ALTER TABLE concerts
ADD COLUMN IF NOT EXISTS visibility VARCHAR(20) NOT NULL DEFAULT 'public'
CHECK (visibility IN ('public', 'friends', 'private'));

CREATE TABLE IF NOT EXISTS event_invitations (
    concert_id INTEGER NOT NULL REFERENCES concerts(id) ON DELETE CASCADE,
    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
    invited_by INTEGER REFERENCES users(id) ON DELETE SET NULL,
    viewed_at TIMESTAMP,
    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (concert_id, user_id)
);

CREATE INDEX IF NOT EXISTS idx_event_invitations_user
ON event_invitations (user_id, viewed_at);