Add PrefixPrinter and HybridPrinter decorators.

Author: tkutcher

lib/logger.dart

@@ -13,6 +13,8 @@ export 'src/outputs/memory_output.dart';
 export 'src/printers/pretty_printer.dart';
 export 'src/printers/logfmt_printer.dart';
 export 'src/printers/simple_printer.dart';
+export 'src/printers/hybrid_printer.dart';
+export 'src/printers/prefix_printer.dart';
 
 export 'src/log_output.dart'
     if (dart.library.io) 'src/outputs/file_output.dart';

lib/src/printers/hybrid_printer.dart

@@ -0,0 +1,34 @@
+import 'package:logger/logger.dart';
+import 'package:logger/src/logger.dart';
+import 'package:logger/src/log_printer.dart';
+
+/// A decorator for a [LogPrinter] that allows for the composition of
+/// different printers to handle different log messages. Provide it's
+/// constructor with a base printer, but include named parameters for
+/// any levels that have a different printer:
+///
+/// ```
+/// HybridPrinter(PrettyPrinter(), debug: SimplePrinter());
+/// ```
+///
+/// Will use the pretty printer for all logs except Level.debug
+/// logs, which will use SimplePrinter().
+class HybridPrinter extends LogPrinter {
+  final LogPrinter _realPrinter;
+  var _printerMap;
+
+  HybridPrinter(this._realPrinter,
+      {debug, verbose, wtf, info, warning, error}) {
+    _printerMap = {
+      Level.debug: debug ?? _realPrinter,
+      Level.verbose: verbose ?? _realPrinter,
+      Level.wtf: wtf ?? _realPrinter,
+      Level.info: info ?? _realPrinter,
+      Level.warning: warning ?? _realPrinter,
+      Level.error: error ?? _realPrinter,
+    };
+  }
+
+  @override
+  List<String> log(LogEvent event) => _printerMap[event.level].log(event);
+}

lib/src/printers/prefix_printer.dart

@@ -0,0 +1,43 @@
+import 'package:logger/src/logger.dart';
+import 'package:logger/src/log_printer.dart';
+
+/// A decorator for a [LogPrinter] that allows for the prepending of every
+/// line in the log output with a string for the level of that log. For
+/// example:
+///
+/// ```
+/// PrefixPrinter(PrettyPrinter());
+/// ```
+///
+/// Would prepend "DEBUG" to every line in a debug log. You can supply
+/// parameters for a custom message for a specific log level.
+class PrefixPrinter extends LogPrinter {
+  final LogPrinter _realPrinter;
+  Map<Level, String> _prefixMap;
+
+  PrefixPrinter(this._realPrinter,
+      {debug, verbose, wtf, info, warning, error}) {
+    _prefixMap = {
+      Level.debug: debug ?? 'DEBUG',
+      Level.verbose: verbose ?? 'VERBOSE',
+      Level.wtf: wtf ?? 'WTF',
+      Level.info: info ?? 'INFO',
+      Level.warning: warning ?? 'WARNING',
+      Level.error: error ?? 'ERROR',
+    };
+
+    var len = _longestPrefixLength();
+    _prefixMap.forEach((k, v) => _prefixMap[k] = '${v.padLeft(len)} ');
+  }
+
+  @override
+  List<String> log(LogEvent event) {
+    var realLogs = _realPrinter.log(event);
+    return realLogs.map((s) => '${_prefixMap[event.level]}$s').toList();
+  }
+
+  int _longestPrefixLength() {
+    var compFunc = (String a, String b) => a.length > b.length ? a : b;
+    return _prefixMap.values.reduce(compFunc).length;
+  }
+}

test/printers/hybrid_printer_test.dart

@@ -0,0 +1,42 @@
+import 'package:test/test.dart';
+
+import 'package:logger/src/printers/hybrid_printer.dart';
+import 'package:logger/logger.dart';
+
+final realPrinter = SimplePrinter();
+
+class TestLogPrinter extends LogPrinter {
+  LogEvent latestEvent;
+  @override
+  List<String> log(LogEvent event) {
+    latestEvent = event;
+    return realPrinter.log(event);
+  }
+}
+
+void main() {
+  var printerA = TestLogPrinter();
+  var printerB = TestLogPrinter();
+  var printerC = TestLogPrinter();
+
+  var debugEvent = LogEvent(Level.debug, 'debug', 'blah', StackTrace.current);
+  var infoEvent = LogEvent(Level.info, 'info', 'blah', StackTrace.current);
+  var warningEvent =
+      LogEvent(Level.warning, 'warning', 'blah', StackTrace.current);
+  var errorEvent = LogEvent(Level.error, 'error', 'blah', StackTrace.current);
+
+  var hybridPrinter = HybridPrinter(printerA, debug: printerB, error: printerC);
+  test('uses wrapped printer by default', () {
+    hybridPrinter.log(infoEvent);
+    expect(printerA.latestEvent, equals(infoEvent));
+  });
+
+  test('forwards logs to correct logger', () {
+    hybridPrinter.log(debugEvent);
+    hybridPrinter.log(errorEvent);
+    hybridPrinter.log(warningEvent);
+    expect(printerA.latestEvent, equals(warningEvent));
+    expect(printerB.latestEvent, equals(debugEvent));
+    expect(printerC.latestEvent, equals(errorEvent));
+  });
+}

test/printers/prefix_printer_test.dart

@@ -0,0 +1,56 @@
+import 'package:logger/src/printers/prefix_printer.dart';
+import 'package:test/test.dart';
+
+import 'package:logger/logger.dart';
+
+void main() {
+  var debugEvent = LogEvent(Level.debug, 'debug', 'blah', StackTrace.current);
+  var infoEvent = LogEvent(Level.info, 'info', 'blah', StackTrace.current);
+  var warningEvent =
+      LogEvent(Level.warning, 'warning', 'blah', StackTrace.current);
+  var errorEvent = LogEvent(Level.error, 'debug', 'blah', StackTrace.current);
+  var verboseEvent =
+      LogEvent(Level.verbose, 'debug', 'blah', StackTrace.current);
+  var wtfEvent = LogEvent(Level.wtf, 'debug', 'blah', StackTrace.current);
+
+  var allEvents = [
+    debugEvent,
+    warningEvent,
+    errorEvent,
+    verboseEvent,
+    wtfEvent
+  ];
+
+  test('prefixes logs', () {
+    var printer = PrefixPrinter(PrettyPrinter());
+    var actualLog = printer.log(infoEvent);
+    actualLog.forEach((logString) {
+      expect(logString, contains('INFO'));
+    });
+
+    var debugLog = printer.log(debugEvent);
+    debugLog.forEach((logString) {
+      expect(logString, contains('DEBUG'));
+    });
+  });
+
+  test('can supply own prefixes', () {
+    var printer = PrefixPrinter(PrettyPrinter(), debug: 'BLAH');
+    var actualLog = printer.log(debugEvent);
+    actualLog.forEach((logString) {
+      expect(logString, contains('BLAH'));
+    });
+  });
+
+  test('pads to same length', () {
+    const longPrefix = 'EXTRALONGPREFIX';
+    const len = longPrefix.length;
+    var printer = PrefixPrinter(SimplePrinter(), debug: longPrefix);
+    for (var event in allEvents) {
+      var l1 = printer.log(event);
+      l1.forEach((logString) {
+        expect(logString.substring(0, len), isNot(contains('[')));
+      });
+    }
+  });
+}