-- allium: 1
-- bDS Navigation Menu
-- Distilled from: src/main/engine/MenuEngine.ts

value MenuItem {
    kind: page | submenu | category_archive | home
    label: String
    slug: String?
    children: List<MenuItem>?       -- only for submenu kind
}

entity Menu {
    items: List<MenuItem>

    -- Derived
    home_items: items where kind = home
    home_entry: home_items.first
}

invariant HomeAlwaysPresent {
    -- The menu always has a Home entry, extracted and prepended
    for menu in Menus:
        menu.items.first.kind = home
}

invariant MenuPersistedAsOpml {
    -- meta/menu.opml is the canonical storage format
    -- Uses OPML with outline elements for each item
    parse_opml(read_file("meta/menu.opml")) = menu.items
}

rule UpdateMenu {
    when: UpdateMenuRequested(menu, items)
    -- Normalizes Home entry: extracts from items, prepends
    let without_home = items where kind != home
    let home = MenuItem{kind: home, label: "Home"}
    ensures: menu.items = build_menu_items(home, without_home)
    ensures: MenuFileWritten(menu)
}