/*
 * 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.event.logical.shared.ValueChangeEvent;
import com.google.gwt.event.logical.shared.ValueChangeHandler;
import com.google.gwt.user.client.History;

import org.waveprotocol.box.webclient.client.events.WaveSelectionEvent;
import org.waveprotocol.box.webclient.util.Log;
import org.waveprotocol.wave.model.id.ModernIdSerialiser;
import org.waveprotocol.wave.model.waveref.InvalidWaveRefException;
import org.waveprotocol.wave.model.waveref.WaveRef;
import org.waveprotocol.wave.util.escapers.GwtWaverefEncoder;

import javax.annotation.Nullable;

/**
 * Contains the code to interface the history event mechanism with the client's
 * event bus. At the moment, a history token encodes a wave id or wave ref.
 */
public class HistorySupport {
  private static final Log LOG = Log.get(HistorySupport.class);

  public static void init() {
    History.addValueChangeHandler(new ValueChangeHandler<String>() {
      @Override
      public void onValueChange(ValueChangeEvent<String> event) {
        String encodedToken = event.getValue();
        if (encodedToken == null || encodedToken.length() == 0) {
          return;
        }
        WaveRef waveRef = waveRefFromHistoryToken(encodedToken);
        if (waveRef == null) {
          LOG.info("History token contains invalid path: " + encodedToken);
          return;
        }
        LOG.info("Changing selected wave based on history event to " + waveRef.toString());
        ClientEvents.get().fireEvent(new WaveSelectionEvent(waveRef));
      }
    });
  }

  /**
   * @param encodedToken token to parse into waveref
   * @return null if cannot parse into valid waveRef
   */
  @Nullable
  static WaveRef waveRefFromHistoryToken(String encodedToken) {
    try {
      return GwtWaverefEncoder.decodeWaveRefFromPath(encodedToken);
    } catch (InvalidWaveRefException e) {
      return null;
    }
  }

  static String historyTokenFromWaveref(WaveRef ref) {
    return GwtWaverefEncoder.encodeToUriPathSegment(ref);
  }

  private HistorySupport() {
  }
}