Add Debouncer (#3590)

Supersedes #2358 with updates and cleanups.

Closes #2482 and closes #2487 because we shouldn't support both
time-based and count-based debouncing approaches.

Co-authored-by: oblarg <emichaelbarnett@gmail.com>

wpilibj/src/main/java/edu/wpi/first/wpilibj/Debouncer.java

@@ -0,0 +1,79 @@
+// 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;
+
+/**
+ * A simple debounce filter for boolean streams. Requires that the boolean change value from
+ * baseline for a specified period of time before the filtered value changes.
+ */
+public class Debouncer {
+  public enum DebounceType {
+    kRising,
+    kFalling,
+    kBoth
+  }
+
+  private final Timer m_timer = new Timer();
+  private final double m_debounceTime;
+  private final DebounceType m_debounceType;
+  private boolean m_baseline;
+
+  /**
+   * Creates a new Debouncer.
+   *
+   * @param debounceTime The number of seconds the value must change from baseline for the filtered
+   *     value to change.
+   * @param type Which type of state change the debouncing will be performed on.
+   */
+  public Debouncer(double debounceTime, DebounceType type) {
+    m_debounceTime = debounceTime;
+    m_debounceType = type;
+    m_timer.start();
+
+    switch (m_debounceType) {
+      case kBoth: // fall-through
+      case kRising:
+        m_baseline = false;
+        break;
+      case kFalling:
+        m_baseline = true;
+        break;
+      default:
+        throw new IllegalArgumentException("Invalid debounce type!");
+    }
+  }
+
+  /**
+   * Creates a new Debouncer. Baseline value defaulted to "false."
+   *
+   * @param debounceTime The number of seconds the value must change from baseline for the filtered
+   *     value to change.
+   */
+  public Debouncer(double debounceTime) {
+    this(debounceTime, DebounceType.kRising);
+  }
+
+  /**
+   * Applies the debouncer to the input stream.
+   *
+   * @param input The current value of the input stream.
+   * @return The debounced value of the input stream.
+   */
+  public boolean calculate(boolean input) {
+    if (input == m_baseline) {
+      m_timer.reset();
+    }
+
+    if (m_timer.hasElapsed(m_debounceTime)) {
+      if (m_debounceType == DebounceType.kBoth) {
+        m_baseline = input;
+        m_timer.reset();
+      }
+      return input;
+    } else {
+      return m_baseline;
+    }
+  }
+}