-- SSCTopper Database Schema
-- Complete SSC CGL Question Bank

CREATE TABLE IF NOT EXISTS subjects (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL UNIQUE,
    tier TEXT NOT NULL,
    description TEXT,
    target_questions INTEGER DEFAULT 0
);

CREATE TABLE IF NOT EXISTS subtopics (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    subject_id INTEGER NOT NULL,
    name TEXT NOT NULL,
    description TEXT,
    FOREIGN KEY (subject_id) REFERENCES subjects(id),
    UNIQUE(subject_id, name)
);

CREATE TABLE IF NOT EXISTS topics (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    subtopic_id INTEGER NOT NULL,
    name TEXT NOT NULL,
    description TEXT,
    FOREIGN KEY (subtopic_id) REFERENCES subtopics(id),
    UNIQUE(subtopic_id, name)
);

CREATE TABLE IF NOT EXISTS question_types (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    topic_id INTEGER NOT NULL,
    name TEXT NOT NULL,
    FOREIGN KEY (topic_id) REFERENCES topics(id),
    UNIQUE(topic_id, name)
);

CREATE TABLE IF NOT EXISTS questions (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    question_type_id INTEGER NOT NULL,
    question_text TEXT NOT NULL,
    option_a TEXT NOT NULL,
    option_b TEXT NOT NULL,
    option_c TEXT NOT NULL,
    option_d TEXT NOT NULL,
    correct_option TEXT NOT NULL CHECK(correct_option IN ('A','B','C','D')),
    explanation TEXT,
    difficulty INTEGER DEFAULT 1 CHECK(difficulty BETWEEN 1 AND 3),
    year_appeared TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (question_type_id) REFERENCES question_types(id)
);

-- Performance indexes
CREATE INDEX IF NOT EXISTS idx_questions_type ON questions(question_type_id);
CREATE INDEX IF NOT EXISTS idx_questions_difficulty ON questions(difficulty);
CREATE INDEX IF NOT EXISTS idx_topics_subtopic ON topics(subtopic_id);
CREATE INDEX IF NOT EXISTS idx_subtopics_subject ON subtopics(subject_id);
CREATE INDEX IF NOT EXISTS idx_qtypes_topic ON question_types(topic_id);

-- User Management
CREATE TABLE IF NOT EXISTS users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    username TEXT NOT NULL UNIQUE,
    email TEXT NOT NULL UNIQUE,
    password_hash TEXT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Progress Tracking (Question level)
CREATE TABLE IF NOT EXISTS user_answers (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    user_id INTEGER NOT NULL,
    question_id INTEGER NOT NULL,
    is_correct BOOLEAN NOT NULL,
    time_taken REAL DEFAULT 0.0,
    answered_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (question_id) REFERENCES questions(id)
);

CREATE INDEX IF NOT EXISTS idx_user_answers_user ON user_answers(user_id);
CREATE INDEX IF NOT EXISTS idx_user_answers_question ON user_answers(question_id);