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/*
 * Copyright 2021 Google LLC
 *
 * 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
 *
 *     https://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.apphosting.runtime.jetty;

import com.google.apphosting.base.AppVersionKey;
import com.google.apphosting.runtime.AppEngineConstants;
import com.google.apphosting.runtime.AppVersion;
import java.util.Objects;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.Response;
import org.eclipse.jetty.server.handler.HotSwapHandler;
import org.eclipse.jetty.util.Callback;

/**
 * {@code AppVersionHandlerMap} is a {@code HandlerContainer} that identifies each child {@code
 * Handler} with a particular {@code AppVersionKey}.
 *
 * In order to identify which application version each request should be sent to, this class
 * assumes that an attribute will be set on the {@code HttpServletRequest} with a value of the
 * {@code AppVersionKey} that should be used.
 *
 */
public class AppVersionHandler extends HotSwapHandler {
  private final AppVersionHandlerFactory appVersionHandlerFactory;
  private AppVersion appVersion;
  private volatile boolean initialized;

  public AppVersionHandler(AppVersionHandlerFactory appVersionHandlerFactory) {
    this.appVersionHandlerFactory = appVersionHandlerFactory;
  }

  public AppVersion getAppVersion() {
    return appVersion;
  }

  public void addAppVersion(AppVersion appVersion) {
    if (this.appVersion != null) {
      throw new IllegalStateException("Already have an AppVersion " + this.appVersion);
    }
    this.initialized = false;
    this.appVersion = Objects.requireNonNull(appVersion);
  }

  public void removeAppVersion(AppVersionKey appVersionKey) {
    if (!Objects.equals(appVersionKey, appVersion.getKey()))
      throw new IllegalArgumentException(
          "AppVersionKey does not match AppVersion " + appVersion.getKey());
    this.initialized = false;
    this.appVersion = null;
    setHandler((Handler)null);
  }

  @Override
  public boolean handle(Request request, Response response, Callback callback) throws Exception {
    // In RPC mode, this initialization is done by JettyServletEngineAdapter.serviceRequest().
    if (!initialized) {
      AppVersionKey appVersionKey =
              (AppVersionKey) request.getAttribute(AppEngineConstants.APP_VERSION_KEY_REQUEST_ATTR);
      if (appVersionKey == null) {
        Response.writeError(request, response, callback, 500, "Request did not provide an application version");
        return true;
      }

      if (!ensureHandler(appVersionKey)) {
        Response.writeError(request, response, callback, 500, "Unknown app: " + appVersionKey);
        return true;
      }
    }
    return super.handle(request, response, callback);
  }

  /**
   * Returns the {@code Handler} that will handle requests for the specified application version.
   */
  public synchronized boolean ensureHandler(AppVersionKey appVersionKey) throws Exception {
    if (!Objects.equals(appVersionKey, appVersion.getKey()))
      return false;

    Handler handler = getHandler();
    if (handler == null) {
      handler = appVersionHandlerFactory.createHandler(appVersion);
      setHandler(handler);

      if (Boolean.getBoolean("jetty.server.dumpAfterStart")) {
        handler.getServer().dumpStdErr();
      }
    }

    initialized = true;
    return (handler != null);
  }
}