-- backend/db/schema.sql
-- Run once via: uv run python backend/db/apply_schema.py

-- batches first (no FK to users yet — circular dependency resolved below)
CREATE TABLE IF NOT EXISTS batches (
  id            UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  name          TEXT NOT NULL,
  instructor_id UUID NOT NULL,
  class_code    TEXT NOT NULL UNIQUE DEFAULT upper(substring(gen_random_uuid()::text, 1, 8)),
  created_at    TIMESTAMPTZ DEFAULT NOW()
);

-- users references batches
CREATE TABLE IF NOT EXISTS users (
  id            UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  full_name     TEXT NOT NULL,
  email         TEXT NOT NULL UNIQUE,
  password_hash TEXT NOT NULL,
  role          TEXT NOT NULL CHECK (role IN ('student', 'instructor')),
  batch_id      UUID REFERENCES batches(id) ON DELETE SET NULL,
  created_at    TIMESTAMPTZ DEFAULT NOW()
);

-- add FK from batches.instructor_id → users.id (deferred until users exists)
DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM information_schema.table_constraints
    WHERE constraint_name = 'batches_instructor_id_fkey'
      AND table_name = 'batches'
  ) THEN
    ALTER TABLE batches
      ADD CONSTRAINT batches_instructor_id_fkey
      FOREIGN KEY (instructor_id) REFERENCES users(id) ON DELETE CASCADE;
  END IF;
END $$;

CREATE TABLE IF NOT EXISTS refresh_tokens (
  id         UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  user_id    UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
  token_hash TEXT NOT NULL,
  expires_at TIMESTAMPTZ NOT NULL,
  created_at TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS topics (
  id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  batch_id    UUID NOT NULL REFERENCES batches(id) ON DELETE CASCADE,
  name        TEXT NOT NULL,
  is_unlocked BOOLEAN NOT NULL DEFAULT FALSE,
  order_index INTEGER NOT NULL DEFAULT 0,
  created_at  TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS questions (
  id            UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  topic_id      UUID NOT NULL REFERENCES topics(id) ON DELETE CASCADE,
  question_text TEXT NOT NULL,
  difficulty    TEXT NOT NULL CHECK (difficulty IN ('easy', 'medium', 'hard')) DEFAULT 'medium',
  created_at    TIMESTAMPTZ DEFAULT NOW()
);

CREATE TABLE IF NOT EXISTS interview_sessions (
  id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  student_id   UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
  topic_id     UUID NOT NULL REFERENCES topics(id) ON DELETE CASCADE,
  status       TEXT NOT NULL CHECK (status IN ('active', 'completed')) DEFAULT 'active',
  score        INTEGER CHECK (score >= 0 AND score <= 100),
  feedback     JSONB,
  started_at   TIMESTAMPTZ DEFAULT NOW(),
  completed_at TIMESTAMPTZ
);