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

use std::convert::TryFrom;

use regex_syntax::hir::{Hir, HirKind, RepetitionKind};
use regex_syntax::ParserBuilder;

pub use regex_syntax::hir::{Class, ClassUnicode, Literal};

use crate::error::{Error, Result};

/// Middle Intermediate Representation of the regex, built from
/// `regex_syntax`'s `Hir`. The goal here is to strip and canonicalize
/// the tree, so that we don't have to do transformations later on the
/// graph, with the potential of running into looping references.
#[derive(Clone, Debug)]
pub enum Mir {
    Empty,
    Loop(Box<Mir>),
    Maybe(Box<Mir>),
    Concat(Vec<Mir>),
    Alternation(Vec<Mir>),
    Class(Class),
    Literal(Literal),
}

impl Mir {
    pub fn utf8(source: &str) -> Result<Mir> {
        Mir::try_from(ParserBuilder::new().build().parse(source)?)
    }

    pub fn utf8_ignore_case(source: &str) -> Result<Mir> {
        Mir::try_from(
            ParserBuilder::new()
                .case_insensitive(true)
                .build()
                .parse(source)?,
        )
    }

    pub fn binary(source: &str) -> Result<Mir> {
        Mir::try_from(
            ParserBuilder::new()
                .allow_invalid_utf8(true)
                .unicode(false)
                .build()
                .parse(source)?,
        )
    }

    pub fn binary_ignore_case(source: &str) -> Result<Mir> {
        Mir::try_from(
            ParserBuilder::new()
                .allow_invalid_utf8(true)
                .unicode(false)
                .case_insensitive(true)
                .build()
                .parse(source)?,
        )
    }

    pub fn priority(&self) -> usize {
        match self {
            Mir::Empty | Mir::Loop(_) | Mir::Maybe(_) => 0,
            Mir::Concat(concat) => concat.iter().map(Mir::priority).sum(),
            Mir::Alternation(alt) => alt.iter().map(Mir::priority).min().unwrap_or(0),
            Mir::Class(_) => 1,
            Mir::Literal(_) => 2,
        }
    }
}

impl TryFrom<Hir> for Mir {
    type Error = Error;

    fn try_from(hir: Hir) -> Result<Mir> {
        match hir.into_kind() {
            HirKind::Empty => Ok(Mir::Empty),
            HirKind::Concat(concat) => {
                let mut out = Vec::with_capacity(concat.len());

                fn extend(mir: Mir, out: &mut Vec<Mir>) {
                    match mir {
                        Mir::Concat(nested) => {
                            for child in nested {
                                extend(child, out);
                            }
                        }
                        mir => out.push(mir),
                    }
                }

                for hir in concat {
                    extend(Mir::try_from(hir)?, &mut out);
                }

                Ok(Mir::Concat(out))
            }
            HirKind::Alternation(alternation) => {
                let alternation = alternation
                    .into_iter()
                    .map(Mir::try_from)
                    .collect::<Result<_>>()?;

                Ok(Mir::Alternation(alternation))
            }
            HirKind::Literal(literal) => Ok(Mir::Literal(literal)),
            HirKind::Class(class) => Ok(Mir::Class(class)),
            HirKind::Repetition(repetition) => {
                if !repetition.greedy {
                    return Err("#[regex]: non-greedy parsing is currently unsupported.".into());
                }

                let kind = repetition.kind;
                let mir = Mir::try_from(*repetition.hir)?;

                match kind {
                    RepetitionKind::ZeroOrOne => Ok(Mir::Maybe(Box::new(mir))),
                    RepetitionKind::ZeroOrMore => Ok(Mir::Loop(Box::new(mir))),
                    RepetitionKind::OneOrMore => {
                        Ok(Mir::Concat(vec![mir.clone(), Mir::Loop(Box::new(mir))]))
                    }
                    RepetitionKind::Range(..) => {
                        Err("#[regex]: {n,m} repetition range is currently unsupported.".into())
                    }
                }
            }
            HirKind::Group(group) => Mir::try_from(*group.hir),
            HirKind::WordBoundary(_) => {
                Err("#[regex]: word boundaries are currently unsupported.".into())
            }
            HirKind::Anchor(_) => {
                Err("#[regex]: anchors in #[regex] are currently unsupported.".into())
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Mir;

    #[test]
    fn priorities() {
        let regexes = [
            ("[a-z]+", 1),
            ("a|b", 2),
            ("a|[b-z]", 1),
            ("(foo)+", 6),
            ("foobar", 12),
            ("(fooz|bar)+qux", 12),
        ];

        for (regex, expected) in regexes.iter() {
            let mir = Mir::utf8(regex).unwrap();
            assert_eq!(mir.priority(), *expected);
        }
    }
}