import struct
from cStringIO import StringIO
import math

_scalarMagic = float.fromhex('0x1.62e42fefa39efp+2')

def loads( sIn ):
	return load( StringIO( sIn ) )

def dumps( obj ):
	sTmp = StringIO()
	dump( obj, sTmp )
	return sTmp.getvalue()

def load( sIn ):
	# Scan for a valid packet header
	while True:
		version = sIn.read(1)
		if len(version) == 0:
			return None
		version = ord(version[0])
		if version != 0:
			break

	if version == 1:
		size = struct.unpack('>I', sIn.read(4) )[0]
		return _readObj( sIn )

def dump( obj, sOut ):
	sTmp = StringIO()
	_writeObj( obj, sTmp )
	sCore = sTmp.getvalue()
	sOut.write(	struct.pack('>BI', 1, len(sCore)+5 ) )
	sOut.write( sCore )

def _readObj( sIn ):
	t = sIn.read( 1 )
	if t == 'i':	# Integer
		return _readPackedInt( sIn )
	elif t == 's':	# String
		lng = _readPackedInt( sIn )
		return sIn.read( lng )
	elif t == '0':	# Boolean false
		return False
	elif t == '1':	# Boolean true
		return True
	elif t == 'l':	# List
		ret = []
		while True:
			value = _readObj( sIn )
			if value is None:
				return ret
			ret.append( value )
	elif t == 'd':	# Dictionary
		ret = {}
		while True:
			key = _readObj( sIn )
			if key is None:
				return ret
			if not isinstance( key, str ):
				raise Exception('Only strings can be used as keys in gats dictionaries')
			value = _readObj( sIn );
			ret[key] = value
	elif t == 'f':	# Float
		pLng = _readPackedInt( sIn )
		bNeg = False
		if pLng < 0:
			bNeg = True
			pLng = -pLng

		dValue = 0.0
		dat = sIn.read( pLng )
		for i in xrange(len(dat)-1,0,-1):
			dValue = (dValue+ord(dat[i]))*(1.0/256.0)
		dValue += ord(dat[0])
		iScale = _readPackedInt( sIn )
		dValue *= pow( 256.0, iScale )
		if bNeg:
			return -dValue
		return dValue
	elif t == 'F':	# Exceptional float
		st = sIn.read(1)
		if st == 'N':
			return float('-nan')
		elif st == 'n':
			return float('nan')
		elif st == 'I':
			return float('-inf')
		elif st == 'i':
			return float('inf')
		elif st == 'Z':
			return -0.0
		elif st == 'z':
			return 0.0
		else:
			raise Exception('Invalid exceptional float subtype found.')
	elif t == 'e':	# End marker
		return None
	else:
		raise Exception('Invalid gats type discovered: ' + t)
	return 'not implemented yet';

def _writeObj( obj, sOut ):
	if isinstance( obj, int ):
		sOut.write('i')
		_writePackedInt( obj, sOut )
	elif isinstance( obj, str ):
		sOut.write('s')
		_writePackedInt( len(obj), sOut )
		sOut.write( obj )
	elif isinstance( obj, list ) or isinstance( obj, tuple ):
		sOut.write('l')
		for s in obj:
			_writeObj( s, sOut )
		sOut.write('e')
	elif isinstance( obj, dict ):
		sOut.write('d')
		for key in obj.iterkeys():
			_writeObj( key, sOut )
			_writeObj( obj[key], sOut )
		sOut.write('e')
	elif isinstance( obj, bool ):
		if obj == True:
			sOut.write('1')
		else:
			sOut.write('0')
	elif isinstance( obj, float ):
		if math.isnan( obj ):
			if math.copysign( 1.0, obj ) < 0.0:
				sOut.write('FN')
			else:
				sOut.write('Fn')
		elif math.isinf( obj ):
			if math.copysign( 1.0, obj ) < 0.0:
				sOut.write('FI')
			else:
				sOut.write('Fi')
		elif obj == 0.0:
			if math.copysign( 1.0, obj ) < 0.0:
				sOut.write('FZ')
			else:
				sOut.write('Fz')
		else:
			sOut.write('f')
			d = obj
			bNeg = False
			if d < 0.0:
				bNeg = True
				d = -d

			iScale = int(math.log( d ) / _scalarMagic)
			if iScale < 0:
				iScale -= 1

			sTmp = StringIO()

			d /= pow( 256.0, iScale )
			sTmp.write( chr( int(d) ) )
			d -= int(d)
			for j in xrange( 0, 150 ):
				d = d*256.0
				sTmp.write( chr(int(d)) )
				d -= int(d)
				if d == 0.0:
					break

			sTmp = sTmp.getvalue()
			if bNeg:
				_writePackedInt( -len(sTmp), sOut )
			else:
				_writePackedInt( len(sTmp), sOut )
			sOut.write( sTmp )
			_writePackedInt( iScale, sOut )
	else:
		raise Exception('A type that is not gats-encodable was encountered: ' + str(type(obj)))

def _readPackedInt( sIn ):
	bNeg = False

	b = ord(sIn.read(1)[0])
	bNeg = (b&0x40) == 0x40;
	rOut = b&0x3F;

	c = 0
	while (b&0x80) == 0x80:
		b = ord(sIn.read(1)[0])
		rOut |= (b&0x7F)<<(6+7*c)
		c += 1
	if bNeg:
		return -rOut
	return rOut

def _writePackedInt( iIn, sOut ):
	if iIn < 0:
		iIn = -iIn
		b = iIn&0x3F
		if iIn > b:
			b |= 0x80 | 0x40
		else:
			b |= 0x40
	else:
		b = iIn&0x3F
		if iIn > b:
			b |= 0x80
	sOut.write( chr( b ) )

	iIn = iIn >> 6

	while iIn > 0:
		b = iIn&0x7F
		if iIn > b:
			b |= 0x80
		sOut.write( chr( b ) )
		iIn = iIn >> 7