From efac56f80f609dc3e4cd139a300c0be7352f1990 Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@tremily.us>
Date: Tue, 5 Feb 2013 10:37:41 -0500
Subject: [PATCH] ui: Add dependency handling to UserInterface.get_question

We start the stack with all the leaf questions (i.e. questions that
are not dependencies of other question).  If the user gets one wrong,
we push the question back on the stack (so they can try again later),
and also push all of that questions direct dependencies onto the stack
(so they can get the background they need to answer the question they
got wrong).
---
 quizzer/quiz.py        | 16 ++++++++++++++++
 quizzer/ui/__init__.py | 15 +++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/quizzer/quiz.py b/quizzer/quiz.py
index 86b029a..c3fa5a5 100644
--- a/quizzer/quiz.py
+++ b/quizzer/quiz.py
@@ -41,3 +41,19 @@ class Quiz (list):
             _json.dump(
                 data, f, indent=2, separators=(',', ': '), sort_keys=True)
             f.write('\n')
+
+    def leaf_questions(self):
+        "Questions that are not dependencies of other question"
+        dependents = set()
+        for question in self:
+            dependents.update(question.dependencies)
+        return [q for q in self if q.id not in dependents]
+
+    def get(self, id=None):
+        matches = [q for q in self if q.id == id]
+        if len(matches) == 1:
+            return matches[0]
+        elif len(matches) == 0:
+            raise KeyError(id)
+        raise NotImplementedError(
+            'multiple questions with one ID: {}'.format(matches))
diff --git a/quizzer/ui/__init__.py b/quizzer/ui/__init__.py
index 8fb8b06..3a1c37f 100644
--- a/quizzer/ui/__init__.py
+++ b/quizzer/ui/__init__.py
@@ -3,11 +3,14 @@ from .. import answerdb as _answerdb
 
 class UserInterface (object):
     "Give a quiz over a generic user interface"
-    def __init__(self, quiz=None, answers=None):
+    def __init__(self, quiz=None, answers=None, stack=None):
         self.quiz = quiz
         if answers is None:
             answers = _answerdb.AnswerDatabase()
         self.answers = answers
+        if stack is None:
+            stack = quiz.leaf_questions()
+        self.stack = stack
 
     def run(self):
         raise NotImplementedError()
@@ -16,11 +19,15 @@ class UserInterface (object):
         raise NotImplementedError()
 
     def get_question(self):
-        remaining = self.answers.get_unanswered(questions=self.quiz)
-        if remaining:
-            return remaining[0]
+        if self.stack:
+            print(self.stack)
+            return self.stack.pop(0)
 
     def process_answer(self, question, answer):
         correct = question.check(answer)
         self.answers.add(question=question, answer=answer, correct=correct)
+        if not correct:
+            self.stack.insert(0, question)
+            for qid in reversed(question.dependencies):
+                self.stack.insert(0, self.quiz.get(id=qid))
         return correct
-- 
2.26.2