#include <avr/wdt.h>

#define KEYBD_DATA_PIN 4

const unsigned char scancode_to_apple[] PROGMEM = {
 //$0    $1    $2    $3    $4    $5    $6    $7    $8    $9    $A    $B    $C    $D    $E    $F
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //$00
  0x00, 0x00, 0x00, 0x00, 0x00, 0xD1, 0xB1, 0x00, 0x00, 0x00, 0xDA, 0xD3, 0xC1, 0xD7, 0xB2, 0x00, //$10
  0x00, 0xC3, 0xD8, 0xC4, 0xC5, 0xB4, 0xB3, 0x00, 0x00, 0xA0, 0xD6, 0xC6, 0xD4, 0xD2, 0xB5, 0x00, //$20
  0x00, 0xCE, 0xC2, 0xC8, 0xC7, 0xD9, 0xB6, 0x00, 0x00, 0x00, 0xCD, 0xCA, 0xD5, 0xB7, 0xB8, 0x00, //$30
  0x00, 0xAC, 0xCB, 0xC9, 0xCF, 0xB0, 0xB9, 0x00, 0x00, 0xAE, 0xAF, 0xCC, 0xBB, 0xD0, 0xAD, 0x00, //$40
  0x00, 0x00, 0xA7, 0x00, 0x00, 0xBD, 0x00, 0x00, 0x00, 0x00, 0x8D, 0x00, 0x00, 0x00, 0x00, 0x00, //$50
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x00, 0x00, 0xB1, 0x00, 0xB4, 0xB7, 0x00, 0x00, 0x00, //$60
  0xB0, 0xAE, 0xB2, 0xB5, 0xB6, 0xB8, 0x9B, 0x00, 0x00, 0xAB, 0xB3, 0xAD, 0xAA, 0xB9, 0x00, 0x00,  //$70
  // High mirror, shift modified keys
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //$80 0
  0x00, 0x00, 0x00, 0x00, 0x00, 0xD1, 0xA1, 0x00, 0x00, 0x00, 0xDA, 0xD3, 0xC1, 0xD7, 0xC0, 0x00, //$90 1
  0x00, 0xC3, 0xD8, 0xC4, 0xC5, 0xA4, 0xA3, 0x00, 0x00, 0xA0, 0xD6, 0xC6, 0xD4, 0xD2, 0xA5, 0x00, //$A0 2
  0x00, 0xCE, 0xC2, 0xC8, 0xC7, 0xD9, 0xDE, 0x00, 0x00, 0x00, 0xCD, 0xCA, 0xD5, 0xA6, 0xAA, 0x00, //$B0 3
  0x00, 0xBC, 0xCB, 0xC9, 0xCF, 0xA9, 0xA8, 0x00, 0x00, 0xBE, 0xBF, 0xCC, 0xBA, 0xD0, 0xAD, 0x00, //$C0 4 
  0x00, 0x00, 0xA2, 0x00, 0x00, 0xAB, 0x00, 0x00, 0x00, 0x00, 0x8D, 0x00, 0x00, 0x00, 0x00, 0x00, //$D0 5
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x00, 0x00, 0xB1, 0x00, 0xB4, 0xB7, 0x00, 0x00, 0x00, //$E0 6
  0xB0, 0xAE, 0xB2, 0xB5, 0xB6, 0xB8, 0x9B, 0x00, 0x00, 0xAB, 0xB3, 0xAD, 0xAA, 0xB9, 0x00, 0x00  //$F0 7
};

// keyboard scan buffer
unsigned short keyboard_data[3] = {0, 0, 0};
unsigned char keyboard_buf_indx = 0, keyboard_mbyte = 0;
boolean shift_enabled = false;

// In apple II scancode format
volatile unsigned char keymem = 0;

unsigned char keyboard_read() {
  return keymem;
}

void keyboard_strobe() {
  keymem&=0x7F;
}

// clock must be on digital 3
void keyboard_begin() {
  pinMode(3, INPUT_PULLUP);
  pinMode(KEYBD_DATA_PIN, INPUT_PULLUP);
  attachInterrupt(1, keyboard_bit, FALLING);
}

void keyboard_bit() {
  if(digitalRead(KEYBD_DATA_PIN))keyboard_data[2] |= _BV(keyboard_buf_indx);
  else keyboard_data[2] &= ~(_BV(keyboard_buf_indx));
  if(++keyboard_buf_indx == 11) {
    // Ignore parity checks for now
    keyboard_data[2] = (keyboard_data[2]>>1)&0xFF;
    
    // extended keys
    if(keyboard_data[2] == 0xF0 || keyboard_data[2] == 0xE0) keyboard_mbyte = 1;
    else {
      //decrement counter for multibyte commands
      if(keyboard_mbyte) keyboard_mbyte--;
      // multibyte command is finished / normal command, process it
      if(!keyboard_mbyte) {
        if(keyboard_data[1] != 0xF0 && keyboard_data[1] != 0xE0) {
          //Standard keys
          if(keyboard_data[2] == 0x12 || keyboard_data[2] == 0x59) shift_enabled = true; //shift modifiers
          else keymem = pgm_read_byte_near(scancode_to_apple+keyboard_data[2]+((shift_enabled)?0x80:0x00));
        } else if(keyboard_data[0] != 0xF0 && keyboard_data[1] == 0xE0) {
          //Extended keys
          if(keyboard_data[2] == 0x6B) keymem = 0x95; //back key
          if(keyboard_data[2] == 0x74) keymem = 0x88; //forward key
          // Power management keys, hardware reset
          if(keyboard_data[2] == 0x37) {
            // enable watchdog with min timeout
            // wait until reset
            wdt_enable(WDTO_15MS);
            for(;;);            
          }
        } else if(keyboard_data[1] == 0xF0 && (keyboard_data[2] == 0x12 || keyboard_data[2] == 0x59)) shift_enabled = false;  
      }      
    }

    //shuffle buffer
    keyboard_data[0] = keyboard_data[1];
    keyboard_data[1] = keyboard_data[2];
    keyboard_buf_indx = 0;
  }
}