// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.time;
using zx;

/// Metadata about a device's approximation of UTC time, commonly referred to as "system time."
[Discoverable]
protocol Utc {
    /// Notifies clients of updates to the UTC timeline. The first call on a channel returns
    /// immediately, and subsequent calls on the same channel will return when the state
    /// has changed.
    WatchState() -> (UtcState state);
};

/// Describes the state of the clock.
table UtcState {
    /// The monotonic time at which this `UtcState` was observed.
    1: zx.time timestamp;
    /// The source of our current UTC approximation.
    2: UtcSource source;
};

/// Describes the source from which the current UTC approximation was retrieved.
enum UtcSource {
    /// The clock has been initialized to a known-prior reference time but may be highly inaccurate.
    BACKSTOP = 2;
    /// The clock has been initialized from a suitably accurate external time source. For many
    /// devices the most common external time source is a network time server.
    EXTERNAL = 3;
};