// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library test.timing;

import 'dart:async';
import 'dart:io';
import 'dart:math';

import 'package:path/path.dart';

import '../integration/integration_test_methods.dart';
import '../integration/integration_tests.dart';

/**
 * The abstract class [TimingTest] defines the behavior of objects that measure
 * the time required to perform some sequence of server operations.
 */
abstract class TimingTest extends IntegrationTestMixin {
  /**
   * The connection to the analysis server.
   */
  Server server;

  /**
   * The temporary directory in which source files can be stored.
   */
  Directory sourceDirectory;

  /**
   * A flag indicating whether the teardown process should skip sending a
   * "server.shutdown" request because the server is known to have already
   * shutdown.
   */
  bool skipShutdown = false;

  /**
   * The number of times the test will be performed in order to warm up the VM.
   */
  static final int DEFAULT_WARMUP_COUNT = 10;

  /**
   * The number of times the test will be performed in order to compute a time.
   */
  static final int DEFAULT_TIMING_COUNT = 10;

  /**
   * The file suffix used to identify Dart files.
   */
  static final String DART_SUFFIX = '.dart';

  /**
   * The file suffix used to identify HTML files.
   */
  static final String HTML_SUFFIX = '.html';

  /**
   * The amount of time to give the server to respond to a shutdown request
   * before forcibly terminating it.
   */
  static const Duration SHUTDOWN_TIMEOUT = const Duration(seconds: 5);

  /**
   * Initialize a newly created test.
   */
  TimingTest();

  /**
   * Return the number of iterations that should be performed in order to warm
   * up the VM.
   */
  int get warmupCount => DEFAULT_WARMUP_COUNT;

  /**
   * Return the number of iterations that should be performed in order to
   * compute a time.
   */
  int get timingCount => DEFAULT_TIMING_COUNT;

  /**
   * Perform any operations that need to be performed once before any iterations.
   */
  Future oneTimeSetUp() {
    initializeInttestMixin();
    server = new Server();
    sourceDirectory = Directory.systemTemp.createTempSync('analysisServer');
    Completer serverConnected = new Completer();
    onServerConnected.listen((_) {
      serverConnected.complete();
    });
    return server.start().then((params) {
      server.listenToOutput(dispatchNotification);
      server.exitCode.then((_) {
        skipShutdown = true;
      });
      return serverConnected.future;
    });
  }

  /**
   * Perform any operations that need to be performed before each iteration.
   */
  Future setUp();

  /**
   * Perform any operations that part of a single iteration. It is the execution
   * of this method that will be measured.
   */
  Future perform();

  /**
   * Perform any operations that need to be performed after each iteration.
   */
  Future tearDown();

  /**
   * Perform any operations that need to be performed once after all iterations.
   */
  Future oneTimeTearDown() {
    return _shutdownIfNeeded().then((_) {
      sourceDirectory.deleteSync(recursive: true);
    });
  }

  /**
   * Return a future that will complete with a timing result representing the
   * number of milliseconds required to perform the operation the specified
   * number of times.
   */
  Future<TimingResult> run() {
    List<int> times = new List<int>();
    return oneTimeSetUp().then((_) {
      return _repeat(warmupCount, null).then((_) {
        return _repeat(timingCount, times).then((_) {
          return oneTimeTearDown().then((_) {
            return new Future.value(new TimingResult(times));
          });
        });
      });
    });
  }

  /**
   * Convert the given [relativePath] to an absolute path, by interpreting it
   * relative to [sourceDirectory].  On Windows any forward slashes in
   * [relativePath] are converted to backslashes.
   */
  String sourcePath(String relativePath) {
    return join(sourceDirectory.path, relativePath.replaceAll('/', separator));
  }

  /**
   * Write a source file with the given absolute [pathname] and [contents].
   *
   * If the file didn't previously exist, it is created.  If it did, it is
   * overwritten.
   *
   * Parent directories are created as necessary.
   */
  void writeFile(String pathname, String contents) {
    new Directory(dirname(pathname)).createSync(recursive: true);
    new File(pathname).writeAsStringSync(contents);
  }

  /**
   * Return the number of nanoseconds that have elapsed since the given
   * [stopwatch] was last stopped.
   */
  int _elapsedNanoseconds(Stopwatch stopwatch) {
    return (stopwatch.elapsedTicks * 1000000000) ~/ stopwatch.frequency;
  }

  /**
   * Repeatedly execute this test [count] times, adding timing information to
   * the given list of [times] if it is non-`null`.
   */
  Future _repeat(int count, List<int> times) {
    Stopwatch stopwatch = new Stopwatch();
    return setUp().then((_) {
      stopwatch.start();
      return perform().then((_) {
        stopwatch.stop();
        if (times != null) {
          times.add(_elapsedNanoseconds(stopwatch));
        }
        return tearDown().then((_) {
          if (count > 0) {
            return _repeat(count - 1, times);
          } else {
            return new Future.value();
          }
        });
      });
    });
  }

  /**
   * Shut the server down unless [skipShutdown] is `true`.
   */
  Future _shutdownIfNeeded() {
    if (skipShutdown) {
      return new Future.value();
    }
    // Give the server a short time to comply with the shutdown request; if it
    // doesn't exit, then forcibly terminate it.
    Completer processExited = new Completer();
    sendServerShutdown();
    return server.exitCode.timeout(SHUTDOWN_TIMEOUT, onTimeout: () {
      return server.kill();
    });
  }
}

/**
 * Instances of the class [TimingResult] represent the timing information
 * gathered while executing a given timing test.
 */
class TimingResult {
  /**
   * The amount of time spent executing each test, in nanoseconds.
   */
  List<int> times;

  /**
   * The number of nanoseconds in a millisecond.
   */
  static int NANOSECONDS_PER_MILLISECOND = 1000000;

  /**
   * Initialize a newly created timing result.
   */
  TimingResult(this.times);

  /**
   * The average amount of time spent executing a single iteration, in
   * milliseconds.
   */
  int get averageTime {
    return totalTime ~/ times.length;
  }

  /**
   * The maximum amount of time spent executing a single iteration, in
   * milliseconds.
   */
  int get maxTime {
    int maxTime = 0;
    int count = times.length;
    for (int i = 0; i < count; i++) {
      maxTime = max(maxTime, times[i]);
    }
    return maxTime ~/ NANOSECONDS_PER_MILLISECOND;
  }

  /**
   * The minimum amount of time spent executing a single iteration, in
   * milliseconds.
   */
  int get minTime {

    int minTime = times[0];
    int count = times.length;
    for (int i = 1; i < count; i++) {
      minTime = min(minTime, times[i]);
    }
    return minTime ~/ NANOSECONDS_PER_MILLISECOND;
  }

  /**
   * The standard deviation of the times.
   */
  double get standardDeviation {
    return computeStandardDeviation(toMilliseconds(times));
  }

  /**
   * The total amount of time spent executing the test, in milliseconds.
   */
  int get totalTime {
    int totalTime = 0;
    int count = times.length;
    for (int i = 0; i < count; i++) {
      totalTime += times[i];
    }
    return totalTime ~/ NANOSECONDS_PER_MILLISECOND;
  }

  /**
   * Compute the standard deviation of the given set of [values].
   */
  double computeStandardDeviation(List<int> values) {
    int count = values.length;
    double sumOfValues = 0.0;
    for (int i = 0; i < count; i++) {
      sumOfValues += values[i];
    }
    double average = sumOfValues / count;
    double sumOfDiffSquared = 0.0;
    for (int i = 0; i < count; i++) {
      double diff = values[i] - average;
      sumOfDiffSquared += diff * diff;
    }
    return sqrt((sumOfDiffSquared / (count - 1)));
  }

  /**
   * Convert the given [times], expressed in nanoseconds, to times expressed in
   * milliseconds.
   */
  List<int> toMilliseconds(List<int> times) {
    int count = times.length;
    List<int> convertedValues = new List<int>();
    for (int i = 0; i < count; i++) {
      convertedValues.add(times[i] ~/ NANOSECONDS_PER_MILLISECOND);
    }
    return convertedValues;
  }
}