#include "types.h"
#include "defs.h"
#include "param.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "fs.h"
#include "file.h"
#include "x86.h"
#include "errno.h"

extern int consoleread(struct inode*, uint64, char*, int);
extern int consolewrite(struct inode*, uint64, char*, int);
extern int mouseread(struct inode*, uint64, char*, int);

static uint64 rseed = 0x2A99554433221100ULL;

int
nullwrite(struct inode *ip, uint64 off, char *dst, int n)
{
  return n;
}

int
nullread(struct inode *ip, uint64 off, char *dst, int n)
{
  return 0;
}

int
zeroread(struct inode *ip, uint64 off, char *dst, int n)
{
  memset(dst, 0, n);
  return n;
}

int
randomread(struct inode *ip, uint64 off, char *dst, int n)
{
  for(int i = 0; i < n; i++){
    rseed = rseed * 6364136223846793005ULL + 1442695040888963407ULL;
    dst[i] = (rseed >> 32) & 0xFF;
  }
  return n;
}

// /dev/full — reads as an endless run of zero bytes, every write fails with
// ENOSPC. Programs use it to exercise their out-of-disk-space paths.
int
fullwrite(struct inode *ip, uint64 off, char *dst, int n)
{
  return -ENOSPC;
}

int
mousewrite(struct inode *ip, uint64 off, char *dst, int n)
{
  return n;
}

int
memread(struct inode *ip, uint64 off, char *dst, int n)
{
  switch(ip->minor) {
    case 1: return consoleread(ip, off, dst, n); 
    case 2: return nullread(ip, off, dst, n);    
    case 3: return consoleread(ip, off, dst, n);
    /* 10 = /dev/tty, 11..16 = /dev/tty1..tty6. consoleread resolves the
       minor to a terminal; see vt_for_minor(). */
    case 10: case 11: case 12: case 13: case 14: case 15: case 16:
            return consoleread(ip, off, dst, n);
    case 5: return zeroread(ip, off, dst, n);
    case 7: return zeroread(ip, off, dst, n);   // /dev/full reads as zeros
    case 8: 
    case 9: return randomread(ip, off, dst, n);  
    default: return -1;
  }
}

int
memwrite(struct inode *ip, uint64 off, char *dst, int n)
{
  switch(ip->minor) {
    case 1: return consolewrite(ip, off, dst, n);
    case 10: case 11: case 12: case 13: case 14: case 15: case 16:
            return consolewrite(ip, off, dst, n);
    case 7: return fullwrite(ip, off, dst, n);   // /dev/full: always ENOSPC
    case 2:
    case 5:
    case 8:
    case 9: return nullwrite(ip, off, dst, n); 
    default: return -1;
  }
}

struct devsw devsw[] = {
  [0] = { 0, 0 },
  [1] = { memread,   memwrite   },
  // /dev/fb0 (major 2) — the framebuffer, kernel/dev/fb.c. This used to be
  // { nullread, nullwrite }, so writing pixels to it succeeded and did
  // nothing.
  // The close hook gives the text console its screen back when whatever was
  // drawing on the framebuffer exits — see fbclose().
  [2] = { fbread,    fbwrite,   0, fbclose },
  [3] = { mouseread, mousewrite },
  [4] = { 0, 0 },
  // /dev/tty (major 5) — alias for the console
  [5] = { memread,   memwrite   },
  // /proc status files (major 6) — see kernel/dev/procfs.c
  [6] = { procread,  procwrite  },
  // /dev/input/eventN (major 7) — raw evdev events, kernel/dev/input.c. The
  // minor is the device index, so event0 is the keyboard and event1 the mouse.
  [7] = { inputread, inputwrite, inputready, inputclose, inputopen },
  // /dev/hdN (major 8) — raw disks, kernel/dev/disk.c. The minor is the IDE
  // device number. No `ready` hook: a disk is always ready, which is what
  // fileread assumes when one is absent.
  [8] = { diskread,  diskwrite  },
  // /dev/pci (major 9) -- PCI devices reachable from userspace, for drivers
  // that do not live in the kernel. Registers arrive through mmap and
  // everything else through ioctl; see include/pciuser.h.
  [9] = { pciuser_read, pciuser_write },
};