// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.

package edu.wpi.first.wpilibj;

import static java.util.Objects.requireNonNull;

import edu.wpi.first.hal.FRCNetComm.tResourceType;
import edu.wpi.first.hal.HAL;
import edu.wpi.first.hal.SimBoolean;
import edu.wpi.first.hal.SimDevice;
import edu.wpi.first.hal.SimDevice.Direction;
import edu.wpi.first.hal.SimDouble;
import edu.wpi.first.util.sendable.Sendable;
import edu.wpi.first.util.sendable.SendableBuilder;
import edu.wpi.first.util.sendable.SendableRegistry;
import java.util.ArrayList;
import java.util.List;

/**
 * Ultrasonic rangefinder class. The Ultrasonic rangefinder measures absolute distance based on the
 * round-trip time of a ping generated by the controller. These sensors use two transducers, a
 * speaker and a microphone both tuned to the ultrasonic range. A common ultrasonic sensor, the
 * Daventech SRF04 requires a short pulse to be generated on a digital channel. This causes the
 * chirp to be emitted. A second line becomes high as the ping is transmitted and goes low when the
 * echo is received. The time that the line is high determines the round trip distance (time of
 * flight).
 */
public class Ultrasonic implements Sendable, AutoCloseable {
  // Time (sec) for the ping trigger pulse.
  private static final double kPingTime = 10 * 1e-6;
  private static final double kSpeedOfSoundInchesPerSec = 1130.0 * 12.0;
  // ultrasonic sensor list
  private static final List<Ultrasonic> m_sensors = new ArrayList<>();
  // automatic round robin mode
  private static volatile boolean m_automaticEnabled;
  private DigitalInput m_echoChannel;
  private DigitalOutput m_pingChannel;
  private final boolean m_allocatedChannels;
  private boolean m_enabled;
  private Counter m_counter;
  // task doing the round-robin automatic sensing
  private static Thread m_task;
  private static int m_instances;

  private SimDevice m_simDevice;
  private SimBoolean m_simRangeValid;
  private SimDouble m_simRange;

  /**
   * Background task that goes through the list of ultrasonic sensors and pings each one in turn.
   * The counter is configured to read the timing of the returned echo pulse.
   *
   * <p><b>DANGER WILL ROBINSON, DANGER WILL ROBINSON:</b> This code runs as a task and assumes that
   * none of the ultrasonic sensors will change while it's running. If one does, then this will
   * certainly break. Make sure to disable automatic mode before changing anything with the
   * sensors!!
   */
  private static class UltrasonicChecker extends Thread {
    @Override
    public synchronized void run() {
      while (m_automaticEnabled) {
        for (Ultrasonic sensor : m_sensors) {
          if (!m_automaticEnabled) {
            break;
          }

          if (sensor.isEnabled()) {
            sensor.m_pingChannel.pulse(kPingTime); // do the ping
          }

          Timer.delay(0.1); // wait for ping to return
        }
      }
    }
  }

  /**
   * Initialize the Ultrasonic Sensor. This is the common code that initializes the ultrasonic
   * sensor given that there are two digital I/O channels allocated. If the system was running in
   * automatic mode (round robin) when the new sensor is added, it is stopped, the sensor is added,
   * then automatic mode is restored.
   */
  private synchronized void initialize() {
    m_simDevice = SimDevice.create("Ultrasonic", m_echoChannel.getChannel());
    if (m_simDevice != null) {
      m_simRangeValid = m_simDevice.createBoolean("Range Valid", Direction.kInput, true);
      m_simRange = m_simDevice.createDouble("Range (in)", Direction.kInput, 0.0);
      m_pingChannel.setSimDevice(m_simDevice);
      m_echoChannel.setSimDevice(m_simDevice);
    }
    if (m_task == null) {
      m_task = new UltrasonicChecker();
    }
    final boolean originalMode = m_automaticEnabled;
    setAutomaticMode(false); // kill task when adding a new sensor
    m_sensors.add(this);

    m_counter = new Counter(m_echoChannel); // set up counter for this
    SendableRegistry.addChild(this, m_counter);
    // sensor
    m_counter.setMaxPeriod(1.0);
    m_counter.setSemiPeriodMode(true);
    m_counter.reset();
    m_enabled = true; // make it available for round robin scheduling
    setAutomaticMode(originalMode);

    m_instances++;
    HAL.report(tResourceType.kResourceType_Ultrasonic, m_instances);
    SendableRegistry.addLW(this, "Ultrasonic", m_echoChannel.getChannel());
  }

  public int getEchoChannel() {
    return m_echoChannel.getChannel();
  }

  /**
   * Create an instance of the Ultrasonic Sensor. This is designed to supchannel the Daventech SRF04
   * and Vex ultrasonic sensors.
   *
   * @param pingChannel The digital output channel that sends the pulse to initiate the sensor
   *     sending the ping.
   * @param echoChannel The digital input channel that receives the echo. The length of time that
   *     the echo is high represents the round trip time of the ping, and the distance.
   */
  public Ultrasonic(final int pingChannel, final int echoChannel) {
    m_pingChannel = new DigitalOutput(pingChannel);
    m_echoChannel = new DigitalInput(echoChannel);
    SendableRegistry.addChild(this, m_pingChannel);
    SendableRegistry.addChild(this, m_echoChannel);
    m_allocatedChannels = true;
    initialize();
  }

  /**
   * Create an instance of an Ultrasonic Sensor from a DigitalInput for the echo channel and a
   * DigitalOutput for the ping channel.
   *
   * @param pingChannel The digital output object that starts the sensor doing a ping. Requires a
   *     10uS pulse to start.
   * @param echoChannel The digital input object that times the return pulse to determine the range.
   */
  public Ultrasonic(DigitalOutput pingChannel, DigitalInput echoChannel) {
    requireNonNull(pingChannel, "Provided ping channel was null");
    requireNonNull(echoChannel, "Provided echo channel was null");

    m_allocatedChannels = false;
    m_pingChannel = pingChannel;
    m_echoChannel = echoChannel;
    initialize();
  }

  /**
   * Destructor for the ultrasonic sensor. Delete the instance of the ultrasonic sensor by freeing
   * the allocated digital channels. If the system was in automatic mode (round robin), then it is
   * stopped, then started again after this sensor is removed (provided this wasn't the last
   * sensor).
   */
  @Override
  public synchronized void close() {
    SendableRegistry.remove(this);
    final boolean wasAutomaticMode = m_automaticEnabled;
    setAutomaticMode(false);
    if (m_allocatedChannels) {
      if (m_pingChannel != null) {
        m_pingChannel.close();
      }
      if (m_echoChannel != null) {
        m_echoChannel.close();
      }
    }

    if (m_counter != null) {
      m_counter.close();
      m_counter = null;
    }

    m_pingChannel = null;
    m_echoChannel = null;
    synchronized (m_sensors) {
      m_sensors.remove(this);
    }
    if (!m_sensors.isEmpty() && wasAutomaticMode) {
      setAutomaticMode(true);
    }

    if (m_simDevice != null) {
      m_simDevice.close();
      m_simDevice = null;
    }
  }

  /**
   * Turn Automatic mode on/off for all sensors.
   *
   * <p>When in Automatic mode, all sensors will fire in round robin, waiting a set time between
   * each sensor.
   *
   * @param enabling Set to true if round robin scheduling should start for all the ultrasonic
   *     sensors. This scheduling method assures that the sensors are non-interfering because no two
   *     sensors fire at the same time. If another scheduling algorithm is preferred, it can be
   *     implemented by pinging the sensors manually and waiting for the results to come back.
   */
  public static void setAutomaticMode(boolean enabling) {
    if (enabling == m_automaticEnabled) {
      return; // ignore the case of no change
    }
    m_automaticEnabled = enabling;

    if (enabling) {
      /* Clear all the counters so no data is valid. No synchronization is
       * needed because the background task is stopped.
       */
      for (Ultrasonic u : m_sensors) {
        u.m_counter.reset();
      }

      // Start round robin task
      m_task.start();
    } else {
      // Wait for background task to stop running
      try {
        m_task.join();
      } catch (InterruptedException ex) {
        Thread.currentThread().interrupt();
        ex.printStackTrace();
      }

      /* Clear all the counters (data now invalid) since automatic mode is
       * disabled. No synchronization is needed because the background task is
       * stopped.
       */
      for (Ultrasonic u : m_sensors) {
        u.m_counter.reset();
      }
    }
  }

  /**
   * Single ping to ultrasonic sensor. Send out a single ping to the ultrasonic sensor. This only
   * works if automatic (round robin) mode is disabled. A single ping is sent out, and the counter
   * should count the semi-period when it comes in. The counter is reset to make the current value
   * invalid.
   */
  public void ping() {
    setAutomaticMode(false); // turn off automatic round robin if pinging
    // single sensor
    m_counter.reset(); // reset the counter to zero (invalid data now)
    // do the ping to start getting a single range
    m_pingChannel.pulse(kPingTime);
  }

  /**
   * Check if there is a valid range measurement. The ranges are accumulated in a counter that will
   * increment on each edge of the echo (return) signal. If the count is not at least 2, then the
   * range has not yet been measured, and is invalid.
   *
   * @return true if the range is valid
   */
  public boolean isRangeValid() {
    if (m_simRangeValid != null) {
      return m_simRangeValid.get();
    }
    return m_counter.get() > 1;
  }

  /**
   * Get the range in inches from the ultrasonic sensor. If there is no valid value yet, i.e. at
   * least one measurement hasn't completed, then return 0.
   *
   * @return double Range in inches of the target returned from the ultrasonic sensor.
   */
  public double getRangeInches() {
    if (isRangeValid()) {
      if (m_simRange != null) {
        return m_simRange.get();
      }
      return m_counter.getPeriod() * kSpeedOfSoundInchesPerSec / 2.0;
    } else {
      return 0;
    }
  }

  /**
   * Get the range in millimeters from the ultrasonic sensor. If there is no valid value yet, i.e.
   * at least one measurement hasn't completed, then return 0.
   *
   * @return double Range in millimeters of the target returned by the ultrasonic sensor.
   */
  public double getRangeMM() {
    return getRangeInches() * 25.4;
  }

  /**
   * Is the ultrasonic enabled.
   *
   * @return true if the ultrasonic is enabled
   */
  public boolean isEnabled() {
    return m_enabled;
  }

  /**
   * Set if the ultrasonic is enabled.
   *
   * @param enable set to true to enable the ultrasonic
   */
  public void setEnabled(boolean enable) {
    m_enabled = enable;
  }

  @Override
  public void initSendable(SendableBuilder builder) {
    builder.setSmartDashboardType("Ultrasonic");
    builder.addDoubleProperty("Value", this::getRangeInches, null);
  }
}