disable post button if draft buffer empty

closes: https://github.com/damus-io/notedeck/issues/417

Signed-off-by: kernelkind <kernelkind@gmail.com>

src/ui/note/post.rs

@@ -209,7 +209,10 @@ impl<'a> PostView<'a> {
 
                             ui.with_layout(egui::Layout::right_to_left(egui::Align::BOTTOM), |ui| {
                                 if ui
-                                    .add_sized([91.0, 32.0], egui::Button::new("Post now"))
+                                    .add_sized(
+                                        [91.0, 32.0],
+                                        post_button(!self.draft.buffer.is_empty()),
+                                    )
                                     .clicked()
                                 {
                                     let new_post = NewPost::new(
@@ -236,6 +239,23 @@ impl<'a> PostView<'a> {
     }
 }
 
+fn post_button(interactive: bool) -> impl egui::Widget {
+    move |ui: &mut egui::Ui| {
+        let button = egui::Button::new("Post now");
+        if interactive {
+            ui.add(button)
+        } else {
+            ui.add(
+                button
+                    .sense(egui::Sense::hover())
+                    .fill(ui.visuals().widgets.noninteractive.bg_fill)
+                    .stroke(ui.visuals().widgets.noninteractive.bg_stroke),
+            )
+            .on_hover_cursor(egui::CursorIcon::NotAllowed)
+        }
+    }
+}
+
 mod preview {
     use super::*;