/**
 * Copyright 2010 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 *
 */

package org.waveprotocol.box.webclient.client;

import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.RequestException;
import com.google.gwt.http.client.Response;

import org.waveprotocol.box.common.comms.jso.WaveViewSnapshotJsoImpl;
import org.waveprotocol.box.webclient.common.SnapshotSerializer;
import org.waveprotocol.box.webclient.common.communication.callback.SimpleCallback;
import org.waveprotocol.wave.client.debug.logger.DomLogger;
import org.waveprotocol.wave.common.logging.LoggerBundle;
import org.waveprotocol.wave.communication.gwt.JsonMessage;
import org.waveprotocol.wave.communication.json.JsonException;
import org.waveprotocol.wave.model.id.InvalidIdException;
import org.waveprotocol.wave.model.id.WaveId;
import org.waveprotocol.wave.model.operation.OperationException;
import org.waveprotocol.wave.model.wave.InvalidParticipantAddress;
import org.waveprotocol.wave.model.wave.data.DocumentFactory;
import org.waveprotocol.wave.model.wave.data.WaveViewData;
import org.waveprotocol.wave.model.waveref.WaveRef;
import org.waveprotocol.wave.util.escapers.GwtWaverefEncoder;

/**
 * Helper class to fetch wavelet snapshots using the snapshot fetch service.
 *
 * @author josephg@gmail.com (Joseph Gentle)
 */
public final class SnapshotFetcher {
  private static final LoggerBundle LOG = new DomLogger("SnapshotFetcher");
  private static final String FETCH_URL_BASE = "/fetch";

  private SnapshotFetcher() {
  }

  private static String getUrl(WaveRef waveRef) {
    String pathSegment = GwtWaverefEncoder.encodeToUriPathSegment(waveRef);
    return FETCH_URL_BASE + "/" + pathSegment;
  }

  /**
   * Fetches a wave view snapshot from the static fetch servlet.
   *
   * @param waveId The wave to fetch
   * @param callback A callback through which the fetched wave will be returned.
   */
  public static void fetchWave(WaveId waveId,
      final SimpleCallback<WaveViewData, Throwable> callback,
      final DocumentFactory<?> docFactory) {
    String url = getUrl(WaveRef.of(waveId));
    LOG.trace().log("Fetching wavelet ", waveId.toString(), " at ", url);

    RequestBuilder requestBuilder = new RequestBuilder(RequestBuilder.GET, url);
    requestBuilder.setCallback(new RequestCallback() {
      @Override
      public void onResponseReceived(Request request, Response response) {
        LOG.trace().log("Snapshot response recieved: ", response.getText());
        // Pull the snapshot out of the response object and return it using
        // the provided callback function.
        if (response.getStatusCode() != Response.SC_OK) {
          callback.onFailure(
              new RequestException("Got back status code " + response.getStatusCode()));
        } else if (!response.getHeader("Content-Type").startsWith("application/json")) {
          callback.onFailure(new RuntimeException("Fetch service did not return json"));
        } else {
          WaveViewData waveView;
          try {
            WaveViewSnapshotJsoImpl snapshot = JsonMessage.parse(response.getText());
            waveView = SnapshotSerializer.deserializeWave(snapshot, docFactory);
          } catch (OperationException e) {
            callback.onFailure(e);
            return;
          } catch (InvalidParticipantAddress e) {
            callback.onFailure(e);
            return;
          } catch (InvalidIdException e) {
            callback.onFailure(e);
            return;
          } catch (JsonException e) {
            callback.onFailure(e);
            return;
          }
          callback.onSuccess(waveView);
        }
      }

      @Override
      public void onError(Request request, Throwable exception) {
        LOG.error().log("Snapshot error: ", exception);
        callback.onFailure(exception);
      }
    });

    try {
      requestBuilder.send();
    } catch (RequestException e) {
      callback.onFailure(e);
    }
  }
}