Add timezone. (#327)

* Add timezone.

* Move implementation to cap-time-ext.

The cap-std crate is intended to focus on features which are provided by
Rust's `std`.

cap-time-ext/Cargo.toml

@@ -13,8 +13,10 @@ repository = "https://github.com/bytecodealliance/cap-std"
 edition = "2021"
 
 [dependencies]
+ambient-authority = "0.0.2"
 cap-primitives = { path = "../cap-primitives", version = "^2.0.0" }
 cap-std = { path = "../cap-std", optional = true, version = "^2.0.0" }
+iana-time-zone = "0.1.57"
 
 [target.'cfg(not(windows))'.dependencies]
 rustix = { version = "0.38.0", features = ["time"] }

cap-time-ext/src/lib.rs

@@ -11,6 +11,8 @@
 
 mod monotonic_clock;
 mod system_clock;
+mod timezone;
 
 pub use monotonic_clock::MonotonicClockExt;
 pub use system_clock::SystemClockExt;
+pub use timezone::Timezone;

cap-time-ext/src/timezone.rs

@@ -0,0 +1,29 @@
+use ambient_authority::AmbientAuthority;
+use iana_time_zone::get_timezone;
+
+/// A reference to a timezone resource.
+pub struct Timezone(());
+
+#[derive(Debug)]
+pub struct TimezoneError(String);
+
+impl Timezone {
+    /// Constructs a new instance of `Self`.
+    ///
+    /// # Ambient Authority
+    ///
+    /// This uses ambient authority to accesses clocks.
+    #[inline]
+    pub const fn new(ambient_authority: AmbientAuthority) -> Self {
+        let _ = ambient_authority;
+        Self(())
+    }
+
+    /// Returns the combined date and time with timezone.
+    ///
+    /// Converts NaiveTime to DateTime
+    #[inline]
+    pub fn timezone_name(&self) -> Result<String, TimezoneError> {
+        get_timezone().map_err(|e| TimezoneError(e.to_string()))
+    }
+}