1use anyhow::{anyhow, Result};
 2use std::{borrow::Cow, cell::RefCell, collections::HashMap};
 3
 4pub trait AssetSource: 'static + Send + Sync {
 5    fn load(&self, path: &str) -> Result<Cow<[u8]>>;
 6    fn list(&self, path: &str) -> Vec<Cow<'static, str>>;
 7}
 8
 9impl AssetSource for () {
10    fn load(&self, path: &str) -> Result<Cow<[u8]>> {
11        Err(anyhow!(
12            "get called on empty asset provider with \"{}\"",
13            path
14        ))
15    }
16
17    fn list(&self, _: &str) -> Vec<Cow<'static, str>> {
18        vec![]
19    }
20}
21
22pub struct AssetCache {
23    source: Box<dyn AssetSource>,
24    svgs: RefCell<HashMap<String, usvg::Tree>>,
25}
26
27impl AssetCache {
28    pub fn new(source: impl AssetSource) -> Self {
29        Self {
30            source: Box::new(source),
31            svgs: RefCell::new(HashMap::new()),
32        }
33    }
34
35    pub fn svg(&self, path: &str) -> Result<usvg::Tree> {
36        let mut svgs = self.svgs.borrow_mut();
37        if let Some(svg) = svgs.get(path) {
38            Ok(svg.clone())
39        } else {
40            let bytes = self.source.load(path)?;
41            let svg = usvg::Tree::from_data(&bytes, &usvg::Options::default())?;
42            svgs.insert(path.to_string(), svg.clone());
43            Ok(svg)
44        }
45    }
46}