kiwix-resources preprocesses all resources

kiwix-resources preprocesses all resources rather than only templates. At
this point this doesn't change anything since only (some) template resources
contain KIWIXCACHEID placeholders. But this enhancement opens the door
to the preprocessing of static/skin/index.js (after preprocessing is
able to handle relative links, which comes in the next commit).

scripts/kiwix-resources

@@ -61,14 +61,21 @@ def preprocess_line(line):
         assert not 'KIWIXCACHEID' in line
     return line
 
-def preprocess_template(srcpath, dstpath):
+def get_preprocessed_resource(srcpath):
+    modified_line_count = 0
     preprocessed_lines = []
-    with open(srcpath, 'r') as source:
-        for line in source:
-            preprocessed_lines.append(preprocess_line(line))
+    try:
+        with open(srcpath, 'r') as source:
+            for line in source:
+                ppline = preprocess_line(line)
+                if ppline != line:
+                    modified_line_count += 1
+                preprocessed_lines.append(ppline)
+        return "".join(preprocessed_lines), modified_line_count
+    except UnicodeDecodeError:
+        # It was a binary resource
+        return None, 0
 
-    with open(dstpath, 'w') as target:
-        print("".join(preprocessed_lines), end='', file=target)
 
 def symlink_resource(src, resource_path):
     if os.path.exists(resource_path):
@@ -78,15 +85,19 @@ def symlink_resource(src, resource_path):
     os.symlink(src, resource_path)
 
 def preprocess_resource(srcdir, resource_path, outdir):
+    print(f'Preprocessing {resource_path}...')
     resource_dir = os.path.dirname(resource_path)
     if resource_dir != '':
         os.makedirs(os.path.join(outdir, resource_dir), exist_ok=True)
     srcpath = os.path.join(srcdir, resource_path)
     outpath = os.path.join(outdir, resource_path)
-    if resource_path.startswith('templates/'):
-        preprocess_template(srcpath, outpath)
-    else:
+    preprocessed_content, modified_line_count = get_preprocessed_resource(srcpath)
+    if modified_line_count == 0:
         symlink_resource(srcpath, outpath)
+    else:
+        with open(outpath, 'w') as target:
+            print(preprocessed_content, end='', file=target)
+
 
 def copy_file(src_path, dst_path):
     with open(src_path, 'rb') as src: