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#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

#include "tiny-twi.h"

#define SDA PB0

#define SCL PB2

#define RECV_BUF_SIZE 3

#define SEND_BUF_SIZE 100

uint8_t address;

typedef enum {

  IDLE,

  ADDRESS,

  SEND_READ_ACK,

  SEND_WRITE_ACK,

  SEND_DATA,

  RECV_DATA,

  RECV_ACK

} state_t;

state_t state;

uint8_t recv_idx;

uint8_t recv_data[RECV_BUF_SIZE];

slave_rx_t onDataRecieved;

typedef struct {

  uint8_t start;

  uint8_t end;

  uint8_t data[SEND_BUF_SIZE];

  bool    full;

} queue;

queue send_queue;

static void twi_set_ctr(char n) {

  USISR = n;

}

static void twi_ready() {

  USISR = _BV(USISIF) | _BV(USIOIF) | _BV(USIPF) | _BV(USIDC);

  DDRB |= _BV(SCL);  //SCL output

  DDRB &= ~_BV(SDA); //SDA input

  // enable start condition interrupt

  USICR |= _BV(USISIE);

  // disable counter overflow interrupt

  USICR &= ~_BV(USIOIE);

  state = IDLE;

}

static void twi_start() {

  // enable counter overflow interrupt (fires after 8 bits)

  USICR |= _BV(USIOIE);

  USISR = _BV(USISIF);

  // zero counter

  twi_set_ctr(0);

  state = ADDRESS;

  recv_idx = 0;

}

static void twi_send_ack(char is_read) {

  // set counter to 14

  twi_set_ctr(14);

  // set SDA low

  USIDR = 0;

  DDRB |= _BV(SDA);

  // set state

  state = is_read? SEND_READ_ACK : SEND_WRITE_ACK;

}

static void twi_send_data() {

  twi_set_ctr(0);

  if (send_queue.start == send_queue.end && !send_queue.full) {

    USIDR = 0xFF;

  } else {

    USIDR = send_queue.data[send_queue.start++];

    if (send_queue.start == SEND_BUF_SIZE)

      send_queue.start = 0;

    send_queue.full = 0;

  }

  DDRB |= _BV(SDA);

  state = SEND_DATA;

}

static void twi_recv_ack() {

  twi_set_ctr(14);

  DDRB &= ~_BV(SDA);

  state = RECV_ACK;

}

ISR(USI_START_vect) {

  twi_start();

}

ISR(USI_OVF_vect) {

  uint8_t input = USIDR; // TODO make sure this is correct

  switch (state) {

    case IDLE:

      // shouldn't reach here

      twi_ready();

      break;

    case ADDRESS:

      if (input >> 1 == address) {

        // send ack

        twi_send_ack(input & 1);

      } else {

        // go back to listening for start condition

        twi_ready();

      }

      break;

    case SEND_WRITE_ACK:

      if (recv_idx == RECV_BUF_SIZE) {

        twi_ready();

        onDataRecieved(recv_data, RECV_BUF_SIZE);

      } else {

        DDRB &= ~_BV(SDA);

        state = RECV_DATA;

      }

      break;

    case RECV_DATA:

      twi_send_ack(0);

      recv_data[recv_idx] = input;

      recv_idx++;

      break;

    case SEND_READ_ACK:

      twi_send_data();

      break;

    case SEND_DATA:

      twi_recv_ack();

      break;

    case RECV_ACK:

      if (input & 1) {

        // received nak

        twi_ready();

      } else {

        // received ack

        twi_send_data();

      }

      break;

  }

  USISR = _BV(USIOIF) | (USISR & 0xF);

}

void smb_init(slave_rx_t callback) {

  // TODO do we want USICS0 (3)?

  USICR = _BV(USIWM1) | _BV(USIWM0) | _BV(USICS1);

  PORTB |= _BV(SDA) | _BV(SCL);

  twi_ready();

  onDataRecieved = callback;

}

void smb_set_address(uint8_t addr) {

  address = addr;

}

void smb_send_data(uint8_t* data, uint8_t length) {

  uint8_t i;

  for (i=0; i<length && !send_queue.full; i++) {

    send_queue.data[send_queue.end++] = data[i];

    if (send_queue.end == SEND_BUF_SIZE)

      send_queue.end = 0;

    if (send_queue.end == send_queue.start)

      send_queue.full = 1;

  }

}