/* 1. Include Library
Purpose: The Keypad.h library simplifies the scanning and debouncing of matrix keypads.
Key Features:
Automatically handles key matrix rows and columns.
Provides the getKey() function to detect key presses. */

#include <Keypad.h> //header for keypad commands enabling


/* 2. Keypad Configuration
rows: Number of horizontal lines in the keypad matrix.
cols: Number of vertical lines in the keypad matrix. */

const byte rows = 4; // Four rows
const byte cols = 4; // Four columns

// Defines the mapping of keys on the keypad
char keys [rows][cols] = 
{{ '1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}};

/* - rowpin: Specifies which STM32 GPIO pins are connected to the keypad rows.
   - colpin: Specifies which STM32 GPIO pins are connected to the keypad columns. */

// Connect keypad ROW1, ROW2, ROW3 and ROW4 to these GPIO pins.
  byte rowpin[rows] = {10,11,12,13};

// Connect keypad COL1, COL2, COL3 and COL4 to these GPIO pins.
  byte colpin[cols] = {6,7,8,9};

/* 3. Create Keypad Object
  - makeKeymap(keys): Converts the keys array into a format usable by the Keypad library.
  - Keypad Constructor Parameters:
      - The keymap (keys).
      - GPIO pins connected to rows (rowpin).
      - GPIO pins connected to columns (colpin).
      - Dimensions of the keypad matrix (rows, cols). */

  Keypad keypad = Keypad( makeKeymap(keys), rowpin, colpin, rows, cols);


/* 4. Setup Function
Serial.begin(9600): Initializes serial communication at a baud rate of 9600.
Serial.println(): Outputs text messages to the serial monitor for user instructions or debugging. */

void setup() {
  
  Serial.begin(9600);
  Serial.println("Hello, Welcome to STM32 Nucleo Keypad Interfacing Demo!");
  Serial.println("Enter Number or Character:");
}

/* 5. Loop Function
keypad.getKey():
  - Continuously scans the keypad for key presses.
  - Returns the character of the pressed key (e.g., '1', 'A').
  - Returns NO_KEY if no key is pressed. */

void loop() {
    char key = keypad.getKey(); //storing pressed key value in a char


/* - Ensures that only valid key presses are processed (key != NO_KEY).
   - Displays the pressed key on the serial monitor.
   - The delay(10) prevents multiple detections of the same key due to bouncing. */

  if (key != NO_KEY){
  Serial.print("Key Pressed: ");
  Serial.println(key);
  delay(10); // this speeds up the simulation 
  }
}