// Copyright (C) 2018 The Android Open Source Project
//
// 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 com.google.gerrit.httpd;

import static com.google.common.collect.ImmutableList.toImmutableList;

import com.google.common.collect.ImmutableList;
import com.google.gerrit.common.PageLinks;
import com.google.gerrit.entities.Change;
import com.google.gerrit.extensions.restapi.ResourceConflictException;
import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
import com.google.gerrit.server.change.ChangeResource;
import com.google.gerrit.server.permissions.PermissionBackendException;
import com.google.gerrit.server.restapi.change.ChangesCollection;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import java.io.IOException;
import java.util.Arrays;
import java.util.Optional;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Redirects:
 *
 * <ul>
 *   <li>{@code domain.tld/123} to {@code domain.tld/c/project/+/123}
 *   <li/>
 *   <li>{@code domain.tld/123/comment/bc630c55_3e265b44} to {@code
 *       domain.tld/c/project/+/123/comment/bc630c55_3e265b44/}
 *   <li/>
 * </ul>
 */
@Singleton
public class NumericChangeIdRedirectServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;

  private final ChangesCollection changesCollection;

  @Inject
  NumericChangeIdRedirectServlet(ChangesCollection changesCollection) {
    this.changesCollection = changesCollection;
  }

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse rsp) throws IOException {
    String uriPath = req.getPathInfo();

    ImmutableList<String> uriSegments =
        Arrays.stream(uriPath.split("/", 2)).collect(toImmutableList());

    String idString = uriSegments.get(0);
    String finalSegment = (uriSegments.size() > 1) ? uriSegments.get(1) : null;

    Optional<Change.Id> id = Change.Id.tryParse(idString);
    if (id.isEmpty()) {
      rsp.sendError(HttpServletResponse.SC_NOT_FOUND);
      return;
    }

    ChangeResource changeResource;
    try {
      changeResource = changesCollection.parse(id.get());
    } catch (ResourceConflictException | ResourceNotFoundException e) {
      rsp.sendError(HttpServletResponse.SC_NOT_FOUND);
      return;
    } catch (PermissionBackendException | RuntimeException e) {
      throw new IOException("Unable to lookup change " + id.get(), e);
    }
    String path =
        PageLinks.toChange(changeResource.getProject(), changeResource.getChange().getId());
    if (finalSegment != null) {
      path += finalSegment;
    }
    UrlModule.toGerrit(path, req, rsp);
  }
}