use super::funejson::Value;
use super::dates_add_days::iso_from_epoch_day;

/// 0001-01-01T00:00:00Z and 9999-12-31T23:59:59Z in Unix seconds.
const MIN_SECONDS: i64 = -62135596800;
const MAX_SECONDS: i64 = 253402300799;

/// Unix seconds as YYYY-MM-DDTHH:MM:SSZ. The day is floored (`div_euclid`),
/// so a negative time falls on the day before the epoch rather than rounding
/// towards it.
///
/// # Panics
/// Panics outside years 0001 to 9999.
pub fn unix_to_iso(seconds: i64) -> String {
    if !(MIN_SECONDS..=MAX_SECONDS).contains(&seconds) {
        panic!(
            "seconds must be from {} to {} (years 0001 to 9999), received {}",
            MIN_SECONDS, MAX_SECONDS, seconds
        );
    }
    let day = seconds.div_euclid(86400);
    let rest = seconds.rem_euclid(86400);
    format!(
        "{}T{:02}:{:02}:{:02}Z",
        iso_from_epoch_day(day),
        rest / 3600,
        (rest % 3600) / 60,
        rest % 60
    )
}

pub fn fune_vector(args: &[Value]) -> Value {
    let seconds = match &args[0] {
        Value::Int(i) => *i,
        other => panic!("seconds must be a whole number, received {}", other),
    };
    Value::str(&unix_to_iso(seconds))
}