More datetime changes

* Accept the format string as Into<String> rather than String to allow
  &str to be provided.
* set_colors accepts Into<Vec<TimeColor>> rather than &[TimeColor]. The
  function needs a Vec<TimeColor>. Previously it would unconditionally
  clone the slice into a Vec, now it can accept a Vec if the user provides
  one and avoid an allocation in those cases (while still cloning a slice
  if that's what the user provides).
* DateTime::colors was an Option<Vec<TimeColor>> it's now simply a
  Vec<TimeColor>. There was no difference in logic between a None and an
  empty Vec so the code could be simplified by removing the Option.
* No longer allocate a String when formatting the time.
* Collapse the logic setting color. Calculating whether to set a color
  and storing the result in Option<ColorRGB> only to then set data.color
  if the Option is Some, can be collapsed to simply set data.color if the
  configuration dictates.

src/bin/home.rs

@@ -25,8 +25,8 @@ fn main() {
     // Realtime upload/download rate for a interface
     bar.push(NetworkSpeedWidget::new(&opts.nic, 6));
 
-    let mut dt = DateTimeWidget::new("%m/%d %H:%M".to_string());
-    dt.set_colors(&vec![
+    let mut dt = DateTimeWidget::new("%m/%d %H:%M");
+    dt.set_colors(vec![
         TimeColor {
             start: NaiveTime::from_hms(19, 0, 0),
             color: ColorRGB::yellow(),

src/bin/work.rs

@@ -25,8 +25,8 @@ fn main() {
     // Realtime upload/download rate for a interface
     bar.push(NetworkSpeedWidget::new(&opts.nic, 6));
 
-    let mut dt = DateTimeWidget::tz("%H:%M %Z".to_string(), chrono_tz::Europe::London);
-    dt.set_colors(&vec![
+    let mut dt = DateTimeWidget::tz("%H:%M %Z", chrono_tz::Europe::London);
+    dt.set_colors(vec![
         TimeColor {
             start: NaiveTime::from_hms(0, 0, 0),
             color: ColorRGB::red(),
@@ -46,8 +46,8 @@ fn main() {
     ]);
     bar.push(dt);
 
-    let mut dt = DateTimeWidget::new("%m/%d %H:%M".to_string());
-    dt.set_colors(&vec![
+    let mut dt = DateTimeWidget::new("%m/%d %H:%M");
+    dt.set_colors(vec![
         TimeColor {
             start: NaiveTime::from_hms(0, 0, 0),
             color: ColorRGB::red(),

src/widgets/datetime.rs

@@ -1,5 +1,5 @@
+use chrono::{offset::TimeZone, Local, NaiveTime, Utc};
 use std::fmt::Display;
-use chrono::{Local, Utc, NaiveTime, offset::TimeZone};
 
 use i3monkit::Block;
 use i3monkit::ColorRGB;
@@ -11,7 +11,7 @@ pub struct DateTimeWidget<Tz> {
     /// https://docs.rs/chrono/*/chrono/format/strftime/index.html for documentation.
     fmt: String,
     tz: Tz,
-    colors: Option<Vec<TimeColor>>,
+    colors: Vec<TimeColor>,
 }
 
 #[derive(Clone)]
@@ -21,7 +21,7 @@ pub struct TimeColor {
 }
 
 impl DateTimeWidget<Local> {
-    pub fn new(fmt: String) -> Self {
+    pub fn new(fmt: impl Into<String>) -> Self {
         DateTimeWidget::tz(fmt, Local)
     }
 }
@@ -31,17 +31,20 @@ where
     Tz: TimeZone,
     Tz::Offset: Display,
 {
-    pub fn tz(fmt: String, tz: Tz) -> Self {
+    pub fn tz(fmt: impl Into<String>, tz: Tz) -> Self {
         DateTimeWidget {
-            fmt,
+            fmt: fmt.into(),
             tz,
-            colors: None,
+            colors: Vec::new(),
         }
     }
-    pub fn set_colors(&mut self, colors: &[TimeColor]) {
-        let mut colors = colors.to_vec();
+    pub fn set_colors(&mut self, colors: impl Into<Vec<TimeColor>>) {
+        let mut colors = colors.into();
         colors.sort_by(|l, r| l.start.cmp(&r.start));
-        self.colors = Some(colors);
+        self.colors = colors;
+    }
+    fn now(&self) -> chrono::DateTime<Tz> {
+        Utc::now().with_timezone(&self.tz)
     }
 }
 
@@ -51,29 +54,25 @@ where
     Tz::Offset: Display,
 {
     fn update(&mut self) -> Option<WidgetUpdate> {
-        let (time, time_string) = {
-            let now = Utc::now().with_timezone(&self.tz);
-            (now.time(), now.format(&self.fmt).to_string())
-        };
-        let color = if let Some(colors) = &self.colors {
-            colors
-                .iter()
-                .filter(|tc| tc.start < time)
-                .last()
-                .map(|tc| tc.color.clone())
-        } else {
-            None
-        };
+        let now = self.now();
 
         let time_string = format!(
             r#"<span size="x-large" weight="heavy">{}</span>"#,
-            time_string
+            now.format(&self.fmt)
         );
         let mut data = Block::new()
             .append_full_text(&time_string)
             .use_pango()
             .clone();
-        if let Some(color) = color {
+
+        let time = now.time();
+        if let Some(color) = self
+            .colors
+            .iter()
+            .filter(|tc| tc.start < time)
+            .last()
+            .map(|tc| tc.color.clone())
+        {
             data.color(color);
         }
         Some(WidgetUpdate {