/*
 * con.c
 *
 * Basic VGA text console. Implements printk().
 */

#include <asm/io.h>
#include <kernel/tty.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdio.h>

#define COLS 80
#define ROWS 25

/* internal function prototypes */
static void con_write(void);

struct tty_struct tty_con = {
  .init = NULL,
  .write = &con_write
};

static uint8_t *vram = (uint8_t*) 0xB8000;
static int pos;

static inline void cursorpos(int pos) {
	outb(0x3D4, 0x0E);
	outb(0x3D5, (uint8_t) ((pos >> 9) & 0xFF));
  outb(0x3D4, 0x0F);
	outb(0x3D5, (uint8_t) ((pos >> 1) & 0xFF));
}

/* scrolls the console up one line */
static void scroll_up(void) {
  int n = (COLS * (ROWS - 1)) << 1;
  uint8_t *p = vram;

  while(n--) {
    *p = p[COLS << 1];
    p++;
  }

  p = (uint8_t*) (vram + (COLS * (ROWS - 1) << 1));
  n = COLS;
  while(n--) {
    *p = ' ';
    p += 2;
  }

  pos -= COLS << 1;
  cursorpos(pos);
}

/* clear the console and reset the cursor to the starting position */
void con_clear(void) {
  int n = COLS * ROWS;
  uint8_t *p = vram;

  while(n--) {
    *(p++) = 0x20;
    *(p++) = 0x07;
  }

  pos = 0;
  cursorpos(0);
}

/* must be called before any console output */
void con_init(void) {
  /* clear the console */
  con_clear();
}

/* write a zero-terminated string to console */
static int con_puts(char *s) {
  uint8_t *p = &vram[pos];

  while(*s) {
    if(*s == '\n') {
      pos = (int) (p - vram);
      pos = ((pos / (COLS << 1)) + 1) * (COLS << 1);
      p = &vram[pos];
      s++;
    } else {
      *p = *(s++);
      p += 2;
    }

    pos = (int) (p - vram);

    if(pos >= (COLS * ROWS) << 1)
      scroll_up();
  }

  /* update the cursor position */
  cursorpos(pos);

  /* this always succeeds */
  return 0;
}

/* same as con_puts() but deals with bytes rather than strings */
static void con_write(void) {
  char c;
  int copied = 0;
  uint8_t *p = &vram[pos];
  struct tty_queue *q = &tty_con.wqueue;

  while(q->pread != q->pwrite) {
    c = q->buf[q->pread];
    if(c == '\n') {
      pos = (int) (p - vram);
      pos = ((pos / (COLS << 1)) + 1) * (COLS << 1);
      p = &vram[pos];
    } else {
      *p = c;
      p += 2;
    }

    q->pread = (q->pread + 1) % TTY_BUF_SIZE;
    copied = 1;

    pos = (int) (p - vram);

    if(pos >= (COLS * ROWS) << 1)
      scroll_up();
  }

  /* update the cursor position */
  cursorpos(pos);

  if(copied)
    wake_up(&q->waiting);
}

int printk(char *fmt, ...) {
  int ret;
  char buf[1024];
  va_list ap;

  va_start(ap, fmt);
  ret = vsprintf(buf, fmt, ap);
  va_end(ap);

  con_puts(buf);
  return ret;
}