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

from mojom.generate import module as mojom

# This module provides a mechanism for determining the packed order and offsets
# of a mojom.Struct.
#
# ps = pack.PackedStruct(struct)
# ps.packed_fields will access a list of PackedField objects, each of which
# will have an offset, a size and a bit (for mojom.BOOLs).

# Size of struct header in bytes: num_bytes [4B] + version [4B].
HEADER_SIZE = 8


class PackedField(object):
  kind_to_size = {
      mojom.BOOL: 1,
      mojom.INT8: 1,
      mojom.UINT8: 1,
      mojom.INT16: 2,
      mojom.UINT16: 2,
      mojom.INT32: 4,
      mojom.UINT32: 4,
      mojom.FLOAT: 4,
      mojom.HANDLE: 4,
      mojom.MSGPIPE: 4,
      mojom.SHAREDBUFFER: 4,
      mojom.PLATFORMHANDLE: 4,
      mojom.DCPIPE: 4,
      mojom.DPPIPE: 4,
      mojom.NULLABLE_HANDLE: 4,
      mojom.NULLABLE_MSGPIPE: 4,
      mojom.NULLABLE_SHAREDBUFFER: 4,
      mojom.NULLABLE_PLATFORMHANDLE: 4,
      mojom.NULLABLE_DCPIPE: 4,
      mojom.NULLABLE_DPPIPE: 4,
      mojom.INT64: 8,
      mojom.UINT64: 8,
      mojom.DOUBLE: 8,
      mojom.STRING: 8,
      mojom.NULLABLE_STRING: 8
  }

  @classmethod
  def GetSizeForKind(cls, kind):
    if isinstance(kind, (mojom.Array, mojom.Map, mojom.Struct, mojom.Interface,
                         mojom.AssociatedInterface, mojom.PendingRemote,
                         mojom.PendingAssociatedRemote)):
      return 8
    if isinstance(kind, mojom.Union):
      return 16
    if isinstance(kind, (mojom.InterfaceRequest, mojom.PendingReceiver)):
      kind = mojom.MSGPIPE
    if isinstance(
        kind,
        (mojom.AssociatedInterfaceRequest, mojom.PendingAssociatedReceiver)):
      return 4
    if isinstance(kind, mojom.Enum):
      # TODO(mpcomplete): what about big enums?
      return cls.kind_to_size[mojom.INT32]
    if not kind in cls.kind_to_size:
      raise Exception("Undefined type: %s. Did you forget to import the file "
                      "containing the definition?" % kind.spec)
    return cls.kind_to_size[kind]

  @classmethod
  def GetAlignmentForKind(cls, kind):
    if isinstance(kind, (mojom.Interface, mojom.AssociatedInterface,
                         mojom.PendingRemote, mojom.PendingAssociatedRemote)):
      return 4
    if isinstance(kind, mojom.Union):
      return 8
    return cls.GetSizeForKind(kind)

  def __init__(self, field, index, ordinal):
    """
    Args:
      field: the original field.
      index: the position of the original field in the struct.
      ordinal: the ordinal of the field for serialization.
    """
    self.field = field
    self.index = index
    self.ordinal = ordinal
    self.size = self.GetSizeForKind(field.kind)
    self.alignment = self.GetAlignmentForKind(field.kind)
    self.offset = None
    self.bit = None
    self.min_version = None


def GetPad(offset, alignment):
  """Returns the pad necessary to reserve space so that |offset + pad| equals to
  some multiple of |alignment|."""
  return (alignment - (offset % alignment)) % alignment


def GetFieldOffset(field, last_field):
  """Returns a 2-tuple of the field offset and bit (for BOOLs)."""
  if (field.field.kind == mojom.BOOL and last_field.field.kind == mojom.BOOL
      and last_field.bit < 7):
    return (last_field.offset, last_field.bit + 1)

  offset = last_field.offset + last_field.size
  pad = GetPad(offset, field.alignment)
  return (offset + pad, 0)


def GetPayloadSizeUpToField(field):
  """Returns the payload size (not including struct header) if |field| is the