img: add _IfdEntries.from_stream()

Steve Canny · Steve Canny · commit e72d14d22a77 · 2014-02-27T12:08:36.000-08:00
diff --git a/docx/image/tiff.py b/docx/image/tiff.py
@@ -113,4 +113,44 @@ def from_stream(cls, stream, offset):
         Return a new |_IfdEntries| instance parsed from *stream* starting at
         *offset*.
         """
+        ifd_parser = _IfdParser(stream, offset)
+        entries = dict((e.tag, e.value) for e in ifd_parser.iter_entries())
+        return cls(entries)
+
+
+class _IfdParser(object):
+    """
+    Service object that knows how to extract directory entries from an Image
+    File Directory (IFD)
+    """
+    def __init__(self, stream_rdr, offset):
+        super(_IfdParser, self).__init__()
+        self._stream_rdr = stream_rdr
+        self._offset = offset
+
+    def iter_entries(self):
+        """
+        Generate an |_IfdEntry| instance corresponding to each entry in the
+        directory.
+        """
+        raise NotImplementedError
+
+
+class _IfdEntry(object):
+    """
+    Base class for IFD entry classes. Subclasses are differentiated by value
+    type, e.g. ASCII, long int, etc.
+    """
+    @property
+    def tag(self):
+        """
+        Short int code that identifies this IFD entry
+        """
+        raise NotImplementedError
+
+    @property
+    def value(self):
+        """
+        Value of this tag, its type being dependent on the tag.
+        """
         raise NotImplementedError
diff --git a/tests/image/test_tiff.py b/tests/image/test_tiff.py
@@ -10,7 +10,9 @@
 
 from docx.compat import BytesIO
 from docx.image.helpers import BIG_ENDIAN, LITTLE_ENDIAN, StreamReader
-from docx.image.tiff import _IfdEntries, Tiff, _TiffParser
+from docx.image.tiff import (
+    _IfdEntries, _IfdEntry, _IfdParser, Tiff, _TiffParser
+)
 
 from ..unitutil import (
     initializer_mock, class_mock, instance_mock, method_mock
@@ -153,3 +155,55 @@ def stream_rdr_(self, request, ifd0_offset_):
     @pytest.fixture
     def _TiffParser__init_(self, request):
         return initializer_mock(request, _TiffParser)
+
+
+class Describe_IfdEntries(object):
+
+    def it_can_construct_from_a_stream_and_offset(self, from_stream_fixture):
+        stream_, offset_, _IfdParser_, _IfdEntries__init_, entries_ = (
+            from_stream_fixture
+        )
+        ifd_entries = _IfdEntries.from_stream(stream_, offset_)
+        _IfdParser_.assert_called_once_with(stream_, offset_)
+        _IfdEntries__init_.assert_called_once_with(entries_)
+        assert isinstance(ifd_entries, _IfdEntries)
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture
+    def from_stream_fixture(
+            self, stream_, offset_, _IfdParser_, ifd_parser_,
+            _IfdEntries__init_, ifd_entry_, ifd_entry_2_):
+        ifd_parser_.iter_entries.return_value = [ifd_entry_, ifd_entry_2_]
+        entries_ = {1: 42, 2: 24}
+        return stream_, offset_, _IfdParser_, _IfdEntries__init_, entries_
+
+    @pytest.fixture
+    def ifd_entry_(self, request):
+        return instance_mock(request, _IfdEntry, tag=1, value=42)
+
+    @pytest.fixture
+    def ifd_entry_2_(self, request):
+        return instance_mock(request, _IfdEntry, tag=2, value=24)
+
+    @pytest.fixture
+    def _IfdEntries__init_(self, request):
+        return initializer_mock(request, _IfdEntries)
+
+    @pytest.fixture
+    def _IfdParser_(self, request, ifd_parser_):
+        return class_mock(
+            request, 'docx.image.tiff._IfdParser', return_value=ifd_parser_
+        )
+
+    @pytest.fixture
+    def ifd_parser_(self, request):
+        return instance_mock(request, _IfdParser)
+
+    @pytest.fixture
+    def offset_(self, request):
+        return instance_mock(request, int)
+
+    @pytest.fixture
+    def stream_(self, request):
+        return instance_mock(request, BytesIO)
