other: slightly reduce the CPU time spent for draws (#918)

* other: group all dataset draws in a time chart

We used to draw each data set separately as a new canvas. Now, in one
canvas, we draw all datasets.

Note that this changes how dataset  lines are drawn - rather than
drawing one on top of another, it now draws kinda all at once. This
effect is *kinda* a bit better IMO, but it might also look a bit
more cluttered.

* other: optimize truncate_text

Flamegraphs showed that this area seems to be a bit heavy at times with
some inefficient use of iterators and collection. This change should
hopefully optimize this a bit by reducing some collections or
reallocations.

There can also be some further optimizations with less allocations from
callers.

* Reduce some redundant draws

12 files changed, 119 insertions, 73 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 61f68e20..27b01edf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,6 +41,8 @@ doctest = true
 doc = true
 
 [profile.release]
+# debug = true
+# strip = false
 debug = 0
 strip = "symbols"
 lto = true
diff --git a/src/app/data_harvester/memory/general/heim.rs b/src/app/data_harvester/memory/general/heim.rs
index eb596ea7..bb63d2b5 100644
--- a/src/app/data_harvester/memory/general/heim.rs
+++ b/src/app/data_harvester/memory/general/heim.rs
@@ -32,6 +32,7 @@ pub async fn get_ram_data() -> crate::utils::error::Result<Option<MemHarvest>> {
     let (mem_total_in_kib, mem_used_in_kib) = {
         #[cfg(target_os = "linux")]
         {
+            // TODO: [OPT] is this efficient?
             use smol::fs::read_to_string;
             let meminfo = read_to_string("/proc/meminfo").await?;
 
diff --git a/src/canvas/canvas_colours.rs b/src/canvas/canvas_colours.rs
index 742bdb28..e7996a32 100644
--- a/src/canvas/canvas_colours.rs
+++ b/src/canvas/canvas_colours.rs
@@ -73,11 +73,9 @@ impl Default for CanvasColours {
                 Style::default().fg(Color::LightCyan),
                 Style::default().fg(Color::LightGreen),
                 Style::default().fg(Color::LightBlue),
-                Style::default().fg(Color::LightRed),
                 Style::default().fg(Color::Cyan),
                 Style::default().fg(Color::Green),
                 Style::default().fg(Color::Blue),
-                Style::default().fg(Color::Red),
             ],
             border_style: Style::default().fg(text_colour),
             highlighted_border_style: Style::default().fg(HIGHLIGHT_COLOUR),
diff --git a/src/canvas/widgets/cpu_graph.rs b/src/canvas/widgets/cpu_graph.rs
index bb996e0d..a9ee8f43 100644
--- a/src/canvas/widgets/cpu_graph.rs
+++ b/src/canvas/widgets/cpu_graph.rs
@@ -4,6 +4,7 @@ use concat_string::concat_string;
 use tui::{
     backend::Backend,
     layout::{Constraint, Direction, Layout, Rect},
+    symbols::Marker,
     terminal::Frame,
 };
 
@@ -209,8 +210,13 @@ impl Painter {
                 " CPU ".into()
             };
 
+            let marker = if app_state.app_config_fields.use_dot {
+                Marker::Dot
+            } else {
+                Marker::Braille
+            };
+
             TimeGraph {
-                use_dot: app_state.app_config_fields.use_dot,
                 x_bounds,
                 hide_x_labels,
                 y_bounds: Y_BOUNDS,
@@ -221,6 +227,7 @@ impl Painter {
                 is_expanded: app_state.is_expanded,
                 title_style: self.colours.widget_title_style,
                 legend_constraints: None,
+                marker,
             }
             .draw_time_graph(f, draw_loc, &points);
         }
diff --git a/src/canvas/widgets/mem_graph.rs b/src/canvas/widgets/mem_graph.rs
index 8ee5d96f..4ae7c2a9 100644
--- a/src/canvas/widgets/mem_graph.rs
+++ b/src/canvas/widgets/mem_graph.rs
@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use tui::{
     backend::Backend,
     layout::{Constraint, Rect},
+    symbols::Marker,
     terminal::Frame,
 };
 
@@ -104,8 +105,13 @@ impl Painter {
                 points
             };
 
+            let marker = if app_state.app_config_fields.use_dot {
+                Marker::Dot
+            } else {
+                Marker::Braille
+            };
+
             TimeGraph {
-                use_dot: app_state.app_config_fields.use_dot,
                 x_bounds,
                 hide_x_labels,
                 y_bounds: Y_BOUNDS,
@@ -116,6 +122,7 @@ impl Painter {
                 is_expanded: app_state.is_expanded,
                 title_style: self.colours.widget_title_style,
                 legend_constraints: Some((Constraint::Ratio(3, 4), Constraint::Ratio(3, 4))),
+                marker,
             }
             .draw_time_graph(f, draw_loc, &points);
         }
diff --git a/src/canvas/widgets/network_graph.rs b/src/canvas/widgets/network_graph.rs
index de21a6c2..d8c84031 100644
--- a/src/canvas/widgets/network_graph.rs
+++ b/src/canvas/widgets/network_graph.rs
@@ -1,6 +1,7 @@
 use tui::{
     backend::Backend,
     layout::{Constraint, Direction, Layout, Rect},
+    symbols::Marker,
     terminal::Frame,
     text::Text,
     widgets::{Block, Borders, Row, Table},
@@ -142,8 +143,13 @@ impl Painter {
                 ]
             };
 
+            let marker = if app_state.app_config_fields.use_dot {
+                Marker::Dot
+            } else {
+                Marker::Braille
+            };
+
             TimeGraph {
-                use_dot: app_state.app_config_fields.use_dot,
                 x_bounds,
                 hide_x_labels,
                 y_bounds,
@@ -154,6 +160,7 @@ impl Painter {
                 is_expanded: app_state.is_expanded,
                 title_style: self.colours.widget_title_style,
                 legend_constraints: Some(legend_constraints),
+                marker,
             }
             .draw_time_graph(f, draw_loc, &points);
         }
diff --git a/src/components/data_table/draw.rs b/src/components/data_table/draw.rs
index fa3958dd..f94e8505 100644
--- a/src/components/data_table/draw.rs
+++ b/src/components/data_table/draw.rs
@@ -221,7 +221,11 @@ where
                                 .iter()
                                 .zip(&self.state.calculated_widths)
                                 .filter_map(|(column, &width)| {
-                                    data_row.to_cell(column.inner(), width)
+                                    if width > 0 {
+                                        data_row.to_cell(column.inner(), width)
+                                    } else {
+                                        None
+                                    }
                                 }),
                         );
 
diff --git a/src/components/time_graph.rs b/src/components/time_graph.rs
index 26ef1d72..7e53a82a 100644
--- a/src/components/time_graph.rs
+++ b/src/components/time_graph.rs
@@ -22,9 +22,6 @@ pub struct GraphData<'a> {
 }
 
 pub struct TimeGraph<'a> {
-    /// Whether to use a dot marker over the default braille markers.
-    pub use_dot: bool,
-
     /// The min and max x boundaries. Expects a f64 representing the time range in milliseconds.
     pub x_bounds: [u64; 2],
 
@@ -54,6 +51,10 @@ pub struct TimeGraph<'a> {
 
     /// Any legend constraints.
     pub legend_constraints: Option<(Constraint, Constraint)>,
+
+    /// The marker type. Unlike tui-rs' native charts, we assume
+    /// only a single type of market.
+    pub marker: Marker,
 }
 
 impl<'a> TimeGraph<'a> {
@@ -131,18 +132,7 @@ impl<'a> TimeGraph<'a> {
 
         // This is some ugly manual loop unswitching. Maybe unnecessary.
         // TODO: Optimize this step. Cut out unneeded points.
-        let data = if self.use_dot {
-            graph_data
-                .iter()
-                .map(|data| create_dataset(data, Marker::Dot))
-                .collect()
-        } else {
-            graph_data
-                .iter()
-                .map(|data| create_dataset(data, Marker::Braille))
-                .collect()
-        };
-
+        let data = graph_data.iter().map(create_dataset).collect();
         let block = Block::default()
             .title(self.generate_title(draw_loc))
             .borders(Borders::ALL)
@@ -164,7 +154,7 @@ impl<'a> TimeGraph<'a> {
 }
 
 /// Creates a new [`Dataset`].
-fn create_dataset<'a>(data: &'a GraphData<'a>, marker: Marker) -> Dataset<'a> {
+fn create_dataset<'a>(data: &'a GraphData<'a>) -> Dataset<'a> {
     let GraphData {
         points,
         style,
@@ -174,8 +164,7 @@ fn create_dataset<'a>(data: &'a GraphData<'a>, marker: Marker) -> Dataset<'a> {
     let dataset = Dataset::default()
         .style(*style)
         .data(points)
-        .graph_type(GraphType::Line)
-        .marker(marker);
+        .graph_type(GraphType::Line);
 
     if let Some(name) = name {
         dataset.name(name.as_ref())
@@ -191,6 +180,7 @@ mod test {
     use tui::{
         layout::Rect,
         style::{Color, Style},
+        symbols::Marker,
         text::{Span, Spans},
     };
 
@@ -206,7 +196,6 @@ mod test {
     fn create_time_graph() -> TimeGraph<'static> {
         TimeGraph {
             title: " Network ".into(),
-            use_dot: true,
             x_bounds: [0, 15000],
             hide_x_labels: false,
             y_bounds: [0.0, 100.5],
@@ -216,6 +205,7 @@ mod test {
             is_expanded: false,
             title_style: Style::default().fg(Color::Cyan),
             legend_constraints: None,
+            marker: Marker::Braille,
         }
     }
 
diff --git a/src/components/tui_widget/time_chart.rs b/src/components/tui_widget/time_chart.rs
index 730c3076..ae1d6642 100644
--- a/src/components/tui_widget/time_chart.rs
+++ b/src/components/tui_widget/time_chart.rs
@@ -4,7 +4,7 @@ use tui::{
     buffer::Buffer,
     layout::{Constraint, Rect},
     style::{Color, Style},
-    symbols,
+    symbols::{self, Marker},
     text::{Span, Spans},
     widgets::{
         canvas::{Canvas, Line, Points},
@@ -75,8 +75,6 @@ pub struct Dataset<'a> {
     name: Cow<'a, str>,
     /// A reference to the actual data
     data: &'a [Point],
-    /// Symbol used for each points of this dataset
-    marker: symbols::Marker,
     /// Determines graph type used for drawing points
     graph_type: GraphType,
     /// Style used to plot this dataset
@@ -88,7 +86,6 @@ impl<'a> Default for Dataset<'a> {
         Dataset {
             name: Cow::from(""),
             data: &[],
-            marker: symbols::Marker::Dot,
             graph_type: GraphType::Scatter,
             style: Style::default(),
         }
@@ -110,11 +107,6 @@ impl<'a> Dataset<'a> {
         self
     }
 
-    pub fn marker(mut self, marker: symbols::Marker) -> Dataset<'a> {
-        self.marker = marker;
-        self
-    }
-
     pub fn graph_type(mut self, graph_type: GraphType) -> Dataset<'a> {
         self.graph_type = graph_type;
         self
@@ -173,10 +165,12 @@ pub struct TimeChart<'a> {
     legend_style: Style,
     /// Constraints used to determine whether the legend should be shown or not
     hidden_legend_constraints: (Constraint, Constraint),
+    /// The marker type.
+    marker: Marker,
 }
 
 pub const DEFAULT_LEGEND_CONSTRAINTS: (Constraint, Constraint) =
-    (Constraint::Ratio(1, 4), Constraint::Ratio(1, 4));
+    (Constraint::Ratio(1, 4), Constraint::Length(4));
 
 #[allow(dead_code)]
 impl<'a> TimeChart<'a> {
@@ -192,6 +186,7 @@ impl<'a> TimeChart<'a> {
             legend_style: Default::default(),
             datasets,
             hidden_legend_constraints: DEFAULT_LEGEND_CONSTRAINTS,
+            marker: Marker::Braille,
         }
     }
 
@@ -220,6 +215,11 @@ impl<'a> TimeChart<'a> {
         self
     }
 
+    pub fn marker(mut self, marker: Marker) -> TimeChart<'a> {
+        self.marker = marker;
+        self
+    }
+
     /// Set the constraints used to determine whether the legend should be shown or not.
     pub fn hidden_legend_constraints(
         mut self, constraints: (Constraint, Constraint),
@@ -422,14 +422,14 @@ impl<'a> Widget for TimeChart<'a> {
             }
         }
 
-        // Probably better to move the dataset inside.
-        for dataset in &self.datasets {
-            Canvas::default()
-                .background_color(self.style.bg.unwrap_or(Color::Reset))
-                .x_bounds(self.x_axis.bounds)
-                .y_bounds(self.y_axis.bounds)
-                .marker(dataset.marker)
-                .paint(|ctx| {
+        Canvas::default()
+            .background_color(self.style.bg.unwrap_or(Color::Reset))
+            .x_bounds(self.x_axis.bounds)
+            .y_bounds(self.y_axis.bounds)
+            .paint(|ctx| {
+                for dataset in &self.datasets {
+                    let color = dataset.style.fg.unwrap_or(Color::Reset);
+
                     let start_bound = self.x_axis.bounds[0];
                     let end_bound = self.x_axis.bounds[1];
 
@@ -438,11 +438,6 @@ impl<'a> Widget for TimeChart<'a> {
 
                     let data_slice = &dataset.data[start_index..end_index];
 
-                    ctx.draw(&Points {
-                        coords: data_slice,
-                        color: dataset.style.fg.unwrap_or(Color::Reset),
-                    });
-
                     if let Some(interpolate_start) = interpolate_start {
                         if let (Some(older_point), Some(newer_point)) = (
                             dataset.data.get(interpolate_start),
@@ -453,18 +448,18 @@ impl<'a> Widget for TimeChart<'a> {
                                 interpolate_point(older_point, newer_point, self.x_axis.bounds[0]),
                             );
 
-                            ctx.draw(&Points {
-                                coords: &[interpolated_point],
-                                color: dataset.style.fg.unwrap_or(Color::Reset),
-                            });
-
                             if let GraphType::Line = dataset.graph_type {
                                 ctx.draw(&Line {
                                     x1: interpolated_point.0,
                                     y1: interpolated_point.1,
                                     x2: newer_point.0,
                                     y2: newer_point.1,
-                                    color: dataset.style.fg.unwrap_or(Color::Reset),
+                                    color,
+                                });
+                            } else {
+                                ctx.draw(&Points {
+                                    coords: &[interpolated_point],
+                                    color,
                                 });
                             }
                         }
@@ -477,9 +472,14 @@ impl<'a> Widget for TimeChart<'a> {
                                 y1: data[0].1,
                                 x2: data[1].0,
                                 y2: data[1].1,
-                                color: dataset.style.fg.unwrap_or(Color::Reset),
+                                color,
                             });
                         }
+                    } else {
+                        ctx.draw(&Points {
+                            coords: data_slice,
+                            color,
+                        });
                     }
 
                     if let Some(interpolate_end) = interpolate_end {
@@ -492,25 +492,25 @@ impl<'a> Widget for TimeChart<'a> {
                                 interpolate_point(older_point, newer_point, self.x_axis.bounds[1]),
                             );
 
-                            ctx.draw(&Points {
-                                coords: &[interpolated_point],
-                                color: dataset.style.fg.unwrap_or(Color::Reset),
-                            });
-
                             if let GraphType::Line = dataset.graph_type {
                                 ctx.draw(&Line {
                                     x1: older_point.0,
                                     y1: older_point.1,
                                     x2: interpolated_point.0,
                                     y2: interpolated_point.1,
-                                    color: dataset.style.fg.unwrap_or(Color::Reset),
+                                    color,
+                                });
+                            } else {
+                                ctx.draw(&Points {
+                                    coords: &[interpolated_point],
+                                    color,
                                 });
                             }
                         }
                     }
-                })
-                .render(graph_area, buf);
-        }
+                }
+            })
+            .render(graph_area, buf);
 
         if let Some(legend_area) = layout.legend_area {
             buf.set_style(legend_area, original_style);
diff --git a/src/lib.rs b/src/lib.rs
index 4987cb84..1adc59df 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -522,6 +522,8 @@ pub fn create_collection_thread(
                     }
                 }
             }
+
+            // TODO: [OPT] this feels like it might not be totally optimal. Hm.
             futures::executor::block_on(data_state.update_data());
 
             // Yet another check to bail if needed...
diff --git a/src/utils/gen_util.rs b/src/utils/gen_util.rs
index ab8c8479..60311105 100644
--- a/src/utils/gen_util.rs
+++ b/src/utils/gen_util.rs
@@ -1,7 +1,6 @@
 use std::cmp::Ordering;
 
-use concat_string::concat_string;
-use tui::text::Text;
+use tui::text::{Span, Spans, Text};
 use unicode_segmentation::UnicodeSegmentation;
 
 pub const KILO_LIMIT: u64 = 1000;
@@ -99,14 +98,37 @@ pub fn get_decimal_prefix(quantity: u64, unit: &str) -> (f64, String) {
 /// Truncates text if it is too long, and adds an ellipsis at the end if needed.
 pub fn truncate_text<'a, U: Into<usize>>(content: &str, width: U) -> Text<'a> {
     let width = width.into();
-    let graphemes: Vec<&str> = UnicodeSegmentation::graphemes(content, true).collect();
-
-    if graphemes.len() > width && width > 0 {
-        // Truncate with ellipsis
-        let first_n = graphemes[..(width - 1)].concat();
-        Text::raw(concat_string!(first_n, "…"))
+    let mut graphemes = UnicodeSegmentation::graphemes(content, true);
+    let grapheme_len = {
+        let (_, upper) = graphemes.size_hint();
+        match upper {
+            Some(upper) => upper,
+            None => graphemes.clone().count(), // Don't think this ever fires.
+        }
+    };
+
+    let text = if grapheme_len > width {
+        let mut text = String::with_capacity(width);
+        // Truncate with ellipsis.
+
+        // Use a hack to reduce the size to size `width`. Think of it like removing
+        // The last `grapheme_len - width` graphemes, which reduces the length to
+        // `width` long.
+        //
+        // This is a way to get around the currently experimental`advance_back_by`.
+        graphemes.nth_back(grapheme_len - width);
+
+        text.push_str(graphemes.as_str());
+        text.push('…');
+
+        text
     } else {
-        Text::raw(content.to_string())
+        content.to_string()
+    };
+
+    // TODO: [OPT] maybe add interning here?
+    Text {
+        lines: vec![Spans(vec![Span::raw(text)])],
     }
 }
 
@@ -156,4 +178,9 @@ mod test {
         y.sort_by(|a, b| sort_partial_fn(true)(a, b));
         assert_eq!(y, vec![16.15, 15.0, 1.0, -1.0, -100.0, -100.0, -100.1]);
     }
+
+    #[test]
+    fn test_truncation() {
+        // TODO: Add tests for `truncate_text`
+    }
 }
diff --git a/src/widgets/process_table/proc_widget_data.rs b/src/widgets/process_table/proc_widget_data.rs
index 94736336..c067f92b 100644
--- a/src/widgets/process_table/proc_widget_data.rs
+++ b/src/widgets/process_table/proc_widget_data.rs
@@ -221,6 +221,7 @@ impl ProcWidgetData {
 
 impl DataToCell<ProcColumn> for ProcWidgetData {
     fn to_cell<'a>(&'a self, column: &ProcColumn, calculated_width: u16) -> Option<Text<'a>> {
+        // TODO: Optimize the string allocations here...
         Some(truncate_text(
             &match column {
                 ProcColumn::CpuPercent => {