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

fn main() {
    println!("cargo:rerun-if-changed=examples");

    let examples_root = PathBuf::from("examples");
    let out_dir = PathBuf::from(env::var("OUT_DIR").expect("OUT_DIR is not set"));
    let out_file = out_dir.join("embedded_examples.rs");

    let mut dirs = Vec::new();
    let mut files = Vec::new();

    if examples_root.is_dir() {
        collect_examples(&examples_root, &examples_root, &mut dirs, &mut files)
            .expect("failed to collect example templates");
    }

    dirs.sort();
    files.sort_by(|a, b| a.0.cmp(&b.0));

    let mut generated = String::new();
    generated.push_str(
        "struct EmbeddedFile {\n    path: &'static str,\n    contents: &'static [u8],\n}\n\n",
    );
    generated.push_str("static EMBEDDED_EXAMPLE_DIRS: &[&str] = &[\n");
    for dir in &dirs {
        generated.push_str(&format!("    {:?},\n", dir));
    }
    generated.push_str("];\n\n");
    generated.push_str("static EMBEDDED_EXAMPLE_FILES: &[EmbeddedFile] = &[\n");
    for (relative_path, absolute_path) in &files {
        generated.push_str(&format!(
            "    EmbeddedFile {{ path: {:?}, contents: include_bytes!(r#\"{}\"#) }},\n",
            relative_path,
            absolute_path.display()
        ));
    }
    generated.push_str("];\n");

    fs::write(out_file, generated).expect("failed to write embedded example list");
}

fn collect_examples(
    root: &Path,
    dir: &Path,
    dirs: &mut Vec<String>,
    files: &mut Vec<(String, PathBuf)>,
) -> io::Result<()> {
    for entry in fs::read_dir(dir)? {
        let entry = entry?;
        let path = entry.path();
        let relative_path = path
            .strip_prefix(root)
            .expect("example path is outside examples root")
            .to_string_lossy()
            .replace('\\', "/");

        if path.is_dir() {
            dirs.push(relative_path);
            collect_examples(root, &path, dirs, files)?;
        } else if path.is_file() {
            files.push((relative_path, path.canonicalize()?));
        }
    }

    Ok(())
}