1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119

// Copyright 2024 New Vector Ltd.
// Copyright 2023, 2024 The Matrix.org Foundation C.I.C.
//
// SPDX-License-Identifier: AGPL-3.0-only
// Please see LICENSE in the repository root for full details.

//! A [`Clock`] is a way to get the current date and time.
//!
//! This module defines two implemetation of the [`Clock`] trait:
//! [`SystemClock`] which uses the system time, and a [`MockClock`], which can
//! be used and freely manipulated in tests.

use std::sync::{atomic::AtomicI64, Arc};

use chrono::{DateTime, TimeZone, Utc};

/// Represents a clock which can give the current date and time
pub trait Clock: Sync {
    /// Get the current date and time
    fn now(&self) -> DateTime<Utc>;
}

impl<C: Clock + Send + ?Sized> Clock for Arc<C> {
    fn now(&self) -> DateTime<Utc> {
        (**self).now()
    }
}

impl<C: Clock + ?Sized> Clock for Box<C> {
    fn now(&self) -> DateTime<Utc> {
        (**self).now()
    }
}

/// A clock which uses the system time
#[derive(Clone, Default)]
pub struct SystemClock {
    _private: (),
}

impl Clock for SystemClock {
    fn now(&self) -> DateTime<Utc> {
        // This is the clock used elsewhere, it's fine to call Utc::now here
        #[allow(clippy::disallowed_methods)]
        Utc::now()
    }
}

/// A fake clock, which uses a fixed timestamp, and can be advanced with the
/// [`MockClock::advance`] method.
pub struct MockClock {
    timestamp: AtomicI64,
}

impl Default for MockClock {
    fn default() -> Self {
        let datetime = Utc.with_ymd_and_hms(2022, 1, 16, 14, 40, 0).unwrap();
        Self::new(datetime)
    }
}

impl MockClock {
    /// Create a new clock which starts at the given datetime
    #[must_use]
    pub fn new(datetime: DateTime<Utc>) -> Self {
        let timestamp = AtomicI64::new(datetime.timestamp());
        Self { timestamp }
    }

    /// Move the clock forward by the given amount of time
    pub fn advance(&self, duration: chrono::Duration) {
        self.timestamp
            .fetch_add(duration.num_seconds(), std::sync::atomic::Ordering::Relaxed);
    }
}

impl Clock for MockClock {
    fn now(&self) -> DateTime<Utc> {
        let timestamp = self.timestamp.load(std::sync::atomic::Ordering::Relaxed);
        chrono::TimeZone::timestamp_opt(&Utc, timestamp, 0).unwrap()
    }
}

#[cfg(test)]
mod tests {
    use chrono::Duration;

    use super::*;

    #[test]
    fn test_mocked_clock() {
        let clock = MockClock::default();

        // Time should be frozen, and give out the same timestamp on each call
        let first = clock.now();
        std::thread::sleep(std::time::Duration::from_millis(10));
        let second = clock.now();

        assert_eq!(first, second);

        // Clock can be advanced by a fixed duration
        clock.advance(Duration::microseconds(10 * 1000 * 1000));
        let third = clock.now();
        assert_eq!(first + Duration::microseconds(10 * 1000 * 1000), third);
    }

    #[test]
    fn test_real_clock() {
        let clock = SystemClock::default();

        // Time should not be frozen
        let first = clock.now();
        std::thread::sleep(std::time::Duration::from_millis(10));
        let second = clock.now();

        assert_ne!(first, second);
        assert!(first < second);
    }
}