packages/flutter_tools/lib/src/base/logger.dart - mirrors/flutter - Git at Google

 // Copyright 2016 The Chromium Authors. 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:async';

 import 'package:meta/meta.dart';

 import 'io.dart';
 import 'platform.dart';
 import 'terminal.dart';
 import 'utils.dart';

 const int kDefaultStatusPadding = 59;

 typedef VoidCallback = void Function();

 abstract class Logger {
   bool get isVerbose => false;

   bool quiet = false;

   bool get supportsColor => terminal.supportsColor;

   bool get hasTerminal => stdio.hasTerminal;

   /// Display an error [message] to the user. Commands should use this if they
   /// fail in some way.
   ///
   /// The [message] argument is printed to the stderr in red by default.
   /// The [stackTrace] argument is the stack trace that will be printed if
   /// supplied.
   /// The [emphasis] argument will cause the output message be printed in bold text.
   /// The [color] argument will print the message in the supplied color instead
   /// of the default of red. Colors will not be printed if the output terminal
   /// doesn't support them.
   /// The [indent] argument specifies the number of spaces to indent the overall
   /// message. If wrapping is enabled in [outputPreferences], then the wrapped
   /// lines will be indented as well.
   /// If [hangingIndent] is specified, then any wrapped lines will be indented
   /// by this much more than the first line, if wrapping is enabled in
   /// [outputPreferences].
   /// If [wrap] is specified, then it overrides the
   /// [outputPreferences.wrapText] setting.
   void printError(
     String message, {
     StackTrace stackTrace,
     bool emphasis,
     TerminalColor color,
     int indent,
     int hangingIndent,
     bool wrap,
   });

   /// Display normal output of the command. This should be used for things like
   /// progress messages, success messages, or just normal command output.
   ///
   /// The [message] argument is printed to the stderr in red by default.
   /// The [stackTrace] argument is the stack trace that will be printed if
   /// supplied.
   /// If the [emphasis] argument is true, it will cause the output message be
   /// printed in bold text. Defaults to false.
   /// The [color] argument will print the message in the supplied color instead
   /// of the default of red. Colors will not be printed if the output terminal
   /// doesn't support them.
   /// If [newline] is true, then a newline will be added after printing the
   /// status. Defaults to true.
   /// The [indent] argument specifies the number of spaces to indent the overall
   /// message. If wrapping is enabled in [outputPreferences], then the wrapped
   /// lines will be indented as well.
   /// If [hangingIndent] is specified, then any wrapped lines will be indented
   /// by this much more than the first line, if wrapping is enabled in
   /// [outputPreferences].
   /// If [wrap] is specified, then it overrides the
   /// [outputPreferences.wrapText] setting.
   void printStatus(
     String message, {
     bool emphasis,
     TerminalColor color,
     bool newline,
     int indent,
     int hangingIndent,
     bool wrap,
   });

   /// Use this for verbose tracing output. Users can turn this output on in order
   /// to help diagnose issues with the toolchain or with their setup.
   void printTrace(String message);

   /// Start an indeterminate progress display.
   ///
   /// [message] is the message to display to the user; [progressId] provides an ID which can be
   /// used to identify this type of progress (`hot.reload`, `hot.restart`, ...).
   ///
   /// [progressIndicatorPadding] can optionally be used to specify spacing
   /// between the [message] and the progress indicator.
   Status startProgress(
     String message, {
     String progressId,
     bool expectSlowOperation,
     bool multilineOutput,
     int progressIndicatorPadding,
   });
 }

 class StdoutLogger extends Logger {
   Status _status;

   @override
   bool get isVerbose => false;

   @override
   void printError(
     String message, {
     StackTrace stackTrace,
     bool emphasis,
     TerminalColor color,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     message ??= '';
     message = wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap);
     _status?.cancel();
     _status = null;
     if (emphasis == true)
       message = terminal.bolden(message);
     message = terminal.color(message, color ?? TerminalColor.red);
     stderr.writeln(message);
     if (stackTrace != null) {
       stderr.writeln(stackTrace.toString());
     }
   }

   @override
   void printStatus(
     String message, {
     bool emphasis,
     TerminalColor color,
     bool newline,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     message ??= '';
     message = wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap);
     _status?.cancel();
     _status = null;
     if (emphasis == true)
       message = terminal.bolden(message);
     if (color != null)
       message = terminal.color(message, color);
     if (newline != false)
       message = '$message\n';
     writeToStdOut(message);
   }

   @protected
   void writeToStdOut(String message) {
     stdout.write(message);
   }

   @override
   void printTrace(String message) {}

   @override
   Status startProgress(
     String message, {
     String progressId,
     bool expectSlowOperation,
     bool multilineOutput,
     int progressIndicatorPadding,
   }) {
     expectSlowOperation ??= false;
     progressIndicatorPadding ??= kDefaultStatusPadding;
     if (_status != null) {
       // Ignore nested progresses; return a no-op status object.
       return Status(onFinish: _clearStatus)..start();
     }
     if (terminal.supportsColor) {
       _status = AnsiStatus(
         message: message,
         expectSlowOperation: expectSlowOperation,
         multilineOutput: multilineOutput,
         padding: progressIndicatorPadding,
         onFinish: _clearStatus,
       )..start();
     } else {
       _status = SummaryStatus(
         message: message,
         expectSlowOperation: expectSlowOperation,
         padding: progressIndicatorPadding,
         onFinish: _clearStatus,
       )..start();
     }
     return _status;
   }

   void _clearStatus() {
     _status = null;
   }
 }

 /// A [StdoutLogger] which replaces Unicode characters that cannot be printed to
 /// the Windows console with alternative symbols.
 ///
 /// By default, Windows uses either "Consolas" or "Lucida Console" as fonts to
 /// render text in the console. Both fonts only have a limited character set.
 /// Unicode characters, that are not available in either of the two default
 /// fonts, should be replaced by this class with printable symbols. Otherwise,
 /// they will show up as the unrepresentable character symbol '�'.
 class WindowsStdoutLogger extends StdoutLogger {
   @override
   void writeToStdOut(String message) {
     // TODO(jcollins-g): wrong abstraction layer for this, move to [Stdio].
     stdout.write(message
         .replaceAll('✗', 'X')
         .replaceAll('✓', '√')
     );
   }
 }

 class BufferLogger extends Logger {
   @override
   bool get isVerbose => false;

   final StringBuffer _error = StringBuffer();
   final StringBuffer _status = StringBuffer();
   final StringBuffer _trace = StringBuffer();

   String get errorText => _error.toString();
   String get statusText => _status.toString();
   String get traceText => _trace.toString();

   @override
   void printError(
     String message, {
     StackTrace stackTrace,
     bool emphasis,
     TerminalColor color,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     _error.writeln(terminal.color(
       wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap),
       color ?? TerminalColor.red,
     ));
   }

   @override
   void printStatus(
     String message, {
     bool emphasis,
     TerminalColor color,
     bool newline,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     if (newline != false)
       _status.writeln(wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
     else
       _status.write(wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
   }

   @override
   void printTrace(String message) => _trace.writeln(message);

   @override
   Status startProgress(
     String message, {
     String progressId,
     bool expectSlowOperation,
     bool multilineOutput,
     int progressIndicatorPadding,
   }) {
     printStatus(message);
     return Status()..start();
   }

   /// Clears all buffers.
   void clear() {
     _error.clear();
     _status.clear();
     _trace.clear();
   }
 }

 class VerboseLogger extends Logger {
   VerboseLogger(this.parent) : assert(terminal != null) {
     stopwatch.start();
   }

   final Logger parent;

   Stopwatch stopwatch = Stopwatch();

   @override
   bool get isVerbose => true;

   @override
   void printError(
     String message, {
     StackTrace stackTrace,
     bool emphasis,
     TerminalColor color,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     _emit(
       _LogType.error,
       wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap),
       stackTrace,
     );
   }

   @override
   void printStatus(
     String message, {
     bool emphasis,
     TerminalColor color,
     bool newline,
     int indent,
     int hangingIndent,
     bool wrap,
   }) {
     _emit(_LogType.status, wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
   }

   @override
   void printTrace(String message) {
     _emit(_LogType.trace, message);
   }

   @override
   Status startProgress(
     String message, {
     String progressId,
     bool expectSlowOperation,
     bool multilineOutput,
     int progressIndicatorPadding,
   }) {
     printStatus(message);
     return Status(onFinish: () {
       printTrace('$message (completed)');
     })..start();
   }

   void _emit(_LogType type, String message, [StackTrace stackTrace]) {
     if (message.trim().isEmpty)
       return;

     final int millis = stopwatch.elapsedMilliseconds;
     stopwatch.reset();

     String prefix;
     const int prefixWidth = 8;
     if (millis == 0) {
       prefix = ''.padLeft(prefixWidth);
     } else {
       prefix = '+$millis ms'.padLeft(prefixWidth);
       if (millis >= 100)
         prefix = terminal.bolden(prefix);
     }
     prefix = '[$prefix] ';

     final String indent = ''.padLeft(prefix.length);
     final String indentMessage = message.replaceAll('\n', '\n$indent');

     if (type == _LogType.error) {
       parent.printError(prefix + terminal.bolden(indentMessage));
       if (stackTrace != null)
         parent.printError(indent + stackTrace.toString().replaceAll('\n', '\n$indent'));
     } else if (type == _LogType.status) {
       parent.printStatus(prefix + terminal.bolden(indentMessage));
     } else {
       parent.printStatus(prefix + indentMessage);
     }
   }
 }

 enum _LogType { error, status, trace }

 /// A [Status] class begins when start is called, and may produce progress
 /// information asynchronously.
 ///
 /// The [Status] class itself never has any output.
 ///
 /// The [AnsiSpinner] subclass shows a spinner, and replaces it with a single
 /// space character when stopped or canceled.
 ///
 /// The [AnsiStatus] subclass shows a spinner, and replaces it with timing
 /// information when stopped. When canceled, the information isn't shown. In
 /// either case, a newline is printed.
 ///
 /// Generally, consider `logger.startProgress` instead of directly creating
 /// a [Status] or one of its subclasses.
 class Status {
   Status({this.onFinish});

   /// A straight [Status] or an [AnsiSpinner] (depending on whether the
   /// terminal is fancy enough), already started.
   factory Status.withSpinner({ VoidCallback onFinish }) {
     if (terminal.supportsColor)
       return AnsiSpinner(onFinish: onFinish)..start();
     return Status(onFinish: onFinish)..start();
   }

   final VoidCallback onFinish;

   bool _isStarted = false;

   /// Call to start spinning.
   void start() {
     assert(!_isStarted);
     _isStarted = true;
   }

   /// Call to stop spinning after success.
   void stop() {
     assert(_isStarted);
     _isStarted = false;
     if (onFinish != null)
       onFinish();
   }

   /// Call to cancel the spinner after failure or cancellation.
   void cancel() {
     assert(_isStarted);
     _isStarted = false;
     if (onFinish != null)
       onFinish();
   }
 }

 /// An [AnsiSpinner] is a simple animation that does nothing but implement a
 /// ASCII/Unicode spinner. When stopped or canceled, the animation erases
 /// itself.
 class AnsiSpinner extends Status {
   AnsiSpinner({VoidCallback onFinish}) : super(onFinish: onFinish);

   int ticks = 0;
   Timer timer;

   // Windows console font has a limited set of Unicode characters.
   List<String> get _animation => platform.isWindows
       ? <String>[r'-', r'\', r'|', r'/']
       : <String>['⣾', '⣽', '⣻', '⢿', '⡿', '⣟', '⣯', '⣷'];

   String get _backspace => '\b' * _animation[0].length;
   String get _clear => ' ' *  _animation[0].length;

   void _callback(Timer timer) {
     stdout.write('$_backspace${_animation[ticks++ % _animation.length]}');
   }

   @override
   void start() {
     super.start();
     assert(timer == null);
     stdout.write(' ');
     timer = Timer.periodic(const Duration(milliseconds: 100), _callback);
     _callback(timer);
   }

   @override
   void stop() {
     assert(timer.isActive);
     timer.cancel();
     stdout.write('$_backspace$_clear$_backspace');
     super.stop();
   }

   @override
   void cancel() {
     assert(timer.isActive);
     timer.cancel();
     stdout.write('$_backspace$_clear$_backspace');
     super.cancel();
   }
 }

 /// Constructor writes [message] to [stdout] with padding, then starts as an
 /// [AnsiSpinner].  On [cancel] or [stop], will call [onFinish].
 /// On [stop], will additionally print out summary information in
 /// milliseconds if [expectSlowOperation] is false, as seconds otherwise.
 class AnsiStatus extends AnsiSpinner {
   AnsiStatus({
     String message,
     bool expectSlowOperation,
     bool multilineOutput,
     int padding,
     VoidCallback onFinish,
   })  : message = message ?? '',
         padding = padding ?? 0,
         expectSlowOperation = expectSlowOperation ?? false,
         multilineOutput = multilineOutput ?? false,
         super(onFinish: onFinish);

   final String message;
   final bool expectSlowOperation;
   final bool multilineOutput;
   final int padding;

   Stopwatch stopwatch;

   static const String _margin = '     ';

   @override
   void start() {
     assert(stopwatch == null || !stopwatch.isRunning);
     stopwatch = Stopwatch()..start();
     stdout.write('${message.padRight(padding)}$_margin');
     super.start();
   }

   @override
   void stop() {
     super.stop();
     writeSummaryInformation();
     stdout.write('\n');
   }

   @override
   void cancel() {
     super.cancel();
     stdout.write('\n');
   }

   /// Print summary information when a task is done.
   ///
   /// If [multilineOutput] is false, backs up 4 characters and prints a
   /// (minimum) 5 character padded time. If [expectSlowOperation] is true, the
   /// time is in seconds; otherwise, milliseconds. Only backs up 4 characters
   /// because [super.cancel] backs up one.
   ///
   /// If [multilineOutput] is true, then it prints the message again on a new
   /// line before writing the elapsed time, and doesn't back up at all.
   void writeSummaryInformation() {
     final String prefix = multilineOutput
         ? '\n${'$message Done'.padRight(padding - 4)}$_margin'
         : '\b\b\b\b';
     if (expectSlowOperation) {
       stdout.write('$prefix${getElapsedAsSeconds(stopwatch.elapsed).padLeft(5)}');
     } else {
       stdout.write('$prefix${getElapsedAsMilliseconds(stopwatch.elapsed).padLeft(5)}');
     }
   }
 }

 /// Constructor writes [message] to [stdout].  On [cancel] or [stop], will call
 /// [onFinish]. On [stop], will additionally print out summary information in
 /// milliseconds if [expectSlowOperation] is false, as seconds otherwise.
 class SummaryStatus extends Status {
   SummaryStatus({
     String message,
     bool expectSlowOperation,
     int padding,
     VoidCallback onFinish,
   })  : message = message ?? '',
         padding = padding ?? 0,
         expectSlowOperation = expectSlowOperation ?? false,
         super(onFinish: onFinish);

   final String message;
   final bool expectSlowOperation;
   final int padding;

   Stopwatch stopwatch;

   @override
   void start() {
     stopwatch = Stopwatch()..start();
     stdout.write('${message.padRight(padding)}     ');
     super.start();
   }

   @override
   void stop() {
     super.stop();
     writeSummaryInformation();
     stdout.write('\n');
   }

   @override
   void cancel() {
     super.cancel();
     stdout.write('\n');
   }

   /// Prints a (minimum) 5 character padded time.  If [expectSlowOperation] is
   /// true, the time is in seconds; otherwise, milliseconds.
   ///
   /// Example: ' 0.5s', '150ms', '1600ms'
   void writeSummaryInformation() {
     if (expectSlowOperation) {
       stdout.write(getElapsedAsSeconds(stopwatch.elapsed).padLeft(5));
     } else {
       stdout.write(getElapsedAsMilliseconds(stopwatch.elapsed).padLeft(5));
     }
   }
 }
	// Copyright 2016 The Chromium Authors. 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:async';

	import 'package:meta/meta.dart';

	import 'io.dart';
	import 'platform.dart';
	import 'terminal.dart';
	import 'utils.dart';

	const int kDefaultStatusPadding = 59;

	typedef VoidCallback = void Function();

	abstract class Logger {
	bool get isVerbose => false;

	bool quiet = false;

	bool get supportsColor => terminal.supportsColor;

	bool get hasTerminal => stdio.hasTerminal;

	/// Display an error [message] to the user. Commands should use this if they
	/// fail in some way.
	///
	/// The [message] argument is printed to the stderr in red by default.
	/// The [stackTrace] argument is the stack trace that will be printed if
	/// supplied.
	/// The [emphasis] argument will cause the output message be printed in bold text.
	/// The [color] argument will print the message in the supplied color instead
	/// of the default of red. Colors will not be printed if the output terminal
	/// doesn't support them.
	/// The [indent] argument specifies the number of spaces to indent the overall
	/// message. If wrapping is enabled in [outputPreferences], then the wrapped
	/// lines will be indented as well.
	/// If [hangingIndent] is specified, then any wrapped lines will be indented
	/// by this much more than the first line, if wrapping is enabled in
	/// [outputPreferences].
	/// If [wrap] is specified, then it overrides the
	/// [outputPreferences.wrapText] setting.
	void printError(
	String message, {
	StackTrace stackTrace,
	bool emphasis,
	TerminalColor color,
	int indent,
	int hangingIndent,
	bool wrap,
	});

	/// Display normal output of the command. This should be used for things like
	/// progress messages, success messages, or just normal command output.
	///
	/// The [message] argument is printed to the stderr in red by default.
	/// The [stackTrace] argument is the stack trace that will be printed if
	/// supplied.
	/// If the [emphasis] argument is true, it will cause the output message be
	/// printed in bold text. Defaults to false.
	/// The [color] argument will print the message in the supplied color instead
	/// of the default of red. Colors will not be printed if the output terminal
	/// doesn't support them.
	/// If [newline] is true, then a newline will be added after printing the
	/// status. Defaults to true.
	/// The [indent] argument specifies the number of spaces to indent the overall
	/// message. If wrapping is enabled in [outputPreferences], then the wrapped
	/// lines will be indented as well.
	/// If [hangingIndent] is specified, then any wrapped lines will be indented
	/// by this much more than the first line, if wrapping is enabled in
	/// [outputPreferences].
	/// If [wrap] is specified, then it overrides the
	/// [outputPreferences.wrapText] setting.
	void printStatus(
	String message, {
	bool emphasis,
	TerminalColor color,
	bool newline,
	int indent,
	int hangingIndent,
	bool wrap,
	});

	/// Use this for verbose tracing output. Users can turn this output on in order
	/// to help diagnose issues with the toolchain or with their setup.
	void printTrace(String message);

	/// Start an indeterminate progress display.
	///
	/// [message] is the message to display to the user; [progressId] provides an ID which can be
	/// used to identify this type of progress (`hot.reload`, `hot.restart`, ...).
	///
	/// [progressIndicatorPadding] can optionally be used to specify spacing
	/// between the [message] and the progress indicator.
	Status startProgress(
	String message, {
	String progressId,
	bool expectSlowOperation,
	bool multilineOutput,
	int progressIndicatorPadding,
	});
	}

	class StdoutLogger extends Logger {
	Status _status;

	@override
	bool get isVerbose => false;

	@override
	void printError(
	String message, {
	StackTrace stackTrace,
	bool emphasis,
	TerminalColor color,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	message ??= '';
	message = wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap);
	_status?.cancel();
	_status = null;
	if (emphasis == true)
	message = terminal.bolden(message);
	message = terminal.color(message, color ?? TerminalColor.red);
	stderr.writeln(message);
	if (stackTrace != null) {
	stderr.writeln(stackTrace.toString());
	}
	}

	@override
	void printStatus(
	String message, {
	bool emphasis,
	TerminalColor color,
	bool newline,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	message ??= '';
	message = wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap);
	_status?.cancel();
	_status = null;
	if (emphasis == true)
	message = terminal.bolden(message);
	if (color != null)
	message = terminal.color(message, color);
	if (newline != false)
	message = '$message\n';
	writeToStdOut(message);
	}

	@protected
	void writeToStdOut(String message) {
	stdout.write(message);
	}

	@override
	void printTrace(String message) {}

	@override
	Status startProgress(
	String message, {
	String progressId,
	bool expectSlowOperation,
	bool multilineOutput,
	int progressIndicatorPadding,
	}) {
	expectSlowOperation ??= false;
	progressIndicatorPadding ??= kDefaultStatusPadding;
	if (_status != null) {
	// Ignore nested progresses; return a no-op status object.
	return Status(onFinish: _clearStatus)..start();
	}
	if (terminal.supportsColor) {
	_status = AnsiStatus(
	message: message,
	expectSlowOperation: expectSlowOperation,
	multilineOutput: multilineOutput,
	padding: progressIndicatorPadding,
	onFinish: _clearStatus,
	)..start();
	} else {
	_status = SummaryStatus(
	message: message,
	expectSlowOperation: expectSlowOperation,
	padding: progressIndicatorPadding,
	onFinish: _clearStatus,
	)..start();
	}
	return _status;
	}

	void _clearStatus() {
	_status = null;
	}
	}

	/// A [StdoutLogger] which replaces Unicode characters that cannot be printed to
	/// the Windows console with alternative symbols.
	///
	/// By default, Windows uses either "Consolas" or "Lucida Console" as fonts to
	/// render text in the console. Both fonts only have a limited character set.
	/// Unicode characters, that are not available in either of the two default
	/// fonts, should be replaced by this class with printable symbols. Otherwise,
	/// they will show up as the unrepresentable character symbol '�'.
	class WindowsStdoutLogger extends StdoutLogger {
	@override
	void writeToStdOut(String message) {
	// TODO(jcollins-g): wrong abstraction layer for this, move to [Stdio].
	stdout.write(message
	.replaceAll('✗', 'X')
	.replaceAll('✓', '√')
	);
	}
	}

	class BufferLogger extends Logger {
	@override
	bool get isVerbose => false;

	final StringBuffer _error = StringBuffer();
	final StringBuffer _status = StringBuffer();
	final StringBuffer _trace = StringBuffer();

	String get errorText => _error.toString();
	String get statusText => _status.toString();
	String get traceText => _trace.toString();

	@override
	void printError(
	String message, {
	StackTrace stackTrace,
	bool emphasis,
	TerminalColor color,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	_error.writeln(terminal.color(
	wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap),
	color ?? TerminalColor.red,
	));
	}

	@override
	void printStatus(
	String message, {
	bool emphasis,
	TerminalColor color,
	bool newline,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	if (newline != false)
	_status.writeln(wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
	else
	_status.write(wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
	}

	@override
	void printTrace(String message) => _trace.writeln(message);

	@override
	Status startProgress(
	String message, {
	String progressId,
	bool expectSlowOperation,
	bool multilineOutput,
	int progressIndicatorPadding,
	}) {
	printStatus(message);
	return Status()..start();
	}

	/// Clears all buffers.
	void clear() {
	_error.clear();
	_status.clear();
	_trace.clear();
	}
	}

	class VerboseLogger extends Logger {
	VerboseLogger(this.parent) : assert(terminal != null) {
	stopwatch.start();
	}

	final Logger parent;

	Stopwatch stopwatch = Stopwatch();

	@override
	bool get isVerbose => true;

	@override
	void printError(
	String message, {
	StackTrace stackTrace,
	bool emphasis,
	TerminalColor color,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	_emit(
	_LogType.error,
	wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap),
	stackTrace,
	);
	}

	@override
	void printStatus(
	String message, {
	bool emphasis,
	TerminalColor color,
	bool newline,
	int indent,
	int hangingIndent,
	bool wrap,
	}) {
	_emit(_LogType.status, wrapText(message, indent: indent, hangingIndent: hangingIndent, shouldWrap: wrap));
	}

	@override
	void printTrace(String message) {
	_emit(_LogType.trace, message);
	}

	@override
	Status startProgress(
	String message, {
	String progressId,
	bool expectSlowOperation,
	bool multilineOutput,
	int progressIndicatorPadding,
	}) {
	printStatus(message);
	return Status(onFinish: () {
	printTrace('$message (completed)');
	})..start();
	}

	void _emit(_LogType type, String message, [StackTrace stackTrace]) {
	if (message.trim().isEmpty)
	return;

	final int millis = stopwatch.elapsedMilliseconds;
	stopwatch.reset();

	String prefix;
	const int prefixWidth = 8;
	if (millis == 0) {
	prefix = ''.padLeft(prefixWidth);
	} else {
	prefix = '+$millis ms'.padLeft(prefixWidth);
	if (millis >= 100)
	prefix = terminal.bolden(prefix);
	}
	prefix = '[$prefix] ';

	final String indent = ''.padLeft(prefix.length);
	final String indentMessage = message.replaceAll('\n', '\n$indent');

	if (type == _LogType.error) {
	parent.printError(prefix + terminal.bolden(indentMessage));
	if (stackTrace != null)
	parent.printError(indent + stackTrace.toString().replaceAll('\n', '\n$indent'));
	} else if (type == _LogType.status) {
	parent.printStatus(prefix + terminal.bolden(indentMessage));
	} else {
	parent.printStatus(prefix + indentMessage);
	}
	}
	}

	enum _LogType { error, status, trace }

	/// A [Status] class begins when start is called, and may produce progress
	/// information asynchronously.
	///
	/// The [Status] class itself never has any output.
	///
	/// The [AnsiSpinner] subclass shows a spinner, and replaces it with a single
	/// space character when stopped or canceled.
	///
	/// The [AnsiStatus] subclass shows a spinner, and replaces it with timing
	/// information when stopped. When canceled, the information isn't shown. In
	/// either case, a newline is printed.
	///
	/// Generally, consider `logger.startProgress` instead of directly creating
	/// a [Status] or one of its subclasses.
	class Status {
	Status({this.onFinish});

	/// A straight [Status] or an [AnsiSpinner] (depending on whether the
	/// terminal is fancy enough), already started.
	factory Status.withSpinner({ VoidCallback onFinish }) {
	if (terminal.supportsColor)
	return AnsiSpinner(onFinish: onFinish)..start();
	return Status(onFinish: onFinish)..start();
	}

	final VoidCallback onFinish;

	bool _isStarted = false;

	/// Call to start spinning.
	void start() {
	assert(!_isStarted);
	_isStarted = true;
	}

	/// Call to stop spinning after success.
	void stop() {
	assert(_isStarted);
	_isStarted = false;
	if (onFinish != null)
	onFinish();
	}

	/// Call to cancel the spinner after failure or cancellation.
	void cancel() {
	assert(_isStarted);
	_isStarted = false;
	if (onFinish != null)
	onFinish();
	}
	}

	/// An [AnsiSpinner] is a simple animation that does nothing but implement a
	/// ASCII/Unicode spinner. When stopped or canceled, the animation erases
	/// itself.
	class AnsiSpinner extends Status {
	AnsiSpinner({VoidCallback onFinish}) : super(onFinish: onFinish);

	int ticks = 0;
	Timer timer;

	// Windows console font has a limited set of Unicode characters.
	List<String> get _animation => platform.isWindows
	? <String>[r'-', r'\', r'\|', r'/']
	: <String>['⣾', '⣽', '⣻', '⢿', '⡿', '⣟', '⣯', '⣷'];

	String get _backspace => '\b' * _animation[0].length;
	String get _clear => ' ' * _animation[0].length;

	void _callback(Timer timer) {
	stdout.write('$_backspace${_animation[ticks++ % _animation.length]}');
	}

	@override
	void start() {
	super.start();
	assert(timer == null);
	stdout.write(' ');
	timer = Timer.periodic(const Duration(milliseconds: 100), _callback);
	_callback(timer);
	}

	@override
	void stop() {
	assert(timer.isActive);
	timer.cancel();
	stdout.write('$_backspace$_clear$_backspace');
	super.stop();
	}

	@override
	void cancel() {
	assert(timer.isActive);
	timer.cancel();
	stdout.write('$_backspace$_clear$_backspace');
	super.cancel();
	}
	}

	/// Constructor writes [message] to [stdout] with padding, then starts as an
	/// [AnsiSpinner]. On [cancel] or [stop], will call [onFinish].
	/// On [stop], will additionally print out summary information in
	/// milliseconds if [expectSlowOperation] is false, as seconds otherwise.
	class AnsiStatus extends AnsiSpinner {
	AnsiStatus({
	String message,
	bool expectSlowOperation,
	bool multilineOutput,
	int padding,
	VoidCallback onFinish,
	}) : message = message ?? '',
	padding = padding ?? 0,
	expectSlowOperation = expectSlowOperation ?? false,
	multilineOutput = multilineOutput ?? false,
	super(onFinish: onFinish);

	final String message;
	final bool expectSlowOperation;
	final bool multilineOutput;
	final int padding;

	Stopwatch stopwatch;

	static const String _margin = ' ';

	@override
	void start() {
	assert(stopwatch == null \|\| !stopwatch.isRunning);
	stopwatch = Stopwatch()..start();
	stdout.write('${message.padRight(padding)}$_margin');
	super.start();
	}

	@override
	void stop() {
	super.stop();
	writeSummaryInformation();
	stdout.write('\n');
	}

	@override
	void cancel() {
	super.cancel();
	stdout.write('\n');
	}

	/// Print summary information when a task is done.
	///
	/// If [multilineOutput] is false, backs up 4 characters and prints a
	/// (minimum) 5 character padded time. If [expectSlowOperation] is true, the
	/// time is in seconds; otherwise, milliseconds. Only backs up 4 characters
	/// because [super.cancel] backs up one.
	///
	/// If [multilineOutput] is true, then it prints the message again on a new
	/// line before writing the elapsed time, and doesn't back up at all.
	void writeSummaryInformation() {
	final String prefix = multilineOutput
	? '\n${'$message Done'.padRight(padding - 4)}$_margin'
	: '\b\b\b\b';
	if (expectSlowOperation) {
	stdout.write('$prefix${getElapsedAsSeconds(stopwatch.elapsed).padLeft(5)}');
	} else {
	stdout.write('$prefix${getElapsedAsMilliseconds(stopwatch.elapsed).padLeft(5)}');
	}
	}
	}

	/// Constructor writes [message] to [stdout]. On [cancel] or [stop], will call
	/// [onFinish]. On [stop], will additionally print out summary information in
	/// milliseconds if [expectSlowOperation] is false, as seconds otherwise.
	class SummaryStatus extends Status {
	SummaryStatus({
	String message,
	bool expectSlowOperation,
	int padding,
	VoidCallback onFinish,
	}) : message = message ?? '',
	padding = padding ?? 0,
	expectSlowOperation = expectSlowOperation ?? false,
	super(onFinish: onFinish);

	final String message;
	final bool expectSlowOperation;
	final int padding;

	Stopwatch stopwatch;

	@override
	void start() {
	stopwatch = Stopwatch()..start();
	stdout.write('${message.padRight(padding)} ');
	super.start();
	}

	@override
	void stop() {
	super.stop();
	writeSummaryInformation();
	stdout.write('\n');
	}

	@override
	void cancel() {
	super.cancel();
	stdout.write('\n');
	}

	/// Prints a (minimum) 5 character padded time. If [expectSlowOperation] is
	/// true, the time is in seconds; otherwise, milliseconds.
	///
	/// Example: ' 0.5s', '150ms', '1600ms'
	void writeSummaryInformation() {
	if (expectSlowOperation) {
	stdout.write(getElapsedAsSeconds(stopwatch.elapsed).padLeft(5));
	} else {
	stdout.write(getElapsedAsMilliseconds(stopwatch.elapsed).padLeft(5));
	}
	}
	}