lix 0.12.2

Embeddable version control for apps and AI agents.
Documentation 
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
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162

use crate::common::LixTimestamp;
use crate::functions::{FunctionProvider, FunctionProviderCheckpoint};

const DETERMINISTIC_UUID_COUNTER_MASK: u64 = 0x0000_FFFF_FFFF_FFFF;

/// Deterministic function provider for engine execution.
///
/// The provider is pure runtime state: it does not load or persist the sequence
/// itself. Session/transaction code owns that boundary so tests can decide when
/// deterministic state is read and written.
#[derive(Debug, Clone)]
pub(crate) struct DeterministicFunctionProvider {
    next_sequence: i64,
    timestamp_shuffle: bool,
    highest_seen: Option<i64>,
}

impl DeterministicFunctionProvider {
    pub(crate) fn new(next_sequence: i64, timestamp_shuffle: bool) -> Self {
        Self {
            next_sequence,
            timestamp_shuffle,
            highest_seen: None,
        }
    }

    pub(crate) fn highest_seen(&self) -> Option<i64> {
        self.highest_seen
    }

    fn take_sequence(&mut self) -> i64 {
        let current = self.next_sequence;
        self.next_sequence += 1;
        self.highest_seen = Some(current);
        current
    }
}

impl FunctionProvider for DeterministicFunctionProvider {
    #[expect(clippy::cast_sign_loss)]
    fn uuid_v7(&mut self) -> uuid::Uuid {
        let counter = self.take_sequence();
        let counter_bits = (counter as u64) & DETERMINISTIC_UUID_COUNTER_MASK;
        uuid::Uuid::from_u128(0x0192_0000_0000_7000_8000_0000_0000_0000 + u128::from(counter_bits))
    }

    fn timestamp(&mut self) -> LixTimestamp {
        let counter = self.take_sequence();
        let millis = if self.timestamp_shuffle {
            shuffled_timestamp_millis(counter)
        } else {
            counter
        };
        LixTimestamp::from_unix_millis_utc_lossy(millis)
    }

    fn deterministic_sequence_persist_highest_seen(&self) -> Option<i64> {
        self.highest_seen()
    }

    fn statement_checkpoint(&self) -> Option<FunctionProviderCheckpoint> {
        Some(FunctionProviderCheckpoint::DeterministicSequence {
            next_sequence: self.next_sequence,
            highest_seen: self.highest_seen,
        })
    }

    fn restore_statement_checkpoint(&mut self, checkpoint: FunctionProviderCheckpoint) {
        let FunctionProviderCheckpoint::DeterministicSequence {
            next_sequence,
            highest_seen,
        } = checkpoint;
        self.next_sequence = next_sequence;
        self.highest_seen = highest_seen;
    }
}

fn shuffled_timestamp_millis(counter: i64) -> i64 {
    const WINDOW: i64 = 1000;
    const MULTIPLIER: i64 = 733;
    const OFFSET: i64 = 271;

    let cycle = counter.div_euclid(WINDOW);
    let within = counter.rem_euclid(WINDOW);
    let shuffled = (within * MULTIPLIER + OFFSET).rem_euclid(WINDOW);
    cycle * WINDOW + shuffled
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::functions::DeterministicSequence;

    #[test]
    fn deterministic_uuid_uses_sequence_counter() {
        let mut provider = DeterministicFunctionProvider::new(0, false);

        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-000000000000"
        );
        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-000000000001"
        );
        assert_eq!(provider.highest_seen(), Some(1));
    }

    #[test]
    fn deterministic_timestamp_uses_sequence_counter() {
        let mut provider = DeterministicFunctionProvider::new(1, false);

        assert_eq!(provider.timestamp().to_string(), "1970-01-01T00:00:00.001Z");
        assert_eq!(provider.highest_seen(), Some(1));
    }

    #[test]
    fn deterministic_timestamp_shuffle_can_be_non_monotonic() {
        let mut provider = DeterministicFunctionProvider::new(0, true);
        let first = provider.timestamp();
        let second = provider.timestamp();

        assert!(second < first);
        assert_eq!(provider.highest_seen(), Some(1));
    }

    #[test]
    fn deterministic_sequence_can_start_after_persisted_highest_seen() {
        let sequence = DeterministicSequence { highest_seen: 41 };
        let mut provider = DeterministicFunctionProvider::new(sequence.next_sequence(), false);

        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-00000000002a"
        );
        assert_eq!(provider.highest_seen(), Some(42));
    }

    #[test]
    fn statement_checkpoint_restores_consumed_sequence() {
        let mut provider = DeterministicFunctionProvider::new(0, false);
        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-000000000000"
        );

        let checkpoint = provider
            .statement_checkpoint()
            .expect("deterministic provider should be checkpointable");
        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-000000000001"
        );

        provider.restore_statement_checkpoint(checkpoint);
        assert_eq!(
            provider.uuid_v7().to_string(),
            "01920000-0000-7000-8000-000000000001"
        );
        assert_eq!(provider.highest_seen(), Some(1));
    }
}