/*
  * Foot pedal prototype
  */

#include <HID.h>
#include <Keyboard.h>

#define PIN_CTRL    2
#define PIN_ALT     3
#define PIN_SHIFT   4

#define MASK_CTRL   (1 << PIN_CTRL)
#define MASK_ALT    (1 << PIN_ALT)
#define MASK_SHIFT  (1 << PIN_SHIFT)

#define IDLE_DELAY  100

#define READ_PIN(key) digitalRead(PIN_##key) == LOW ? MASK_##key : 0
#define TOGGLE_KEY(key)                           \
 if (key ^ (pin_stat & MASK_##key)) {             \
   if (key) Keyboard.press(KEY_LEFT_##key);       \
   else Keyboard.release(KEY_LEFT_##key);         \
 }

unsigned int pin_stat;

void setup() {
  pin_stat = 0;
  pinMode(PIN_CTRL, INPUT_PULLUP);
  pinMode(PIN_ALT, INPUT_PULLUP);
  pinMode(PIN_SHIFT, INPUT_PULLUP);
  Keyboard.begin();
}

void loop() {
  unsigned int CTRL = READ_PIN(CTRL);
  unsigned int ALT = READ_PIN(ALT);
  unsigned int SHIFT = READ_PIN(SHIFT);
  if ((CTRL | ALT | SHIFT) == pin_stat) {
    delay(IDLE_DELAY);
    return;
  }

  TOGGLE_KEY(CTRL);
  TOGGLE_KEY(ALT);
  TOGGLE_KEY(SHIFT);
  pin_stat = CTRL | ALT | SHIFT;
  delay(IDLE_DELAY);
}