#include <asm/interrupt.h>
#include <asm/io.h>
#include <errno.h>
#include <kernel/con.h>
#include <kernel/sched.h>
#include <sys/types.h>
#include <unistd.h>

/* 115200 baud */
#define DIVISOR 1

#define RSBASE 0x3F8

#define RSDATA    RSBASE
#define RSINTEN   (RSBASE + 1)
#define RSFIFOC   (RSBASE + 2)
#define RSLINEC   (RSBASE + 3)
#define RSMODEMC  (RSBASE + 4)
#define RSLINES   (RSBASE + 5)
#define RSMODEMS  (RSBASE + 6)
#define RSSCRATCH (RSBASE + 7)

#define rswait()\
  while((inb(RSLINES) & 0x20) == 0);

extern void rs_isr(void);

static char present;

static char rxbuf[256];
static unsigned rxread, rxwrite;
static struct task_struct *waiting_task;

int rsputs(char *s) {
  if(!present)
    return -ENXIO;

  while(*s) {
    rswait();
    if(*s == '\n' || *s == '\r') {
      outb(RSDATA, '\n');
      rswait();
      outb(RSDATA, '\r');
      s++;
    } else {
      outb(RSDATA, *s++);
    }
  }

  return 0;
}

void serial_init(void) {
  present = 0;

  outb(RSSCRATCH, 0x00);
  outb(RSSCRATCH, 0xAA);
  if(inb(RSSCRATCH) != 0xAA) {
    printk("[rs] COM0 not detected!\n");
    return;
  }

  /* enable access to the divisor */
  outb(RSLINEC, inb(RSLINEC) | 0x80);
  /* write the divisor */
  outb(RSBASE, DIVISOR);
  outb(RSBASE + 1, DIVISOR >> 8);
  /* restore access to the divisor */
  outb(RSLINEC, inb(RSLINEC) & 0x7F);
  /* configure port parameters */
  outb(RSFIFOC, 0x06);
  outb(RSLINEC, 0x03);
  outb(RSMODEMC, 0x0B);
  outb(RSINTEN, 0x01);
  inb(RSDATA);
  /* register the interrupt handler */
  register_isr(0x24, 0, &rs_isr);
  irq_enable(0x10);

  rsputs("[kernel] Serial monitor initialized!\n\r");
  printk("[rs] Serial port COM0 initialized!\n");

  rxread = 0;
  rxwrite = 1;
  waiting_task = NULL;
  present = 1;
}

ssize_t rsread(void *buf, size_t len) {
  ssize_t n = len;
  char *b = buf;

  if(!present)
    return -ENXIO;

  if(len == 0)
    return 0;

  while(n--) {
    if(rxread == rxwrite) {
      /* put the current task to sleep */
      waiting_task = ctask;
      ctask->state = TSTATE_INTERRUPTIBLE;
      reschedule();
    }
    /* check again to see if anything was read, or we were interrupted */
    if(rxread == rxwrite) {
      waiting_task = NULL;
      return -EINTR;
    }

    *b++ = rxbuf[rxread];
    rxread = rxread + 1 % sizeof(rxbuf);
  }

  return len;
}

void rs_handler(void) {
  if((inb(RSLINES) & 1) == 0)
    return;
  if(rxwrite == (rxread - 1 % sizeof(rxbuf)))
    return;
  rxbuf[rxwrite] = inb(RSDATA);
  rxwrite = rxwrite + 1 % sizeof(rxbuf);

  if(waiting_task != NULL) {
    waiting_task->state = TSTATE_RUNNING;
    waiting_task = NULL;
  }
}