use std::io::Write;
fn main() {
    println!("cargo:rerun-if-changed=build.rs");

    cuda::set_include_dir();
    let (write, kernel_paths) = cuda::build_ptx();
    if write {
        let mut file = std::fs::File::create("src/lib.rs").unwrap();
        for kernel_path in kernel_paths {
            let name = kernel_path.file_stem().unwrap().to_str().unwrap();
            file.write_all(
                format!(
                    r#"pub const {}: &str = include_str!(concat!(env!("OUT_DIR"), "/{}.ptx"));"#,
                    name.to_uppercase().replace('.', "_"),
                    name
                )
                .as_bytes(),
            )
            .unwrap();
            file.write_all(&[b'\n']).unwrap();
        }
    }
}

mod cuda {
    pub fn set_include_dir() {
        use std::path::PathBuf;
        // NOTE: copied from cudarc build.rs.
        // We can't actually set a env!() value from another crate,
        // so we have to do that here.

        // use PathBuf;

        let env_vars = [
            "CUDA_PATH",
            "CUDA_ROOT",
            "CUDA_TOOLKIT_ROOT_DIR",
            "CUDNN_LIB",
        ];
        #[allow(unused)]
        let env_vars = env_vars
            .into_iter()
            .map(std::env::var)
            .filter_map(Result::ok)
            .map(Into::<PathBuf>::into);

        let roots = [
            "/usr",
            "/usr/local/cuda",
            "/opt/cuda",
            "/usr/lib/cuda",
            "C:/Program Files/NVIDIA GPU Computing Toolkit",
            "C:/CUDA",
        ];
        #[allow(unused)]
        let roots = roots.into_iter().map(Into::<PathBuf>::into);

        #[cfg(feature = "ci-check")]
        let root: PathBuf = "ci".into();

        #[cfg(not(feature = "ci-check"))]
        let root = env_vars
            .chain(roots)
            .find(|path| path.join("include").join("cuda.h").is_file())
            .unwrap();

        println!(
            "cargo:rustc-env=CUDA_INCLUDE_DIR={}",
            root.join("include").display()
        );
    }

    pub fn build_ptx() -> (bool, Vec<std::path::PathBuf>) {
        use rayon::prelude::*;
        use std::path::PathBuf;
        let out_dir = std::env::var("OUT_DIR").unwrap();
        let kernel_paths: Vec<PathBuf> = glob::glob("src/*.cu")
            .unwrap()
            .map(|p| p.unwrap())
            .collect();
        let mut include_directories: Vec<PathBuf> = glob::glob("src/**/*.cuh")
            .unwrap()
            .map(|p| p.unwrap())
            .collect();

        println!("cargo:rerun-if-changed=src/");
        // for path in &kernel_paths {
        //     println!("cargo:rerun-if-changed={}", path.display());
        // }

        for path in &mut include_directories {
            // println!("cargo:rerun-if-changed={}", path.display());
            let destination =
                std::format!("{out_dir}/{}", path.file_name().unwrap().to_str().unwrap());
            std::fs::copy(path.clone(), destination).unwrap();
            // remove the filename from the path so it's just the directory
            path.pop();
        }

        include_directories.sort();
        include_directories.dedup();

        #[allow(unused)]
        let include_options: Vec<String> = include_directories
            .into_iter()
            .map(|s| "-I".to_string() + &s.into_os_string().into_string().unwrap())
            .collect::<Vec<_>>();

        // let start = std::time::Instant::now();

        // Grab compute code from nvidia-smi
        let mut compute_cap = {
            let out = std::process::Command::new("nvidia-smi")
                    .arg("--query-gpu=compute_cap")
                    .arg("--format=csv")
                    .output()
                    .expect("`nvidia-smi` failed. Ensure that you have CUDA installed and that `nvidia-smi` is in your PATH.");
            let out = std::str::from_utf8(&out.stdout).unwrap();
            let mut lines = out.lines();
            assert_eq!(lines.next().unwrap(), "compute_cap");
            let cap = lines.next().unwrap().replace('.', "");
            cap.parse::<usize>().unwrap()
        };

        // Grab available GPU codes from nvcc and select the highest one
        let max_nvcc_code = {
            let out = std::process::Command::new("nvcc")
                    .arg("--list-gpu-code")
                    .output()
                    .expect("`nvcc` failed. Ensure that you have CUDA installed and that `nvcc` is in your PATH.");
            let out = std::str::from_utf8(&out.stdout).unwrap();

            let out = out.lines().collect::<Vec<&str>>();
            let mut codes = Vec::with_capacity(out.len());
            for code in out {
                let code = code.split('_').collect::<Vec<&str>>();
                if !code.is_empty() && code.contains(&"sm") {
                    if let Ok(num) = code[1].parse::<usize>() {
                        codes.push(num);
                    }
                }
            }
            codes.sort();
            if !codes.contains(&compute_cap) {
                panic!("nvcc cannot target gpu arch {compute_cap}. Available nvcc targets are {codes:?}.");
            }
            *codes.last().unwrap()
        };

        // If nvidia-smi compute_cap is higher than the highest gpu code from nvcc,
        // then choose the highest gpu code in nvcc
        if compute_cap > max_nvcc_code {
            println!(
                "cargo:warning=Lowering gpu arch {compute_cap} to max nvcc target {max_nvcc_code}."
            );
            compute_cap = max_nvcc_code;
        }

        println!("cargo:rerun-if-env-changed=CUDA_COMPUTE_CAP");
        if let Ok(compute_cap_str) = std::env::var("CUDA_COMPUTE_CAP") {
            compute_cap = compute_cap_str.parse::<usize>().unwrap();
            println!("cargo:warning=Using gpu arch {compute_cap} from $CUDA_COMPUTE_CAP");
        }

        println!("cargo:rustc-env=CUDA_COMPUTE_CAP=sm_{compute_cap}");

        let ccbin_env = std::env::var("CANDLE_NVCC_CCBIN");
        println!("cargo:rerun-if-env-changed=CANDLE_NVCC_CCBIN");
        let children = kernel_paths
                .par_iter()
                .flat_map(|p| {
                    let mut output = p.clone();
                    output.set_extension("ptx");
                    let output_filename = std::path::Path::new(&out_dir).to_path_buf().join("out").with_file_name(output.file_name().unwrap());

                    let ignore = if output_filename.exists() {
                        let out_modified = output_filename.metadata().unwrap().modified().unwrap();
                        let in_modified = p.metadata().unwrap().modified().unwrap();
                        out_modified.duration_since(in_modified).is_ok()
                    }else{
                        false
                    };
                    if ignore{
                        None
                    }else{
                        let mut command = std::process::Command::new("nvcc");
                            command.arg(format!("--gpu-architecture=sm_{compute_cap}"))
                            .arg("--ptx")
                            .args(["--default-stream", "per-thread"])
                            .args(["--output-directory", &out_dir])
                            // Flash attention only
                            // .arg("--expt-relaxed-constexpr")
                            .args(&include_options);
                        if let Ok(ccbin_path) = &ccbin_env {
                            command
                                .arg("-allow-unsupported-compiler")
                                .args(["-ccbin", ccbin_path]);
                        }
                        command.arg(p);
                        Some((p,  command.spawn()
                        .expect("nvcc failed to start. Ensure that you have CUDA installed and that `nvcc` is in your PATH.").wait_with_output()))
                    }})
                .collect::<Vec<_>>();

        let ptx_paths: Vec<PathBuf> = glob::glob(&format!("{out_dir}/**/*.ptx"))
            .unwrap()
            .map(|p| p.unwrap())
            .collect();
        // We should rewrite `src/lib.rs` only if there are some newly compiled kernels, or removed
        // some old ones
        let write = !children.is_empty() || kernel_paths.len() < ptx_paths.len();
        for (kernel_path, child) in children {
            let output = child.expect("nvcc failed to run. Ensure that you have CUDA installed and that `nvcc` is in your PATH.");
            assert!(
                output.status.success(),
                "nvcc error while compiling {kernel_path:?}:\n\n# stdout\n{:#}\n\n# stderr\n{:#}",
                String::from_utf8_lossy(&output.stdout),
                String::from_utf8_lossy(&output.stderr)
            );
        }
        (write, kernel_paths)
    }
}