refactor: remove app::Message type from Graph

I wonder, given the description of canvas::Program,
would the graph be better as a true widget?

I'll have to learn how to actually implement a widget though.

src/app/graph.rs

@@ -0,0 +1,64 @@
+use std::collections::VecDeque;
+
+use iced::{Color, Point, Renderer, Theme, mouse, widget::canvas};
+
+const CYAN: Color = Color::from_rgb8(0, 255, 255);
+
+#[derive(Default)]
+pub struct Graph {
+    timeline: VecDeque<f32>,
+
+    pub cache: canvas::Cache,
+}
+
+impl Graph {
+    pub fn new(value: f32) -> Self {
+        Self {
+            timeline: {
+                let mut vec = VecDeque::new();
+                vec.push_front(value);
+                vec
+            },
+            ..Default::default()
+        }
+    }
+
+    pub fn update(&mut self, value: f32) {
+        self.timeline.push_back(value);
+        if self.timeline.len() > 1000 {
+            self.timeline.pop_front();
+        }
+    }
+}
+
+impl canvas::Program<(), Theme, Renderer> for Graph {
+    type State = ();
+    fn draw(
+        &self,
+        _state: &Self::State,
+        renderer: &Renderer,
+        _theme: &Theme,
+        bounds: iced::Rectangle,
+        _cursor: mouse::Cursor,
+    ) -> Vec<canvas::Geometry<Renderer>> {
+        let geometry = self.cache.draw(renderer, bounds.size(), |frame| {
+            frame.stroke_rectangle(
+                Point::new(0., 0.),
+                bounds.size(),
+                canvas::Stroke::default().with_color(Color::from_rgb8(255, 0, 0)),
+            );
+            frame.stroke(
+                &canvas::Path::new(|builder| {
+                    for (index, value) in self.timeline.iter().enumerate() {
+                        let x = index as f32 / self.timeline.len() as f32 * bounds.width;
+                        let y = bounds.height - value / 100. * bounds.height;
+                        builder.line_to(Point::new(x, y))
+                    }
+                }),
+                canvas::Stroke::default().with_color(CYAN),
+            );
+        });
+
+        vec![geometry]
+    }
+}

src/app/mod.rs

@@ -4,9 +4,9 @@ use iced::{
 };
 use smol::Timer;
 
-use crate::{app::cpu_graph::CpuGraph, sysinfo_snapshot::SysinfoSnapshot};
+use crate::{app::graph::Graph, sysinfo_snapshot::SysinfoSnapshot};
 
-mod cpu_graph;
+mod graph;
 
 enum Message {
     Info(SysinfoSnapshot),
@@ -14,8 +14,8 @@ enum Message {
 
 #[derive(Default)]
 struct State {
-    total_cpu_graph: CpuGraph,
+    total_cpu_graph: Graph,
-    cpu_graphs: Vec<CpuGraph>,
+    cpu_graphs: Vec<Graph>,
 }
 
 impl State {
@@ -51,12 +51,12 @@ impl State {
                     self.cpu_graphs = snapshot
                         .cpus
                         .into_iter()
-                        .map(|usage| CpuGraph::new(usage))
+                        .map(|value| Graph::new(value))
                         .collect();
                 } else {
-                    for (graph, usage) in self.cpu_graphs.iter_mut().zip(snapshot.cpus.into_iter())
+                    for (graph, value) in self.cpu_graphs.iter_mut().zip(snapshot.cpus.into_iter())
                     {
-                        graph.update(usage);
+                        graph.update(value);
                         graph.cache.clear();
                     }
                 }