-- Per-user interface preferences.
--
-- These live in their own table rather than as columns on users, because users is
-- a projection of the identity provider's claims: UpsertUser rewrites it on every
-- login. A row appears the first time somebody saves a preference and is keyed by
-- the same subject, so the choice survives re-login and follows the account to
-- another browser.
--
-- An empty selected_theme means the person has not chosen a theme, which the UI
-- renders as its own default rather than as a stored value.
--
-- There is deliberately no foreign key to users. That table is a projection of the
-- identity provider's claims and can be rebuilt from a backup, so a cascade from it
-- would silently discard people's choices, and requiring the row to exist would make
-- saving a preference depend on projection state that has nothing to do with the
-- preference. A row whose subject never logs in again is inert and costs nothing.
CREATE TABLE IF NOT EXISTS user_preferences (
    subject             TEXT NOT NULL PRIMARY KEY,
    selected_theme      TEXT NOT NULL DEFAULT '',
    selected_appearance TEXT NOT NULL DEFAULT '',
    updated_at          TEXT NOT NULL
);

-- Lets an operator answer "who is using this theme?" without scanning every row.
CREATE INDEX IF NOT EXISTS idx_user_preferences_theme
    ON user_preferences (selected_theme);