Add basic conversion methods

.gitignore

+/target
+/Cargo.lock

Cargo.toml

+[package]
+name = "web_instant"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/instant_desktop.rs

+use std::ops::Sub;
+use std::time::{Duration, Instant};
+
+#[derive(Copy, Clone, PartialEq, PartialOrd, Debug)]
+pub struct Spot {
+	inner: Instant,
+}
+
+impl Spot {
+	pub fn now() -> Self {
+		Spot {
+			inner: Instant::now(),
+		}
+	}
+	pub fn as_secs(&self) -> u64 {
+		self.as_duration().as_secs()
+	}
+	pub fn as_duration(&self) -> Duration {
+		self.inner.elapsed()
+	}
+
+	pub fn elapsed(&self) -> Duration {
+		self.as_duration()
+	}
+}
+
+impl Sub<Spot> for Spot {
+	type Output = Duration;
+
+	fn sub(self, rhs: Spot) -> Self::Output {
+		self.inner - rhs.inner
+	}
+}

src/instant_web.rs

+use std::ops::Sub;
+use std::time::Duration;
+
+#[derive(Copy, Clone, PartialEq, PartialOrd, Debug)]
+pub struct Spot {
+	/// Millisecond offset from the Unix Epoch - equivalent to Date.now()
+	inner: f64,
+}
+
+impl Spot {
+	pub fn now() -> Self {
+		Spot {
+			inner: js_sys::Date::now(),
+		}
+	}
+	pub fn as_secs(&self) -> u64 {
+		self.as_duration().as_secs()
+	}
+	pub fn as_duration(&self) -> Duration {
+		Self::now() - *self
+	}
+	pub fn elapsed(&self) -> Duration {
+		self.as_duration()
+	}
+}
+
+impl Sub<Spot> for Spot {
+	type Output = Duration;
+
+	fn sub(self, rhs: Spot) -> Self::Output {
+		let diff = (self.inner - rhs.inner).max(0.0);
+		let secs = (diff as u64) / 1_000;
+		let nanos = (((diff as u64) % 1_000) as u32) * 1_000_000;
+
+		Duration::new(secs, nanos)
+	}
+}

src/lib.rs

+#[cfg(not(target_arch = "wasm32"))]
+mod instant_desktop;
+#[cfg(target_arch = "wasm32")]
+mod instant_web;
+
+#[cfg(not(target_arch = "wasm32"))]
+pub use instant_desktop::Spot;
+#[cfg(target_arch = "wasm32")]
+pub use instant_web::Spot;