use time::Duration;
use time::OffsetDateTime;

#[cfg(target_arch = "wasm32")]
pub fn now_utc() -> OffsetDateTime {
    return OffsetDateTime::from_unix_timestamp_nanos((js_sys::Date::now() * 1_000_000f64) as i128)
        .expect("current time outside supported range");
}

#[cfg(not(target_arch = "wasm32"))]
#[inline(always)]
pub fn now_utc() -> OffsetDateTime {
    return OffsetDateTime::now_utc();
}

#[cfg(target_arch = "wasm32")]
type InnerInstant = Duration;
#[cfg(not(target_arch = "wasm32"))]
type InnerInstant = time::Instant;

/// On wasm32, represented as a [`Duration`] from an arbitrary epoch. On other architectures,
/// represented as [`time::Instant`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct Instant(InnerInstant);

impl Instant {
    #[cfg(target_arch = "wasm32")]
    pub fn now() -> Instant {
        let stamp = web_sys::window()
            .expect("cannot get window")
            .performance()
            .expect("cannot get performance")
            .now();
        return Instant(Duration::seconds_f64(stamp / 1_000f64));
    }

    #[cfg(not(target_arch = "wasm32"))]
    #[inline(always)]
    pub fn now() -> Instant {
        return Instant(time::Instant::now());
    }

    #[inline(always)]
    pub fn elapsed(self) -> Duration {
        Self::now() - self
    }
}

impl std::ops::Sub for Instant {
    type Output = Duration;

    #[inline(always)]
    fn sub(self, rhs: Self) -> Self::Output {
        self.0 - rhs.0
    }
}

#[cfg(feature = "local-offset")]
#[cfg(target_arch = "wasm32")]
pub fn current_local_offset() -> Result<time::UtcOffset, time::error::IndeterminateOffset> {
    // The value returned by `getTimezoneOffset()` is inverted. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset#negative_values_and_positive_values.
    time::UtcOffset::from_whole_seconds(
        (-js_sys::Date::new_0().get_timezone_offset() * 60f64) as i32,
    )
    .map_err(|_| time::error::IndeterminateOffset)
}

#[cfg(feature = "local-offset")]
#[cfg(not(target_arch = "wasm32"))]
#[inline(always)]
pub fn current_local_offset() -> Result<time::UtcOffset, time::error::IndeterminateOffset> {
    time::UtcOffset::current_local_offset()
}