use std::env;

fn main() {
    let rev = get_value_from_env("GIT_VERSION")
        .or_else(|| get_value_from_command("git", ["rev-parse", "--short", "HEAD"]))
        .unwrap_or_else(|| "unknown".to_owned());

    let branch = get_value_from_env("GIT_BRANCH")
        .or_else(|| get_value_from_command("git", ["rev-parse", "--abbrev-ref", "HEAD"]))
        .unwrap_or_else(|| "unknown".to_owned());

    println!("cargo:rustc-env=GIT_REVISION={}", rev);
    println!("cargo:rustc-env=GIT_BRANCH={}", branch);
    println!("cargo:rerun-if-env-changed=GIT_REVISION");
}

fn get_value_from_env(key: &str) -> Option<String> {
    env::var(key).map_or_else(|_| None, Some)
}

fn get_value_from_command<I: IntoIterator<Item = S>, S: AsRef<std::ffi::OsStr>>(
    cmd: &str,
    args: I,
) -> Option<String> {
    std::process::Command::new(cmd)
        .args(args)
        .output()
        .map_or_else(
            |_| None,
            |out| {
                if !out.status.success() {
                    return None;
                }

                match std::str::from_utf8(&out.stdout) {
                    Ok(value) => Some(value.to_owned()),
                    Err(_) => None,
                }
            },
        )
}