# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Utilities for unit testing."""

import cStringIO
import hashlib
import struct
import subprocess

import common
import payload
import update_metadata_pb2


class TestError(Exception):
  """An error during testing of update payload code."""


def _WriteInt(file_obj, size, is_unsigned, val):
  """Writes a binary-encoded integer to a file.

  It will do the correct conversion based on the reported size and whether or
  not a signed number is expected. Assumes a network (big-endian) byte
  ordering.

  Args:
    file_obj: a file object
    size: the integer size in bytes (2, 4 or 8)
    is_unsigned: whether it is signed or not
    val: integer value to encode
  Raises:
    PayloadError if a write error occurred.

  """
  try:
    file_obj.write(struct.pack(common.IntPackingFmtStr(size, is_unsigned), val))
  except IOError, e:
    raise payload.PayloadError('error writing to file (%s): %s' %
                               (file_obj.name, e))


def _SetMsgField(msg, field_name, val):
  """Sets or clears a field in a protobuf message."""
  if val is None:
    msg.ClearField(field_name)
  else:
    setattr(msg, field_name, val)


def SignSha256(data, privkey_file_name):
  """Signs the data's SHA256 hash with an RSA private key.

  Args:
    data: the data whose SHA256 hash we want to sign
    privkey_file_name: private key used for signing data
  Returns:
    The signature string, prepended with an ASN1 header.
  Raises:
    TestError if something goes wrong.

  """
  # pylint: disable=E1101
  data_sha256_hash = common.SIG_ASN1_HEADER + hashlib.sha256(data).digest()
  sign_cmd = ['openssl', 'rsautl', '-sign', '-inkey', privkey_file_name]
  try:
    sign_process = subprocess.Popen(sign_cmd, stdin=subprocess.PIPE,
                                    stdout=subprocess.PIPE)
    sig, _ = sign_process.communicate(input=data_sha256_hash)
  except Exception as e:
    raise TestError('signing subprocess failed: %s' % e)

  return sig


class SignaturesGenerator(object):
  """Generates a payload signatures data block."""

  def __init__(self):
    self.sigs = update_metadata_pb2.Signatures()

  def AddSig(self, version, data):
    """Adds a signature to the signature sequence.

    Args:
      version: signature version (None means do not assign)
      data: signature binary data (None means do not assign)

    """
    # Pylint fails to identify a member of the Signatures message.
    # pylint: disable=E1101
    sig = self.sigs.signatures.add()
    if version is not None:
      sig.version = version
    if data is not None:
      sig.data = data

  def ToBinary(self):
    """Returns the binary representation of the signature block."""
    return self.sigs.SerializeToString()


class PayloadGenerator(object):
  """Generates an update payload allowing low-level control.

  Attributes:
    manifest: the protobuf containing the payload manifest
    version: the payload version identifier
    block_size: the block size pertaining to update operations

  """

  def __init__(self, version=1):
    self.manifest = update_metadata_pb2.DeltaArchiveManifest()
    self.version = version
    self.block_size = 0

  @staticmethod
  def _WriteExtent(ex, val):
    """Returns an Extent message."""
    start_block, num_blocks = val
    _SetMsgField(ex, 'start_block', start_block)
    _SetMsgField(ex, 'num_blocks', num_blocks)

  @staticmethod
  def _AddValuesToRepeatedField(repeated_field, values, write_func):
    """Adds values to a repeated message field."""
    if values:
      for val in values:
        new_item = repeated_field.add()
        write_func(new_item, val)

  @staticmethod
  def _AddExtents(extents_field, values):
    """Adds extents to an extents field."""
    PayloadGenerator._AddValuesToRepeatedField(
        extents_field, values, PayloadGenerator._WriteExtent)

  def SetBlockSize(self, block_size):
    """Sets the payload's block size."""
    self.block_size = block_size
    _SetMsgField(self.manifest, 'block_size', block_size)

  def SetPartInfo(self, is_kernel, is_new, part_size, part_hash):
    """Set the partition info entry.

    Args:
      is_kernel: whether this is kernel partition info
      is_new: whether to set old (False) or new (True) info
      part_size: the partition size (in fact, filesystem size)
      part_hash: the partition hash

    """
    if is_kernel:
      # pylint: disable=E1101
      part_info = (self.manifest.new_kernel_info if is_new
                   else self.manifest.old_kernel_info)
    else:
      # pylint: disable=E1101
      part_info = (self.manifest.new_rootfs_info if is_new
                   else self.manifest.old_rootfs_info)
    _SetMsgField(part_info, 'size', part_size)
    _SetMsgField(part_info, 'hash', part_hash)

  def AddOperation(self, is_kernel, op_type, data_offset=None,
                   data_length=None, src_extents=None, src_length=None,
                   dst_extents=None, dst_length=None, data_sha256_hash=None):
    """Adds an InstallOperation entry."""
    # pylint: disable=E1101
    operations = (self.manifest.kernel_install_operations if is_kernel
                  else self.manifest.install_operations)

    op = operations.add()
    op.type = op_type

    _SetMsgField(op, 'data_offset', data_offset)
    _SetMsgField(op, 'data_length', data_length)

    self._AddExtents(op.src_extents, src_extents)
    _SetMsgField(op, 'src_length', src_length)

    self._AddExtents(op.dst_extents, dst_extents)
    _SetMsgField(op, 'dst_length', dst_length)

    _SetMsgField(op, 'data_sha256_hash', data_sha256_hash)

  def SetSignatures(self, sigs_offset, sigs_size):
    """Set the payload's signature block descriptors."""
    _SetMsgField(self.manifest, 'signatures_offset', sigs_offset)
    _SetMsgField(self.manifest, 'signatures_size', sigs_size)

  def _WriteHeaderToFile(self, file_obj, manifest_len):
    """Writes a payload heaer to a file."""
    # We need to access protected members in Payload for writing the header.
    # pylint: disable=W0212
    file_obj.write(payload.Payload._MAGIC)
    _WriteInt(file_obj, payload.Payload._VERSION_SIZE, True, self.version)
    _WriteInt(file_obj, payload.Payload._MANIFEST_LEN_SIZE, True, manifest_len)

  def WriteToFile(self, file_obj, manifest_len=-1, data_blobs=None,
                  sigs_data=None, padding=None):
    """Writes the payload content to a file.

    Args:
      file_obj: a file object open for writing
      manifest_len: manifest len to dump (otherwise computed automatically)
      data_blobs: a list of data blobs to be concatenated to the payload
      sigs_data: a binary Signatures message to be concatenated to the payload
      padding: stuff to dump past the normal data blobs provided (optional)

    """
    manifest = self.manifest.SerializeToString()
    if manifest_len < 0:
      manifest_len = len(manifest)
    self._WriteHeaderToFile(file_obj, manifest_len)
    file_obj.write(manifest)
    if data_blobs:
      for data_blob in data_blobs:
        file_obj.write(data_blob)
    if sigs_data:
      file_obj.write(sigs_data)
    if padding:
      file_obj.write(padding)


class EnhancedPayloadGenerator(PayloadGenerator):
  """Payload generator with automatic handling of data blobs.

  Attributes:
    data_blobs: a list of blobs, in the order they were added
    curr_offset: the currently consumed offset of blobs added to the payload

  """

  def __init__(self):
    super(EnhancedPayloadGenerator, self).__init__()
    self.data_blobs = []
    self.curr_offset = 0

  def AddData(self, data_blob):
    """Adds a (possibly orphan) data blob."""
    data_length = len(data_blob)
    data_offset = self.curr_offset
    self.curr_offset += data_length
    self.data_blobs.append(data_blob)
    return data_length, data_offset

  def AddOperationWithData(self, is_kernel, op_type, src_extents=None,
                           src_length=None, dst_extents=None, dst_length=None,
                           data_blob=None, do_hash_data_blob=True):
    """Adds an install operation and associated data blob.

    This takes care of obtaining a hash of the data blob (if so instructed)
    and appending it to the internally maintained list of blobs, including the
    necessary offset/length accounting.

    Args:
      is_kernel: whether this is a kernel (True) or rootfs (False) operation
      op_type: one of REPLACE, REPLACE_BZ, MOVE or BSDIFF
      src_extents: list of (start, length) pairs indicating src block ranges
      src_length: size of the src data in bytes (needed for BSDIFF)
      dst_extents: list of (start, length) pairs indicating dst block ranges
      dst_length: size of the dst data in bytes (needed for BSDIFF)
      data_blob: a data blob associated with this operation
      do_hash_data_blob: whether or not to compute and add a data blob hash

    """
    data_offset = data_length = data_sha256_hash = None
    if data_blob is not None:
      if do_hash_data_blob:
        # pylint: disable=E1101
        data_sha256_hash = hashlib.sha256(data_blob).digest()
      data_length, data_offset = self.AddData(data_blob)

    self.AddOperation(is_kernel, op_type, data_offset=data_offset,
                      data_length=data_length, src_extents=src_extents,
                      src_length=src_length, dst_extents=dst_extents,
                      dst_length=dst_length, data_sha256_hash=data_sha256_hash)

  def WriteToFileWithData(self, file_obj, sigs_data=None,
                          privkey_file_name=None,
                          do_add_pseudo_operation=False,
                          is_pseudo_in_kernel=False, padding=None):
    """Writes the payload content to a file, optionally signing the content.

    Args:
      file_obj: a file object open for writing
      sigs_data: signatures blob to be appended to the payload (optional;
                 payload signature fields assumed to be preset by the caller)
      privkey_file_name: key used for signing the payload (optional; used only
                         if explicit signatures blob not provided)
      do_add_pseudo_operation: whether a pseudo-operation should be added to
                               account for the signature blob
      is_pseudo_in_kernel: whether the pseudo-operation should be added to
                           kernel (True) or rootfs (False) operations
      padding: stuff to dump past the normal data blobs provided (optional)
    Raises:
      TestError: if arguments are inconsistent or something goes wrong.

    """
    sigs_len = len(sigs_data) if sigs_data else 0

    # Do we need to generate a genuine signatures blob?
    do_generate_sigs_data = sigs_data is None and privkey_file_name

    if do_generate_sigs_data:
      # First, sign some arbitrary data to obtain the size of a signature blob.
      fake_sig = SignSha256('fake-payload-data', privkey_file_name)
      fake_sigs_gen = SignaturesGenerator()
      fake_sigs_gen.AddSig(1, fake_sig)
      sigs_len = len(fake_sigs_gen.ToBinary())

      # Update the payload with proper signature attributes.
      self.SetSignatures(self.curr_offset, sigs_len)

    # Add a pseudo-operation to account for the signature blob, if requested.
    if do_add_pseudo_operation:
      if not self.block_size:
        raise TestError('cannot add pseudo-operation without knowing the '
                        'payload block size')
      self.AddOperation(
          is_pseudo_in_kernel, common.OpType.REPLACE,
          data_offset=self.curr_offset, data_length=sigs_len,
          dst_extents=[(common.PSEUDO_EXTENT_MARKER,
                        (sigs_len + self.block_size - 1) / self.block_size)])

    if do_generate_sigs_data:
      # Once all payload fields are updated, dump and sign it.
      temp_payload_file = cStringIO.StringIO()
      self.WriteToFile(temp_payload_file, data_blobs=self.data_blobs)
      sig = SignSha256(temp_payload_file.getvalue(), privkey_file_name)
      sigs_gen = SignaturesGenerator()
      sigs_gen.AddSig(1, sig)
      sigs_data = sigs_gen.ToBinary()
      assert len(sigs_data) == sigs_len, 'signature blob lengths mismatch'

    # Dump the whole thing, complete with data and signature blob, to a file.
    self.WriteToFile(file_obj, data_blobs=self.data_blobs, sigs_data=sigs_data,
                     padding=padding)