web: add scrollbar for read progress

web/src/state.rs

@@ -37,15 +37,36 @@ pub fn init(url: Url, orders: &mut impl Orders<Msg>) -> Model {
     // 'notmuch new' on the server periodically?
     orders.stream(streams::interval(30_000, || Msg::RefreshStart));
     orders.subscribe(on_url_changed);
+    orders.stream(streams::window_event(Ev::Scroll, |_| {
+        compute_scroll_ratio()
+    }));
 
     Model {
         context: Context::None,
         query: "".to_string(),
         refreshing_state: RefreshingState::None,
         tags: None,
+        read_completion_ratio: 0.,
     }
 }
 
+fn compute_scroll_ratio() -> Msg {
+    // TODO: compute completion based on contents of the post, not the overall body (which includes
+    // the tags at the end on mobile/tablet).
+    let body = document().body().expect("body");
+    let sh = body.scroll_height() as f64;
+    let window = window();
+    let ih = window
+        .inner_height()
+        .expect("window height")
+        .unchecked_into::<js_sys::Number>()
+        .value_of();
+    let scroll_y = window.scroll_y().expect("scroll Y");
+
+    let end = sh - ih;
+    let ratio = scroll_y / end;
+    Msg::SetProgress(ratio)
+}
 fn on_url_changed(uc: subs::UrlChanged) -> Msg {
     let mut url = uc.0;
     info!(
@@ -489,6 +510,9 @@ pub fn update(msg: Msg, model: &mut Model, orders: &mut impl Orders<Msg>) {
                     .expect("failed to copy to clipboard");
             });
         }
+        Msg::SetProgress(ratio) => {
+            model.read_completion_ratio = ratio;
+        }
     }
 }
 // `Model` describes our app state.
@@ -497,6 +521,7 @@ pub struct Model {
     pub context: Context,
     pub refreshing_state: RefreshingState,
     pub tags: Option<Vec<Tag>>,
+    pub read_completion_ratio: f64,
 }
 
 #[derive(Error, Debug)]
@@ -590,4 +615,6 @@ pub enum Msg {
     MultiMsg(Vec<Msg>),
 
     CopyToClipboard(String),
+
+    SetProgress(f64),
 }