fix: sluggish mouse scroll

tui_test.go

@@ -1267,6 +1267,79 @@ func TestLongThreadReplyComposerIsVisibleWithDifflet(t *testing.T) {
 	}
 }
 
+func TestMouseWheelScrollsFocusedPaneByThree(t *testing.T) {
+	m := NewApp(nil, "o", "r", false, 50, time.Second)
+	m.screen, m.loading, m.width, m.height = threadScreen, false, 60, 12
+	m.listHidden, m.focus = true, threadDetailPane
+	m.details = PRDetails{
+		PullRequest: PullRequest{RepoWithOwner: "o/r", Number: 1, Title: "Title"},
+		Threads: []ReviewThread{{
+			ID: "thread", Path: "main.go",
+			Comments: []ReviewComment{{
+				ID: "comment", Author: "reviewer",
+				Body: strings.Repeat("A long discussion line. ", 80),
+			}},
+		}},
+	}
+
+	updated, _ := m.Update(tea.MouseMsg{
+		Button: tea.MouseButtonWheelDown,
+		Action: tea.MouseActionPress,
+	})
+	m = updated.(App)
+	if m.scroll != mouseWheelScrollStep {
+		t.Fatalf("wheel down scrolled %d lines, want %d", m.scroll, mouseWheelScrollStep)
+	}
+
+	updated, _ = m.Update(tea.MouseMsg{
+		Button: tea.MouseButtonWheelUp,
+		Action: tea.MouseActionPress,
+	})
+	m = updated.(App)
+	if m.scroll != 0 {
+		t.Fatalf("wheel up did not return to the top: %d", m.scroll)
+	}
+
+	m.writeMode, m.writeThreadID = writeReply, "thread"
+	updated, _ = m.Update(tea.MouseMsg{
+		Button: tea.MouseButtonWheelDown,
+		Action: tea.MouseActionPress,
+	})
+	m = updated.(App)
+	if m.scroll != mouseWheelScrollStep {
+		t.Fatalf("reply-mode wheel down scrolled %d lines, want %d",
+			m.scroll, mouseWheelScrollStep)
+	}
+
+	m.scroll = max(0, m.detailMaxScroll()-1)
+	updated, _ = m.Update(tea.MouseMsg{
+		Button: tea.MouseButtonWheelDown,
+		Action: tea.MouseActionPress,
+	})
+	m = updated.(App)
+	if m.scroll != m.detailMaxScroll() {
+		t.Fatalf("wheel scrolling exceeded or missed the lower bound: %d/%d",
+			m.scroll, m.detailMaxScroll())
+	}
+
+	m.writeMode, m.writeThreadID = writeNone, ""
+	m.focus, m.threadIndex = threadListPane, 0
+	for index := 1; index < 8; index++ {
+		m.details.Threads = append(m.details.Threads, ReviewThread{
+			ID: fmt.Sprintf("thread-%d", index),
+		})
+	}
+	updated, _ = m.Update(tea.MouseMsg{
+		Button: tea.MouseButtonWheelDown,
+		Action: tea.MouseActionPress,
+	})
+	m = updated.(App)
+	if m.threadIndex != mouseWheelScrollStep {
+		t.Fatalf("thread-list wheel moved %d items, want %d",
+			m.threadIndex, mouseWheelScrollStep)
+	}
+}
+
 func TestResolveToggleConfirmsAndUsesCurrentThreadState(t *testing.T) {
 	service := &recordingService{}
 	m := NewApp(service, "o", "r", false, 50, time.Second)