use std::env;
use std::fs;
use std::path::PathBuf;

fn main() {
    if env::var_os("CARGO_FEATURE_FFI").is_none() {
        return;
    }

    println!("cargo:rerun-if-changed=src/ffi.rs");
    println!("cargo:rerun-if-changed=cbindgen.toml");

    let crate_dir =
        PathBuf::from(env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set"));
    let crate_dir_string = crate_dir
        .to_str()
        .expect("crate directory must be valid UTF-8")
        .to_owned();

    let header_dir = crate_dir.join("ffi");
    fs::create_dir_all(&header_dir).expect("failed to create ffi output directory");

    let config_path = crate_dir.join("cbindgen.toml");
    let config = if config_path.exists() {
        cbindgen::Config::from_file(&config_path)
            .unwrap_or_else(|err| panic!("failed to load cbindgen config: {err}"))
    } else {
        cbindgen::Config::default()
    };

    let bindings = cbindgen::Builder::new()
        .with_config(config)
        .with_crate(crate_dir_string)
        .generate()
        .expect("unable to generate cbindgen bindings");

    let mut generated = Vec::new();
    bindings.write(&mut generated);

    let header_contents =
        String::from_utf8(generated).expect("generated header was not valid UTF-8");

    let header_path = header_dir.join("medicallib.h");
    let needs_write = fs::read_to_string(&header_path)
        .map(|existing| existing != header_contents)
        .unwrap_or(true);

    if needs_write {
        fs::write(&header_path, header_contents).expect("failed to write medicallib.h");
        println!("cargo:warning=Updated ffi/medicallib.h via cbindgen");
    }
}