#include <asm/interrupt.h>
#include <errno.h>
#include <kernel/con.h>
#include <kernel/sched.h>
#include <kernel/serial.h>
#include <kernel/tty.h>
#include <limits.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#define NRTTY \
  (sizeof(ttys) / sizeof(struct tty_struct*))

static struct tty_struct *ttys[] = {
  &tty_con,
  &tty_rs
};

/* check if a buffer's empty and if so, go to sleep */
static int sleep_while_empty(struct tty_queue *q) {
  cli();
  for(;;) {
    if(q->pread == q->pwrite)
      interruptible_sleep_on(&q->waiting);

    /* check again to see if anything was read, or we were interrupted */
    if(q->pread == q->pwrite) {
      sti();
      return -1;
    }

    sti();
    return 0;
  }
}

/* check if a buffer's full and if so, go to sleep */
static int sleep_while_full(struct tty_queue *q, struct tty_struct *tty) {
  cli();
  for(;;) {
    /*
     * if the buffer is full, first notify the
     * driver so it can try to remove some
     * data then, check again and if it's
     * still full, go to sleep.
     */
    if(q->pwrite == ((q->pread - 1) % sizeof(q->buf)))
      if(tty->write)
        tty->write();

    if(q->pwrite == ((q->pread - 1) % sizeof(q->buf)))
      interruptible_sleep_on(&q->waiting);

    /* check again to see if anything was removed, or we were interrupted */
    if(q->pwrite == ((q->pread - 1) % sizeof(q->buf))) {
      sti();
      return -1;
    }

    sti();
    return 0;
  }
}

ssize_t tty_read(unsigned tty, void *buf, size_t len) {
  size_t i;
  char *b = buf;
  struct tty_queue *q = &ttys[tty]->rqueue;

  if(tty > NRTTY || ttys[tty] == NULL)
    return -1;

  if(len == 0)
    return 0;

  if(len > SSIZE_MAX)
    len = SSIZE_MAX;

  for(i = 0; i < len; i++) {
    /* check if the buffer's empty and if so, go to sleep */
    if(sleep_while_empty(q) < 0)
      return i == 0 ? -EINTR : i;

    *b++ = q->buf[q->pread];
    q->pread = (q->pread + 1) % TTY_BUF_SIZE;
  }

  return len;
}

ssize_t tty_write(unsigned tty, void *buf, size_t len) {
  size_t i;
  char *b = buf;
  struct tty_queue *q = &ttys[tty]->wqueue;

  if(tty > NRTTY || ttys[tty] == NULL)
    return -1;

  if(len == 0)
    return 0;

  if(len > SSIZE_MAX)
    len = SSIZE_MAX;

  for(i = 0; i < len; i++) {
    /* check if the buffer's full and if so, go to sleep */
    if(sleep_while_full(q, ttys[tty]) < 0)
      return i == 0 ? -EINTR : i;

    q->buf[q->pwrite] = *b++;
    q->pwrite = (q->pwrite + 1) % TTY_BUF_SIZE;
  }

  /* tell the driver that new data is available */
  cli();
  if(ttys[tty]->write)
    ttys[tty]->write();
  sti();

  return len;
}

void tty_init(void) {
  int i;

  for(i = 0; i < NRTTY; i++) {
    if(!ttys[i])
      continue;

    memset(&ttys[i]->rqueue, 0, sizeof(struct tty_queue));
    memset(&ttys[i]->wqueue, 0, sizeof(struct tty_queue));

    if(ttys[i]->init)
      ttys[i]->init();
  }
}