// 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 org.wpilib.smartdashboard;

import static org.wpilib.util.ErrorMessages.requireNonNullParam;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import org.wpilib.util.sendable.Sendable;
import org.wpilib.util.sendable.SendableBuilder;
import org.wpilib.util.sendable.SendableRegistry;

/**
 * The {@link SendableChooser} class is a useful tool for presenting a selection of options to the
 * {@link SmartDashboard}.
 *
 * <p>For instance, you may wish to be able to select between multiple autonomous modes. You can do
 * this by putting every possible Command you want to run as an autonomous into a {@link
 * SendableChooser} and then put it into the {@link SmartDashboard} to have a list of options appear
 * on the laptop. Once autonomous starts, simply ask the {@link SendableChooser} what the selected
 * value is.
 *
 * @param <V> The type of the values to be stored
 */
public class SendableChooser<V> implements Sendable, AutoCloseable {
  /** The key for the default value. */
  private static final String DEFAULT = "default";

  /** The key for the selected option. */
  private static final String SELECTED = "selected";

  /** The key for the active option. */
  private static final String ACTIVE = "active";

  /** The key for the option array. */
  private static final String OPTIONS = "options";

  /** The key for the instance number. */
  private static final String INSTANCE = ".instance";

  /** A map linking strings to the objects they represent. */
  private final Map<String, V> m_map = new LinkedHashMap<>();

  private String m_defaultChoice = "";
  private final int m_instance;
  private String m_previousVal;
  private Consumer<V> m_listener;
  private static final AtomicInteger s_instances = new AtomicInteger();

  /** Instantiates a {@link SendableChooser}. */
  @SuppressWarnings("this-escape")
  public SendableChooser() {
    m_instance = s_instances.getAndIncrement();
    SendableRegistry.add(this, "SendableChooser", m_instance);
  }

  @Override
  public void close() {
    SendableRegistry.remove(this);
  }

  /**
   * Adds the given object to the list of options. On the {@link SmartDashboard} on the desktop, the
   * object will appear as the given name.
   *
   * @param name the name of the option
   * @param object the option
   */
  public void addOption(String name, V object) {
    m_map.put(name, object);
  }

  /**
   * Adds the given object to the list of options and marks it as the default. Functionally, this is
   * very close to {@link #addOption(String, Object)} except that it will use this as the default
   * option if none other is explicitly selected.
   *
   * @param name the name of the option
   * @param object the option
   */
  public void setDefaultOption(String name, V object) {
    requireNonNullParam(name, "name", "setDefaultOption");

    m_defaultChoice = name;
    addOption(name, object);
  }

  /**
   * Returns the selected option. If there is none selected, it will return the default. If there is
   * none selected and no default, then it will return {@code null}.
   *
   * @return the option selected
   */
  public V getSelected() {
    m_mutex.lock();
    try {
      if (m_selected != null) {
        return m_map.get(m_selected);
      } else {
        return m_map.get(m_defaultChoice);
      }
    } finally {
      m_mutex.unlock();
    }
  }

  /**
   * Bind a listener that's called when the selected value changes. Only one listener can be bound.
   * Calling this function will replace the previous listener.
   *
   * @param listener The function to call that accepts the new value
   */
  public void onChange(Consumer<V> listener) {
    requireNonNullParam(listener, "listener", "onChange");
    m_mutex.lock();
    m_listener = listener;
    m_mutex.unlock();
  }

  private String m_selected;
  private final ReentrantLock m_mutex = new ReentrantLock();

  @Override
  public void initSendable(SendableBuilder builder) {
    builder.setSmartDashboardType("String Chooser");
    builder.publishConstInteger(INSTANCE, m_instance);
    builder.addStringProperty(DEFAULT, () -> m_defaultChoice, null);
    builder.addStringArrayProperty(OPTIONS, () -> m_map.keySet().toArray(new String[0]), null);
    builder.addStringProperty(
        ACTIVE,
        () -> {
          m_mutex.lock();
          try {
            if (m_selected != null) {
              return m_selected;
            } else {
              return m_defaultChoice;
            }
          } finally {
            m_mutex.unlock();
          }
        },
        null);
    builder.addStringProperty(
        SELECTED,
        null,
        val -> {
          V choice;
          Consumer<V> listener;
          m_mutex.lock();
          try {
            m_selected = val;
            if (!m_selected.equals(m_previousVal) && m_listener != null) {
              choice = m_map.get(val);
              listener = m_listener;
            } else {
              choice = null;
              listener = null;
            }
            m_previousVal = val;
          } finally {
            m_mutex.unlock();
          }
          if (listener != null) {
            listener.accept(choice);
          }
        });
  }
}