"""

Copyright (c) 2006, Jari Sukanen

All rights reserved.

Redistribution and use in source and binary forms, with or 

without modification, are permitted provided that the following 

conditions are met:

	* Redistributions of source code must retain the above copyright 

	  notice, this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright 

	  notice, this list of conditions and the following disclaimer in 

	  the documentation and/or other materials provided with the 

	  distribution.

    * Names of the contributors may not be used to endorse or promote 

	  products derived from this software without specific prior written 

	  permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 

"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 

TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 

PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS 

BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 

CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 

SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 

INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 

CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 

ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 

THE POSSIBILITY OF SUCH DAMAGE.

"""

import struct

import sisfields

class SISReader :

	def __init__(self) :

		pass

	def readUnsignedBytes(self, numBytes) :

		buf = self.readPlainBytes(numBytes)

		if len(buf) < numBytes :

			return []

		format = ""

		for i in range(numBytes) :

			format += "B"

		return struct.unpack(format, buf)

	def readSignedBytes(self, numBytes) :

		buf = self.readPlainBytes(numBytes)

		if len(buf) < numBytes :

			return []

		format = ""

		for i in range(numBytes) :

			format += "b"

		return struct.unpack(format, buf)

	def readBytesAsUint(self, numBytes) :

		result = 0

		bytes = self.readUnsignedBytes(numBytes)

		if len(bytes) == numBytes :

			for i in range(numBytes) :

				result |= bytes[i] << (i*8)

		return result

	def readBytesAsInt(self, numBytes) :

		result = 0

		bytes = self.readSignedBytes(numBytes)

		if len(bytes) == numBytes :

			for i in range(numBytes) :

				result |= bytes[i] << (i*8)

		return result

	def skipPadding(self) :

		result = 0

		if self.bytesRead % 4 != 0 :

			paddingLength = 4 - self.bytesRead % 4

			self.readPlainBytes(paddingLength)

			result = paddingLength

		return result

class SISFileReader(SISReader) : 

	def __init__(self, inStream) :

		self.inStream = inStream

		self.eof = False

		self.bytesRead = 0

	def readPlainBytes(self, numBytes) :

		if self.eof :

			return ""

		if numBytes == 0 :

			return ""

		buf = ""

		buf = self.inStream.read(numBytes)

		if len(buf) < numBytes :

			self.eof = True

			return ""

		self.bytesRead += numBytes

		return buf

	def isEof(self) :

		return self.eof

class SISBufferReader(SISReader) :

	def __init__(self, buffer) :

		self.buffer = buffer

		self.bytesRead = 0

	def readPlainBytes(self, numBytes) :

		if self.isEof() :

			return ""

		if numBytes == 0 :

			return ""

		result = self.buffer[self.bytesRead:self.bytesRead+numBytes]

		self.bytesRead += numBytes

		return result

	def isEof(self) :

		return self.bytesRead >= len(self.buffer)

class SISFieldParser :

	def __init__(self) :

		self.lastReadBytes = 0

	def parseField(self, fileReader) :

		"""Reads the next field from the fileReader stream and returns it"""

		field = None

		self.lastReadBytes = 0

		type = fileReader.readBytesAsUint(4)

		self.lastReadBytes += 4

		if type != 0 :

			field = sisfields.SISFieldTypes[type]()

			field.type = type

			field.initFromFile(fileReader)

			self.lastReadBytes += field.length + 4 # Field length + length field

			self.lastReadBytes += fileReader.skipPadding()

		return field