# /***********************************************************
# * Name of program: 
# * Authors: 
# * Description: Starter code for Project 4
# **********************************************************/
import struct
import sys
import math

# Seeking to an aribitrary position and reading in a set number of bytes.
# This function unpacks bytes according to little endian disk format and
# host order of running computer.
# https://docs.python.org/3/library/struct.html
def get_bytes(f, pos, numBytes):
	f.seek(pos)
	byte = f.read(numBytes)
	if (numBytes == 2):
		formatString = "H"
	elif (numBytes == 1):
		formatString = "B"
	elif (numBytes == 4):
		formatString = "i"
	else:
		raise Exception("Not implemented")

	return struct.unpack(ENDIAN_FORMAT+formatString, byte)[0]

# the info command, prints general information about this image
def info():

	print("BPB_BytesPerSec is ", hex(BPB_BytesPerSec), BPB_BytesPerSec)

	print("BPB_SecPerClus is ", hex(BPB_SecPerClus), BPB_SecPerClus)

	print("BPB_RsvdSecCnt is ", hex(BPB_RsvdSecCnt), BPB_RsvdSecCnt)

	print("BPB_NumFATs is ", hex(BPB_NumFATs), BPB_NumFATs)

	print("BPB_FATSz32 is ", hex(BPB_FATSz32), BPB_FATSz32)
	return True


def main():
	# BPB Constants
	global BPB_BytesPerSec
	global BPB_SecPerClus
	global BPB_RsvdSecCnt
	global BPB_NumFATs
	global BPB_FATSz32
	
	global ENDIAN_FORMAT
	
	f = open("fat32.img", 'rb')

	if sys.byteorder == 'little':
		ENDIAN_FORMAT = "<"
	else:
		ENDIAN_FORMAT = ">"


	BPB_BytesPerSec = get_bytes(f, 11, 2)
	BPB_SecPerClus = get_bytes(f, 13, 1)
	BPB_RsvdSecCnt = get_bytes(f, 14, 2)
	BPB_NumFATs = get_bytes(f, 16, 1)
	BPB_FATSz32 = get_bytes(f, 36, 4)

	#TODO: Get and seek to the root directory

	# Begin taking arguments
	while True:
		user_input = input("] ")
		user_input_list = user_input.split()
		command = user_input_list[0].strip()

		args = user_input_list[1:]

		#Start processing the commands

		if command == "info":
			info() #TODO: Finish this function

		elif command == "stat":
			print("Not yet implemented\n")

		elif command == "cd":
			print("Not yet implemented\n")

		elif command == "ls":
			print("Not yet implemented\n")

		elif command == "read":
			print("Not yet implemented\n")

		elif command == "volume":
			print("Not yet implemented\n")

		elif command == "deleted":
			print("Not yet implemented\n")

		elif command == "quit":
			print("Quitting.\n")
			f.close()
			quit()

		else:
			print("Unrecognized command\n")

				
main()