#include "userprog/syscall.h"
#include <stdio.h>
#include <syscall-nr.h>
#include "threads/interrupt.h"
#include "threads/thread.h"
#include <string.h>
#include "userprog/process.h"
#include "threads/vaddr.h"
#include "userprog/pagedir.h"

typedef int (*handler) (uint32_t, uint32_t, uint32_t);
static handler syscall_vec[128];

static int sys_write (int fd, const void *buffer, unsigned length);
static int sys_exit (int status);
static int sys_wait (tid_t tid);
static tid_t sys_exec (const char* file_name);
static void syscall_nop(void);

static void syscall_handler (struct intr_frame *);

void
syscall_init (void) 
{
  intr_register_int (0x30, 3, INTR_ON, syscall_handler, "syscall");
  memset(syscall_vec, (int)&syscall_nop, 128);
  syscall_vec[SYS_EXIT] = (handler)sys_exit;
  syscall_vec[SYS_WAIT] = (handler)sys_wait;
  syscall_vec[SYS_EXEC] = (handler)sys_exec;
  syscall_vec[SYS_WRITE] = (handler)sys_write;
}

static void
syscall_nop(void) {
  printf("Syscall not implemented");
}

static void
syscall_handler (struct intr_frame *f) 
{
  handler h;
  int *p;
  int ret;
  
  p = f->esp;
  h = syscall_vec[*p];
  ret = h (*(p + 1), *(p + 2), *(p + 3));
  
  f->eax = ret;
}

static int
sys_write (int fd, const void *buffer, unsigned length) {
  if (fd == 1) { // if stdout 
    putbuf (buffer, length);
    return length;
  } else {
    return -1;
  }
}

int
sys_exit (int status)
{
  struct thread* t = thread_current();
  printf("%s: exit(%d)\n", t->name, status);
  t->exit_status = status;
  thread_exit();
  return -1;
}

int
sys_wait (tid_t tid)
{
  printf("system call wait\n");
  int status = process_wait(tid);
  //printf("wait has returned status(%d)\n", status);
  return status;
}

tid_t
sys_exec (const char* file_name) {
  if (file_name == NULL || is_kernel_vaddr(file_name) || 
      pagedir_get_page(thread_current()->pagedir, file_name) == NULL) {
    return -1;
  }

  return process_execute(file_name);
}