// Shared by Mail, Contacts and Files. Wait for the next committed revision and
// settled ListView geometry before requesting another page. Errors retry only
// after a fresh user gesture, preventing an automatic request loop.
export component InfiniteScrollController inherits Rectangle {
    width: 0px; height: 0px;
    in property <bool> active: true;
    in property <bool> can-load-more;
    in property <bool> loading;
    in property <int> row-count;
    in property <int> revision;
    in property <length> content-height;
    in property <length> content-y;
    in property <length> visible-height;
    in property <length> prefetch-distance: 246px;
    callback load-more;
    private property <bool> armed: true;
    private property <int> request-rows: -1;
    private property <int> request-revision: -1;
    private property <length> request-height: -1px;
    function check() {
        if root.active && root.visible-height > 0px && root.can-load-more
            && !root.loading && root.armed
            && root.content-height + root.content-y - root.visible-height <= root.prefetch-distance {
            root.armed = false;
            root.request-rows = root.row-count;
            root.request-revision = root.revision;
            root.request-height = root.content-height;
            root.load-more();
        }
    }
    public function reset() {
        root.armed = true;
        root.request-rows = -1;
        root.request-revision = -1;
        root.request-height = -1px;
        check-timer.restart();
    }
    public function user-scrolled() {
        if !root.loading && !root.armed && root.revision == root.request-revision {
            root.armed = true;
        }
        root.check();
    }
    changed content-height => {
        if !root.armed && root.revision != root.request-revision && root.content-height != root.request-height { root.armed = true; }
        check-timer.restart();
    }
    changed revision => {
        if !root.armed && root.revision != root.request-revision
            && (root.row-count == root.request-rows || root.content-height != root.request-height) { root.armed = true; }
        check-timer.restart();
    }
    changed can-load-more => { check-timer.restart(); }
    changed loading => { if !root.loading { check-timer.restart(); } }
    changed active => { check-timer.restart(); }
    changed visible-height => { check-timer.restart(); }
    check-timer := Timer {
        interval: 1ms; running: true;
        triggered => { self.stop(); root.check(); }
    }
}