//! Server-start-time utilities for stale-merge detection.

/// Wall-clock time captured the first time this server process touches the
/// merge subsystem. Used to detect merge_jobs left over from a previous
/// server instance: a re-exec on `rebuild_and_restart` keeps the same PID,
/// so PID alone cannot distinguish "current" vs "previous" server. This
/// timestamp is fresh per-process (the static is reset by execve) and is
/// the source of truth for stale-merge detection.
static SERVER_START_TIME: std::sync::OnceLock<f64> = std::sync::OnceLock::new();

/// Return this server process's start time (lazily captured on first call).
pub(crate) fn server_start_time() -> f64 {
    *SERVER_START_TIME.get_or_init(unix_now)
}

/// Encode the current server's start-time into the CRDT `error` field for
/// a Running merge job.
pub(crate) fn encode_server_start_time(t: f64) -> String {
    format!("{{\"server_start\":{t}}}")
}

/// Decode the server-start-time from a Running merge job's `error` field.
/// Returns `None` for legacy entries (which encoded `pid` instead) — those
/// are treated as stale by the cleanup pass.
pub(crate) fn decode_server_start_time(error: Option<&str>) -> Option<f64> {
    error
        .and_then(|e| serde_json::from_str::<serde_json::Value>(e).ok())
        .and_then(|v| v["server_start"].as_f64())
}

/// Current Unix timestamp in seconds as `f64`.
pub(crate) fn unix_now() -> f64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap_or_default()
        .as_secs_f64()
}