ui,preview: fix preview pane ctrl-u/d scrolling (#472)

Commit 8481b92 broke ctrl-u/d scrolling in the preview pane, see below
code:
```
if common.IsInputMessage(msg) {
    if m.oplog != nil {
        cmds = append(cmds, m.oplog.Update(msg))
    } else {
        cmds = append(cmds, m.revisions.Update(msg))
    }
    return tea.Batch(cmds...)
}
```
This causes unhandled key messages to be routed only to oplog or
revisions, and then returns early, so they never reach the preview
model's Update() call which happens later in the function.


This fix groups preview related commands and make sure they are always
handled.

Also, added a YOffset() method to internal/ui/preview/preview.go to
expose the viewport's Y offset for testing purposes.

Author: baggiiiie

internal/ui/preview/preview.go

@@ -110,6 +110,10 @@ func (m *Model) WindowPercentage() float64 {
 	return m.previewWindowPercentage
 }
 
+func (m *Model) YOffset() int {
+	return m.view.YOffset
+}
+
 func (m *Model) Scroll(delta int) tea.Cmd {
 	if delta > 0 {
 		m.view.ScrollDown(delta)
@@ -204,6 +208,10 @@ func (m *Model) Update(msg tea.Msg) tea.Cmd {
 			m.view.HalfPageDown()
 		case key.Matches(msg, m.keyMap.Preview.HalfPageUp):
 			m.view.HalfPageUp()
+		case key.Matches(msg, m.keyMap.Preview.Expand):
+			m.Expand()
+		case key.Matches(msg, m.keyMap.Preview.Shrink):
+			m.Shrink()
 		}
 	}
 	return nil

internal/ui/ui.go

@@ -274,11 +274,15 @@ func (m *Model) Update(msg tea.Msg) tea.Cmd {
 			m.previewModel.ToggleVisible()
 			cmds = append(cmds, common.SelectionChanged(m.context.SelectedItem))
 			return tea.Batch(cmds...)
-		case key.Matches(msg, m.keyMap.Preview.Expand) && m.previewModel.Visible():
-			m.previewModel.Expand()
-			return tea.Batch(cmds...)
-		case key.Matches(msg, m.keyMap.Preview.Shrink) && m.previewModel.Visible():
-			m.previewModel.Shrink()
+		case m.previewModel.Visible() && key.Matches(msg,
+			m.keyMap.Preview.Expand,
+			m.keyMap.Preview.Shrink,
+			m.keyMap.Preview.HalfPageDown,
+			m.keyMap.Preview.HalfPageUp,
+			m.keyMap.Preview.ScrollDown,
+			m.keyMap.Preview.ScrollUp):
+			cmd := m.previewModel.Update(msg)
+			cmds = append(cmds, cmd)
 			return tea.Batch(cmds...)
 		case key.Matches(msg, m.keyMap.CustomCommands):
 			model := customcommands.NewModel(m.context)

internal/ui/ui_test.go

@@ -1,8 +1,11 @@
 package ui
 
 import (
+	"strings"
 	"testing"
 
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/charmbracelet/x/cellbuf"
 	"github.com/stretchr/testify/assert"
 
 	"github.com/idursun/jjui/internal/ui/common"
@@ -21,3 +24,111 @@ func Test_Update_RevsetWithEmptyInputKeepsDefaultRevset(t *testing.T) {
 
 	assert.Equal(t, ctx.DefaultRevset, ctx.CurrentRevset)
 }
+
+func Test_Update_PreviewScrollKeysWorkWhenVisible(t *testing.T) {
+	tests := []struct {
+		name           string
+		key            tea.KeyMsg
+		expectedScroll int // positive = down, negative = up
+	}{
+		{
+			name:           "ctrl+d scrolls half page down",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlD},
+			expectedScroll: 1,
+		},
+		{
+			name:           "ctrl+u scrolls half page up",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlU},
+			expectedScroll: -1,
+		},
+		{
+			name:           "ctrl+n scrolls down",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlN},
+			expectedScroll: 1,
+		},
+		{
+			name:           "ctrl+p scrolls up",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlP},
+			expectedScroll: -1,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			commandRunner := test.NewTestCommandRunner(t)
+			ctx := test.NewTestContext(commandRunner)
+
+			model := NewUI(ctx)
+			model.SetFrame(cellbuf.Rect(0, 0, 100, 50))
+
+			model.previewModel.SetVisible(true)
+			model.previewModel.SetFrame(cellbuf.Rect(50, 0, 50, 5))
+
+			var content strings.Builder
+			for range 100 {
+				content.WriteString("line content here\n")
+			}
+			model.previewModel.SetContent(content.String())
+
+			initialYOffset := model.previewModel.YOffset()
+
+			// Send the key message
+			model.Update(tc.key)
+
+			newYOffset := model.previewModel.YOffset()
+			if tc.expectedScroll > 0 {
+				assert.Greater(t, newYOffset, initialYOffset, "expected scroll down for key %s", tc.name)
+			} else {
+				// For scroll up, we need content scrolled down first
+				model.previewModel.Scroll(50) // scroll down first
+				scrolledYOffset := model.previewModel.YOffset()
+				model.Update(tc.key)
+				newYOffset = model.previewModel.YOffset()
+				assert.Less(t, newYOffset, scrolledYOffset, "expected scroll up for key %s", tc.name)
+			}
+		})
+	}
+}
+
+func Test_Update_PreviewResizeKeysWorkWhenVisible(t *testing.T) {
+	tests := []struct {
+		name           string
+		key            tea.KeyMsg
+		expectedResize int // positive = expand, negative = shrink
+	}{
+		{
+			name:           "ctrl+l shrinks preview",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlL},
+			expectedResize: -1,
+		},
+		{
+			name:           "ctrl+h expands preview",
+			key:            tea.KeyMsg{Type: tea.KeyCtrlH},
+			expectedResize: 1,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			commandRunner := test.NewTestCommandRunner(t)
+			ctx := test.NewTestContext(commandRunner)
+
+			model := NewUI(ctx)
+			model.SetFrame(cellbuf.Rect(0, 0, 100, 50))
+
+			model.previewModel.SetVisible(true)
+			model.previewModel.SetFrame(cellbuf.Rect(50, 0, 50, 5))
+
+			initialWidth := model.previewModel.WindowPercentage()
+
+			model.Update(tc.key)
+
+			newWidth := model.previewModel.WindowPercentage()
+			if tc.expectedResize > 0 {
+				assert.Greater(t, newWidth, initialWidth, "expected preview to expand for key %s", tc.name)
+			} else {
+				assert.Less(t, newWidth, initialWidth, "expected preview to shrink for key %s", tc.name)
+			}
+		})
+	}
+}