Refactor Raspberry Pi GPIO and add GPIO mock

pkg/gpio/lib/gpio_mock.dart

+// Copyright (c) 2015, the Fletch 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.md file.
+library gpio_mock;
+
+import 'package:gpio/gpio.dart';
+
+/// Mock implementation of the GPIO interface.
+class MockGPIO extends GPIOBase {
+  Function _setPin;
+  Function _getPin;
+
+  List<bool> _pinValues;
+
+  MockGPIO([int pins = GPIO.defaultPins]) : super(pins) {
+    _pinValues = new List.filled(pins, false);
+  }
+
+  /// The simulated values of the pins.
+  ///
+  /// The default ´getPin´ will return the value in this `List`. The default
+  /// ´setPin´ will update it. Initially all values are ´false´.
+  List<bool> get pinValues => _pinValues;
+
+  void setMode(int pin, Mode mode) {
+    checkPinRange(pin);
+    print('Setting mode for pin $pin to $mode');
+  }
+
+  Mode getMode(int pin) {
+    checkPinRange(pin);
+    print('Reading mode of pin $pin');
+  }
+
+  void setPin(int pin, bool value) {
+    checkPinRange(pin);
+    if (_setPin == null) {
+      _pinValues[pin] = value;
+      print('Writing pin $pin value $value');
+    } else {
+      _setPin(pin, value);
+    }
+  }
+
+  bool getPin(int pin) {
+    checkPinRange(pin);
+    if (_getPin == null) {
+      bool value = _pinValues[pin];
+      print('Reading pin $pin value $value');
+      return value;
+    } else {
+      return _getPin(pin);
+    }
+  }
+
+  /// Register ´callback´ to be called for ´setPin´.
+  void registerSetPin(void callback(int pin, bool value)) {
+    _setPin = callback;
+  }
+
+  /// Register ´callback´ to be called for ´getPin´.
+  void registerGetPin(bool callback(int pin)) {
+    _getPin = callback;
+  }
+}