Switch to using the Derive API for Clap

This is the recommended approach in the Clap docs, and I'm not doing
anything complicated enough to require the Builder API.  Let's simplify!

Cargo.toml

@@ -5,7 +5,7 @@ edition = "2018"
 
 [dependencies]
 assert_cmd = "2.0.14"
-clap = "4.5.7"
+clap = { version = "4.5.7", features = ["derive"] }
 regex = "1.10.5"
 
 [dependencies.kmeans_colors]

src/get_image_colors.rs

@@ -6,20 +6,22 @@
 //
 // It returns a Vec<Lab>, which can be passed to the k-means process.
 
+use std::ffi::OsStr;
 use std::fs::File;
 use std::io::BufReader;
+use std::path::PathBuf;
 
 use image::codecs::gif::GifDecoder;
 use image::imageops::FilterType;
 use image::{AnimationDecoder, DynamicImage, Frame};
 use palette::cast::from_component_slice;
 use palette::{IntoColor, Lab, Srgba};
 
-pub fn get_image_colors(path: &str) -> Vec<Lab> {
-    let image_bytes = if path.to_lowercase().ends_with(".gif") {
-        get_bytes_for_gif(&path)
-    } else {
-        get_bytes_for_non_gif(&path)
+pub fn get_image_colors(path: &PathBuf) -> Vec<Lab> {
+    let image_bytes = match path.extension().and_then(OsStr::to_str) {
+        Some("gif") => get_bytes_for_gif(&path),
+        Some("GIF") => get_bytes_for_gif(&path),
+        _ => get_bytes_for_non_gif(&path),
     };
 
     let lab: Vec<Lab> = from_component_slice::<Srgba<u8>>(&image_bytes)
@@ -30,7 +32,7 @@ pub fn get_image_colors(path: &str) -> Vec<Lab> {
     lab
 }
 
-fn get_bytes_for_non_gif(path: &str) -> Vec<u8> {
+fn get_bytes_for_non_gif(path: &PathBuf) -> Vec<u8> {
     let img = match image::open(&path) {
         Ok(im) => im,
         Err(e) => {
@@ -59,7 +61,7 @@ fn get_bytes_for_non_gif(path: &str) -> Vec<u8> {
     resized_img.into_rgba8().into_raw()
 }
 
-fn get_bytes_for_gif(path: &str) -> Vec<u8> {
+fn get_bytes_for_gif(path: &PathBuf) -> Vec<u8> {
     let f = match File::open(path) {
         Ok(im) => im,
         Err(e) => {
@@ -132,6 +134,8 @@ fn get_bytes_for_gif(path: &str) -> Vec<u8> {
 
 #[cfg(test)]
 mod test {
+    use std::path::PathBuf;
+
     use crate::get_image_colors::get_image_colors;
 
     // This image comes from https://stacks.wellcomecollection.org/peering-through-mri-scans-of-fruit-and-veg-part-1-a2e8b07bde6f
@@ -141,11 +145,11 @@ mod test {
     // processed correctly.
     #[test]
     fn it_gets_colors_for_mri_fruit() {
-        get_image_colors("./src/tests/garlic.gif");
+        get_image_colors(&PathBuf::from("./src/tests/garlic.gif"));
     }
 
     #[test]
     fn get_colors_for_webp() {
-        get_image_colors("./src/tests/purple.webp");
+        get_image_colors(&PathBuf::from("./src/tests/purple.webp"));
     }
 }

src/main.rs

@@ -1,44 +1,53 @@
 #![deny(warnings)]
 
-#[macro_use]
-extern crate clap;
+use std::path::PathBuf;
 
+use clap::Parser;
 use palette::{FromColor, Lab, Srgb};
 
-mod cli;
 mod find_dominant_colors;
 mod get_image_colors;
 mod printing;
 
-fn main() {
-    let matches = cli::app().get_matches();
+#[derive(Parser, Debug)]
+#[command(version, about, long_about=None)]
+struct Cli {
+    /// path to the image to inspect
+    path: PathBuf,
+
+    /// how many colours to find
+    #[arg(long="max-colours", default_value_t=5)]
+    max_colours: usize,
 
-    let path = matches
-        .get_one::<String>("PATH")
-        .expect("`path` is required");
+    /// find a single colour that will look best against this background
+    #[arg(long="best-against-bg")]
+    background: Option<Srgb<u8>>,
 
-    let max_colours: usize = *matches
-        .get_one::<usize>("MAX_COLOURS")
-        .expect("`max-colours` is required");
+    /// just print the hex values, not colour previews
+    #[arg(long="no-palette")]
+    no_palette: bool,
+}
 
-    let lab: Vec<Lab> = get_image_colors::get_image_colors(&path);
 
-    let dominant_colors = find_dominant_colors::find_dominant_colors(&lab, max_colours);
+fn main() {
+    let cli = Cli::parse();
 
-    let background = matches.get_one::<Srgb<u8>>("BACKGROUND_HEX");
+    let lab: Vec<Lab> = get_image_colors::get_image_colors(&cli.path);
 
-    let selected_colors = match background {
-        Some(bg) => find_dominant_colors::choose_best_color_for_bg(dominant_colors.clone(), bg),
+    let dominant_colors = find_dominant_colors::find_dominant_colors(&lab, cli.max_colours);
+
+    let selected_colors = match cli.background {
+        Some(bg) => find_dominant_colors::choose_best_color_for_bg(dominant_colors.clone(), &bg),
         None => dominant_colors,
     };
-
+    //
     let rgb_colors = selected_colors
         .iter()
         .map(|c| Srgb::from_color(*c).into_format())
         .collect::<Vec<Srgb<u8>>>();
 
     for c in rgb_colors {
-        printing::print_color(c, &background, matches.get_flag("no-palette"));
+        printing::print_color(c, &cli.background, cli.no_palette);
     }
 }
 

src/printing.rs

@@ -5,7 +5,7 @@ use palette::Srgb;
 //
 // See https://alexwlchan.net/2021/04/coloured-squares/
 // See: https://gist.github.com/fnky/458719343aabd01cfb17a3a4f7296797?permalink_comment_id=3857871
-pub fn print_color(c: Srgb<u8>, background: &Option<&Srgb<u8>>, no_palette: bool) {
+pub fn print_color(c: Srgb<u8>, background: &Option<Srgb<u8>>, no_palette: bool) {
     let display_value = format!("#{:02x}{:02x}{:02x}", c.red, c.green, c.blue);
 
     if no_palette {