#include "serial.h"

// File device stream for uart
FILE uart_str = FDEV_SETUP_STREAM(uart_putchar, uart_getchar, _FDEV_SETUP_RW);

volatile char serial_rx_index;
// Buffer to hold received string
volatile char serial_rx_buffer[16];
// Flag for ready when return entered
volatile char serial_rx_ready;
// Save character
volatile char serial_rx_char;
// Position in the serial_tx_buffer
volatile char serial_tx_index;
// Buffer to hold transmitting string
volatile char serial_tx_buffer[16];
// Flag for ready once transmission is complete
volatile char serial_tx_ready;
// Current character to send
volatile char serial_tx_char;

/****
 * Handle receiving
 ****/
ISR (USART0_RX_vect) {
  // Save received character
  serial_rx_char = UDR0;
  // Echo
  UDR0 = serial_rx_char;
  // Build the input string
  switch(serial_rx_char) {
  case '\r': // Hit return
    // Send newline
    putchar('\n');
    // Null-terminate 
    serial_rx_buffer[(int)serial_rx_index] = 0x00;
    // Set receive ready
    serial_rx_ready = 1;
    // Turn off interrupt until needed again
    UCSR0B &= ~(1<<RXCIE0);
    break;
  case '\b': // Backspace
    // Erase character from echo above
    putchar(' ');
    // Erase previous char for echo
    putchar('\b');
    // Erase a character in buffer
    serial_rx_index--;
    break;
  default: // Other characters
    // Add character to the buffer
    serial_rx_buffer[(int)serial_rx_index] = serial_rx_char;    
    serial_rx_index++;
  }
}

/****
 * Handle transmitting
 ****/
ISR(USART0_UDRE_vect) {
  // Put character from buffer for transmitting
  serial_tx_char = serial_tx_buffer[(int)++serial_tx_index];
  // If the last character transmitted
  if (serial_tx_char == 0x00) {
    // Disable transmission
    UCSR0B &= ~(1<<UDRIE0);
    // Ready for sending next message
    serial_tx_ready = 1;
  } else {
    // Put char in register for transmitting
    UDR0 = serial_tx_char;
  }
}

char serial_getstr() {
  if (serial_rx_ready == 0) return 1;
  // Serial busy receiving
  serial_rx_ready = 0;
  // Reset index
  serial_rx_index = 0;
  // Enable interrupt for receiving a string
  UCSR0B |= (1<<RXCIE0);
  return 0;
}

char serial_putstr() {
  if (serial_tx_ready == 0) return 1;
  serial_tx_ready = 0;
  serial_tx_index = 0;
  if (serial_tx_buffer[0] > 0) {
    putchar(serial_tx_buffer[0]);
    UCSR0B |= (1<<UDRIE0);
  }
  return 0;
}

void serial_initialize() {
  uart_init();
  stdout = stdin = stderr = &uart_str;
  fprintf(stdout, "S\n\r");
  serial_rx_ready = 1;
  serial_tx_ready = 1;
  sei();
}