// For MPLAB X with the XC8 Compiler
// by Ido Gendel (info AT idogendel.com)

// Connections : Red LED to GP4, Green LED to GP5
// Three momentary buttons from GND to GP0-GP2

#define _XTAL_FREQ 4000000
#include <xc.h>

#pragma config FOSC = INTRCIO   // Oscillator Selection bits (INTOSC oscillator: I/O function on GP4/OSC2/CLKOUT , GP5/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-Up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = OFF      // GP3/MCLR pin function select (GP3/MCLR pin function is digital I/O, MCLR internally tied to VDD)
#pragma config BOREN = OFF      // Brown-out Detect Enable bit (BOD disabled)
#pragma config CP = OFF         // Code Protection bit (Program Memory code protection is disabled)
#pragma config CPD = OFF        // Data Code Protection bit (Data memory code protection is disabled)

#define redLedIO 4
#define greenLedIO 5

char buttonInput() {
  // Reversed logic reversed...
  return 7 - (GPIO & 7);
}

int main() {

  const char secretCode[] = {1, 2, 4 ,2 ,1};
  char codeIndex;

  ANSEL = 0;            // ANalog SELect; all digital
  CMCON = 7;            // CoMparator CONtrol; comparator off
  ADCON0 = 0;           // A/D CONtrol; A/D conversion off
  TRISIO = 7;           // GP0-2 inputs
  OPTION_REG &= 127;    // GPPU clear - pullups enabled
  WPU = 7;              // Internal pull-up on GP0-2

  while (1) {
    
    GPIO = 1 << redLedIO; // Red LED pin High
    codeIndex = 0;

    while (codeIndex < sizeof(secretCode)) {

      // Wait for input on any button, then debounce
      while (!buttonInput()) ;
      __delay_ms(10);

      // Check input
      if (buttonInput() == secretCode[codeIndex]) codeIndex++;
       else codeIndex = (buttonInput() == secretCode[0]) ? 1 : 0;

      // Wait for button release, then debounce
      while (buttonInput()) ;
      __delay_ms(10);

    } // while

    // Correct combination sequence
    GPIO = 1 << greenLedIO; // Green LED pin High
    __delay_ms(1000);

  } // while

  return 0;

} // main