📝 Added documentation for the cqa-file-format used for quizzes

classquiz/routers/cqa-file-format.md

@@ -0,0 +1,26 @@
+# .cqa - ClassQuizArchive
+
+A file-format for ClassQuiz-quizzes which stores images and the quiz in one compact file
+
+## How the file format works
+
+```
+[QUIZ_DATA] {C7 C7 C7 00}
+{C6 C6 C6 00} [UTF-8 encoded image-index] {C5 C5 00} [IMAGE as it is]
+{C6 C6 C6 00} [UTF-8 encoded image-index] {C5 C5 00} [IMAGE as it is]
+```
+## Understanding the schema
+
+### in {}
+- `{C7 C7 C7 00}`: separates the quiz-data from the images
+- `{C6 C6 C6 00}`: Indicates that a new image-block starts
+- `{C5 C5 00}`: separates image-index and image
+
+### in []
+- `[QUIZ_DATA]`: The **gzipped JSON** of the quiz with some modifications:
+  - Removed `id`-field and `user_id`-field
+  - Dates (`created_at` and `updated_at`) formatted as ISO-Dates
+  - Images replaced with their question-index
+  - Cover-image with index `-1`
+- `[UTF-8 encoded image-index]`: The index of the question which the image belongs to.
+- `[IMAGE as it is]`: The unmodified uploaded image (jpg, png, webp, etc.)