Rewrite asset path wrapper

RewriteAssetFetch allows to rewrite requested asset path to some other. This is useful for scenarios like localized assets or assets versioning, where there might be different versions of assets based on some runtime state.

use keket::{
    database::{path::AssetPath, AssetDatabase},
    fetch::{file::FileAssetFetch, rewrite::RewriteAssetFetch},
    protocol::text::TextAssetProtocol,
};
use std::{
    error::Error,
    sync::{Arc, RwLock},
};

fn main() -> Result<(), Box<dyn Error>> {
    let language = Arc::new(RwLock::new("en"));
    let language2 = language.clone();

    let mut database = AssetDatabase::default()
        .with_protocol(TextAssetProtocol)
        .with_fetch(RewriteAssetFetch::new(
            FileAssetFetch::default().with_root("resources"),
            move |path| {
                // Rewrite input path to localized one.
                Ok(AssetPath::from_parts(
                    path.protocol(),
                    &format!(
                        "{}.{}{}",
                        path.path_without_extension(),
                        *language2.read().unwrap(),
                        path.path_dot_extension().unwrap_or_default()
                    ),
                    path.meta(),
                ))
            },
        ));

    // Gets `text://localized.en.txt`.
    let asset = database.ensure("text://localized.txt")?;
    println!("English: {}", asset.access::<&String>(&database));

    // Change language.
    *language.write().unwrap() = "de";
    database.storage.clear();

    // Gets `text://localized.de.txt`.
    let asset = database.ensure("text://localized.txt")?;
    println!("German: {}", asset.access::<&String>(&database));

    Ok(())
}

Rewritten asset paths do not change path in asset entity - this is deliberate design decision to make outside systems not care about possible asset path change when trying to resolve asset handle by its path.