use std::process::Command;

fn main() {
    // Watch the ref that HEAD points to (detects new commits on current branch),
    // HEAD itself (detects branch switches / detached checkout),
    // and the tags directory (detects new tags created before a rebuild).
    if let Ok(head) = std::fs::read_to_string(".git/HEAD") {
        if let Some(ref_path) = head.trim().strip_prefix("ref: ") {
            println!("cargo:rerun-if-changed=.git/{ref_path}");
        }
    }
    println!("cargo:rerun-if-changed=.git/HEAD");
    println!("cargo:rerun-if-changed=.git/refs/tags");

    let version = Command::new("git")
        .args(["describe", "--tags", "--always"])
        .output()
        .ok()
        .filter(|o| o.status.success())
        .and_then(|o| String::from_utf8(o.stdout).ok())
        .map(|s| s.trim().to_string())
        .unwrap_or_else(|| env!("CARGO_PKG_VERSION").to_string());

    let out = std::env::var("OUT_DIR").unwrap();
    std::fs::write(format!("{out}/version.txt"), &version).unwrap();
}