// Copyright (c) 2017, 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.

import 'dart:convert';
import 'dart:io';

/// A class that can return memory and cpu usage information for a given
/// process.
abstract class ProcessProfiler {
  ProcessProfiler._();

  Future<UsageInfo?> getProcessUsage(int processId);

  /// Return a [ProcessProfiler] instance suitable for the current host
  /// platform. This can return `null` if we're not able to gather memory and
  /// cpu information for the current platform.
  static ProcessProfiler? getProfilerForPlatform() {
    if (Platform.isLinux || Platform.isMacOS) {
      return _PosixProcessProfiler();
    }

    if (Platform.isWindows) {
      return _WindowsProcessProfiler();
    }

    // Not a supported platform.
    return null;
  }
}

class UsageInfo {
  /// A number between 0.0 and 100.0 * the number of host CPUs (but typically
  /// never more than slightly above 100.0).
  final double? cpuPercentage;

  /// The process memory usage in kilobytes.
  final int memoryKB;

  UsageInfo(this.cpuPercentage, this.memoryKB);

  double get memoryMB => memoryKB / 1024;

  @override
  String toString() {
    if (cpuPercentage != null) {
      return '$cpuPercentage% ${memoryMB.toStringAsFixed(1)}MB';
    }
    return '${memoryMB.toStringAsFixed(1)}MB';
  }
}

class _PosixProcessProfiler extends ProcessProfiler {
  static final RegExp stringSplitRegExp = RegExp(r'\s+');

  _PosixProcessProfiler() : super._();

  @override
  Future<UsageInfo?> getProcessUsage(int processId) {
    try {
      // Execution time is typically 2-4ms.
      var future = Process.run('ps', [
        '-o',
        '%cpu=,rss=',
        processId.toString(),
      ]);
      return future.then((ProcessResult result) {
        if (result.exitCode != 0) {
          return Future.value();
        }

        return Future.value(_parse(result.stdout as String));
      });
    } catch (e) {
      return Future.error(e);
    }
  }

  UsageInfo? _parse(String psResults) {
    try {
      // "  0.0 378940"
      var line = psResults.split('\n').first.trim();
      var values = line.split(stringSplitRegExp);
      return UsageInfo(double.parse(values[0]), int.parse(values[1]));
    } catch (e) {
      return null;
    }
  }
}

class _WindowsProcessProfiler extends ProcessProfiler {
  _WindowsProcessProfiler() : super._();

  @override
  Future<UsageInfo?> getProcessUsage(int processId) async {
    try {
      var result = await Process.run('tasklist', [
        '/FI',
        'PID eq $processId',
        '/NH',
        '/FO',
        'csv',
      ]);

      if (result.exitCode != 0) {
        return Future.value();
      }

      return Future.value(_parse(result.stdout as String));
    } catch (e) {
      return Future.error(e);
    }
  }

  UsageInfo? _parse(String tasklistResults) {
    try {
      var lines = tasklistResults.split(RegExp('\r?\n'));
      for (var line in lines) {
        if (line.trim().isEmpty) continue;
        // Hacky parsing of csv line.
        var entries = jsonDecode('[$line]') as List;
        if (entries.length != 5) continue;
        // E.g. 123,456 K
        var memory = entries[4] as String;
        memory = memory.substring(0, memory.indexOf(' '));
        memory = memory.replaceAll(',', '');
        memory = memory.replaceAll('.', '');
        return UsageInfo(null, int.parse(memory));
      }
      return null;
    } catch (e) {
      return null;
    }
  }
}