font-patcher: Allow patching of True Type Collections

[why]
Someone might want to patch a whole lot of fonts that come in a ttc.

[how]
Just open all fonts that the input file contains (1 or more) and create
a single font or collection font file.

The automatic layer detection does not work in all cases for me, so we
need to manually search for the foreground layer (usually '1').

Code inspiration taken from
powerline/fontpatcher#6

[note]
Changed output in the end to the filename (before it was the font name),
so that one can easily copy&paste or open that file.

Reported-by: Lily Ballard <lily@ballards.net>
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

font-patcher

@@ -977,43 +977,64 @@ def setup_arguments():
             sys.exit("{}: Font file does not exist: {}".format(projectName, args.font))
         if not os.access(args.font, os.R_OK):
             sys.exit("{}: Can not open font file for reading: {}".format(projectName, args.font))
-        if len(fontforge.fontsInFile(args.font)) > 1:
-            sys.exit("{}: Font file contains {} fonts, can only handle single font files".format(projectName,
-                len(fontforge.fontsInFile(args.font))))
+        is_ttc = len(fontforge.fontsInFile(args.font)) > 1
 
         if args.extension == "":
             args.extension = os.path.splitext(args.font)[1]
         else:
             args.extension = '.' + args.extension
         if re.match("\.ttc$", args.extension, re.IGNORECASE):
-            sys.exit(projectName + ": Can not create True Type Collections")
+            if not is_ttc:
+                sys.exit(projectName + ": Can not create True Type Collections from single font files")
+        else:
+            if is_ttc:
+                sys.exit(projectName + ": Can not create single font files from True Type Collections")
 
     return args
 
 
 def main():
-    print("{} Patcher v{} executing\n".format(projectName, version))
+    print("{} Patcher v{} executing".format(projectName, version))
     check_fontforge_min_version()
     args = setup_arguments()
     patcher = font_patcher(args)
 
-    try:
-        sourceFont = fontforge.open(args.font, 1) # 1 = ("fstypepermitted",))
-    except Exception:
-        sys.exit(projectName + ": Can not open font, try to open with fontforge interactively to get more information")
+    sourceFonts = []
+    for subfont in fontforge.fontsInFile(args.font):
+        print("\n{}: Processing {}".format(projectName, subfont))
+        try:
+            sourceFonts.append(fontforge.open("{}({})".format(args.font, subfont), 1)) # 1 = ("fstypepermitted",))
+        except Exception:
+            sys.exit("{}: Can not open font '{}', try to open with fontforge interactively to get more information".format(
+                projectName, subfont))
 
-    patcher.patch(sourceFont)
+        patcher.patch(sourceFonts[-1])
 
     print("\nDone with Patch Sets, generating font...")
 
-    # the `PfEd-comments` flag is required for Fontforge to save '.comment' and '.fontlog'.
-    if sourceFont.fullname != None:
-        sourceFont.generate(args.outputdir + "/" + sourceFont.fullname + args.extension, flags=(str('opentype'), str('PfEd-comments')))
-        print("\nGenerated: {}".format(sourceFont.fontname))
+    sourceFont = sourceFonts[0]
+    if len(sourceFonts) > 1:
+        layer = None
+        # use first non-background layer
+        for l in sourceFont.layers:
+            if not sourceFont.layers[l].is_background:
+                layer = l
+                break
+        fontname = args.outputdir + "/" + sourceFont.familyname + ".ttc"
+        # the `PfEd-comments` flag is required for Fontforge to save '.comment' and '.fontlog'.
+        sourceFonts[0].generateTtc(fontname, sourceFonts[1:], flags=(str('opentype'), str('PfEd-comments')), layer=layer)
     else:
-        sourceFont.generate(args.outputdir + "/" + sourceFont.cidfontname + args.extension, flags=(str('opentype'), str('PfEd-comments')))
-        print("\nGenerated: {}".format(sourceFont.fullname))
-    sourceFont.close()
+        fontname = sourceFont.fullname
+        if not fontname:
+            fontname = sourceFont.cidfontname
+        fontname = args.outputdir + "/" + fontname + args.extension
+        # the `PfEd-comments` flag is required for Fontforge to save '.comment' and '.fontlog'.
+        sourceFont.generate(fontname, flags=(str('opentype'), str('PfEd-comments')))
+
+    print("\nGenerated: '{}'".format(fontname))
+
+    for f in sourceFonts:
+        f.close()
 
     if args.postprocess:
         subprocess.call([args.postprocess, args.outputdir + "/" + sourceFont.fullname + args.extension])