-- ============================================
-- PastPaper Master — Question taxonomy fields
-- Version: 003
-- Date: 2026-03-24
-- ============================================

-- A question needs multiple classification layers:
-- 1) question_format: how the student interacts with it
-- 2) topic_tags / topic_primary / analytics_topic: course knowledge taxonomy
-- 3) skill_tags: what kind of thinking task the question requires
ALTER TABLE paper_questions
  ADD COLUMN IF NOT EXISTS question_format TEXT
    CHECK (
      question_format IN (
        'mc',
        'true_false',
        'fill_blank',
        'short_answer',
        'long_answer',
        'coding'
      )
    ),
  ADD COLUMN IF NOT EXISTS topic_primary TEXT,
  ADD COLUMN IF NOT EXISTS analytics_topic TEXT,
  ADD COLUMN IF NOT EXISTS topic_tags TEXT[],
  ADD COLUMN IF NOT EXISTS skill_tags TEXT[];

-- Keep the legacy topics column for backward compatibility for now.
-- New analytics and retrieval code should gradually move to analytics_topic/topic_tags.

CREATE INDEX IF NOT EXISTS idx_questions_question_format
  ON paper_questions(question_format);

CREATE INDEX IF NOT EXISTS idx_questions_analytics_topic
  ON paper_questions(analytics_topic);

CREATE INDEX IF NOT EXISTS idx_questions_topic_tags
  ON paper_questions USING GIN(topic_tags);

CREATE INDEX IF NOT EXISTS idx_questions_skill_tags
  ON paper_questions USING GIN(skill_tags);