util.py

import json
from Fs import Fs
import os
from inode import Inode
from block import Block
from super_block import SuperBlock
import enum
import constants

false = False
null = None

class FileType(enum.Enum): 
    regular = 1
    dir = 2

def load(bytearr):
    stringfied = str(bytearr)
    null_index = find_null_index(stringfied)
    if null_index != -1:
        stringfied = stringfied[:null_index]
    return eval(json.loads(json.dumps(stringfied)))

def save(bytearr, offset, filepath):
  with open(filepath, "rw+") as disk:
    disk.seek(offset, os.SEEK_SET)
    disk.write(bytearr)
    disk.close()

def read(filepath, offset, size):
  with open(filepath, "rw+") as disk:
    disk.seek(offset, os.SEEK_SET)
    result = disk.read(size)
    disk.close()
    return result

def instance_from_obj(class_constructor, obj):
    instance = class_constructor()
    for key in obj:
        setattr(instance, key, obj[key])
    return instance

def get_sb():
    sb_bytearr = read('disk', 0, constants.SUPER_BLOCK_SIZE)
    sb_json = load(sb_bytearr)
    sb_instance = instance_from_obj(SuperBlock, sb_json)
    return sb_instance

def get_inode(number):
    inode_bytearr = read('disk', constants.SUPER_BLOCK_SIZE + (number * constants.INODE_SIZE), constants.INODE_SIZE)
    inode_json = load(inode_bytearr)
    inode_instance = instance_from_obj(Inode, inode_json)
    return inode_instance
    
def get_block(number):
    offset = (constants.SUPER_BLOCK_SIZE + (constants.INODES_AMOUNT + 1) * constants.INODE_SIZE) + number * constants.BLOCK_SIZE
    block_bytearr = read('disk', offset, constants.BLOCK_SIZE)
    block_json = load(block_bytearr)
    block_instance = instance_from_obj(Block, block_json)
    return block_instance

def find_null_index(string):
    for i in xrange(len(string)):
        if string[i] == '\x00':
            return i
    return -1

def create_empty_inode(number):
    inode = Inode()
    inode.number = number
    inode.size = 4096*12
    save(inode.bytefy(), inode.get_offset(), 'disk')

def create_empty_block(number):
    block = Block()
    block.number = number
    block.size = 4096
    save(block.bytefy(), block.get_offset(), 'disk')