use std::env;
use std::path::Path;
use std::process::Command;

// Mirror the per-crate convention (see xtrain-cuda/build.rs): with no nvcc/GPU
// locally, emit `no_cuda` so the NCCL FFI + DDP code compiles (but is not linked
// or run). On dash5, link NCCL exactly like xserv-distributed's build.rs.
fn main() {
    println!("cargo:rustc-check-cfg=cfg(no_cuda)");

    let cuda_path = env::var("CUDA_HOME")
        .or_else(|_| env::var("CUDA_PATH"))
        .unwrap_or_else(|_| "/usr/local/cuda".to_string());

    if !nvcc_available(&cuda_path) {
        println!("cargo:warning=nvcc not found — skipping NCCL link (host-only build).");
        println!("cargo:rustc-cfg=no_cuda");
        return;
    }

    println!("cargo:rustc-link-search=native={cuda_path}/lib64");
    // NCCL is installed as a system library on dash5.
    println!("cargo:rustc-link-search=native=/usr/lib/x86_64-linux-gnu");
    println!("cargo:rustc-link-lib=dylib=nccl");
    println!("cargo:rustc-link-lib=dylib=cudart");
}

fn nvcc_available(cuda_path: &str) -> bool {
    if Command::new("nvcc").arg("--version").output().is_ok() {
        return true;
    }
    Path::new(&format!("{cuda_path}/bin/nvcc")).exists()
}