Make PageUp/PageDown behavior configurable and default to 50%

Cargo.toml

@@ -24,6 +24,7 @@ tracing-subscriber = { version = "0.3.17", features = ["env-filter", "serde"] }
 clap = { version = "4.4.5", features = ["derive", "cargo", "wrap_help", "unicode", "string", "unstable-styles"] }
 
 # Config
+bounded-integer = { version = "0.5.7", features = ["types"] }
 config = "0.13.3"
 derive_deref = "1.1.1"
 directories = "5.0.1"
@@ -31,6 +32,7 @@ hostname = "0.3.1"
 json5 = "0.4.1"
 serde = { version = "1.0.188", features = ["derive"] }
 serde_json = "1.0.107"
+serde_path_to_error = "0.1.14"
 # TODO: switch to toml_edit to preserve (and write) doc comments
 
 # Error handling

src/components/backlog.rs

@@ -22,6 +22,7 @@ use enum_dispatch::enum_dispatch;
 use ratatui::{prelude::*, widgets::*};
 
 use crate::components::Action;
+use crate::config::{Config, ScrollAmount};
 use crate::widgets::prerender::{PrerenderInner, PrerenderValue};
 use crate::widgets::{
   BacklogItemWidget, BottomAlignedParagraph, Divider, EmptyWidget, OverlappableWidget,
@@ -38,8 +39,11 @@ struct ScrollPosition {
   relative_scroll: i64,
 }
 
-#[derive(Default, Debug)]
+#[derive(Debug)]
 pub struct Backlog {
+  config: Config,
+  /// Used to compute scroll on PageUp/PageDown when configured to a percentage.
+  last_height: u16,
   scroll_position: Option<ScrollPosition>,
   /// Fallback used if the scroll_position is missing or unusable
   absolute_scroll: u64,
@@ -58,16 +62,22 @@ impl Component for Backlog {
         modifiers: KeyModifiers::NONE,
         kind: KeyEventKind::Press,
         state: _,
-      } => {
-        self.scroll_up(20); // TODO: use the component height
+      } => match self.config.keyboard.scroll_page {
+        ScrollAmount::Absolute(n) => self.scroll_up(n.into()),
+        ScrollAmount::Percentage(n) => {
+          self.scroll_up(u64::from(n) * u64::from(self.last_height) / 100)
+        },
       },
       KeyEvent {
         code: KeyCode::PageDown,
         modifiers: KeyModifiers::NONE,
         kind: KeyEventKind::Press,
         state: _,
-      } => {
-        self.scroll_down(20) // TODO: use the component height
+      } => match self.config.keyboard.scroll_page {
+        ScrollAmount::Absolute(n) => self.scroll_down(n.into()),
+        ScrollAmount::Percentage(n) => {
+          self.scroll_down(u64::from(n) * u64::from(self.last_height) / 100)
+        },
       },
       _ => {},
     }
@@ -96,6 +106,16 @@ impl Component for Backlog {
 }
 
 impl Backlog {
+  pub fn new(config: Config) -> Self {
+    Backlog {
+      config,
+      last_height: 30, // Arbitrary default, only useful when user scrolls before first render
+      scroll_position: None,
+      absolute_scroll: 0,
+      pending_scroll: 0,
+    }
+  }
+
   pub fn scroll_up(&mut self, lines: u64) {
     self.pending_scroll = self.pending_scroll.saturating_add(lines as i64);
   }
@@ -156,6 +176,7 @@ impl Backlog {
     let block = Block::new().borders(Borders::ALL);
     let mut text_area = block.inner(area);
     block.render(area, frame_buffer);
+    self.last_height = text_area.height;
 
     // Recompute absolute scroll position if we are not at the bottom of the backlog
     if self.absolute_scroll != 0 || self.pending_scroll != 0 {
@@ -206,7 +227,7 @@ impl Backlog {
       };
       let expected_height = self.get_item_height(&item, text_area.width);
 
-      if scroll.saturating_sub(expected_height) > text_area.height.into() {
+      if scroll.saturating_sub(expected_height) > u64::from(text_area.height) {
         // Paragraph is too far down, not displayed
         scroll -= expected_height;
         continue;

src/components/home.rs

@@ -43,7 +43,7 @@ impl Home {
     let mut self_ = Home {
       command_tx: None,
       buflist: Buflist::new(config.clone()),
-      backlog: Backlog::default(),
+      backlog: Backlog::new(config.clone()),
       textarea: TextArea::default(),
       config,
     };

src/config.rs

@@ -1,5 +1,6 @@
 use std::{collections::HashMap, fmt, path::PathBuf};
 
+use bounded_integer::BoundedU8;
 use color_eyre::eyre::Result;
 use config::Value;
 use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
@@ -40,11 +41,77 @@ fn default_device_name() -> String {
   }
 }
 
+#[derive(Clone, Debug)]
+pub enum ScrollAmount {
+  Percentage(BoundedU8<1, 100>),
+  Absolute(u16),
+}
+
+impl<'de> Deserialize<'de> for ScrollAmount {
+  fn deserialize<D>(deserializer: D) -> Result<ScrollAmount, D::Error>
+  where
+    D: Deserializer<'de>,
+  {
+    deserializer.deserialize_str(ScrollAmountVisitor)
+  }
+}
+
+struct ScrollAmountVisitor;
+
+impl<'de> Visitor<'de> for ScrollAmountVisitor {
+  type Value = ScrollAmount;
+
+  fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    formatter.write_str("a positive integer or a percentage")
+  }
+
+  fn visit_u16<E>(self, value: u16) -> Result<Self::Value, E>
+  where
+    E: de::Error,
+  {
+    Ok(ScrollAmount::Absolute(value))
+  }
+
+  fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+  where
+    E: de::Error,
+  {
+    let s: String = s.chars().filter(|c| !c.is_whitespace()).collect(); // strip whitespaces
+    match s.strip_suffix('%') {
+      Some(percent_str) => match percent_str.parse() {
+        Ok(percent) => {
+          if 0 < percent && percent <= 100 {
+            Ok(ScrollAmount::Percentage(percent))
+          } else {
+            Err(E::invalid_value(
+              de::Unexpected::Unsigned(percent.into()),
+              &"integer between 1 and 100 (inclusive)",
+            ))
+          }
+        },
+        Err(_) => Err(E::invalid_value(
+          de::Unexpected::Other(percent_str),
+          &"integer between 1 and 100 (inclusive)",
+        )),
+      },
+      None => Err(E::invalid_value(
+        de::Unexpected::Str(&s),
+        &"integer or quoted percentage (ending with '%')",
+      )),
+    }
+  }
+}
+
 #[derive(Clone, Debug, Deserialize)]
 pub struct MouseConfig {
   pub enable: bool,
 }
 
+#[derive(Clone, Debug, Deserialize)]
+pub struct KeyboardConfig {
+  pub scroll_page: ScrollAmount,
+}
+
 #[derive(Clone, Debug, Deserialize)]
 pub struct BuflistLayoutConfig {
   pub column_width: u16,
@@ -84,13 +151,14 @@ pub struct Config {
   pub accounts: nonempty::NonEmpty<AccountConfig>,
   #[serde(default)]
   pub keybindings: KeyBindings,
+  pub keyboard: KeyboardConfig,
   pub mouse: MouseConfig,
   pub style: StylesConfig,
   pub layout: LayoutConfig,
 }
 
 impl Config {
-  pub fn new() -> Result<Self, config::ConfigError> {
+  pub fn new() -> Result<Self> {
     let data_dir = crate::utils::get_data_dir();
     let config_dir = crate::utils::get_config_dir();
     let mut builder = config::Config::builder()
@@ -123,7 +191,7 @@ impl Config {
       log::error!("No configuration file found. Application may not behave as expected");
     }
 
-    builder.build()?.try_deserialize()
+    Ok(serde_path_to_error::deserialize(builder.build()?)?)
   }
 }
 

src/default_config.toml

@@ -6,6 +6,11 @@
 "<Alt-left>" = "/previous"
 "<Alt-right>" = "/next"
 
+[keyboard]
+# How much to scroll when pressing PageUp/PageDown. This can be either a number of lines
+# eg. 42) or a percentage wrapped in quotes (eg. "100%") of the screen size.
+scroll_page = "50%"
+
 [mouse]
 enable = true