/*
  matrix-scan a set of LEDs

  pins:

  "rows" 12 & 13 go to a 220Ω resistor, then to 2 LEDs each (positive
  / long stem side); also to a 10kΩ resistor then to 2
  phototransistors (collector / long stem side)

  also, from between the 10kΩ and the phototransistors, wire goes to
  A1 & A2

  "columns"
  14 & 15 go to 2 LEDs each (negative / short stem side)

  so that given one of 12|13 and one of 14|15, one LED is identified
 */

#include <driver/dac.h>

hw_timer_t * timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;

bool play = false;
int wave_pos = 0;
int wave_period = 1000;

// stupid square wave
int wave() {
  if (wave_pos < wave_period/2) {
    return 255;
  }
  else {
    return 0;
  }
}

void IRAM_ATTR onTimer() {
  portENTER_CRITICAL_ISR(&timerMux);

  if (play) {
    dac_output_voltage(DAC_CHANNEL_1, wave());
    wave_pos = (wave_pos+1)%wave_period;
  }

  portEXIT_CRITICAL_ISR(&timerMux);
}


int currentLed = 0;
int lastSeen = 100;

const int rows[] = { 5, 23, 19, 18, 26 };
const int cols[] = { 34, 33, 35, 21, 22 };
const int adc[] = { 2, 4, 12, 27, 14 };
const int ampEnable = 32;

void setup() {
  Serial.begin(19200);

  pinMode(ampEnable, OUTPUT);

  for (int i=0;i<5;++i) {
    pinMode(rows[i], OUTPUT);
    pinMode(cols[i], OUTPUT);
    pinMode(adc[i], INPUT);
  }

  currentLed = 0;
  lastSeen = 100;

  timer = timerBegin(0, 2, true); // use a prescaler of 2
  timerAttachInterrupt(timer, &onTimer, true);
  timerAlarmWrite(timer, 5000, true);
  timerAlarmEnable(timer);

  play=true;
}

void tristate(int pin) {
  pinMode(pin,OUTPUT);
  digitalWrite(pin,LOW);
  pinMode(pin,INPUT);
}

void power(int pin) {
  pinMode(pin,OUTPUT);
  digitalWrite(pin,HIGH);
}

void ground(int pin) {
  pinMode(pin,OUTPUT);
  digitalWrite(pin,LOW);
}

void enableLed(int led) {
  int row = led/5;
  int col = led%5;
  /* Serial.print("enabling "); */
  /* Serial.print(row); */
  /* Serial.print(" "); */
  /* Serial.println(col); */

  for (int i=0;i<5;++i) {
    if (i==row) { power(rows[i]); }
    else { ground(rows[i]); }

    if (i==col) { ground(cols[i]); }
    else { tristate(cols[i]); }
  }
}

int sense(int led) {
  int row = led/5;

  int value = analogRead(adc[row]);

  //Serial.println(value);
  return value < 500;
}

void loop() {
  /* Serial.print("current led "); */
  /* Serial.println(currentLed); */

  enableLed(currentLed);
  delay(1);
  if (sense(currentLed)) {
    if (lastSeen != currentLed) {
      lastSeen = currentLed;
      Serial.print(currentLed);
      Serial.println(" proximity!");
    }
  }
  else if (lastSeen == currentLed) {
    lastSeen = 100;
  }

  currentLed = (currentLed+1)%25;
}