use std::process::Command;

const F_COMMIT :&str = ".commit";

fn main()
{
    let output = Command::new("git")
        .args(&["rev-parse", "HEAD"])
        .output()
        .expect("Failed to acquire git HEAD");
    let git_hash = String::from_utf8(output.stdout).expect("Invalid UTF-8 output from git HEAD");
    let git_hash = git_hash.trim();

    let previous_hash = std::fs::read_to_string(F_COMMIT).unwrap_or_default();
    if git_hash != previous_hash {
        std::fs::write(F_COMMIT, &git_hash).ok();
    }

    println!("cargo:rerun-if-changed={}", F_COMMIT);
    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
}