//! The car unit has no RTC battery: the clock boots stale and is stepped later by
//! chrony (NTP or GNSS). Recordings therefore carry enough to correct timestamps
//! afterwards — sync state at start, monotonic time, and every step observed.

use serde_json::{json, Value};

fn clock(id: libc::clockid_t) -> f64 {
    let mut ts: libc::timespec = unsafe { std::mem::zeroed() };
    unsafe { libc::clock_gettime(id, &mut ts) };
    ts.tv_sec as f64 + ts.tv_nsec as f64 * 1e-9
}

pub fn realtime() -> f64 {
    clock(libc::CLOCK_REALTIME)
}

pub fn monotonic() -> f64 {
    clock(libc::CLOCK_MONOTONIC)
}

/// realtime − monotonic. Constant while the clock only slews; a jump means a step.
pub fn offset() -> f64 {
    realtime() - monotonic()
}

pub fn boot_id() -> String {
    std::fs::read_to_string("/proc/sys/kernel/random/boot_id").map(|s| s.trim().to_string()).unwrap_or_default()
}

/// Kernel view of synchronisation, read without privilege (adjtimex with modes = 0).
pub fn sync_state() -> Value {
    let mut tx: libc::timex = unsafe { std::mem::zeroed() };
    let state = unsafe { libc::adjtimex(&mut tx) };
    let unsync = state == libc::TIME_ERROR || tx.status & libc::STA_UNSYNC != 0;
    json!({ "synced": !unsync, "maxerror_us": tx.maxerror, "esterror_us": tx.esterror })
}

pub fn hostname() -> String {
    std::fs::read_to_string("/proc/sys/kernel/hostname").map(|s| s.trim().to_string()).unwrap_or_default()
}