-- Quizzes on the library's content.
--
-- A quiz is attached to a piece of content by its app path — a book chapter
-- (/books/bg/2), or a lecture or conversation (/transcriptions/{slug}) — or to
-- nothing at all, for a stand-alone quiz. The path is what the content page
-- already knows about itself, so it can ask "is there a quiz for me?" without
-- the content's Mongo id ever reaching Postgres.
CREATE TABLE IF NOT EXISTS quizzes (
    id           UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
    title        VARCHAR(200) NOT NULL,
    -- Light formatting markers, rendered like the rest of the admin text.
    description  TEXT         NOT NULL DEFAULT '',
    -- chapter | lecture | conversation | standalone
    target_kind  VARCHAR(16)  NOT NULL DEFAULT 'standalone',
    -- App path of the content, NULL for a stand-alone quiz.
    target_path  TEXT,
    -- Display name of the content, captured when the quiz is made.
    target_title TEXT         NOT NULL DEFAULT '',
    published_at TIMESTAMPTZ,
    created_by   UUID         REFERENCES users(id) ON DELETE SET NULL,
    created_at   TIMESTAMPTZ  NOT NULL DEFAULT now(),
    updated_at   TIMESTAMPTZ  NOT NULL DEFAULT now(),
    -- Soft delete: participants' results stay intact for the record.
    deleted_at   TIMESTAMPTZ,
    CONSTRAINT quizzes_target_kind_check
        CHECK (target_kind IN ('chapter', 'lecture', 'conversation', 'standalone')),
    CONSTRAINT quizzes_target_consistent
        CHECK ((target_kind = 'standalone') = (target_path IS NULL))
);

-- "Is there a quiz for this page?" — asked by every content page load.
CREATE INDEX IF NOT EXISTS quizzes_target_idx
    ON quizzes (target_path, published_at DESC)
    WHERE deleted_at IS NULL AND published_at IS NOT NULL;

CREATE TABLE IF NOT EXISTS quiz_questions (
    id         UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
    quiz_id    UUID        NOT NULL REFERENCES quizzes(id) ON DELETE CASCADE,
    ord        SMALLINT    NOT NULL,
    prompt     TEXT        NOT NULL,
    -- Optional note shown with the answer on the results screen.
    explanation TEXT       NOT NULL DEFAULT '',
    UNIQUE (quiz_id, ord)
);

CREATE TABLE IF NOT EXISTS quiz_options (
    id          UUID     PRIMARY KEY DEFAULT gen_random_uuid(),
    question_id UUID     NOT NULL REFERENCES quiz_questions(id) ON DELETE CASCADE,
    ord         SMALLINT NOT NULL,
    body        TEXT     NOT NULL,
    is_correct  BOOLEAN  NOT NULL DEFAULT FALSE,
    UNIQUE (question_id, ord),
    -- Five options at most; the service also enforces two at least and
    -- exactly one correct.
    CONSTRAINT quiz_options_ord_check CHECK (ord BETWEEN 0 AND 4)
);

-- One attempt per person per quiz: it is what "Continue" resumes and what
-- "View results" shows.
CREATE TABLE IF NOT EXISTS quiz_attempts (
    id           UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
    quiz_id      UUID        NOT NULL REFERENCES quizzes(id) ON DELETE CASCADE,
    user_id      UUID        NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    started_at   TIMESTAMPTZ NOT NULL DEFAULT now(),
    completed_at TIMESTAMPTZ,
    score        INTEGER     NOT NULL DEFAULT 0,
    total        INTEGER     NOT NULL DEFAULT 0,
    UNIQUE (quiz_id, user_id)
);

CREATE INDEX IF NOT EXISTS quiz_attempts_user_idx ON quiz_attempts (user_id);

-- One row per question an attempt has reached.
--
-- Timing is measured by the SERVER: shown_at is stamped when the question is
-- handed to the client, answered_at when the answer arrives. A client-reported
-- duration could be anything; these two timestamps can't be edited from the
-- browser.
CREATE TABLE IF NOT EXISTS quiz_answers (
    attempt_id  UUID        NOT NULL REFERENCES quiz_attempts(id) ON DELETE CASCADE,
    question_id UUID        NOT NULL REFERENCES quiz_questions(id) ON DELETE CASCADE,
    option_id   UUID        REFERENCES quiz_options(id) ON DELETE SET NULL,
    shown_at    TIMESTAMPTZ NOT NULL DEFAULT now(),
    answered_at TIMESTAMPTZ,
    response_ms INTEGER,
    is_correct  BOOLEAN,
    PRIMARY KEY (attempt_id, question_id)
);