#include "uart_16550.h"
#include <stddef.h>

int
uart_thre(enum UART port)
{
  return inb(port + LineStatus) & THRE;
}

void
uart_putc(const FILE *self, char a)
{
  while (uart_thre((enum UART)self->id) == 0) {}
  outb(a, self->id);

  if (a == '\n') {
    while (uart_thre((enum UART)self->id) == 0) {}
    outb('\r', self->id);
  }
}

int
uart_puts(const FILE *self, const char *string, int length)
{
  int written = 0;

  if (length == -1)
    while (*string != '\0') {
      uart_putc(self, *string);
      ++string;
      ++written;
    }

  else
    for (int i = 0; i < length; ++i) {
      uart_putc(self, string[i]);
      ++written;
    }

  return written;
}

void
uart_flush(__attribute__((unused)) const FILE *self)
{
}

FILE uart_stream;

FILE *
uart_init(enum UART port)
{
  outb(0x00, port + 1); // Disable all interrupts
  outb(0x80, port + 3); // Enable DLAB (set baud rate divisor)
  outb(0x03, port + 0); // Set divisor to 3 (lo byte) 38400 baud
  outb(0x00, port + 1); //                  (hi byte)
  outb(0x03, port + 3); // 8 bits, no parity, one stop bit
  outb(0xc7, port + 2); // Enable FIFO, clear them, with 14-byte threshold
  outb(0x0b, port + 4); // IRQs enabled, RTS/DSR set
  outb(0x1e, port + 4); // Set in loopback mode, test the serial chip
  outb(0xae, port + 0); // Test serial chip (send byte 0xAE and check if serial
                        // returns same byte)

  // Check if serial is faulty (i.e: not same byte as sent)
  if (inb(port + 0) != 0xae) { return NULL; }

  // If serial is not faulty set it in normal operation mode
  // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
  outb(0x0f, port + 4);
  uart_stream.id = port;
  uart_stream.putc = &uart_putc;
  uart_stream.puts = &uart_puts;
  uart_stream.flush = &uart_flush;
  return &uart_stream;
}