/*
  serial-display-debounced — QPad XIAO RP2040
  ──────────────────────────────────────────────────────────────
  Bi-directional serial interface for the QPad board:

  PC → Arduino  (key 0):  "0,<text to show on OLED>\n"
  Arduino → PC  (key 1):  "1,<button_index>,<0|1>\n"
                           button_index  0=A  1=B  2=DOWN  3=LEFT  4=RIGHT  5=UP
                           state         0=released  1=pressed

  Baud rate: 9600
  Libraries:  Adafruit SSD1306, Adafruit GFX
  Board:      Seeed XIAO RP2040
              (install via earlephilhower/arduino-pico)

  Change from serial-display.ino:
    Asymmetric debounce: a press is registered immediately on the first
    detected touch so response feels instant.  Release is only confirmed
    after DEBOUNCE_COUNT consecutive "not touched" readings (~60 ms),
    so brief noise dips while holding cannot re-fire a press.
*/

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// ── Display ────────────────────────────────────────────────
#define SCREEN_WIDTH   128
#define SCREEN_HEIGHT   64
#define OLED_RESET      -1
#define SCREEN_ADDRESS 0x3C

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ── Touch buttons ──────────────────────────────────────────
//  Order:  A     B     DOWN  LEFT  RIGHT  UP
const int TOUCH_PINS[]  = {3,    4,    2,    27,   1,     26};
const char* BTN_NAMES[] = {"A",  "B",  "DOWN","LEFT","RIGHT","UP"};
const int NUM_BUTTONS   = 6;

// Capacitive touch threshold (lower = more sensitive).
// Raise if getting false positives; lower if pads feel unresponsive.
const int TOUCH_THRESHOLD = 30;

// Consecutive "not touched" readings required to confirm a release.
// Press fires immediately; only release is debounced.
// At ~50 Hz: 3 × 20 ms = ~60 ms hold-off against noise while held.
const int DEBOUNCE_COUNT = 3;

bool btnCurrent[NUM_BUTTONS];   // confirmed (debounced) state
bool btnLast[NUM_BUTTONS];      // previous confirmed state
int  btnDebounce[NUM_BUTTONS];  // counts consecutive "not touched" readings

// ── State ──────────────────────────────────────────────────
String displayText = "Ready.\nSend text via\nserial port.";


// ── Touch reading ──────────────────────────────────────────
// Matches the algorithm in qpad-xiao/code/Arduino/test_touch_RP2040.
// The pad capacitance is discharged, then we count raw loop iterations
// until the pin rises through INPUT_PULLUP.  A finger on the pad adds
// capacitance and slows the rise → higher count → touch detected.
// digitalWriteFast / digitalReadFast skip Arduino overhead for accuracy.
int touchValue(int pin) {
  int t = 0;
  const int T_MAX = 200;

  pinMode(pin, OUTPUT);
  digitalWriteFast(pin, LOW);
  delayMicroseconds(25);

  pinMode(pin, INPUT_PULLUP);
  while (!digitalReadFast(pin) && t < T_MAX) {
    t++;
  }
  return t;
}

void update_touch() {
  for (int i = 0; i < NUM_BUTTONS; i++) {
    bool reading = touchValue(TOUCH_PINS[i]) > TOUCH_THRESHOLD;
    btnLast[i] = btnCurrent[i];

    if (!btnCurrent[i]) {
      // Currently released: accept a press immediately.
      if (reading) {
        btnCurrent[i]  = true;
        btnDebounce[i] = 0;
      }
    } else {
      // Currently pressed: only release after DEBOUNCE_COUNT consecutive
      // "not touched" readings, so noise dips cannot re-fire a press.
      if (!reading) {
        btnDebounce[i]++;
        if (btnDebounce[i] >= DEBOUNCE_COUNT) {
          btnCurrent[i]  = false;
          btnDebounce[i] = 0;
        }
      } else {
        btnDebounce[i] = 0; // still touched — reset release counter
      }
    }
  }
}


// ── Display helper ─────────────────────────────────────────
void updateDisplay() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setTextWrap(true);
  display.setCursor(0, 0);
  display.print(displayText);
  display.display();
}


// ── Setup ──────────────────────────────────────────────────
void setup() {
  Serial.begin(9600);
  while (!Serial) delay(10);

  Wire.begin();

  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    // Blink built-in LED if display init fails
    pinMode(LED_BUILTIN, OUTPUT);
    while (true) {
      digitalWrite(LED_BUILTIN, LOW);  delay(150);
      digitalWrite(LED_BUILTIN, HIGH); delay(150);
    }
  }

  // Initialise button state
  for (int i = 0; i < NUM_BUTTONS; i++) {
    btnCurrent[i]  = false;
    btnLast[i]     = false;
    btnDebounce[i] = 0;
  }

  updateDisplay();
}


// ── Loop ───────────────────────────────────────────────────
void loop() {

  // ── Read serial commands ──────────────────────────────
  // Expected format:  "0,<text>\n"
  // The text may contain spaces and punctuation but not commas.
  // Use '|' as a manual line-break character if desired.
  if (Serial.available()) {
    String line = Serial.readStringUntil('\n');
    line.trim();

    int comma = line.indexOf(',');
    if (comma > 0) {
      int key = line.substring(0, comma).toInt();

      if (key == 0) {
        // Replace the pipe character with a real newline for multi-line display
        String text = line.substring(comma + 1);
        text.replace("|", "\n");
        displayText = text;
        updateDisplay();
      }
    }
  }

  // ── Read touch buttons ────────────────────────────────
  // Send a message on every confirmed state change (press and release).
  update_touch();
  for (int i = 0; i < NUM_BUTTONS; i++) {
    if (btnCurrent[i] != btnLast[i]) {
      Serial.print("1,");
      Serial.print(i);
      Serial.print(",");
      Serial.println(btnCurrent[i] ? 1 : 0);
    }
  }

  delay(20);  // ~50 Hz poll rate
}