#include <Wire.h>

const int BTN_HANDSET_PINS[] = {PA0, PA1, PA2, PA3, PA4, PA5, PA6, PA7, PA8, PA9, PA10, PA11, PA12, PB13, PB14, PA15, PB0, PB1};
const int NUM_BUTTONS = 18;
bool buttonStates[NUM_BUTTONS];

#define DEBOUNCE_DELAY 50 // Define debounce delay in milliseconds

unsigned long lastDebounceTime[NUM_BUTTONS]; // Store the last debounce time for each button
bool lastButtonState[NUM_BUTTONS]; // Store the last button state

void setup() {
    Wire.begin(8); // Join I2C bus with address #8
    Wire.onRequest(requestEvent); // Register the request event

    for (int i = 0; i < NUM_BUTTONS; i++) {
        pinMode(BTN_HANDSET_PINS[i], INPUT_PULLUP);
        lastButtonState[i] = digitalRead(BTN_HANDSET_PINS[i]);
        buttonStates[i] = false;
        lastDebounceTime[i] = 0;
    }
}

void loop() {
    for (int i = 0; i < NUM_BUTTONS; i++) {
        bool currentState = digitalRead(BTN_HANDSET_PINS[i]);
        if (currentState != lastButtonState[i]) {
            lastDebounceTime[i] = millis(); // Reset the debounce timer
        }
        if ((millis() - lastDebounceTime[i]) > DEBOUNCE_DELAY) {
            if (currentState != buttonStates[i]) {
                buttonStates[i] = currentState;
            }
        }
        lastButtonState[i] = currentState;
    }
}

void requestEvent() {
    uint32_t buttonStateBits = 0;
    for (int i = 0; i < NUM_BUTTONS; i++) {
        if (buttonStates[i] == LOW) { // Button is pressed when state is LOW
            buttonStateBits |= (1 << i);
        }
    }
    Wire.write((uint8_t*)&buttonStateBits, sizeof(buttonStateBits)); // Send the button states over I2C
}