Add single-file mode and fix annotation input width (#10)

* add plan: single-file-mode

* feat: add singleFile field and detection in handleFilesLoaded

* feat: adjust View rendering for single-file mode

Skip tree pane entirely when singleFile is set, giving the diff pane
full terminal width. handleResize sets treeWidth=0 and diffContentWidth
returns width-3 in single-file mode.

* feat: disable pane-switching keys in single-file mode

feat: verify acceptance criteria for single-file mode

* feat: update documentation for single-file mode

fix: address code smell findings

fix: address code review findings

fix: address codex review findings

* fix: correct annotation input width to fit within diff pane

Use diffContentWidth instead of arbitrary offset to calculate textinput
width, preventing cursor from extending past the pane border.

* fix: correct test comment for N key (prev search match)

Author: umputun

.claude-plugin/skills/revdiff/references/usage.md

@@ -13,6 +13,10 @@ revdiff --staged     # review staged changes
 revdiff HEAD~1       # review last commit
 ```
 
+## Single-File Mode
+
+When a diff contains exactly one file, revdiff automatically hides the file tree pane and gives full terminal width to the diff view. Pane-switching keys (`Tab`, `h/l`, `n/p`, `f`) become no-ops. Search navigation (`n`/`N`) still works normally.
+
 ## Key Bindings
 
 **Navigation:**

CLAUDE.md

@@ -76,3 +76,4 @@ git diff → diff.ParseUnifiedDiff() → []DiffLine
 - **ANSI nesting with lipgloss**: `lipgloss.Render()` emits `\033[0m` (full reset) which breaks outer style backgrounds. For styled substrings inside a lipgloss container (status bar separators, search highlights), use raw ANSI sequences via `ansiColor(hex, code)` — code 38 for fg, 48 for bg. Never use `lipgloss.NewStyle().Render()` for inline elements within a lipgloss-rendered parent.
 - Status bar mode icons (`▼ ◉ ↩ ≋`) are always rendered on the right side via `statusModeIcons()`. Active modes use `StatusFg`, inactive use `Muted` — both via raw ANSI fg sequences. Graceful degradation on narrow terminals drops left segments: search position first (`statusSegmentsNoSearch`), then hunk info (`statusSegmentsMinimal`), then truncates filename.
 - Search and hunk navigation both use `centerViewportOnCursor()` to center the target in the middle of the viewport. Use `syncViewportToCursor()` only for cursor movements that should keep the cursor barely visible (j/k scrolling).
+- Single-file mode (`m.singleFile`): when diff has exactly one file, tree pane is hidden, `treeWidth = 0`, diff gets full width (`m.width - 2` for borders, content width `m.width - 3`). Pane-switching keys (tab, h, l) and file navigation (n/p, f) become no-ops. Search nav (n/N) still works. Detection happens in `handleFilesLoaded`.

README.md

@@ -21,6 +21,7 @@ Built for a specific use case: reviewing code changes without leaving a terminal
 - Collapsed diff mode: shows final text with change markers, toggle with `v`
 - Word wrap mode: wraps long lines at viewport boundary with `↪` continuation markers, toggle with `w`
 - Annotate any line in the diff (added, removed, or context) plus file-level notes
+- Single-file auto-detection: when a diff contains exactly one file, hides the tree pane and gives full terminal width to the diff view
 - Two-pane TUI: file tree (left) + colorized diff viewport (right)
 - Vim-style `/` search within diff with `n`/`N` match navigation
 - Hunk navigation to jump between change groups

docs/plans/completed/20260403-single-file-mode.md

@@ -0,0 +1,105 @@
+# Single-File Mode
+
+## Overview
+When a diff contains exactly one file, automatically hide the file tree pane and give the full terminal width to the diff view. This eliminates the unnecessary tree panel and pane-switching overhead for single-file reviews.
+
+## Context
+- **Key files:** `ui/model.go` (Model struct, handleFilesLoaded, View, handleKey, togglePane, handleDiffNav, handleResize), `ui/diffview.go` (diffContentWidth), `ui/model_test.go`
+- **Detection point:** `handleFilesLoaded` at line 423 — where the file list arrives
+- **Rendering:** `View()` at lines 492-528 — tree pane rendered at lines 499-513, joined with diff at line 528
+- **Width calculation:** `diffContentWidth()` in diffview.go:602 uses `m.width - m.treeWidth - 4 - 1`
+- **Pane switching:** `togglePane()` at line 280, `h` key in `handleDiffNav` at line 352
+
+## Solution Overview
+- Add `singleFile bool` field to Model, set in `handleFilesLoaded` when `len(files) == 1`
+- In single-file mode: skip tree pane rendering, diff pane uses full width (`m.width - 2`), focus stays on `paneDiff`
+- Key no-ops in single-file mode: `tab`, `h`, `l`, `n`/`p` (file nav), `f` (filter)
+- `n`/`N` still work for search navigation when search is active
+- `diffContentWidth()` returns `m.width - 3` (diff borders + cursor bar only)
+- No CLI flag — purely automatic based on file count
+
+## Technical Details
+
+### Width calculations in single-file mode
+- Tree pane: not rendered, `treeWidth = 0`
+- Diff pane in `View()`: `Width(m.width - 2)` (only diff pane borders, 1 left + 1 right)
+- `diffContentWidth()`: `m.width - 2 - 1 = m.width - 3` (diff borders + cursor bar)
+- Viewport in `handleResize`: `diffWidth = m.width - 2`
+
+### Key handling
+- `tab` → no-op (guard in `togglePane`)
+- `h` in diff pane → no-op (guard in `handleDiffNav`)
+- `n`/`p` → file nav no-op, but `n`/`N` search nav still works via `handleFileOrSearchNav`
+- `f` (filter) → no-op
+- All other keys work normally
+
+## Development Approach
+- **Testing approach:** regular (code first, then tests)
+- Complete each task fully before moving to the next
+- Run tests after each change
+- Maintain backward compatibility (multi-file mode unchanged)
+
+## Implementation Steps
+
+### Task 1: Add singleFile field and detection
+
+**Files:**
+- Modify: `ui/model.go`
+- Modify: `ui/model_test.go`
+
+- [x] add `singleFile bool` field to Model struct
+- [x] in `handleFilesLoaded`: set `m.singleFile = len(msg.files) == 1` and `m.focus = paneDiff` when single file
+- [x] write test: single file sets `singleFile = true` and `focus = paneDiff`
+- [x] write test: multiple files keeps `singleFile = false`
+- [x] run `make test` — must pass before task 2
+
+### Task 2: Adjust View rendering for single-file mode
+
+**Files:**
+- Modify: `ui/model.go`
+- Modify: `ui/diffview.go`
+- Modify: `ui/model_test.go`
+
+- [x] in `View()`: when `m.singleFile`, skip tree pane rendering and set diff pane `Width(m.width - 2)`
+- [x] in `handleResize`: when `m.singleFile`, set `m.treeWidth = 0` and `diffWidth = m.width - 2`
+- [x] in `diffContentWidth()`: when `m.singleFile`, return `max(10, m.width-3)`
+- [x] write test: `View()` output in single-file mode does not contain tree pane content
+- [x] write test: `diffContentWidth()` returns correct width in single-file mode
+- [x] run `make test` — must pass before task 3
+
+### Task 3: Disable pane-switching keys in single-file mode
+
+**Files:**
+- Modify: `ui/model.go`
+- Modify: `ui/model_test.go`
+
+- [x] in `togglePane()`: early return when `m.singleFile`
+- [x] in `handleDiffNav`: skip `h` key (switch to tree) when `m.singleFile`
+- [x] in `handleKey`: skip `f` (filter) when `m.singleFile`
+- [x] in `handleFileOrSearchNav` or `handleKey`: `n`/`p` file nav no-op when `m.singleFile` (search nav still works)
+- [x] write tests: tab, h, f keys are no-ops in single-file mode
+- [x] write test: `n` still navigates search matches in single-file mode
+- [x] run `make test` — must pass before task 4
+
+### Task 4: Verify acceptance criteria
+- [x] verify single-file diff shows no tree pane
+- [x] verify diff pane uses full terminal width
+- [x] verify focus starts on diff pane
+- [x] verify pane-switching keys are no-ops
+- [x] verify search, annotations, wrap, collapsed mode all work normally
+- [x] verify multi-file mode is unchanged
+- [x] run full test suite: `make test`
+- [x] run linter: `make lint`
+
+### Task 5: [Final] Update documentation
+- [x] update README.md to mention single-file auto-detection
+- [x] update CLAUDE.md if new patterns discovered
+- [x] move this plan to `docs/plans/completed/`
+
+## Post-Completion
+
+**Manual verification:**
+- test with `revdiff HEAD~1` on a commit that changes exactly 1 file
+- test with `revdiff HEAD~1` on a commit that changes multiple files
+- test resizing terminal in single-file mode
+- test all keyboard shortcuts in single-file mode

ui/annotate.go

@@ -17,7 +17,7 @@ func (m *Model) newAnnotationInput(placeholder string) (textinput.Model, tea.Cmd
 	ti.Placeholder = placeholder
 	cmd := ti.Focus()
 	ti.CharLimit = 500
-	ti.Width = max(10, m.width-m.treeWidth-10)
+	ti.Width = max(10, m.diffContentWidth()-6) // cursor col + emoji prefix "💬 " + border margin
 	return ti, cmd
 }
 

ui/diffview.go

@@ -600,6 +600,10 @@ func (m *Model) handleHorizontalScroll(direction int) {
 
 // diffContentWidth returns the available width for diff line content (excluding cursor bar).
 func (m Model) diffContentWidth() int {
+	if m.singleFile {
+		// single-file mode: diff pane borders (2) + cursor bar (1)
+		return max(10, m.width-3)
+	}
 	// diff pane width minus borders (4) minus tree width, minus bar (1)
 	return max(10, m.width-m.treeWidth-4-1)
 }

ui/model.go

@@ -89,6 +89,7 @@ type Model struct {
 	discarded        bool // true when user chose to discard annotations and quit
 	inConfirmDiscard bool // true when showing discard confirmation prompt
 	noConfirmDiscard bool // skip confirmation prompt on discard quit
+	singleFile       bool // true when diff contains exactly one file, hides tree pane
 }
 
 // fileLoadedMsg is sent when a file's diff has been loaded.
@@ -247,8 +248,7 @@ func (m Model) handleKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		return m.handleFileOrSearchNav(msg.String())
 
 	case msg.String() == "p":
-		m.tree.prevFile()
-		return m.loadSelectedIfChanged()
+		return m.handlePrevFile()
 
 	case msg.String() == "enter":
 		return m.handleEnterKey()
@@ -277,7 +277,11 @@ func (m Model) handleKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 
 // togglePane switches focus between tree and diff panes.
 // only switches to diff pane when a file is loaded.
+// no-op in single-file mode (tree pane is hidden).
 func (m *Model) togglePane() {
+	if m.singleFile {
+		return
+	}
 	if m.focus != paneTree {
 		m.focus = paneTree
 		return
@@ -287,6 +291,15 @@ func (m *Model) togglePane() {
 	}
 }
 
+// handleSwitchToTree switches focus to tree pane from diff.
+// no-op in single-file mode (tree pane is hidden).
+func (m Model) handleSwitchToTree() (tea.Model, tea.Cmd) {
+	if !m.singleFile {
+		m.focus = paneTree
+	}
+	return m, nil
+}
+
 // toggleWrapMode toggles line wrapping on/off.
 // resets horizontal scroll when enabling wrap and re-renders the diff.
 func (m *Model) toggleWrapMode() {
@@ -350,8 +363,7 @@ func (m Model) paneHeight() int {
 func (m Model) handleDiffNav(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	switch {
 	case msg.String() == "h":
-		m.focus = paneTree
-		return m, nil
+		return m.handleSwitchToTree()
 	case msg.String() == "left":
 		m.handleHorizontalScroll(-1)
 		return m, nil
@@ -397,11 +409,16 @@ func (m Model) handleResize(msg tea.WindowSizeMsg) (tea.Model, tea.Cmd) {
 	m.width = msg.Width
 	m.height = msg.Height
 
-	// adjust tree width based on ratio (N out of 10 units)
-	m.treeWidth = max(minTreeWidth, m.width*m.treeWidthRatio/10)
-
-	diffWidth := m.width - m.treeWidth - 4 // borders
-	diffHeight := m.paneHeight() - 1       // pane height minus diff header
+	var diffWidth int
+	if m.singleFile {
+		m.treeWidth = 0
+		diffWidth = m.width - 2 // diff pane borders only
+	} else {
+		// adjust tree width based on ratio (N out of 10 units)
+		m.treeWidth = max(minTreeWidth, m.width*m.treeWidthRatio/10)
+		diffWidth = m.width - m.treeWidth - 4 // borders
+	}
+	diffHeight := m.paneHeight() - 1 // pane height minus diff header
 
 	if !m.ready {
 		m.viewport = viewport.New(diffWidth, diffHeight)
@@ -426,6 +443,14 @@ func (m Model) handleFilesLoaded(msg filesLoadedMsg) (tea.Model, tea.Cmd) {
 		return m, nil
 	}
 	m.tree = newFileTree(msg.files)
+	m.singleFile = len(msg.files) == 1
+	if m.singleFile {
+		m.focus = paneDiff
+		m.treeWidth = 0
+		if m.ready {
+			m.viewport.Width = m.width - 2
+		}
+	}
 
 	// auto-select first file
 	if f := m.tree.selectedFile(); f != "" {
@@ -495,22 +520,6 @@ func (m Model) View() string {
 	}
 
 	ph := m.paneHeight()
-	annotated := m.annotatedFiles()
-	treeContent := m.tree.render(m.treeWidth, ph, annotated, m.styles)
-
-	// apply pane borders based on focus
-	treeStyle := m.styles.TreePane
-	diffStyle := m.styles.DiffPane
-	if m.focus == paneTree {
-		treeStyle = m.styles.TreePaneActive
-	} else {
-		diffStyle = m.styles.DiffPaneActive
-	}
-
-	treePane := treeStyle.
-		Width(m.treeWidth).
-		Height(ph).
-		Render(treeContent)
 
 	// diff pane title
 	diffTitle := "no file selected"
@@ -520,12 +529,39 @@ func (m Model) View() string {
 	diffHeader := m.styles.DirEntry.Render(" " + diffTitle)
 	diffContent := lipgloss.JoinVertical(lipgloss.Left, diffHeader, m.viewport.View())
 
-	diffPane := diffStyle.
-		Width(m.width - m.treeWidth - 4).
-		Height(ph).
-		Render(diffContent)
+	var mainView string
+	if m.singleFile {
+		// single-file mode: no tree pane, diff uses full width
+		diffPane := m.styles.DiffPaneActive.
+			Width(m.width - 2).
+			Height(ph).
+			Render(diffContent)
+		mainView = diffPane
+	} else {
+		annotated := m.annotatedFiles()
+		treeContent := m.tree.render(m.treeWidth, ph, annotated, m.styles)
+
+		// apply pane borders based on focus
+		treeStyle := m.styles.TreePane
+		diffStyle := m.styles.DiffPane
+		if m.focus == paneTree {
+			treeStyle = m.styles.TreePaneActive
+		} else {
+			diffStyle = m.styles.DiffPaneActive
+		}
 
-	mainView := lipgloss.JoinHorizontal(lipgloss.Top, treePane, diffPane)
+		treePane := treeStyle.
+			Width(m.treeWidth).
+			Height(ph).
+			Render(treeContent)
+
+		diffPane := diffStyle.
+			Width(m.width - m.treeWidth - 4).
+			Height(ph).
+			Render(diffContent)
+
+		mainView = lipgloss.JoinHorizontal(lipgloss.Top, treePane, diffPane)
+	}
 
 	if m.showHelp {
 		// overlay help popup on top of current content
@@ -917,7 +953,11 @@ func (m Model) handleConfirmDiscardKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 }
 
 // handleFilterToggle toggles the annotated files filter.
+// no-op in single-file mode (tree pane is hidden).
 func (m Model) handleFilterToggle() (tea.Model, tea.Cmd) {
+	if m.singleFile {
+		return m, nil
+	}
 	annotated := m.annotatedFiles()
 	if len(annotated) > 0 {
 		m.tree.toggleFilter(annotated)
@@ -927,8 +967,19 @@ func (m Model) handleFilterToggle() (tea.Model, tea.Cmd) {
 	return m, nil
 }
 
+// handlePrevFile navigates to previous file.
+// no-op in single-file mode (tree pane is hidden).
+func (m Model) handlePrevFile() (tea.Model, tea.Cmd) {
+	if m.singleFile {
+		return m, nil
+	}
+	m.tree.prevFile()
+	return m.loadSelectedIfChanged()
+}
+
 // handleFileOrSearchNav handles n/N keys: navigates search matches when a search is active,
-// otherwise n falls through to next-file navigation. N does nothing without search.
+// otherwise n falls through to next-file navigation (no-op in single-file mode).
+// N does nothing without search.
 func (m Model) handleFileOrSearchNav(key string) (tea.Model, tea.Cmd) {
 	if len(m.searchMatches) > 0 {
 		if key == "n" {
@@ -939,7 +990,7 @@ func (m Model) handleFileOrSearchNav(key string) (tea.Model, tea.Cmd) {
 		m.viewport.SetContent(m.renderDiff())
 		return m, nil
 	}
-	if key == "n" {
+	if key == "n" && !m.singleFile {
 		m.tree.nextFile()
 		return m.loadSelectedIfChanged()
 	}