import disk_sys
class file:
  def __init__(self):
    self.disk = disk_sys.disk()
  def initialize(self):
    self.dirblock = self.disk.getblockref(0)
    self.freebitmap = self.disk.getblockref(1)
    self.freebitmap.setbyte(0,0xc0) # allocate first 2 blocks for file system
    for i in range(0,disk_sys.block.BlockSize,16): # count in 16 byte increments
      self.dirblock.setbyte(i+2,0) # zero block address byte 1
      self.dirblock.setbyte(i+3,0) # zero block address byte 2
  
  def create(self,fname):
    self.dirblock = self.disk.getblockref(0)
    for free in range(0,disk_sys.block.BlockSize,16):
      pntr = self.dirblock.getword(free+2)
      if pntr == 0:
        break
    else:
      print "*** I/O error: no free directory entries"
      return -1
    
    for i in range(len(fname)):
      b = ord(fname[i])
      self.dirblock.setbyte(free+i+4,b)
    
    index = self.getfreeblock()
    indexblock = self.disk.getblockref(index)
    for i in range(disk_sys.block.BlockSize):
      indexblock.setbyte(i,0)
    self.dirblock.setword(free+2,index)
    
    return 0
  
  def open(self,fname):
    f = self.searchdir(fname)
    if f < 0:
      print "*** I/O error: cannot open file %s" % fname
      return -1
    return [f,0]
  
  
  def writebyte(self,fd,byte):
    byte = byte & 0xff # for safety
    index = fd[0]; posn = fd[1]
    bn = posn / disk_sys.block.BlockSize # block number from origin
    offset = posn % disk_sys.block.BlockSize # byte number within block
    indexblock = self.disk.getblockref(index)
    indexadr = 2+2*bn
    if indexadr >= disk_sys.block.BlockSize:
      print "*** I/O error: no space in index table"
      return -1
    pntr = indexblock.getword(indexadr)
    if pntr == 0:
      pntr = self.getfreeblock()
      indexblock.setword(indexadr,pntr)
    datablock = self.disk.getblockref(pntr)
    
    datablock.setbyte(offset,byte)
    posn = posn + 1
    eof = indexblock.getword(0)
    if posn > eof:
      if posn > 65535:
        print "*** I/O error: no space in file"
        return -1
      else:
        indexblock.setword(0,posn)
        fd[1] = posn
    
    return 0
  def writestr(self,fd,str):
    for i in range(len(str)):
      self.writebyte(fd,ord(str[i]))
  
  def close(self):
    pass
  
  def allocateblock(self,n):
    nbyte = n / 8; nbit = n % 8
    fb = self.freebitmap
    byte = fb.getbyte(nbyte)
    mask = 1 << (7-nbit); clearmask = ~ mask
    byte = byte ^ mask # set the relevant bit
    byte = byte & 255 # for safety
    fb.setbyte(nbyte,byte)
  def freeblock(self,n):
    nbyte = n / 8; nbit = n % 8
    fb = self.freebitmap
    byte = fb.getbyte(nbyte)
    mask = 1 << (7-nbit); clearmask = ~ mask
    byte = byte & clearmask # reset the relevant bit
    byte = byte & 255 # for safety
    fb.setbyte(nbyte,byte)
  def getfreeblock(self):
    fb = self.freebitmap
    for i in range(disk_sys.block.BlockSize):
      byte = fb.getbyte(i)
      if byte < 255:
        break
    else:
      print "*** I/O error: No free disk blocks"
    byteadr = i
    nbyte = (~ byte) & 255; mask = 128; i = i*8
    # find first 1 bit in nbyte from msb
    while nbyte & mask == 0:
      mask = mask >> 1
      i = i + 1
    byte = byte ^ mask # turn bit on
    byte = byte & 255 # for safety
    fb.setbyte(byteadr,byte)
    return i 
  def searchdir(self,fname):
    self.dirblock = self.disk.getblockref(0)
    for direntry in range(0,disk_sys.block.BlockSize,16):
      pntr = self.dirblock.getword(direntry+2)
      if pntr != 0:
        dirfn = ""
        for j in range(12):
          byte = self.dirblock.getbyte(direntry+4+j)
          if byte == 0:
            break
          dirfn = dirfn + chr(byte)
        if fname == dirfn:
          break
      
    else:
      print "*** I/O error: cannot find file %s" % fname
      return -1
    return pntr