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
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183

use super::{nfa, Byte, Nfa, Ref};
use crate::Map;
use std::fmt;
use std::sync::atomic::{AtomicU32, Ordering};

#[derive(PartialEq, Clone, Debug)]
pub(crate) struct Dfa<R>
where
    R: Ref,
{
    pub(crate) transitions: Map<State, Transitions<R>>,
    pub(crate) start: State,
    pub(crate) accepting: State,
}

#[derive(PartialEq, Clone, Debug)]
pub(crate) struct Transitions<R>
where
    R: Ref,
{
    byte_transitions: Map<Byte, State>,
    ref_transitions: Map<R, State>,
}

impl<R> Default for Transitions<R>
where
    R: Ref,
{
    fn default() -> Self {
        Self { byte_transitions: Map::default(), ref_transitions: Map::default() }
    }
}

impl<R> Transitions<R>
where
    R: Ref,
{
    fn insert(&mut self, transition: Transition<R>, state: State) {
        match transition {
            Transition::Byte(b) => {
                self.byte_transitions.insert(b, state);
            }
            Transition::Ref(r) => {
                self.ref_transitions.insert(r, state);
            }
        }
    }
}

/// The states in a `Nfa` represent byte offsets.
#[derive(Hash, Eq, PartialEq, PartialOrd, Ord, Copy, Clone)]
pub(crate) struct State(u32);

#[derive(Hash, Eq, PartialEq, Clone, Copy)]
pub(crate) enum Transition<R>
where
    R: Ref,
{
    Byte(Byte),
    Ref(R),
}

impl fmt::Debug for State {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "S_{}", self.0)
    }
}

impl<R> fmt::Debug for Transition<R>
where
    R: Ref,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self {
            Self::Byte(b) => b.fmt(f),
            Self::Ref(r) => r.fmt(f),
        }
    }
}

impl<R> Dfa<R>
where
    R: Ref,
{
    pub(crate) fn unit() -> Self {
        let transitions: Map<State, Transitions<R>> = Map::default();
        let start = State::new();
        let accepting = start;

        Self { transitions, start, accepting }
    }

    #[cfg(test)]
    pub(crate) fn bool() -> Self {
        let mut transitions: Map<State, Transitions<R>> = Map::default();
        let start = State::new();
        let accepting = State::new();

        transitions.entry(start).or_default().insert(Transition::Byte(Byte::Init(0x00)), accepting);

        transitions.entry(start).or_default().insert(Transition::Byte(Byte::Init(0x01)), accepting);

        Self { transitions, start, accepting }
    }

    #[instrument(level = "debug")]
    pub(crate) fn from_nfa(nfa: Nfa<R>) -> Self {
        let Nfa { transitions: nfa_transitions, start: nfa_start, accepting: nfa_accepting } = nfa;

        let mut dfa_transitions: Map<State, Transitions<R>> = Map::default();
        let mut nfa_to_dfa: Map<nfa::State, State> = Map::default();
        let dfa_start = State::new();
        nfa_to_dfa.insert(nfa_start, dfa_start);

        let mut queue = vec![(nfa_start, dfa_start)];

        while let Some((nfa_state, dfa_state)) = queue.pop() {
            if nfa_state == nfa_accepting {
                continue;
            }

            for (nfa_transition, next_nfa_states) in nfa_transitions[&nfa_state].iter() {
                let dfa_transitions =
                    dfa_transitions.entry(dfa_state).or_insert_with(Default::default);

                let mapped_state = next_nfa_states.iter().find_map(|x| nfa_to_dfa.get(x).copied());

                let next_dfa_state = match nfa_transition {
                    &nfa::Transition::Byte(b) => *dfa_transitions
                        .byte_transitions
                        .entry(b)
                        .or_insert_with(|| mapped_state.unwrap_or_else(State::new)),
                    &nfa::Transition::Ref(r) => *dfa_transitions
                        .ref_transitions
                        .entry(r)
                        .or_insert_with(|| mapped_state.unwrap_or_else(State::new)),
                };

                for &next_nfa_state in next_nfa_states {
                    nfa_to_dfa.entry(next_nfa_state).or_insert_with(|| {
                        queue.push((next_nfa_state, next_dfa_state));
                        next_dfa_state
                    });
                }
            }
        }

        let dfa_accepting = nfa_to_dfa[&nfa_accepting];

        Self { transitions: dfa_transitions, start: dfa_start, accepting: dfa_accepting }
    }

    pub(crate) fn bytes_from(&self, start: State) -> Option<&Map<Byte, State>> {
        Some(&self.transitions.get(&start)?.byte_transitions)
    }

    pub(crate) fn byte_from(&self, start: State, byte: Byte) -> Option<State> {
        self.transitions.get(&start)?.byte_transitions.get(&byte).copied()
    }

    pub(crate) fn refs_from(&self, start: State) -> Option<&Map<R, State>> {
        Some(&self.transitions.get(&start)?.ref_transitions)
    }
}

impl State {
    pub(crate) fn new() -> Self {
        static COUNTER: AtomicU32 = AtomicU32::new(0);
        Self(COUNTER.fetch_add(1, Ordering::SeqCst))
    }
}

impl<R> From<nfa::Transition<R>> for Transition<R>
where
    R: Ref,
{
    fn from(nfa_transition: nfa::Transition<R>) -> Self {
        match nfa_transition {
            nfa::Transition::Byte(byte) => Transition::Byte(byte),
            nfa::Transition::Ref(r) => Transition::Ref(r),
        }
    }
}