#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/gpio.h"
#include "esp_log.h"

void setup_gpio();
char scan_keypad();

#define ROWS 4
#define COLS 4


int scanRowPins[ROWS] = {0, 45, 48, 47};
int colPins[COLS] = {38, 37, 36, 35};


char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'},
};

void app_main() {
  setup_gpio();
  while (1) {
    char key = scan_keypad();
    if (key != '\0') {
      printf("You pressed: %c\n", key);
    }
    vTaskDelay(pdMS_TO_TICKS(50));
  }
}

void setup_gpio() {
  for (int i = 0; i < ROWS; i++) {
    gpio_set_direction(scanRowPins[i], GPIO_MODE_OUTPUT);
    gpio_set_level(scanRowPins[i], 1);
  }
  for (int i = 0; i < COLS; i++) {
    gpio_set_direction(colPins[i], GPIO_MODE_INPUT);
    gpio_set_pull_mode(colPins[i], GPIO_PULLUP_ONLY); // all buttons are set as pullup configuration using the internal pullup resistor in the microcontroller
  }
}

char scan_keypad() {
  uint8_t scanVal = '\0';
  for (int i = 0; i < ROWS; i++) {
    scanVal = ~(0 << i);

    for (int j = 0; j < ROWS; j++) {
      gpio_set_level(scanRowPins[j], (scanVal >>j) & 1); // here, 'pins' can be either row pins or column pins. Select the correct one
    }
    vTaskDelay(pdMS_TO_TICKS(5));

    for (int k = 0; k < COLS; k++) {
      if (gpio_get_level(colPins[k]) == 0) { // pullup configuration
        while (gpio_get_level(colPins[k]) == 0) {
          vTaskDelay(pdMS_TO_TICKS(50));
        }
        return keys[i][k];
      }
    }

  }
  return '\0';
}