# Copyright (C) 2016 The OpenTimestamps developers
#
# This file is part of python-opentimestamps.
#
# It is subject to the license terms in the LICENSE file found in the top-level
# directory of this distribution.
#
# No part of python-opentimestamps including this file, may be copied,
# modified, propagated, or distributed except according to the terms contained
# in the LICENSE file.

"""Consensus-critical recursive descent serialization/deserialization"""

import binascii
import io

class DeserializationError(Exception):
    """Base class for all errors encountered during deserialization"""

class BadMagicError(DeserializationError):
    """A magic number is incorrect

    Raise this when the file format magic number is incorrect.
    """
    def __init__(self, expected_magic, actual_magic):
        super().__init__('Expected magic bytes 0x%s, but got 0x%s instead' % (binascii.hexlify(expected_magic).decode(),
                                                                              binascii.hexlify(actual_magic).decode()))

class UnsupportedMajorVersion(DeserializationError):
    """Unsupported major version

    Raise this a major version is unsupported
    """

class TruncationError(DeserializationError):
    """Truncated data encountered while deserializing"""

class TrailingGarbageError(DeserializationError):
    """Trailing garbage found after deserialization finished

    Raised when deserialization otherwise succeeds without errors, but excess
    data is present after the data we expected to get.
    """

class RecursionLimitError(DeserializationError):
    """Data is too deeply nested to be deserialized

    Raised when deserializing recursively defined data structures that exceed
    the recursion limit for that particular data structure.
    """

class SerializerTypeError(TypeError):
    """Wrong type for specified serializer"""

class SerializerValueError(ValueError):
    """Inappropriate value to be serialized (of correct type)"""


class SerializationContext:
    """Context for serialization

    Allows multiple serialization targets to share the same codebase, for
    instance bytes, memoized serialization, hashing, etc.
    """

    def write_bool(self, value):
        """Write a bool"""
        raise NotImplementedError

    def write_varuint(self, value):
        """Write a variable-length unsigned integer"""
        raise NotImplementedError

    def write_bytes(self, value):
        """Write fixed-length bytes"""
        raise NotImplementedError

    def write_varbytes(self, value):
        """Write variable-length bytes"""
        raise NotImplementedError

class DeserializationContext:
    """Context for deserialization

    Allows multiple deserialization sources to share the same codebase, for
    instance bytes, memoized serialization, hashing, etc.
    """
    def read_bool(self):
        """Read a bool"""
        raise NotImplementedError

    def read_varuint(self, max_int):
        """Read a variable-length unsigned integer"""
        raise NotImplementedError

    def read_bytes(self, expected_length):
        """Read fixed-length bytes"""
        raise NotImplementedError

    def read_varbytes(self, value, max_length=None):
        """Read variable-length bytes

        No more than max_length bytes will be read.
        """
        raise NotImplementedError

    def assert_magic(self, expected_magic):
        """Assert the presence of magic bytes

        Raises BadMagicError if the magic bytes don't match, or if the read was
        truncated.

        Note that this isn't an assertion in the Python sense: debug/production
        does not change the behavior of this function.
        """
        raise NotImplementedError

    def assert_eof(self):
        """Assert that we have reached the end of the data

        Raises TrailingGarbageError(msg) if the end of file has not been reached.

        Note that this isn't an assertion in the Python sense: debug/production
        does not change the behavior of this function.
        """
        raise NotImplementedError

class StreamSerializationContext(SerializationContext):
    def __init__(self, fd):
        """Serialize to a stream"""
        self.fd = fd

    def write_bool(self, value):
        if value is True:
            self.fd.write(b'\xff')

        elif value is False:
            self.fd.write(b'\x00')

        else:
            raise TypeError('Expected bool; got %r' % value.__class__)

    def write_varuint(self, value):
        # unsigned little-endian base128 format (LEB128)
        if value == 0:
            self.fd.write(b'\x00')

        else:
            while value != 0:
                b = value & 0b01111111
                if value > 0b01111111:
                    b |= 0b10000000
                self.fd.write(bytes([b]))
                if value <= 0b01111111:
                    break
                value >>= 7

    def write_bytes(self, value):
        self.fd.write(value)

    def write_varbytes(self, value):
        self.write_varuint(len(value))
        self.fd.write(value)

class StreamDeserializationContext(DeserializationContext):
    def __init__(self, fd):
        """Deserialize from a stream"""
        self.fd = fd

    def fd_read(self, l):
        r = self.fd.read(l)
        if len(r) != l:
            raise TruncationError('Tried to read %d bytes but got only %d bytes' % \
                                  (l, len(r)))
        return r

    def read_bool(self):
        # unsigned little-endian base128 format (LEB128)
        b = self.fd_read(1)[0]
        if b == 0xff:
            return True

        elif b == 0x00:
            return False

        else:
            raise DeserializationError('read_bool() expected 0xff or 0x00; got %d' % b)

    def read_varuint(self):
        value = 0
        shift = 0

        while True:
            b = self.fd_read(1)[0]
            value |= (b & 0b01111111) << shift
            if not (b & 0b10000000):
                break
            shift += 7

        return value

    def read_bytes(self, expected_length=None):
        if expected_length is None:
            expected_length = self.read_varuint(None)
        return self.fd_read(expected_length)

    def read_varbytes(self, max_len, min_len=0):
        l = self.read_varuint()
        if l > max_len:
            raise DeserializationError('varbytes max length exceeded; %d > %d' % (l, max_len))
        if l < min_len:
            raise DeserializationError('varbytes min length not met; %d < %d' % (l, min_len))
        return self.fd_read(l)

    def assert_magic(self, expected_magic):
        actual_magic = self.fd.read(len(expected_magic))
        if expected_magic != actual_magic:
            raise BadMagicError(expected_magic, actual_magic)

    def assert_eof(self):
        excess = self.fd.read(1)
        if excess:
            raise TrailingGarbageError("Trailing garbage found after end of deserialized data")

class BytesSerializationContext(StreamSerializationContext):
    def __init__(self):
        """Serialize to bytes"""
        super().__init__(io.BytesIO())

    def getbytes(self):
        """Return the bytes serialized to date"""
        return self.fd.getvalue()

class BytesDeserializationContext(StreamDeserializationContext):
    def __init__(self, buf):
        """Deserialize from bytes"""
        super().__init__(io.BytesIO(buf))

    # FIXME: need to check that there isn't extra crap at end of object