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
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
use crate::parse::{parse_decimal, parse_id};
use crate::{Captures, CompileError, Error, ParseError, Regex};
use std::borrow::Cow;
use std::io;
use std::mem;

/// A set of options for expanding a template string using the contents
/// of capture groups.
#[derive(Debug)]
pub struct Expander {
    sub_char: char,
    open: &'static str,
    close: &'static str,
    allow_undelimited_name: bool,
}

impl Default for Expander {
    /// Returns the default expander used by [`Captures::expand`].
    ///
    /// [`Captures::expand`]: struct.Captures.html#expand
    fn default() -> Self {
        Expander {
            sub_char: '$',
            open: "{",
            close: "}",
            allow_undelimited_name: true,
        }
    }
}

impl Expander {
    /// Returns an expander that uses Python-compatible syntax.
    ///
    /// Expands all instances of `\num` or `\g<name>` in `replacement`
    /// to the corresponding capture group `num` or `name`, and writes
    /// them to the `dst` buffer given.
    ///
    /// `name` may be an integer corresponding to the index of the
    /// capture group (counted by order of opening parenthesis where `\0` is the
    /// entire match) or it can be a name (consisting of letters, digits or
    /// underscores) corresponding to a named capture group.
    ///
    /// `num` must be an integer corresponding to the index of the
    /// capture group.
    ///
    /// If `num` or `name` isn't a valid capture group (whether the name doesn't exist
    /// or isn't a valid index), then it is replaced with the empty string.
    ///
    /// The longest possible number is used. e.g., `\10` looks up capture
    /// group 10 and not capture group 1 followed by a literal 0.
    ///
    /// To write a literal `\`, use `\\`.
    pub fn python() -> Expander {
        Expander {
            sub_char: '\\',
            open: "g<",
            close: ">",
            allow_undelimited_name: false,
        }
    }

    /// Checks `template` for errors.  The following conditions are checked for:
    ///
    /// - A reference to a numbered group that does not exist in `regex`
    /// - A reference to a numbered group (other than 0) when `regex` contains named groups
    /// - A reference to a named group that does not occur in `regex`
    /// - An opening group name delimiter without a closing delimiter
    /// - Using an empty string as a group name
    pub fn check(&self, template: &str, regex: &Regex) -> crate::Result<()> {
        let on_group_num = |num| {
            if num == 0 {
                Ok(())
            } else if !regex.named_groups.is_empty() {
                Err(Error::CompileError(CompileError::NamedBackrefOnly))
            } else if num < regex.captures_len() {
                Ok(())
            } else {
                Err(Error::CompileError(CompileError::InvalidBackref))
            }
        };
        self.exec(template, |step| match step {
            Step::Char(_) => Ok(()),
            Step::GroupName(name) => {
                if regex.named_groups.contains_key(name) {
                    Ok(())
                } else if let Ok(num) = name.parse() {
                    on_group_num(num)
                } else {
                    Err(Error::CompileError(CompileError::InvalidBackref))
                }
            }
            Step::GroupNum(num) => on_group_num(num),
            Step::Error => Err(Error::ParseError(
                0,
                ParseError::GeneralParseError(
                    "parse error in template while expanding".to_string(),
                ),
            )),
        })
    }

    /// Escapes the substitution character in `text` so it appears literally
    /// in the output of `expansion`.
    ///
    /// ```
    /// assert_eq!(
    ///     fancy_regex::Expander::default().escape("Has a literal $ sign."),
    ///     "Has a literal $$ sign.",
    /// );
    /// ```
    pub fn escape<'a>(&self, text: &'a str) -> Cow<'a, str> {
        if text.contains(self.sub_char) {
            let mut quoted = String::with_capacity(self.sub_char.len_utf8() * 2);
            quoted.push(self.sub_char);
            quoted.push(self.sub_char);
            Cow::Owned(text.replace(self.sub_char, &quoted))
        } else {
            Cow::Borrowed(text)
        }
    }

    #[doc(hidden)]
    #[deprecated(since = "0.4.0", note = "Use `escape` instead.")]
    pub fn quote<'a>(&self, text: &'a str) -> Cow<'a, str> {
        self.escape(text)
    }

    /// Expands the template string `template` using the syntax defined
    /// by this expander and the values of capture groups from `captures`.
    pub fn expansion(&self, template: &str, captures: &Captures<'_>) -> String {
        let mut cursor = io::Cursor::new(Vec::with_capacity(template.len()));
        self.write_expansion(&mut cursor, template, captures)
            .expect("expansion succeeded");
        String::from_utf8(cursor.into_inner()).expect("expansion is UTF-8")
    }

    /// Appends the expansion produced by `expansion` to `dst`.  Potentially more efficient
    /// than calling `expansion` directly and appending to an existing string.
    pub fn append_expansion(&self, dst: &mut String, template: &str, captures: &Captures<'_>) {
        let pos = dst.len();
        let mut cursor = io::Cursor::new(mem::replace(dst, String::new()).into_bytes());
        cursor.set_position(pos as u64);
        self.write_expansion(&mut cursor, template, captures)
            .expect("expansion succeeded");
        *dst = String::from_utf8(cursor.into_inner()).expect("expansion is UTF-8");
    }

    /// Writes the expansion produced by `expansion` to `dst`.  Potentially more efficient
    /// than calling `expansion` directly and writing the result.
    pub fn write_expansion(
        &self,
        mut dst: impl io::Write,
        template: &str,
        captures: &Captures<'_>,
    ) -> io::Result<()> {
        self.exec(template, |step| match step {
            Step::Char(c) => write!(dst, "{}", c),
            Step::GroupName(name) => {
                if let Some(m) = captures.name(name) {
                    write!(dst, "{}", m.as_str())
                } else if let Some(m) = name.parse().ok().and_then(|num| captures.get(num)) {
                    write!(dst, "{}", m.as_str())
                } else {
                    Ok(())
                }
            }
            Step::GroupNum(num) => {
                if let Some(m) = captures.get(num) {
                    write!(dst, "{}", m.as_str())
                } else {
                    Ok(())
                }
            }
            Step::Error => Ok(()),
        })
    }

    fn exec<'t, E>(
        &self,
        template: &'t str,
        mut f: impl FnMut(Step<'t>) -> Result<(), E>,
    ) -> Result<(), E> {
        debug_assert!(!self.open.is_empty());
        debug_assert!(!self.close.is_empty());
        let mut iter = template.chars();
        while let Some(c) = iter.next() {
            if c == self.sub_char {
                let tail = iter.as_str();
                let skip = if tail.starts_with(self.sub_char) {
                    f(Step::Char(self.sub_char))?;
                    1
                } else if let Some((id, skip)) =
                    parse_id(tail, self.open, self.close).or_else(|| {
                        if self.allow_undelimited_name {
                            parse_id(tail, "", "")
                        } else {
                            None
                        }
                    })
                {
                    f(Step::GroupName(id))?;
                    skip
                } else if let Some((skip, num)) = parse_decimal(tail, 0) {
                    f(Step::GroupNum(num))?;
                    skip
                } else {
                    f(Step::Error)?;
                    f(Step::Char(self.sub_char))?;
                    0
                };
                iter = iter.as_str()[skip..].chars();
            } else {
                f(Step::Char(c))?;
            }
        }
        Ok(())
    }
}

enum Step<'a> {
    Char(char),
    GroupName(&'a str),
    GroupNum(usize),
    Error,
}