//! Build information for Help › About: the git commit and the build date (UTC). Both fall back to
//! "unknown" when git is missing (a source tarball).

use std::process::Command;
use std::time::{SystemTime, UNIX_EPOCH};

fn git(args: &[&str]) -> Option<String> {
    let out = Command::new("git").args(args).output().ok()?;
    out.status.success().then(|| String::from_utf8_lossy(&out.stdout).trim().to_string()).filter(|s| !s.is_empty())
}

/// Days since 1970-01-01 to a civil date (proleptic Gregorian).
fn civil(days: i64) -> (i64, i64, i64) {
    let z = days + 719_468;
    let era = z.div_euclid(146_097);
    let doe = z - era * 146_097;
    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
    let mp = (5 * doy + 2) / 153;
    let d = doy - (153 * mp + 2) / 5 + 1;
    let m = if mp < 10 { mp + 3 } else { mp - 9 };
    (yoe + era * 400 + i64::from(m <= 2), m, d)
}

fn main() {
    let commit = git(&["rev-parse", "--short", "HEAD"]).unwrap_or_else(|| "unknown".into());
    let dirty = git(&["status", "--porcelain", "--untracked-files=no"]).is_some();
    let secs = SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_secs() as i64).unwrap_or(0);
    let (y, m, d) = civil(secs.div_euclid(86_400));
    println!("cargo:rustc-env=SOLVECRAFT_COMMIT={commit}{}", if dirty { "+" } else { "" });
    println!("cargo:rustc-env=SOLVECRAFT_BUILD_DATE={y:04}-{m:02}-{d:02}");
    // A new commit in this checkout (or worktree) restamps the build.
    if let Some(dir) = git(&["rev-parse", "--git-dir"]) {
        println!("cargo:rerun-if-changed={dir}/logs/HEAD");
    }
    println!("cargo:rerun-if-changed=build.rs");
}