add vertical margin (#48)

this PR adds a vertical margin
- can be configured
- compute and keep track of the top index of each depth of the data

examples/config/default.nuon

@@ -2,6 +2,7 @@
     show_cell_path: true,  # whether or not to show the current cell path above the status bar
     show_table_header: true,  # whether or not to show the table header in "table" layout
     layout: "table",  # the layout of the data, either "table" or "compact"
+    margin: 10, # the number of lines to keep between the cursor and the top / bottom
 
     # "reset" is used instead of "black" in a dark terminal because, when the terminal is actually
     # black, "black" is not really black which is ugly, whereas "reset" is really black.

src/app.rs

@@ -42,6 +42,8 @@ impl std::fmt::Display for Mode {
 pub struct App {
     /// the full current path in the data
     pub position: CellPath,
+    /// used for rendering
+    pub rendering_tops: Vec<i32>,
     /// the current [`Mode`]
     pub mode: Mode,
     /// the editor to modify the cells of the data
@@ -54,6 +56,7 @@ impl Default for App {
     fn default() -> Self {
         Self {
             position: CellPath { members: vec![] },
+            rendering_tops: vec![],
             mode: Mode::default(),
             editor: Editor::default(),
             value: Value::default(),

src/config/mod.rs

@@ -7,14 +7,16 @@
 use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
 use ratatui::style::{Color, Modifier};
 
-use nu_protocol::{LabeledError, Value};
+use nu_protocol::{LabeledError, Span, Value};
 
 mod parsing;
 use parsing::{
     follow_cell_path, invalid_field, invalid_type, try_bool, try_fg_bg_colors, try_key, try_layout,
     try_modifier, try_string,
 };
 
+use self::parsing::{positive_integer, try_int};
+
 /// the configuration for the status bar colors in all [`crate::app::Mode`]s
 #[derive(Clone, PartialEq, Debug)]
 pub struct StatusBarColorConfig {
@@ -135,6 +137,7 @@ pub struct Config {
     pub show_cell_path: bool,
     pub layout: Layout,
     pub show_table_header: bool,
+    pub margin: usize,
 }
 
 impl Default for Config {
@@ -145,6 +148,7 @@ impl Default for Config {
             show_cell_path: true,
             show_table_header: true,
             layout: Layout::Table,
+            margin: 10,
             colors: ColorConfig {
                 normal: TableRowColorConfig {
                     name: BgFgColorConfig {
@@ -248,6 +252,14 @@ impl Config {
                         config.layout = val
                     }
                 }
+                "margin" => {
+                    if let Some(val) = try_int(&value, &["margin"])? {
+                        if val < 0 {
+                            return Err(positive_integer(val, &["margin"], Span::unknown()));
+                        }
+                        config.margin = val as usize
+                    }
+                }
                 "colors" => {
                     let cell = follow_cell_path(&value, &["colors"]).unwrap();
                     let columns = match &cell {

src/config/parsing.rs

@@ -67,6 +67,17 @@ fn u8_out_of_range(value: i64, cell_path: &[&str], span: Span) -> LabeledError {
     )
 }
 
+pub fn positive_integer(value: i64, cell_path: &[&str], span: Span) -> LabeledError {
+    LabeledError::new("invalid config").with_label(
+        format!(
+            "`$.{}` should be a positive integer, found {}",
+            cell_path.join("."),
+            value
+        ),
+        span,
+    )
+}
+
 /// try to parse a bool in the *value* at the given *cell path*
 pub fn try_bool(value: &Value, cell_path: &[&str]) -> Result<Option<bool>, LabeledError> {
     match follow_cell_path(value, cell_path) {
@@ -85,6 +96,15 @@ pub fn try_string(value: &Value, cell_path: &[&str]) -> Result<Option<String>, L
     }
 }
 
+/// try to parse an integer in the *value* at the given *cell path*
+pub fn try_int(value: &Value, cell_path: &[&str]) -> Result<Option<i64>, LabeledError> {
+    match follow_cell_path(value, cell_path) {
+        Some(Value::Int { val, .. }) => Ok(Some(val)),
+        Some(x) => Err(invalid_type(&x, cell_path, "int")),
+        _ => Ok(None),
+    }
+}
+
 /// try to parse an ANSI modifier in the *value* at the given *cell path*
 pub fn try_modifier(value: &Value, cell_path: &[&str]) -> Result<Option<Modifier>, LabeledError> {
     match follow_cell_path(value, cell_path) {
@@ -332,8 +352,8 @@ mod tests {
     use ratatui::style::{Color, Modifier};
 
     use super::{
-        follow_cell_path, try_bool, try_color, try_fg_bg_colors, try_key, try_layout, try_modifier,
-        try_string,
+        follow_cell_path, try_bool, try_color, try_fg_bg_colors, try_int, try_key, try_layout,
+        try_modifier, try_string,
     };
     use crate::config::{BgFgColorConfig, Layout};
 
@@ -420,6 +440,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn trying_int() {
+        test_tried_error(
+            try_int(&Value::test_bool(true), &[]),
+            "",
+            "should be a int, found bool",
+        );
+        test_tried_error(
+            try_int(&Value::test_string("my string"), &[]),
+            "",
+            "should be a int, found string",
+        );
+
+        assert_eq!(try_int(&Value::test_int(123), &[]), Ok(Some(123)));
+        assert_eq!(try_int(&Value::test_int(-123), &[]), Ok(Some(-123)));
+        assert_eq!(try_int(&Value::test_int(123), &["x"]), Ok(None));
+    }
+
     #[test]
     fn trying_key() {
         test_tried_error(

src/navigation.rs

@@ -154,6 +154,8 @@ pub(super) fn go_deeper_in_data(app: &mut App) {
         }
         _ => app.hit_bottom(),
     }
+
+    app.rendering_tops.push(0);
 }
 
 /// pop one level of depth from the data
@@ -166,6 +168,7 @@ pub(super) fn go_back_in_data(app: &mut App) {
         app.position.members.pop();
     }
     app.mode = Mode::Normal;
+    app.rendering_tops.pop();
 }
 
 // TODO: add proper assert error messages

src/ui.rs

@@ -17,7 +17,7 @@ use ratatui::{
 };
 
 /// render the whole ui
-pub(super) fn render_ui(frame: &mut Frame, app: &App, config: &Config, error: Option<&str>) {
+pub(super) fn render_ui(frame: &mut Frame, app: &mut App, config: &Config, error: Option<&str>) {
     render_data(frame, app, config);
     if config.show_cell_path {
         render_cell_path(frame, app);
@@ -223,7 +223,7 @@ fn repr_table(table: &[Record]) -> (Vec<String>, Vec<String>, Vec<Vec<String>>)
 ///
 /// the data will be rendered on top of the bar, and on top of the cell path in case
 /// [`crate::config::Config::show_cell_path`] is set to `true`.
-fn render_data(frame: &mut Frame, app: &App, config: &Config) {
+fn render_data(frame: &mut Frame, app: &mut App, config: &Config) {
     let mut data_path = app.position.members.clone();
     let current = if !app.is_at_bottom() {
         data_path.pop()
@@ -310,6 +310,22 @@ fn render_data(frame: &mut Frame, app: &App, config: &Config) {
         None => 0,
     };
 
+    let height = data_frame_height as i32 - 3; // 3: border x 2 + header
+    let cursor = selected as i32;
+    let top = *app.rendering_tops.last().unwrap_or(&0);
+    let margin = config.margin as i32;
+
+    if cursor >= top + height - margin {
+        app.rendering_tops.pop();
+        app.rendering_tops
+            .push((cursor - height + margin + 1).max(0));
+    } else if cursor <= top + margin {
+        app.rendering_tops.pop();
+        app.rendering_tops.push((cursor - margin).max(0));
+    }
+
+    let margin_offset = *app.rendering_tops.last().unwrap_or(&0) as usize;
+
     if is_a_table {
         let (columns, shapes, cells) = match value {
             Value::List { vals, .. } => {
@@ -359,7 +375,9 @@ fn render_data(frame: &mut Frame, app: &App, config: &Config) {
         frame.render_stateful_widget(
             table,
             rect_without_bottom_bar,
-            &mut TableState::default().with_selected(Some(selected)),
+            &mut TableState::default()
+                .with_selected(Some(selected))
+                .with_offset(margin_offset),
         );
 
         return;
@@ -392,7 +410,9 @@ fn render_data(frame: &mut Frame, app: &App, config: &Config) {
             frame.render_stateful_widget(
                 items,
                 rect_without_bottom_bar,
-                &mut ListState::default().with_selected(Some(selected)),
+                &mut ListState::default()
+                    .with_selected(Some(selected))
+                    .with_offset(margin_offset),
             )
         }
         Layout::Table => {
@@ -488,7 +508,9 @@ fn render_data(frame: &mut Frame, app: &App, config: &Config) {
             frame.render_stateful_widget(
                 table,
                 rect_without_bottom_bar,
-                &mut TableState::default().with_selected(Some(selected)),
+                &mut TableState::default()
+                    .with_selected(Some(selected))
+                    .with_offset(margin_offset),
             )
         }
     }