feat: add vim-style z commands for view positioning

- zz: center current line on screen
- zt: move current line to top of viewport
- zb: move current line to bottom of viewport

Add ZPending input mode for two-key command sequence.

Author: raaymax

README.md

@@ -31,6 +31,9 @@ A fast, universal terminal-based log viewer with live filtering and follow mode.
 - `g` - Jump to start (first line)
 - `G` - Jump to end (last line)
 - `:123` - Jump to line 123 (vim-style)
+- `zz` - Center selection on screen
+- `zt` - Move selection to top of screen
+- `zb` - Move selection to bottom of screen
 - `f` - Toggle follow mode (auto-scroll to new logs)
 - Mouse wheel - Scroll up/down (selection follows scroll)
 

src/app.rs

@@ -23,6 +23,8 @@ pub enum InputMode {
     Normal,
     EnteringFilter,
     EnteringLineJump,
+    /// Waiting for second key after 'z' (for zz, zt, zb commands)
+    ZPending,
 }
 
 /// Main application state
@@ -463,6 +465,23 @@ impl App {
             AppEvent::HistoryUp => self.history_up(),
             AppEvent::HistoryDown => self.history_down(),
 
+            // View positioning (vim z commands)
+            AppEvent::EnterZMode => {
+                self.input_mode = InputMode::ZPending;
+            }
+            AppEvent::ExitZMode => {
+                self.input_mode = InputMode::Normal;
+            }
+            AppEvent::CenterView => {
+                self.active_tab_mut().center_view();
+            }
+            AppEvent::ViewToTop => {
+                self.active_tab_mut().view_to_top();
+            }
+            AppEvent::ViewToBottom => {
+                self.active_tab_mut().view_to_bottom();
+            }
+
             // Future events - not yet implemented
             AppEvent::StartFilter { .. } => {
                 // Will be handled in main loop to trigger background filter

src/event.rs

@@ -64,6 +64,13 @@ pub enum AppEvent {
     HistoryUp,
     HistoryDown,
 
+    // View positioning (vim z commands)
+    CenterView,   // zz
+    ViewToTop,    // zt
+    ViewToBottom, // zb
+    EnterZMode,   // z pressed, waiting for second key
+    ExitZMode,    // cancel z mode
+
     // System events
     Quit,
 }

src/handlers/input.rs

@@ -13,6 +13,7 @@ pub fn handle_input_event(key: KeyEvent, app: &App) -> Vec<AppEvent> {
     match app.input_mode {
         InputMode::EnteringFilter => handle_filter_input_mode(key),
         InputMode::EnteringLineJump => handle_line_jump_input_mode(key),
+        InputMode::ZPending => handle_z_pending_mode(key),
         InputMode::Normal => handle_normal_mode(key),
     }
 }
@@ -53,6 +54,18 @@ fn handle_line_jump_input_mode(key: KeyEvent) -> Vec<AppEvent> {
     }
 }
 
+/// Handle keyboard input in z pending mode (waiting for zz, zt, zb)
+fn handle_z_pending_mode(key: KeyEvent) -> Vec<AppEvent> {
+    match key.code {
+        KeyCode::Char('z') => vec![AppEvent::CenterView, AppEvent::ExitZMode],
+        KeyCode::Char('t') => vec![AppEvent::ViewToTop, AppEvent::ExitZMode],
+        KeyCode::Char('b') => vec![AppEvent::ViewToBottom, AppEvent::ExitZMode],
+        KeyCode::Esc => vec![AppEvent::ExitZMode],
+        // Any other key cancels z mode
+        _ => vec![AppEvent::ExitZMode],
+    }
+}
+
 /// Handle keyboard input in normal navigation mode
 fn handle_normal_mode(key: KeyEvent) -> Vec<AppEvent> {
     match key.code {
@@ -78,6 +91,7 @@ fn handle_normal_mode(key: KeyEvent) -> Vec<AppEvent> {
         KeyCode::Char('/') => vec![AppEvent::StartFilterInput],
         KeyCode::Char(':') => vec![AppEvent::StartLineJumpInput],
         KeyCode::Char('?') => vec![AppEvent::ShowHelp],
+        KeyCode::Char('z') => vec![AppEvent::EnterZMode],
         KeyCode::Esc => vec![AppEvent::ClearFilter],
         // Tab navigation
         KeyCode::Tab => vec![AppEvent::NextTab],

src/tab.rs

@@ -316,6 +316,24 @@ impl TabState {
         self.viewport.jump_to_start(&self.line_indices);
         self.sync_from_viewport();
     }
+
+    /// Center the current selection on screen (zz)
+    pub fn center_view(&mut self) {
+        self.viewport.center(&self.line_indices);
+        self.sync_from_viewport();
+    }
+
+    /// Move current selection to top of viewport (zt)
+    pub fn view_to_top(&mut self) {
+        self.viewport.anchor_to_top(&self.line_indices);
+        self.sync_from_viewport();
+    }
+
+    /// Move current selection to bottom of viewport (zb)
+    pub fn view_to_bottom(&mut self) {
+        self.viewport.anchor_to_bottom(&self.line_indices);
+        self.sync_from_viewport();
+    }
 }
 
 #[cfg(test)]

src/ui/mod.rs

@@ -305,6 +305,9 @@ fn render_help_overlay(f: &mut Frame, area: Rect) {
         Line::from("  g             Jump to start"),
         Line::from("  G             Jump to end"),
         Line::from("  :123          Jump to line 123"),
+        Line::from("  zz            Center selection on screen"),
+        Line::from("  zt            Move selection to top"),
+        Line::from("  zb            Move selection to bottom"),
         Line::from(""),
         Line::from(vec![Span::styled(
             "Tabs",

src/viewport.rs

@@ -5,7 +5,6 @@
 //! The anchor_line (file line number) is stable across filter changes.
 
 /// Result of resolving the viewport against current content
-#[allow(dead_code)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct ResolvedView {
     /// Index into line_indices for the selected line
@@ -15,7 +14,6 @@ pub struct ResolvedView {
 }
 
 /// Viewport manages selection and scrolling with vim-like behavior
-#[allow(dead_code)]
 #[derive(Debug, Clone)]
 pub struct Viewport {
     /// The file line number that is selected (stable across filter changes)
@@ -34,7 +32,6 @@ pub struct Viewport {
     cache: Option<ResolvedView>,
 }
 
-#[allow(dead_code)]
 impl Viewport {
     /// Create a new viewport anchored to the given line
     pub fn new(initial_line: usize) -> Self {
@@ -150,6 +147,7 @@ impl Viewport {
 
     /// Move viewport by delta lines without moving selection
     /// (selection stays on same line, but moves on screen)
+    #[allow(dead_code)] // Future: Ctrl+E/Ctrl+Y vim commands
     pub fn move_viewport(&mut self, delta: i32, line_indices: &[usize]) {
         if line_indices.is_empty() || self.height == 0 {
             return;
@@ -244,6 +242,7 @@ impl Viewport {
     }
 
     /// Jump to a specific index in the current view
+    #[allow(dead_code)] // Future: direct index jumping
     pub fn jump_to_index(&mut self, index: usize, line_indices: &[usize]) {
         if line_indices.is_empty() {
             return;
@@ -344,21 +343,25 @@ impl Viewport {
     }
 
     /// Get the cached selected index (call resolve() first)
+    #[allow(dead_code)] // Public API for future use
     pub fn selected_index(&self) -> usize {
         self.cache.map(|c| c.selected_index).unwrap_or(0)
     }
 
     /// Get the cached scroll position (call resolve() first)
+    #[allow(dead_code)] // Public API for future use
     pub fn scroll_position(&self) -> usize {
         self.cache.map(|c| c.scroll_position).unwrap_or(0)
     }
 
     /// Get current height
+    #[allow(dead_code)] // Public API for future use
     pub fn height(&self) -> usize {
         self.height
     }
 
     /// Set height (usually called during resolve, but can be set explicitly)
+    #[allow(dead_code)] // Public API for future use
     pub fn set_height(&mut self, height: usize) {
         if self.height != height {
             self.height = height;