//! Generates a compile-time manifest of the asset files served on wasm, so
//! the web entrypoint can preload them before the first frame.
//!
//! `WASM_ASSETS` is emitted into `OUT_DIR` and included by
//! `src/wasm_assets.rs` on wasm targets. Native builds keep using
//! `rust-embed` and ignore it.

use std::path::Path;
use std::{env, fs};

fn main() {
    let manifest_dir = env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set by cargo");
    let assets_dir = Path::new(&manifest_dir).join("../../assets");

    let mut paths = Vec::new();
    for dir in ["icons", "brand"] {
        let dir_path = assets_dir.join(dir);
        let entries = fs::read_dir(&dir_path).unwrap_or_else(|error| {
            panic!(
                "expected asset directory {} to exist: {error}",
                dir_path.display()
            )
        });

        for entry in entries {
            let entry = entry.expect("failed to read asset directory entry");
            if entry.file_type().is_ok_and(|t| t.is_file()) {
                let name = entry.file_name().to_string_lossy().into_owned();
                if !name.starts_with('.') {
                    paths.push(format!("{dir}/{name}"));
                }
            }
        }
    }
    paths.sort();

    let manifest = format!(
        "/// Asset files served by the wasm asset loader. Generated by build.rs.\npub const WASM_ASSETS: &[&str] = &[\n{}\n];\n",
        paths
            .iter()
            .map(|path| format!("    \"{path}\","))
            .collect::<Vec<_>>()
            .join("\n")
    );

    let out_dir = env::var("OUT_DIR").expect("OUT_DIR not set by cargo");
    fs::write(Path::new(&out_dir).join("wasm_assets.rs"), manifest)
        .expect("failed to write wasm asset manifest");

    // Rerun when the asset files change (adding/removing files updates the
    // directory mtime).
    for dir in ["icons", "brand"] {
        if let Ok(canonical) = assets_dir.join(dir).canonicalize() {
            println!("cargo:rerun-if-changed={}", canonical.display());
        }
    }
    println!("cargo:rerun-if-changed=build.rs");
}