#![allow(clippy::enum_glob_use)]

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

#[inline]
#[must_use]
#[allow(clippy::as_conversions)]
pub fn now_millis() -> u64 {
	UNIX_EPOCH
		.elapsed()
		.expect("positive duration after epoch")
		.as_millis() as u64
}

#[must_use]
pub fn rfc2822_from_seconds(epoch: i64) -> String {
	use chrono::{DateTime, Utc};

	DateTime::<Utc>::from_timestamp(epoch, 0)
		.unwrap_or_default()
		.to_rfc2822()
}

#[must_use]
pub fn format(ts: SystemTime, str: &str) -> String {
	use chrono::{DateTime, Utc};

	let dt: DateTime<Utc> = ts.into();
	dt.format(str).to_string()
}

#[must_use]
pub fn pretty(d: Duration) -> String {
	use Unit::*;

	let fmt = |w, f, u| format!("{w}.{f} {u}");
	let gen64 = |w, f, u| fmt(w, (f * 100.0) as u64, u);
	let gen128 = |w, f, u| gen64(u64::try_from(w).expect("u128 to u64"), f, u);
	match whole_and_frac(d) {
		(Days(whole), frac) => gen64(whole, frac, "days"),
		(Hours(whole), frac) => gen64(whole, frac, "hours"),
		(Mins(whole), frac) => gen64(whole, frac, "minutes"),
		(Secs(whole), frac) => gen64(whole, frac, "seconds"),
		(Millis(whole), frac) => gen128(whole, frac, "milliseconds"),
		(Micros(whole), frac) => gen128(whole, frac, "microseconds"),
		(Nanos(whole), frac) => gen128(whole, frac, "nanoseconds"),
	}
}

/// Return a pair of (whole part, frac part) from a duration where. The whole
/// part is the largest Unit containing a non-zero value, the frac part is a
/// rational remainder left over.
#[must_use]
pub fn whole_and_frac(d: Duration) -> (Unit, f64) {
	use Unit::*;

	let whole = whole_unit(d);
	(
		whole,
		match whole {
			Days(_) => (d.as_secs() % 86_400) as f64 / 86_400.0,
			Hours(_) => (d.as_secs() % 3_600) as f64 / 3_600.0,
			Mins(_) => (d.as_secs() % 60) as f64 / 60.0,
			Secs(_) => f64::from(d.subsec_millis()) / 1000.0,
			Millis(_) => f64::from(d.subsec_micros()) / 1000.0,
			Micros(_) => f64::from(d.subsec_nanos()) / 1000.0,
			Nanos(_) => 0.0,
		},
	)
}

/// Return the largest Unit which represents the duration. The value is
/// rounded-down, but never zero.
#[must_use]
pub fn whole_unit(d: Duration) -> Unit {
	use Unit::*;

	match d.as_secs() {
		86_400.. => Days(d.as_secs() / 86_400),
		3_600..=86_399 => Hours(d.as_secs() / 3_600),
		60..=3_599 => Mins(d.as_secs() / 60),

		_ => match d.as_micros() {
			1_000_000.. => Secs(d.as_secs()),
			1_000..=999_999 => Millis(d.subsec_millis().into()),

			_ => match d.as_nanos() {
				1_000.. => Micros(d.subsec_micros().into()),

				_ => Nanos(d.subsec_nanos().into()),
			},
		},
	}
}

#[derive(Eq, PartialEq, Clone, Copy, Debug)]
pub enum Unit {
	Days(u64),
	Hours(u64),
	Mins(u64),
	Secs(u64),
	Millis(u128),
	Micros(u128),
	Nanos(u128),
}