret (encrypted). */
    public function set_client_secret(string $secret): void {
        $this->set_secret('rsv_google_client_secret', $secret);
    }

    // -------------------------------------------------------------------------
    // OAuth
    // -------------------------------------------------------------------------

    public function get_oauth_url(): string {
        return 'https://accounts.google.com/o/oauth2/v2/auth?' . http_build_query([
            'client_id'     => $this->get_client_id(),
            'redirect_uri'  => site_url('/wp-json/reservations/v1/google-callback'),
            'response_type' => 'code',
            'scope'         => 'https://www.googleapis.com/auth/calendar',
            'access_type'   => 'offline',
            'prompt'        => 'consent',
        ]);
    }

    public function exchange_code(string $code): bool {
        $response = wp_remote_post('https://oauth2.googleapis.com/token', [
            'body' => [
                'code'          => $code,
                'client_id'     => $this->get_client_id(),
                'client_secret' => $this->get_client_secret(),
                'redirect_uri'  => site_url('/wp-json/reservations/v1/google-callback'),
                'grant_type'    => 'authorization_code',
            ],
        ]);

        $data = json_decode(wp_remote_retrieve_body($response), true);

        if (!isset($data['access_token'])) {
            Logger::error('Google Calendar token exchange failed: ' . json_encode($data));
            return false;
        }

        $this->set_secret('rsv_google_access_token',  $data['access_token']);
        $this->set_secret('rsv_google_refresh_token', $data['refresh_token']);
        update_option('rsv_google_token_expires', time() + $data['expires_in']);
        return true;
    }

    public function disconnect(): void {
        $this->stop_webhook();
        delete_option('rsv_google_access_token');
        delete_option('rsv_google_refresh_token');
        delete_option('rsv_google_token_expires');
        delete_option('rsv_google_sync_token');
    }

    public function get_access_token(): ?string {
        $access_token  = $this->get_secret('rsv_google_access_token');
        $refresh_token = $this->get_secret('rsv_google_refresh_token');
        $expires_at    = (int) get_option('rsv_google_token_expires', 0);

        if (!$access_token) {
            return null;
        }

        if (time() > $expires_at - 60) {
            $response = wp_remote_post('https://oauth2.googleapis.com/token', [
                'body' => [
                    'client_id'     => $this->get_client_id(),
                    'client_secret' => $this->get_client_secret(),
                    'refresh_token' => $refresh_token,
                    'grant_type'    => 'refresh_token',
                ],
            ]);

            $data = json_decode(wp_remote_retrieve_body($response), true);

            if (isset($data['access_token'])) {
                $this->set_secret('rsv_google_access_token',  $data['access_token']);
                update_option('rsv_google_token_expires', time() + $data['expires_in']);
                $access_token = $data['access_token'];
            } else {
                Logger::error('Google Calendar token refresh failed: ' . json_encode($data));
                // Refresh token is permanently invalid — clear credentials so the
                // admin UI shows "reconnect needed" instead of silently failing.
                delete_option('rsv_google_access_token');
                delete_option('rsv_google_refresh_token');
                delete_option('rsv_google_token_expires');
                return null;
            }
        }

        return $access_token;
    }

    // -------------------------------------------------------------------------
    // Calendar list
    // -------------------------------------------------------------------------

    public function list_calendars(): array {
        $access_token = $this->get_access_token();
        if (!$access_token) {
            return [];
        }

        $response = wp_remote_get(
            'https://www.googleapis.com/calendar/v3/users/me/calendarList',
            ['headers' => ['Authorization' => 'Bearer ' . $access_token]]
        );

        if (is_wp_error($response)) {
            return [];
        }

        $data = json_decode(wp_remote_retrieve_body($response), true);
        return array_map(fn($c) => ['id' => $c['id'], 'summary' => $c['summary']], $data['items'] ?? []);
    }

    // -------------------------------------------------------------------------
    // Calendar events
    // -------------------------------------------------------------------------

    public function add_event(
        string  $calendar_id,
        string  $summary,
        string  $start_utc,
        string  $end_utc,
        ?string $attendee_email = null,
        ?int    $reservation_id = null,
        string  $status         = 'confirmed'
    ): void {
        $access_token = $this->get_access_token();
        if (!$access_token) {
            throw new \RuntimeException('Not connected to Google Calendar.');
        }

        $tz    = wp_timezone()->getName();
        $start = (new \DateTime($start_utc, new \DateTimeZone('UTC')))->setTimezone(wp_timezone());
        $end   = (new \DateTime($end_utc,   new \DateTimeZone('UTC')))->setTimezone(wp_timezone());

        $event = [
            'summary' => $summary,
            'status'  => $status,
            'start'   => ['dateTime' => $start->format(\DateTimeInterface::RFC3339), 'timeZone' => $tz],
            'end'     => ['dateTime' => $end->format(\DateTimeInterface::RFC3339),   'timeZone' => $tz],
        ];

        if ($attendee_email) {
            $event['attendees'] = [['email' => $attendee_email]];
        }

        if ($reservation_id !== null) {
            $event['extendedProperties'] = [
                'private' => ['rsv_reservation_id' => (string) $reservation_id],
            ];
        }

        $response = wp_remote_post(
            "https://www.googleapis.com/calendar/v3/calendars/{$calendar_id}/events?sendUpdates=all",
            [
                'headers' => [
                    'Authorization' => 'Bearer ' . $access_token,
                    'Content-Type'  => 'application/json',
                ],
                'body' => json_encode($event),
            ]
        );

        if (is_wp_error($response)) {
            throw new \RuntimeException('Google Calendar request failed: ' . $response->get_error_message());
        }

        $body = json_decode(wp_remote_retrieve_body($response), true);
        if (!isset($body['id'])) {
            throw new \RuntimeException('Google Calendar event creation failed: ' . json_encode($body));
        }
    }

    // -------------------------------------------------------------------------
    // Push notification webhook
    // -------------------------------------------------------------------------

    public function register_webhook(): array {
        $this->stop_webhook();

        $access_token = $this->get_access_token();
        if (!$access_token) {
            return ['error' => 'Not connected to Google Calendar.'];
        }

        // Get an initial sync token so the first process_changes() call works.
        $this->initialize_sync_token();

        $channel_id = uniqid('rsv_gcal_', true);
        $response   = wp_remote_post(
            "https://www.googleapis.com/calendar/v3/calendars/{$this->get_calendar_id()}/events/watch",
            [
                'headers' => [
                    'Authorization' => 'Bearer ' . $access_token,
                    'Content-Type'  => 'application/json',
                ],
                'body' => json_encode([
                    'id'      => $channel_id,
                    'type'    => 'web_hook',
                    'address' => site_url('/wp-json/reservations/v1/google-calendar-hook'),
                ]),
            ]
        );

        $data = json_decode(wp_remote_retrieve_body($response), true);

        if (isset($data['id'])) {
            update_option('rsv_google_webhook_channel_id',  $data['id']);
            update_option('rsv_google_webhook_resource_id', $data['resourceId']);
            update_option('rsv_google_webhook_expiration',  $data['expiration'] / 1000); // ms → s
        } else {
            Logger::error('Google Calendar webhook registration failed: ' . json_encode($data));
        }

        return $data;
    }

    public function stop_webhook(): void {
        $channel_id  = get_option('rsv_google_webhook_channel_id');
        $resource_id = get_option('rsv_google_webhook_resource_id');

        if (!$channel_id || !$resource_id) {
            return;
        }

        $access_token = $this->get_access_token();
        if ($access_token) {
            wp_remote_post('https://www.googleapis.com/calendar/v3/channels/stop', [
                'headers' => [
                    'Authorization' => 'Bearer ' . $access_token,
                    'Content-Type'  => 'application/json',
                ],
                'body' => json_encode([
                    'id'         => $channel_id,
                    'resourceId' => $resource_id,
                ]),
            ]);
        }

        delete_option('rsv_google_webhook_channel_id');
        delete_option('rsv_google_webhook_resource_id');
        delete_option('rsv_google_webhook_expiration');
    }

    // -------------------------------------------------------------------------
    // Change sync
    // -------------------------------------------------------------------------

    public function initialize_sync_token(): void {
        $access_token = $this->get_access_token();
        if (!$access_token) {
            return;
        }

        $response = wp_remote_get(
            'https://www.googleapis.com/calendar/v3/calendars/' . rawurlencode($this->get_calendar_id()) . '/events?' . http_build_query([
                'fields'       => 'nextSyncToken',
                'showDeleted'  => 'true',
                'singleEvents' => 'true',
            ]),
            ['headers' => ['Authorization' => 'Bearer ' . $access_token]]
        );

        $data = json_decode(wp_remote_retrieve_body($response), true);
        if (isset($data['nextSyncToken'])) {
            update_option('rsv_google_sync_token', $data['nextSyncToken']);
        }
    }

    /**
     * Fetch events changed since the last sync and return actions to take.
     *
     * @return array<array{reservation_id: int, action: 'accept'|'refuse'}>
     */
    public function process_changes(): array {
        $access_token = $this->get_access_token();
        if (!$access_token) {
            return [];
        }

        $sync_token = get_option('rsv_google_sync_token');
        if (!$sync_token) {
            $this->initialize_sync_token();
            return [];
        }

        $response = wp_remote_get(
            'https://www.googleapis.com/calendar/v3/calendars/' . rawurlencode($this->get_calendar_id()) . '/events?' . http_build_query([
                'syncToken'   => $sync_token,
                'showDeleted' => 'true',
                'fields'      => 'nextSyncToken,items(id,status,extendedProperties)',
            ]),
            ['headers' => ['Authorization' => 'Bearer ' . $access_token]]
        );

        if (wp_remote_retrieve_response_code($response) === 410) {
            // Sync token expired — reinitialise and process next time.
            delete_option('rsv_google_sync_token');
            $this->initialize_sync_token();
            return [];
        }

        $data = json_decode(wp_remote_retrieve_body($response), true);

        if (isset($data['nextSyncToken'])) {
            update_option('rsv_google_sync_token', $data['nextSyncToken']);
        }

        $actions = [];
        foreach ($data['items'] ?? [] as $event) {
            $reservation_id = (int) ($event['extendedProperties']['private']['rsv_reservation_id'] ?? 0);
            if (!$reservation_id) {
                continue;
            }

            $status = $event['status'] ?? '';
            if ($status === 'confirmed') {
                $actions[] = ['reservation_id' => $reservation_id, 'action' => 'accept'];
            } elseif ($status === 'cancelled') {
                $actions[] = ['reservation_id' => $reservation_id, 'action' => 'refuse'];
            }
        }

        return $actions;
    }
}