Resolve "Fix move slides on backend"

Closes #161 (closed)

server/app/database/controller/utils.py

@@ -18,7 +18,6 @@ def move_slides(item_competition, from_order, to_order):
     assert 0 <= from_order < num_slides, "Invalid order to move from"
     assert 0 <= to_order < num_slides, "Invalid order to move to"
 
-    # TODO: Please improve this terrible piece of code
     # This function is sooo terrible, someone please tell me how to update
     # multiple values in the database at the same time with unique constraints.
     # If you update all the values at the same time none of them will collide
@@ -26,36 +25,54 @@ def move_slides(item_competition, from_order, to_order):
     # other value before and then change every value back to the correct one,
     # so 2 commits.
 
+    # An example will follow the entire code to make it clear what it does
+    # Lets say we have 5 slides, and we want to move the slide at index 1
+    # to index 4.
+    # We begin with a list of slides with orders [0, 1, 2, 3, 4]
+
     slides = item_competition.slides
 
     change = 1 if to_order < from_order else -1
     start_order = min(from_order, to_order)
     end_order = max(from_order, to_order)
 
+    # Move slides up 100
     for item_slide in slides:
         item_slide.order += 100
 
+    # Our slide orders now look like [100, 101, 102, 103, 104]
+
     # Move slides between from and to order either up or down, but minus in front
     for item_slide in slides:
         if start_order <= item_slide.order - 100 <= end_order:
             item_slide.order = -(item_slide.order + change)
 
+    # Our slide orders now look like [100, -100, -101, -102, -103]
+
     # Find the slide that was to be moved and change it to correct order with minus in front
     for item_slide in slides:
         if item_slide.order == -(from_order + change + 100):
             item_slide.order = -(to_order + 100)
             break
 
+    # Our slide orders now look like [100, -104, -101, -102, -103]
+
     db.session.commit()
 
-    # Negate all order so that they become correct and positive
+    # Negate all order so that they become positive
     for item_slide in slides:
         if start_order <= -(item_slide.order + 100) <= end_order:
             item_slide.order = -(item_slide.order)
 
+    # Our slide orders now look like [100, 104, 101, 102, 103]
+
     for item_slide in slides:
         item_slide.order -= 100
 
+    # Our slide orders now look like [0, 4, 1, 2, 3]
+
+    # We have now successfully moved slide 1 to 4
+
     return commit_and_refresh(item_competition)