// Copyright (C) 2015 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 com.google.gerrit.metrics.proc.ThreadMXBeanFactory;
import com.google.gerrit.metrics.proc.ThreadMXBeanInterface;
import com.google.inject.Inject;
import com.google.inject.Module;
import com.google.inject.Singleton;
import com.google.inject.servlet.ServletModule;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

@Singleton
public class RequestMetricsFilter implements Filter {
  public static final String METRICS_CONTEXT = "metrics-context";

  public static Module module() {
    return new ServletModule() {
      @Override
      protected void configureServlets() {
        filter("/*").through(RequestMetricsFilter.class);
      }
    };
  }

  public static class Context {
    private static final ThreadMXBeanInterface threadMxBean = ThreadMXBeanFactory.create();
    private final long startedTotalCpu;
    private final long startedUserCpu;
    private final long startedMemory;

    Context() {
      startedTotalCpu = threadMxBean.getCurrentThreadCpuTime();
      startedUserCpu = threadMxBean.getCurrentThreadUserTime();
      startedMemory = threadMxBean.getCurrentThreadAllocatedBytes();
    }

    /** @return total CPU time in milliseconds for executing request */
    public long getTotalCpuTime() {
      return (threadMxBean.getCurrentThreadCpuTime() - startedTotalCpu) / 1_000_000;
    }

    /** @return CPU time in user mode in milliseconds for executing request */
    public long getUserCpuTime() {
      return (threadMxBean.getCurrentThreadUserTime() - startedUserCpu) / 1_000_000;
    }

    /** @return memory allocated in bytes for executing request */
    public long getAllocatedMemory() {
      return startedMemory == -1
          ? -1
          : threadMxBean.getCurrentThreadAllocatedBytes() - startedMemory;
    }
  }

  private final RequestMetrics metrics;

  @Inject
  RequestMetricsFilter(RequestMetrics metrics) {
    this.metrics = metrics;
  }

  @Override
  public void destroy() {}

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    request.setAttribute(METRICS_CONTEXT, new Context());
    Response rsp = new Response((HttpServletResponse) response, metrics);

    chain.doFilter(request, rsp);
  }

  @Override
  public void init(FilterConfig cfg) throws ServletException {}

  private static class Response extends HttpServletResponseWrapper {
    private final RequestMetrics metrics;

    Response(HttpServletResponse response, RequestMetrics metrics) {
      super(response);
      this.metrics = metrics;
    }

    @Override
    public void sendError(int sc, String msg) throws IOException {
      status(sc);
      super.sendError(sc, msg);
    }

    @Override
    public void sendError(int sc) throws IOException {
      status(sc);
      super.sendError(sc);
    }

    @Override
    @Deprecated
    public void setStatus(int sc, String sm) {
      status(sc);
      super.setStatus(sc, sm);
    }

    @Override
    public void setStatus(int sc) {
      status(sc);
      super.setStatus(sc);
    }

    private void status(int sc) {
      if (sc >= SC_BAD_REQUEST) {
        metrics.errors.increment(sc);
      } else {
        metrics.successes.increment(sc);
      }
    }
  }
}