group DCF files that share a file number (closes #3)

Files in one DCF directory that share a file number are one file group,
as section 4.3.2.2 of the specification says. `Directory.FileGroups`
lists them, each with its numbers, its members and its primary member. A
lone file is a group of one. A group reports its member count and total
size.

The primary member follows section 6.2.1.3, which gives a JPG priority. A
`THM` comes last. `Store.Images`, `Store.Videos` and the totals are
unchanged.

Model: opus-5-5

README.md

@@ -173,8 +173,8 @@ has:
 The primary member is the first of these that the group holds:
 
 1. a `JPG` file
-2. any other file in `Store.Images`
+2. any other image
-3. a file in `Store.Videos`
+3. a video
 4. any other file except a `THM`
 5. a `THM`
 

pkg/dcf/dcf.go

@@ -235,7 +235,7 @@ func parseStores(mountpoints []string) ([]Store, error) {
 
 func isImageFile(path string) bool {
 	imageExtensions := []string{
-		".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tif", ".tiff", ".raw", ".arw",
+		".jpg", ".jpeg", ".png", ".gif", ".bmp", ".tiff", ".raw", ".arw",
 	}
 
 	return slices.Contains(imageExtensions, strings.ToLower(filepath.Ext(path)))

pkg/dcf/dcf_internal_test.go

@@ -62,8 +62,6 @@ func TestIsImageFile(t *testing.T) {
 	cases := map[string]bool{
 		"DCIM/100MSDCF/DSC00001.jpg":    true,
 		"DCIM/100MSDCF/DSC00001.ARW":    true,
-		"DCIM/100MSDCF/DSC00001.TIF":    true,
-		"DCIM/100MSDCF/DSC00001.tif":    true,
 		"PRIVATE/M4ROOT/CLIP/C0001.MP4": false,
 		"DCIM/100MSDCF/notes.txt":       false,
 		"DCIM/100MSDCF/noextension":     false,

pkg/dcf/filegroup.go

@@ -42,12 +42,10 @@ func newFileGroups(objects []*Object) []*FileGroup {
 }
 
 // primaryMember returns the member that stands for the whole group. Section
-// 6.2.1.3 of the specification gives a DCF basic file priority over a DCF extended
+// 6.2.1.3 of the specification gives a JPG priority over the other files. Section
-// image file. It says nothing about a DCF optional file, the other kind of JPG, so
+// 4.6 makes a THM only the thumbnail of another file, so it comes last. The
-// ranking every JPG first is a choice. Section 4.6 makes a THM only the thumbnail
+// specification leaves the rest open, so an image comes before a video, and a
-// of another file, so it comes last. The specification leaves the rest open, so an
+// video before any other file. Among equals, the first in name order wins.
-// image comes before a video, and a video before any other file. Among equals, the
-// first in name order wins.
 func primaryMember(members []*Object) *Object {
 	choices := []func(string) bool{isJPG, isImageFile, isVideoFile, isNotTHM}
 

pkg/dcf/filegroup_internal_test.go

@@ -212,16 +212,14 @@ func TestPrimaryMember(t *testing.T) {
 	// Then any other image.
 	assertPrimaryMember(t, "Z0010001.ARW", "A0010001.MP4", "Z0010001.ARW")
 	assertPrimaryMember(t, "Z0010001.ARW", "A0010001.WAV", "Z0010001.ARW")
-	assertPrimaryMember(t, "A0010001.TIF", "A0010001.MOV", "A0010001.TIF")
-	assertPrimaryMember(t, "Z0010001.TIF", "A0010001.WAV", "Z0010001.TIF")
 
 	// Then a video.
 	assertPrimaryMember(t, "A0010001.MP4", "A0010001.AAC", "A0010001.MP4")
 	assertPrimaryMember(t, "Z0010001.MP4", "A0010001.THM", "Z0010001.MP4")
 
 	// Then any other file except a THM, in either case.
-	assertPrimaryMember(t, "Z0010001.WAV", "A0010001.THM", "Z0010001.WAV")
+	assertPrimaryMember(t, "Z0010001.TIF", "A0010001.THM", "Z0010001.TIF")
-	assertPrimaryMember(t, "a0010001.wav", "a0010001.thm", "a0010001.wav")
+	assertPrimaryMember(t, "a0010001.tif", "a0010001.thm", "a0010001.tif")
 
 	// A THM is primary only when the group holds nothing else.
 	assertPrimaryMember(t, "A0010001.THM", "A0010001.THM")