// Copyright (c) 2012, 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.

/// Helper functionality for invoking Git.
import 'dart:async';
import 'dart:io';

import 'package:stack_trace/stack_trace.dart';

import 'exceptions.dart';
import 'io.dart';
import 'log.dart' as log;
import 'utils.dart';

/// An exception thrown because a git command failed.
class GitException implements ApplicationException {
  /// The arguments to the git command.
  final List<String> args;

  /// The standard error emitted by git.
  final String stderr;

  String get message => 'Git error. Command: git ${args.join(" ")}\n$stderr';

  GitException(Iterable<String> args, this.stderr) : args = args.toList();

  String toString() => message;
}

/// Tests whether or not the git command-line app is available for use.
bool get isInstalled {
  if (_isInstalledCache != null) return _isInstalledCache;
  _isInstalledCache = command != null;
  return _isInstalledCache;
}

bool _isInstalledCache;

/// Run a git process with [args] from [workingDir].
///
/// Returns the stdout as a list of strings if it succeeded. Completes to an
/// exception if it failed.
Future<List<String>> run(List<String> args,
    {String workingDir, Map<String, String> environment}) async {
  if (!isInstalled) {
    fail("Cannot find a Git executable.\n"
        "Please ensure Git is correctly installed.");
  }

  log.muteProgress();
  try {
    var result = await runProcess(command, args,
        workingDir: workingDir, environment: environment);
    if (!result.success) throw new GitException(args, result.stderr.join("\n"));
    return result.stdout;
  } finally {
    log.unmuteProgress();
  }
}

/// Like [run], but synchronous.
List<String> runSync(List<String> args,
    {String workingDir, Map<String, String> environment}) {
  if (!isInstalled) {
    fail("Cannot find a Git executable.\n"
        "Please ensure Git is correctly installed.");
  }

  var result = runProcessSync(command, args,
      workingDir: workingDir, environment: environment);
  if (!result.success) throw new GitException(args, result.stderr.join("\n"));
  return result.stdout;
}

/// Returns the name of the git command-line app, or null if Git could not be
/// found on the user's PATH.
String get command {
  if (_commandCache != null) return _commandCache;

  var command;
  if (_tryGitCommand("git")) {
    _commandCache = "git";
  } else if (_tryGitCommand("git.cmd")) {
    _commandCache = "git.cmd";
  } else {
    return null;
  }

  log.fine('Determined git command $command.');
  return _commandCache;
}

String _commandCache;

/// Checks whether [command] is the Git command for this computer.
bool _tryGitCommand(String command) {
  // If "git --version" prints something familiar, git is working.
  try {
    var result = runProcessSync(command, ["--version"]);
    var regexp = new RegExp("^git version");
    return result.stdout.length == 1 && regexp.hasMatch(result.stdout.single);
  } on ProcessException catch (error, stackTrace) {
    var chain = new Chain.forTrace(stackTrace);
    // If the process failed, they probably don't have it.
    log.error('Git command is not "$command": $error\n$chain');
    return false;
  }
}