#include <stdio.h>

#include "hardware/gpio.h"
#include "hardware/i2c.h"
#include "pico/stdlib.h"
#include "pico/binary_info.h"
#include "pico/i2c_slave.h"

const uint PIN_DIGIT_BASE = 18;
const uint PIN_SEGMENT_BASE = 2;

const uint N_DIGITS = 4;

const uint I2C_PIN_SDA = 0;
const uint I2C_PIN_SCL = 1;
const uint I2C_SLAVE_ADDRESS = 0x17;
const uint I2C_RATE = 100 * 1000;

uint8_t digit_states[4] = { 0 };
static struct {
  bool digit_written;
  uint digit;
} i2c_context;

static void write_digit(uint8_t digit) {
  const uint mask = (0xffffffff << PIN_SEGMENT_BASE) ^ (0xffffffff << PIN_SEGMENT_BASE + 8);
  gpio_put_masked(mask, (~digit & 0xff) << PIN_SEGMENT_BASE);
  gpio_put_masked(mask, digit << PIN_SEGMENT_BASE);
}
static void setup_io() {
  for (uint i = PIN_DIGIT_BASE; i < PIN_DIGIT_BASE + N_DIGITS; i++) {
    gpio_init(i);
    gpio_set_dir(i, GPIO_OUT);
    gpio_put(i, 0);
  }
  for (uint i = PIN_SEGMENT_BASE; i < PIN_SEGMENT_BASE + 8; i++) {
    gpio_init(i);
    gpio_set_dir(i, GPIO_OUT);
  }
  write_digit(0);
}
static void display_loop() {
  for (uint i = 0; i < N_DIGITS; i++) {
    uint prev = i == 0 ? N_DIGITS - 1 : i - 1;

    gpio_put(PIN_DIGIT_BASE + prev, 0);
    sleep_us(100);

    write_digit(digit_states[i]);
    gpio_put(PIN_DIGIT_BASE + i, 1);
    sleep_ms(1);
  }
}

static void i2c_slave_handler(i2c_inst_t *i2c, i2c_slave_event_t event) {
  switch (event) {
  case I2C_SLAVE_RECEIVE: // master has written some data
    if (!i2c_context.digit_written) {
        // writes always start with the memory address
        uint8_t addr = i2c_read_byte_raw(i2c);
        i2c_context.digit = addr < N_DIGITS ? addr : -1;
        i2c_context.digit_written = true;
    } else if (i2c_context.digit != -1) {
        // save into memory
        digit_states[i2c_context.digit] = i2c_read_byte_raw(i2c);
    }
    break;
  case I2C_SLAVE_REQUEST: // master is requesting data
    // load from memory
    uint8_t data = i2c_context.digit != -1 ? digit_states[i2c_context.digit] : 0;
    i2c_write_byte_raw(i2c, data);
    break;
  case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
    i2c_context.digit_written = false;
    break;
  default:
    break;
  }
}
static void setup_i2c() {
  gpio_init(I2C_PIN_SDA);
  gpio_set_function(I2C_PIN_SDA, GPIO_FUNC_I2C);
  gpio_pull_up(I2C_PIN_SDA);

  gpio_init(I2C_PIN_SCL);
  gpio_set_function(I2C_PIN_SCL, GPIO_FUNC_I2C);
  gpio_pull_up(I2C_PIN_SCL);

  i2c_init(i2c0, I2C_RATE);
  // configure I2C0 for slave mode
  i2c_slave_init(i2c0, I2C_SLAVE_ADDRESS, &i2c_slave_handler);
}

int main() {
  bi_decl(bi_program_description("qCLK driver."));

  stdio_init_all();
  setup_io();
  setup_i2c();

  while (1) display_loop();
}