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

// Copyright 2019 Mozilla Foundation. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Final-sigma-correct lowercasing iterator adapter for iterators
//! over `char`. Turkish/Azeri `'I'` handled optionally.

#![doc(html_root_url = "https://docs.rs/iterlower/1.0.1")]

use std::char::ToLowercase;
use std::collections::VecDeque;
use unic_ucd::CaseIgnorable;
use unic_ucd::Cased;

/// An iterator adapter yielding lower-case `char`s.
#[derive(Debug)]
pub struct Lowercase<I> {
    delegate: I,
    sigma_trailing_case_ignorables: VecDeque<char>,
    sigma_trail: Option<char>,
    lower: ToLowercase,
    prev_cased: bool,
    tr_az: bool,
}

impl<I: Iterator<Item = char>> Iterator for Lowercase<I> {
    type Item = char;

    #[inline]
    fn next(&mut self) -> Option<char> {
        if let Some(c) = self.lower.next() {
            return Some(c);
        }
        if let Some(c) = self.sigma_trailing_case_ignorables.pop_front() {
            return Some(c);
        }
        let c = if let Some(c) = self.sigma_trail {
            self.sigma_trail = None;
            c
        } else if let Some(c) = self.delegate.next() {
            c
        } else {
            return None;
        };
        if self.tr_az && c == 'I' {
            self.prev_cased = true;
            return Some('ı');
        }
        if Cased::of(c).as_bool() {
            if c == 'Σ' && self.prev_cased {
                loop {
                    if let Some(t) = self.delegate.next() {
                        if CaseIgnorable::of(t).as_bool() {
                            self.sigma_trailing_case_ignorables.push_back(t);
                            continue;;
                        }
                        self.sigma_trail = Some(t);
                        if Cased::of(t).as_bool() {
                            return Some('σ');
                        }
                    }
                    return Some('ς');
                }
            }
            self.prev_cased = true;
            self.lower = c.to_lowercase();
            return self.lower.next();
        }
        if self.prev_cased && !CaseIgnorable::of(c).as_bool() {
            self.prev_cased = false;
        }
        Some(c)
    }
}

/// Trait that adds a `to_lowercase` method to iterators
/// over `char`.
pub trait IterLowercase<I: Iterator<Item = char>> {
    /// Returns a lower-casing iterator adapter that
    /// handles final sigma correctly.
    ///
    /// `tr_az` set to `true` results in Turkish/Azeri treatment
    /// of `'I'`.
    fn to_lowercase(self, tr_az: bool) -> Lowercase<I>;
}

impl<I: Iterator<Item = char>> IterLowercase<I> for I {
    #[inline]
    fn to_lowercase(self, tr_az: bool) -> Lowercase<I> {
        // Create a consumed `ToLowercase`
        let mut lower = '\0'.to_lowercase();
        lower.next();

        Lowercase {
            delegate: self,
            sigma_trailing_case_ignorables: VecDeque::new(),
            sigma_trail: None,
            lower: lower,
            prev_cased: false,
            tr_az: tr_az,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    fn check(s: &str) {
        assert_eq!(
            s.chars().to_lowercase(false).collect::<String>(),
            s.to_lowercase()
        );
    }

    #[test]
    fn test_sigma() {
        for s in [
            "Σ",
            "Σ\u{0301}",
            "ΣΣ",
            "Σ\u{0301}Σ\u{0301}",
            "ΣΣ ",
            "Σ\u{0301}Σ\u{0301} ",
            " Σ",
            " Σ\u{0301}",
            "ΣΣ-",
            "Σ\u{0301}Σ\u{0301}-",
            "-Σ",
            "-Σ\u{0301}",
            "ΣΣ猪",
            "Σ\u{0301}Σ\u{0301}猪",
            "猪Σ",
            "猪Σ\u{0301}",
            "ΣΣB",
            "Σ\u{0301}Σ\u{0301}B",
            "BΣ",
            "BΣ\u{0301}",
            "ΣΣΔ",
            "Σ\u{0301}Σ\u{0301}Δ",
            "ΔΣ",
            "ΔΣ\u{0301}",
        ]
        .iter()
        {
            check(s);
        }
    }

    #[test]
    fn test_i() {
        assert_eq!(
            "ΣIΣ".chars().to_lowercase(true).collect::<String>(),
            "σıς"
        );
    }

    #[test]
    fn test_uncased() {
        check("猪猪");
    }

}