img: add _ChunkFactory()

Steve Canny · Steve Canny · commit 8f3e5d443393 · 2014-03-01T01:35:30.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -2,7 +2,7 @@
 
 from __future__ import absolute_import, division, print_function
 
-from .constants import MIME_TYPE, TAG
+from .constants import MIME_TYPE, PNG_CHUNK_TYPE, TAG
 from .exceptions import InvalidImageStreamError
 from .helpers import BIG_ENDIAN, StreamReader
 from .image import BaseImageHeader
@@ -270,11 +270,48 @@ def _ChunkFactory(chunk_type, stream_rdr, offset):
     Return a |_Chunk| subclass instance appropriate to *chunk_type* parsed
     from *stream_rdr* at *offset*.
     """
-    raise NotImplementedError
+    chunk_cls_map = {
+        PNG_CHUNK_TYPE.IHDR: _IHDRChunk,
+        PNG_CHUNK_TYPE.pHYs: _pHYsChunk,
+    }
+    chunk_cls = chunk_cls_map.get(chunk_type, _Chunk)
+    return chunk_cls.from_offset(chunk_type, stream_rdr, offset)
 
 
 class _Chunk(object):
     """
     Base class for specific chunk types. Also serves as the default chunk
     type.
     """
+    @classmethod
+    def from_offset(cls, chunk_type, stream_rdr, offset):
+        """
+        Return a default _Chunk instance that only knows its chunk type.
+        """
+        raise NotImplementedError
+
+
+class _IHDRChunk(_Chunk):
+    """
+    IHDR chunk, contains the image dimensions
+    """
+    @classmethod
+    def from_offset(cls, chunk_type, stream_rdr, offset):
+        """
+        Return an _IHDRChunk instance containing the image dimensions
+        extracted from the IHDR chunk in *stream* at *offset*.
+        """
+        raise NotImplementedError
+
+
+class _pHYsChunk(_Chunk):
+    """
+    pYHs chunk, contains the image dpi information
+    """
+    @classmethod
+    def from_offset(cls, chunk_type, stream_rdr, offset):
+        """
+        Return a _pHYsChunk instance containing the image resolution
+        extracted from the pHYs chunk in *stream* at *offset*.
+        """
+        raise NotImplementedError
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -14,7 +14,10 @@
 from docx.image.constants import MIME_TYPE, PNG_CHUNK_TYPE, TAG
 from docx.image.exceptions import InvalidImageStreamError
 from docx.image.helpers import BIG_ENDIAN, StreamReader
-from docx.image.png import _Chunk, _Chunks, _ChunkParser, Png, _PngParser
+from docx.image.png import (
+    _Chunk, _Chunks, _ChunkFactory, _ChunkParser, _IHDRChunk, _pHYsChunk,
+    Png, _PngParser
+)
 
 from ..unitutil import (
     function_mock, class_mock, initializer_mock, instance_mock, method_mock,
@@ -438,3 +441,66 @@ def stream_(self, request):
     @pytest.fixture
     def stream_rdr_(self, request):
         return instance_mock(request, StreamReader)
+
+
+class Describe_ChunkFactory(object):
+
+    def it_constructs_the_appropriate_Chunk_subclass(self, call_fixture):
+        chunk_type, stream_rdr_, offset, chunk_cls_ = call_fixture
+        chunk = _ChunkFactory(chunk_type, stream_rdr_, offset)
+        chunk_cls_.from_offset.assert_called_once_with(
+            chunk_type, stream_rdr_, offset
+        )
+        assert isinstance(chunk, _Chunk)
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture(params=[
+        PNG_CHUNK_TYPE.IHDR,
+        PNG_CHUNK_TYPE.pHYs,
+        PNG_CHUNK_TYPE.IEND,
+    ])
+    def call_fixture(
+            self, request, _IHDRChunk_, _pHYsChunk_, _Chunk_, stream_rdr_):
+        chunk_type = request.param
+        chunk_cls_ = {
+            PNG_CHUNK_TYPE.IHDR: _IHDRChunk_,
+            PNG_CHUNK_TYPE.pHYs: _pHYsChunk_,
+            PNG_CHUNK_TYPE.IEND: _Chunk_,
+        }[chunk_type]
+        offset = 999
+        return chunk_type, stream_rdr_, offset, chunk_cls_
+
+    @pytest.fixture
+    def _Chunk_(self, request, chunk_):
+        _Chunk_ = class_mock(request, 'docx.image.png._Chunk')
+        _Chunk_.from_offset.return_value = chunk_
+        return _Chunk_
+
+    @pytest.fixture
+    def chunk_(self, request):
+        return instance_mock(request, _Chunk)
+
+    @pytest.fixture
+    def _IHDRChunk_(self, request, ihdr_chunk_):
+        _IHDRChunk_ = class_mock(request, 'docx.image.png._IHDRChunk')
+        _IHDRChunk_.from_offset.return_value = ihdr_chunk_
+        return _IHDRChunk_
+
+    @pytest.fixture
+    def ihdr_chunk_(self, request):
+        return instance_mock(request, _IHDRChunk)
+
+    @pytest.fixture
+    def _pHYsChunk_(self, request, phys_chunk_):
+        _pHYsChunk_ = class_mock(request, 'docx.image.png._pHYsChunk')
+        _pHYsChunk_.from_offset.return_value = phys_chunk_
+        return _pHYsChunk_
+
+    @pytest.fixture
+    def phys_chunk_(self, request):
+        return instance_mock(request, _pHYsChunk)
+
+    @pytest.fixture
+    def stream_rdr_(self, request):
+        return instance_mock(request, StreamReader)
