#include <stdint.h>
#include <avr/io.h>
#include <util/delay.h>

#define MX0_PIN 4
#define MX1_PIN 5
#define MX2_PIN 6
#define MX3_PIN 7
#define DEC_PIN 8
#define INC_PIN 9

#define BAUD_RATE  16000000/16/31250-1 // 31250bps  // todo: detect actual baud rate?

class Encoder {
  public:
  byte state;
  int  value;

  Encoder(){
    state = 0;
    value = 0;
  }

  void next(byte tuple){
    if ((state & 0b11) == tuple)
      return;

    state = ((state << 2 ) | tuple ) & 0b111111;

    switch (state){
      case 0b011100:
      case 0b011110:
      case 0b001110:
        value = max( -64, value - 1 );
        break;

      case 0b101100:
      case 0b101101:
      case 0b001101:
        value = min( 63, value + 1 );
        break;
    }
  }

  boolean hasUpdate(){
    return value != 0;
  }

  byte getUpdate(){
    byte result = value;
    value = 0;
    return result;
  }

};


int main(){

  Encoder encs[8];
  byte ctl[8] = {0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70};

  pinMode(MX0_PIN, OUTPUT); /* multiplexer switch bits https://www.ti.com/lit/ds/symlink/cd74hc4067.pdf */
  pinMode(MX1_PIN, OUTPUT);
  pinMode(MX2_PIN, OUTPUT);

  pinMode(MX3_PIN, OUTPUT);
  digitalWrite(MX3_PIN, 0);

  pinMode(INC_PIN, INPUT_PULLUP );
  digitalWrite(INC_PIN, HIGH);

  pinMode(DEC_PIN, INPUT_PULLUP );
  digitalWrite(DEC_PIN, HIGH);

  unsigned int ubrr = BAUD_RATE;

  /* Set Baudrate  */
  UBRR0H = (ubrr>>8); // Shift the 16bit value ubrr 8 times to the right and transfer the upper 8 bits to UBBR0H register.
  UBRR0L = (ubrr);    // Copy the 16 bit value ubrr to the 8 bit UBBR0L register,Upper 8 bits are truncated

  UCSR0C = 0x06;       /* Set frame format: 8data, 1stop bit  */
  UCSR0B = (1<<TXEN0); /* Enable  transmitter   */


  byte tx1 = 0xFF;
  byte tx2 = 0xFF;

  for(;;){
    for (byte i = 0; i < 8; i++ ){
      digitalWrite( MX0_PIN, i & 1 );
      digitalWrite( MX1_PIN, (i>>1) & 1 );
      digitalWrite( MX2_PIN, (i>>2) & 1 );

      byte tuple = ((digitalRead( INC_PIN ) << 1) | digitalRead( DEC_PIN )) ^ 0B11;

      encs[i].next( tuple );

      if ((UCSR0A & (1<<UDRE0))) {

        if (tx1 != 0xFF){ /* has pending byte */

          UDR0 = tx1;
          tx1 = tx2;
          tx2 = 0xFf; /* poor man's queue */

        } else if (encs[i].hasUpdate()) {

          UDR0 = 0xBA; /* hardcoded midi status byte */
          tx1 = ctl[ i ]; /* controller number */
          tx2 = encs[i].getUpdate() & 0x7F; /* increment */

        }
      }
    }
  }
}