/**
 * Batch Progress Realtime client.
 * - Tries WebSocket first
 * - Falls back to HTTP polling on failure
 * - Auto heartbeats and reconnection with backoff
 */
(function(){
  window.progress = window.progress || {};

  function getAuthToken() {
    try {
      return (window.app && window.app.token) || localStorage.getItem('auth_token') || null;
    } catch (_) {
      return null;
    }
  }

  function buildWsUrl(path) {
    const loc = window.location;
    const proto = loc.protocol === 'https:' ? 'wss:' : 'ws:';
    const token = encodeURIComponent(getAuthToken() || '');
    const sep = path.includes('?') ? '&' : '?';
    return `${proto}//${loc.host}${path}${sep}token=${token}`;
  }

  function defaultOnUpdate(){/* no-op */}
  function defaultOnError(){/* no-op */}

  /**
   * Subscribe to a batch progress stream.
   * @param {string} batchId
   * @param {(data: object|null) => void} onUpdate
   * @param {(error: Error|string) => void} onError
   * @param {number} pollIntervalMs
   * @returns {() => void} unsubscribe function
   */
  function subscribe(batchId, onUpdate = defaultOnUpdate, onError = defaultOnError, pollIntervalMs = 2000) {
    let ws = null;
    let closed = false;
    let pollTimer = null;
    let backoffMs = 1000;

    async function pollOnce() {
      try {
        const resp = await window.http.wrappedFetch(`/api/billing/statements/batch-progress/${encodeURIComponent(batchId)}`);
        if (!resp.ok) {
          const err = await window.http.toError(resp, 'Failed to fetch batch progress');
          throw err;
        }
        const json = await resp.json();
        onUpdate(json);
      } catch (e) {
        onError(e);
      }
    }

    function startPolling() {
      if (closed) return;
      if (pollTimer) clearInterval(pollTimer);
      pollTimer = setInterval(pollOnce, pollIntervalMs);
      // immediate first fetch
      pollOnce();
    }

    function stopPolling() {
      if (pollTimer) {
        clearInterval(pollTimer);
        pollTimer = null;
      }
    }

    function tryWebSocket() {
      const url = buildWsUrl(`/api/billing/statements/batch-progress/ws/${encodeURIComponent(batchId)}`);
      try {
        ws = new WebSocket(url);
      } catch (e) {
        onError(e);
        startPolling();
        return;
      }

      let pingTimer = null;

      ws.onopen = function() {
        stopPolling();
        backoffMs = 1000;
        // send heartbeat pings at 30s
        pingTimer = setInterval(function(){
          try { ws.send(JSON.stringify({type: 'ping'})); } catch (_) {}
        }, 30000);
      };

      ws.onmessage = function(ev) {
        try {
          const msg = JSON.parse(ev.data);
          if (msg && msg.type === 'progress') {
            onUpdate(msg.data);
          }
        } catch (_) {
          // ignore
        }
      };

      ws.onerror = function(ev) {
        onError(new Error('WebSocket error'));
      };

      ws.onclose = function() {
        if (pingTimer) { clearInterval(pingTimer); pingTimer = null; }
        if (closed) return;
        // graceful fallback to polling and schedule reconnect with backoff
        startPolling();
        setTimeout(function(){
          if (!closed) {
            backoffMs = Math.min(backoffMs * 2, 30000);
            tryWebSocket();
          }
        }, backoffMs);
      };
    }

    // Kick off
    tryWebSocket();

    return function unsubscribe() {
      closed = true;
      stopPolling();
      try { if (ws && ws.readyState <= 1) ws.close(); } catch(_) {}
      ws = null;
    };
  }

  window.progress.subscribe = subscribe;
})();