content: /*
   * Copyright 2016 Google Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.google.android.things.contrib.driver.button;
  
  import android.os.Handler;
  import android.support.annotation.VisibleForTesting;
  import android.util.Log;
  import android.view.ViewConfiguration;
  
  import com.google.android.things.pio.Gpio;
  import com.google.android.things.pio.GpioCallback;
  import com.google.android.things.pio.PeripheralManager;
  
  import java.io.IOException;
  
  /**
   * Driver for GPIO based buttons with pull-up or pull-down resistors.
   */
  @SuppressWarnings({"unused", "WeakerAccess"})
  public class Button implements AutoCloseable {
      private static final String TAG = Button.class.getSimpleName();
  
      /**
       * Logic level when the button is considered pressed.
       */
      public enum LogicState {
          PRESSED_WHEN_HIGH,
          PRESSED_WHEN_LOW
      }
      private Gpio mButtonGpio;
      private OnButtonEventListener mListener;
  
      private Handler mDebounceHandler;
      private CheckDebounce mPendingCheckDebounce;
      private long mDebounceDelay = ViewConfiguration.getTapTimeout();
  
      /**
       * Interface definition for a callback to be invoked when a Button event occurs.
       */
      public interface OnButtonEventListener {
          /**
           * Called when a Button event occurs
           *
           * @param button the Button for which the event occurred
           * @param pressed true if the Button is now pressed
           */
          void onButtonEvent(Button button, boolean pressed);
      }
  
      /**
       * Create a new Button driver for the given GPIO pin name.
       * @param pin GPIO pin where the button is attached.
       * @param logicLevel Logic level when the button is considered pressed.
       * @throws IOException
       */
      public Button(String pin, LogicState logicLevel) throws IOException {
          PeripheralManager pioService = PeripheralManager.getInstance();
          Gpio buttonGpio = pioService.openGpio(pin);
          try {
              connect(buttonGpio, logicLevel);
          } catch (IOException|RuntimeException e) {
              close();
              throw e;
          }
      }
  
      /**
       * Constructor invoked from unit tests.
       */
      @VisibleForTesting
      /*package*/ Button(Gpio buttonGpio, LogicState logicLevel) throws IOException {
         connect(buttonGpio, logicLevel);
      }
  
      private void connect(Gpio buttonGpio, LogicState logicLevel) throws IOException {
          mButtonGpio = buttonGpio;
          mButtonGpio.setDirection(Gpio.DIRECTION_IN);
          mButtonGpio.setEdgeTriggerType(Gpio.EDGE_BOTH);
          // Configure so pressed is always true
          mButtonGpio.setActiveType(logicLevel == LogicState.PRESSED_WHEN_LOW ?
                  Gpio.ACTIVE_LOW : Gpio.ACTIVE_HIGH);
          mButtonGpio.registerGpioCallback(mInterruptCallback);
  
          mDebounceHandler = new Handler();
      }
  
      /**
       * Local callback to monitor GPIO edge events.
       */
      private GpioCallback mInterruptCallback = new InterruptCallback();
  
      @VisibleForTesting
      /*package*/ class InterruptCallback implements GpioCallback {
          @Override
          public boolean onGpioEdge(Gpio gpio) {
              try {
                  boolean currentState = gpio.getValue();
  
                  if (mDebounceDelay == 0) {
                      // Trigger event immediately
                      performButtonEvent(currentState);
                  } else {
                      // Pass trigger state forward if a check was pending
                      boolean trigger = (mPendingCheckDebounce == null) ?
                              currentState : mPendingCheckDebounce.getTriggerState();
                      // Clear any pending checks
                      removeDebounceCallback();
                      // Set a new pending check
                      mPendingCheckDebounce = new CheckDebounce(trigger);
                      mDebounceHandler.postDelayed(mPendingCheckDebounce, mDebounceDelay);
                  }
              } catch (IOException e) {
                  Log.e(TAG, "Error reading button state", e);
              }
  
              return true;
          }
      }
      
      /**
       * Returns the I/O name of the underlying GPIO.
       *
       * @return the I/O name.
       */
      public String getName() {
          return mButtonGpio.getName();
      }
  
      /**
       * Set the listener to be called when a button event occurred.
       *
       * @param listener button event listener to be invoked.
       */
      public void setOnButtonEventListener(OnButtonEventListener listener) {
          mListener = listener;
      }
  
      /**
       * Set the time delay after an edge trigger that the button
       * must remain stable before generating an event. Debounce
       * is enabled by default for 100ms.
       *
       * Setting this value to zero disables debounce and triggers
       * events on all edges immediately.
       *
       * @param delay Delay, in milliseconds, or 0 to disable.
       */
      public void setDebounceDelay(long delay) {
          if (delay < 0) {
              throw new IllegalArgumentException("Debounce delay cannot be negative.");
          }
          // Clear any pending events
          removeDebounceCallback();
          mDebounceDelay = delay;
      }
  
      @VisibleForTesting
      long getDebounceDelay() {
          return mDebounceDelay;
      }
  
      /**
       * Close the driver and the underlying device.
       * @throws IOException
       */
      @Override
      public void close() throws IOException {
          removeDebounceCallback();
          mListener = null;
  
          if (mButtonGpio != null) {
              mButtonGpio.unregisterGpioCallback(mInterruptCallback);
              try {
                  mButtonGpio.close();
              } finally {
                  mButtonGpio = null;
              }
          }
      }
  
      /**
       * Invoke button event callback
       */
      @VisibleForTesting
      /*package*/ void performButtonEvent(boolean state) {
          if (mListener != null) {
              mListener.onButtonEvent(this, state);
          }
      }
  
      /**
       * Clear pending debouce check
       */
      private void removeDebounceCallback() {
          if (mPendingCheckDebounce != null) {
              mDebounceHandler.removeCallbacks(mPendingCheckDebounce);
              mPendingCheckDebounce = null;
          }
      }
  
      /**
       * Pending check to delay input events from the initial
       * trigger edge.
       */
      private final class CheckDebounce implements Runnable {
          private boolean mTriggerState;
  
          public CheckDebounce(boolean triggerState) {
              mTriggerState = triggerState;
          }
  
          public boolean getTriggerState() {
              return mTriggerState;
          }
  
          @Override
          public void run() {
              if (mButtonGpio != null) {
                  try {
                      // Final check that state hasn't changed
                      if (mButtonGpio.getValue() == mTriggerState) {
                          performButtonEvent(mTriggerState);
                      }
                      removeDebounceCallback();
                  } catch (IOException e) {
                      Log.e(TAG, "Unable to read button value", e);
                  }
              }
          }
      }
  }
  