CREATE TABLE IF NOT EXISTS referral_codes (
    id BIGSERIAL PRIMARY KEY,
    code VARCHAR(12) NOT NULL UNIQUE,

    referrer_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,

    is_active BOOLEAN NOT NULL DEFAULT TRUE,
    max_uses INT,
    current_uses INT NOT NULL DEFAULT 0,

    incentive_type TEXT NOT NULL CHECK (
        incentive_type IN (
            'course_access',
            'discount',
            'certificate_unlock',
            'feature_unlock'
        )
    ),

    incentive_value TEXT, -- e.g. course_id, percentage, feature_key

    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP
);

CREATE INDEX idx_referral_codes_referrer_id
    ON referral_codes (referrer_id);

CREATE INDEX idx_referral_codes_code
    ON referral_codes (code);


CREATE TABLE IF NOT EXISTS user_referrals (
    id BIGSERIAL PRIMARY KEY,

    referrer_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    referred_user_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,

    referral_code_id BIGINT NOT NULL REFERENCES referral_codes(id) ON DELETE CASCADE,

    created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,

    UNIQUE (referred_user_id),
    UNIQUE (referrer_id, referred_user_id)
);