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

use std::convert::From;
use std::fmt::{Display, Error as FmtError, Write};
use std::iter::Iterator;

#[cfg(test)]
mod tests;

#[derive(Debug)]
struct ExpandableStringSplit<'a> {
    src: &'a str,
    chars_iter: std::str::CharIndices<'a>,
    token_start: usize,
    reading_var: bool,
    done: bool,
}

fn split_expandable_string(s: &str) -> ExpandableStringSplit {
    ExpandableStringSplit {
        chars_iter: s.char_indices(),
        src: s,
        token_start: 0,
        reading_var: false,
        done: false,
    }
}

#[derive(Debug, PartialEq, Eq)]
enum ExpandableStrEntry<'a> {
    Substr(&'a str),
    Var(&'a str),
}

#[derive(Debug, PartialEq, Eq)]
pub enum ExpandableStrSplitError {
    /// Invalid input string (basically, non-closed variable name)
    InvalidFormat,

    /// Bad variable name; names should not contain space or equality sign
    InvalidVariableName,
}

type ExpandableStrSplitResult<'a> = Result<ExpandableStrEntry<'a>, ExpandableStrSplitError>;

impl<'a> Iterator for ExpandableStringSplit<'a> {
    type Item = ExpandableStrSplitResult<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.done {
            return None;
        }

        while let Some((n, c)) = self.chars_iter.next() {
            if c == '%' {
                let reading_var = self.reading_var;
                self.reading_var = !reading_var;
                if n > 0 {
                    let token_slice = &self.src[self.token_start..n];
                    self.token_start = n + 1;
                    if !token_slice.is_empty() {
                        if reading_var {
                            return Some(Ok(ExpandableStrEntry::Var(token_slice)));
                        } else {
                            return Some(Ok(ExpandableStrEntry::Substr(token_slice)));
                        }
                    }
                } else {
                    self.token_start = 1;
                }
            } else if self.reading_var {
                match c {
                    '=' | ' ' => {
                        self.done = true;
                        return Some(Err(ExpandableStrSplitError::InvalidVariableName));
                    }
                    _ => (),
                }
            }
        }

        self.done = true;

        if !self.reading_var {
            let token_slice = &self.src[self.token_start..];
            if !token_slice.is_empty() {
                self.token_start = self.src.len();
                Some(Ok(ExpandableStrEntry::Substr(token_slice)))
            } else {
                None
            }
        } else {
            Some(Err(ExpandableStrSplitError::InvalidFormat))
        }
    }
}

#[derive(Debug, PartialEq, Eq)]
pub enum ExpandStringError<'a> {
    Splitting(ExpandableStrSplitError),
    /// Variable specified in source string is missing in provided context (or process environment)
    MissingVariable(&'a str),
    Formatting(FmtError),
}

impl<'a> From<ExpandableStrSplitError> for ExpandStringError<'a> {
    fn from(e: ExpandableStrSplitError) -> Self {
        Self::Splitting(e)
    }
}

impl<'a> From<FmtError> for ExpandStringError<'a> {
    fn from(e: FmtError) -> Self {
        Self::Formatting(e)
    }
}

pub fn expand_string_with_values<F, S>(s: &str, get_value: F) -> Result<String, ExpandStringError>
where
    F: Fn(&str) -> Option<S>,
    S: Display,
{
    let mut expanded_str = String::with_capacity(s.len());

    for entry in split_expandable_string(s) {
        match entry? {
            ExpandableStrEntry::Substr(s) => {
                expanded_str += s;
            }
            ExpandableStrEntry::Var(id) => {
                let val = get_value(id).ok_or(ExpandStringError::MissingVariable(id))?;
                write!(&mut expanded_str, "{}", val)?;
            }
        }
    }

    Ok(expanded_str)
}

#[cfg(feature = "env")]
pub fn expand_string_with_env(s: &str) -> Result<String, ExpandStringError> {
    fn get_var_value(key: &str) -> Option<String> {
        use std::ffi::{OsStr, OsString};

        std::env::var_os(key)
            .as_ref()
            .map(OsString::as_os_str)
            .map(OsStr::to_string_lossy)
            .map(Into::into)
    }

    expand_string_with_values(s, get_var_value)
}