//! Build stamp: lets `llm-gateway --version` tell you when the binary was built.
//!
//! Without it, a stale release binary looks exactly like a fresh one, which has
//! already caused a confusing "unknown argument" report.

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

fn main() {
    let seconds = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|elapsed| elapsed.as_secs())
        .unwrap_or(0);
    println!(
        "cargo:rustc-env=LLM_GATEWAY_BUILD_TIME={}",
        format_utc(seconds)
    );
}

/// `YYYY-MM-DDTHH:MM:SSZ`, without pulling a date crate into the build script.
fn format_utc(seconds: u64) -> String {
    let days = (seconds / 86_400) as i64;
    let rem = seconds % 86_400;

    // Howard Hinnant's civil-from-days algorithm.
    let z = days + 719_468;
    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
    let doe = z - era * 146_097;
    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
    let mut year = yoe + era * 400;
    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
    let mp = (5 * doy + 2) / 153;
    let day = doy - (153 * mp + 2) / 5 + 1;
    let month = if mp < 10 { mp + 3 } else { mp - 9 };
    if month <= 2 {
        year += 1;
    }

    format!(
        "{year:04}-{month:02}-{day:02}T{:02}:{:02}:{:02}Z",
        rem / 3600,
        (rem % 3600) / 60,
        rem % 60
    )
}