//! Build script: embeds the short git commit hash of the build as `WH_GIT_HASH`.

use std::process::Command;

/// Name of the compile-time environment variable holding the commit hash.
const GIT_HASH_ENV: &str = "WH_GIT_HASH";
/// Value used when the hash cannot be read (no git, not a repository).
const UNKNOWN_HASH: &str = "unknown";

/// Purpose: export the short commit hash to the crate and rebuild when the commit changes.
/// Inputs: none (runs `git` in the package directory).
/// Output: none.
/// Side effects: prints cargo directives on stdout.
fn main() {
    println!("cargo:rerun-if-changed=.git/HEAD");
    println!("cargo:rerun-if-changed=.git/refs");
    println!("cargo:rerun-if-changed=.git/packed-refs");
    let hash = git_short_hash().unwrap_or_else(|| UNKNOWN_HASH.to_owned());
    println!("cargo:rustc-env={GIT_HASH_ENV}={hash}");
}

/// Purpose: read the short hash of the checked-out commit.
/// Inputs: none.
/// Output: the hash, or `None` when git is missing, fails or prints nothing.
/// Side effects: runs `git rev-parse --short HEAD`.
fn git_short_hash() -> Option<String> {
    let output = Command::new("git").args(["rev-parse", "--short", "HEAD"]).output().ok()?;
    if !output.status.success() {
        return None;
    }
    let hash = String::from_utf8(output.stdout).ok()?.trim().to_owned();
    (!hash.is_empty()).then_some(hash)
}