Composable UI / TodoStore / Visibility Filter

store.ts

class TodoStore {
    private readonly visibilityFilter: $Predicate$<Todo> & Destroyable
    
    constructor() {
        this.visibilityFilter = map(this.visibility, vis2pred)
    }
    
    getVisibilityFilter(): $Preidcate$<Todo> {
        return this.visibilityFilter
    }
    
    dispose() {
        this.visibilityFilter.destroy()
    }
}

function vis2pred(v: Visibility): Predicate$<Todo> {
    switch (v) {
        case Visibility.ALL:
            const $true = new StreamBox(true)
            return () => $true
        case Visibility.DONE:
            return (todo) => clone(todo.done)
        case Visibility.TODO:
            return (todo) => map(todo.done, (b) => !b)
    }
}