#!/usr/bin/python

import os,sys

NL='\n'

class GPIO:
	EXPORT = '/sys/class/gpio/export'
	UNEXPORT = '/sys/class/gpio/unexport'
	EFILE = None
	IN = 1
	OUT = 0
	## The constructor
	# @param num The kernel id number of the GPIO pin 
	def __init__(self,num):
		# type checks
		if type(num)!=int:
			raise ValueError('num should be int')
		
		# assignments
		self.num=num		

		# Try to open the gio control file
		if GPIO.EFILE==None:
			if !os.path.exists(GPIO.EXPORT):
				raise IOError('file "'+GPIO.EXPORT+'" does not exist')
			GPIO.EFILE=open(EXPORT,'wb')

		# enable GPIO pin
		EFILE.write(str(num)+NL)
		
		self.path = '/sys/class/gpio/gpio' + str(num)
		
		if !os.path.exists(self.path):
				raise IOError('directory "'+self.path+'" does not exist')

		# open the GPIOs value files
		# as the directory was created I imply all of them exist
		self.valuef = open(self.path+'/value','rwb')
		self.directionf = open(self.path+'/direction','wb')
		self.active_lowf = open( +'/active_low',,'wb')
		self.edgef = open(self.path+'/edge',,'wb')

		set_direction(GPIO.IN)
		self.value = False
		
	def _read_value(self):
		tmp=self.valuef.read()
		self.value = tmp=="1"

	def write_value(self,v):
		if self.direction != GPIO.OUT:
			return
		self.value = not(v==0)
		if self.value==0:
			self.valuef.write('0')
		elif self.value==1:
			self.valuef.write('1')
		else:
			assert 0

	def is_high(self):
		if self.direction != GPIO.IN:
			return False
		self._read_value()
		return self.value

	def set_direction(self,d):
		if d==GPIO.IN:
			self.directionf.write('in'+NL)
			self.direction=GPIO.IN
		elif d==GPIO.OUT:
			self.directionf.write('out'+NL)
			self.direction=GPIO.OUT

	## the destructor
	def __del__(self):
		if GPIO.EFILE!=None:
			# free GPIO pin
			# as the export path exists I imply unexport will also exist
			tmpf = open(GPIO.UNEXPORT,'wb')
			tmpf.write(str(self.num)+NL)
			tmpf.close()
			GPIO.EFILE.close()

			self.valuef.close()
			self.directionf.close()
			self.active_lowf.close()
			self.edgef.close()