From 4860306bb613a3df5090da2dfe206968a328892e Mon Sep 17 00:00:00 2001
From: Florian Knoch <florian.knoch@stud.uni-bamberg.de>
Date: Wed, 10 Jun 2020 17:12:49 +0200
Subject: [PATCH] Add option to lazyload images

---
 helper.py | 13 ++++++++++++-
 main.py   | 22 ++++++++++++++++------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/helper.py b/helper.py
index f979184..ff944cd 100644
--- a/helper.py
+++ b/helper.py
@@ -1,6 +1,7 @@
 import os
 import stat
 import yaml
+import re
 
 # Calls a YAML parser for the given relative path inside the presentation root
 # directory. Returns a dictionary with the YAML content.
@@ -29,4 +30,14 @@ def insert_metadata(content, root, lang):
 
 # Retrieve the modification time for a given file.
 def get_modification_time(path):
-    return os.stat(path)[stat.ST_MTIME]
\ No newline at end of file
+    return os.stat(path)[stat.ST_MTIME]
+
+# Replace the "src" attribute on images by "data-src".
+# Should be done after caching because fragments#defragmentize requires 
+# valid XHTML and data-src causes problems with that.
+# Also: Toggling lazyload is easier this way.
+def add_lazyload(source, lazyload_images):
+    if lazyload_images:
+        return re.sub(r'<img(.*)src=', r'<img\1data-src=', source)
+    else:
+        return source
diff --git a/main.py b/main.py
index 4a26b75..0b091b3 100755
--- a/main.py
+++ b/main.py
@@ -10,28 +10,38 @@ import helper
 
 # Compiles a presentation in the given language from the given directory and
 # stores it in a corresponding slides.lang.html file inside the same directory.
-def compile(root, language='en', force_recompile=False):
+
+
+def compile(root, language='en', force_recompile=False, lazyload_images=False):
     wrapper = open(os.path.join(root, 'layouts/root.html'), 'r').read()
     compiled_chapters = chapters.compile_chapters(root, language, force_recompile)
     wrapper = wrapper.replace('@slides', compiled_chapters)
     wrapper = helper.insert_metadata(wrapper, root, language)
     wrapper = fragments.defragmentize(wrapper)
+    wrapper = helper.add_lazyload(wrapper, lazyload_images)
     with open(os.path.join(root, 'slides.' + language + '.html'), 'w+') as output:
         output.write(wrapper)
     print('done')
 
+
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
     parser.add_argument("rootdirectory", help="your project's root directory")
-    parser.add_argument("-l", "--language", default="all", help="the presentation language (default: all)")
-    parser.add_argument("-f", "--force-recompile", action='store_true', help="recompiling the entire presentation without caches")
+    parser.add_argument("-l", "--language", default="all",
+                        help="the presentation language (default: all)")
+    parser.add_argument("-f", "--force-recompile", action='store_true',
+                        help="recompile the entire presentation without caches")
+    parser.add_argument("-i", "--lazyload-images", action='store_true',
+                        help="replace all images' src attributes by data-src for image lazyloading")
 
     args = parser.parse_args()
     force_recompile = False or args.force_recompile
+    lazyload_images = False or args.lazyload_images
 
     if args.language == "all":
         for language in helper.get_available_languages(args.rootdirectory):
-            compile(args.rootdirectory, language=language, force_recompile=force_recompile)
+            compile(args.rootdirectory, language=language,
+                    force_recompile=force_recompile, lazyload_images=lazyload_images)
     else:
-        compile(args.rootdirectory, language=args.language, force_recompile=force_recompile)
-
+        compile(args.rootdirectory, language=args.language,
+                force_recompile=force_recompile, lazyload_images=lazyload_images)