Prefer high-performing distractors

scripts/autoload/block_session_service.gd

@@ -546,6 +546,7 @@ func _prepare_question_choices(question: Dictionary) -> Dictionary:
 
 	var all_choices: Array = question.get("choices", []).duplicate(true)
 	var correct_id := str(question.get("correct_choice_id", ""))
+	var percentages: Dictionary = question.get("choice_selection_percentages", {})
 	var correct_choice: Dictionary = {}
 	var distractors: Array = []
 	for choice in all_choices:
@@ -556,8 +557,7 @@ func _prepare_question_choices(question: Dictionary) -> Dictionary:
 		else:
 			distractors.append(choice)
 
-	distractors.shuffle()
-	var presented: Array = distractors.slice(0, min(4, distractors.size()))
+	var presented: Array = _select_weighted_distractors(distractors, percentages, 4)
 	if not correct_choice.is_empty():
 		presented.append(correct_choice)
 	elif not all_choices.is_empty():
@@ -567,6 +567,31 @@ func _prepare_question_choices(question: Dictionary) -> Dictionary:
 	return question
 
 
+func _select_weighted_distractors(distractors: Array, percentages: Dictionary, count: int) -> Array:
+	var remaining: Array = distractors.duplicate(true)
+	var selected: Array = []
+	while selected.size() < count and not remaining.is_empty():
+		var total_weight := 0.0
+		for choice in remaining:
+			total_weight += _distractor_weight(str(choice.get("id", "")), percentages)
+		var threshold := randf() * total_weight
+		var cumulative := 0.0
+		var selected_index := remaining.size() - 1
+		for index in range(remaining.size()):
+			cumulative += _distractor_weight(str(remaining[index].get("id", "")), percentages)
+			if threshold < cumulative:
+				selected_index = index
+				break
+		selected.append(remaining[selected_index])
+		remaining.remove_at(selected_index)
+	return selected
+
+
+func _distractor_weight(choice_id: String, percentages: Dictionary) -> float:
+	var selection_rate := clampf(float(percentages.get(choice_id, 0)), 0.0, 100.0)
+	return 1.0 + 5.0 * selection_rate / 100.0
+
+
 func _build_core_question_pool() -> Array:
 	var pool: Array = []
 	var profile := ProfileService.get_profile()