#include "uart.h"
#include <stddef.h>
#include <sys/io.h>

enum uart_16550_offset {
  Data = 0,             // read from receive buffer / write to transmit buffer | BaudDiv_l
  InterruptControl = 1, // interrupt enable | BaudDiv_h
  FifoControl = 2,      // interrupt ID and FIFO control
  LineControl = 3,      // most significant bit is the DLAB
  ModemControl = 4,
  LineStatus = 5,
  ModemStatus = 6,
  Scratch = 7,
};
// Line Control
// | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
// |dla|   | parity    | s | data  |

enum LineControl {
  d5bit = 0x00, // 0000 0000  data bits
  d6bit = 0x01, // 0000 0001
  d7bit = 0x02, // 0000 0010
  d8bit = 0x03, // 0000 0011
  // none = 0b00000000, // parity bits
  odd = 0x08,   // 0000 1000
  even = 0x18,  // 0001 1000
  mark = 0x28,  // 0010 1000
  space = 0x38, // 0011 1000
  // s1bit = 0b00000000, // stop bits
  s2bit = 0x04, // 0000 0100  1.5 for 5bit data; 2 otherwise
  dlab = 0x80   // 1000 0000  divisor latch access bit
};

// Line Status Register
enum LineStatus {
  DR = (1 << 0),   // data ready: see if there is data to read
  OE = (1 << 1),   // overrun error: see if there has been data lost
  PE = (1 << 2),   // parity error: see if there was error in transmission
  FE = (1 << 3),   // framing error: see if a stop bit was missing
  BI = (1 << 4),   // break indicator: see if there is a break in data input
  THRE = (1 << 5), // transmitter holding register empty: see if transmission buffer is empty
  TEMT = (1 << 6), // transmitter empty: see if transmitter is not doing anything
  ERRO = (1 << 7), // impending error: see if there is an error with a word in the input buffer
};

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

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

  if (a == '\n') {
    while (uart_thre(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_write(self, *string);
      ++string;
      ++written;
    }

  else
    for (int i = 0; i < length; ++i) {
      uart_write(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_write;
  uart_stream.puts = &uart_puts;
  uart_stream.flush = &uart_flush;
  return &uart_stream;
}