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>

wpilibc/src/main/native/cpp/Debouncer.cpp

@@ -0,0 +1,37 @@
+// 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.
+
+#include "frc/Debouncer.h"
+
+using namespace frc;
+
+Debouncer::Debouncer(units::second_t debounceTime, DebounceType type)
+    : m_debounceTime(debounceTime), m_debounceType(type) {
+  switch (type) {
+    case DebounceType::kBoth:  // fall-through
+    case DebounceType::kRising:
+      m_baseline = false;
+      break;
+    case DebounceType::kFalling:
+      m_baseline = true;
+      break;
+  }
+  m_timer.Start();
+}
+
+bool Debouncer::Calculate(bool 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;
+  }
+}

wpilibc/src/main/native/include/frc/Debouncer.h

@@ -0,0 +1,46 @@
+// 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.
+
+#pragma once
+
+#include <units/time.h>
+
+#include "frc/Timer.h"
+
+namespace frc {
+/**
+ * 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.
+ */
+class Debouncer {
+ public:
+  enum DebounceType { kRising, kFalling, kBoth };
+
+  /**
+   * Creates a new Debouncer.
+   *
+   * @param debounce 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.
+   */
+  explicit Debouncer(units::second_t debounceTime,
+                     DebounceType type = 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.
+   */
+  bool Calculate(bool input);
+
+ private:
+  frc::Timer m_timer;
+  units::second_t m_debounceTime;
+  bool m_baseline;
+  DebounceType m_debounceType;
+};
+}  // namespace frc