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

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::decompose::Decompositions;
use core::fmt::{self, Write};
use tinyvec::TinyVec;

#[derive(Clone)]
enum RecompositionState {
    Composing,
    Purging(usize),
    Finished(usize),
}

/// External iterator for a string recomposition's characters.
#[derive(Clone)]
pub struct Recompositions<I> {
    iter: Decompositions<I>,
    state: RecompositionState,
    buffer: TinyVec<[char; 4]>,
    composee: Option<char>,
    last_ccc: Option<u8>,
}

#[inline]
pub fn new_canonical<I: Iterator<Item = char>>(iter: I) -> Recompositions<I> {
    Recompositions {
        iter: super::decompose::new_canonical(iter),
        state: self::RecompositionState::Composing,
        buffer: TinyVec::new(),
        composee: None,
        last_ccc: None,
    }
}

#[inline]
pub fn new_compatible<I: Iterator<Item = char>>(iter: I) -> Recompositions<I> {
    Recompositions {
        iter: super::decompose::new_compatible(iter),
        state: self::RecompositionState::Composing,
        buffer: TinyVec::new(),
        composee: None,
        last_ccc: None,
    }
}

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

    #[inline]
    fn next(&mut self) -> Option<char> {
        use self::RecompositionState::*;

        loop {
            match self.state {
                Composing => {
                    for ch in self.iter.by_ref() {
                        let ch_class = super::char::canonical_combining_class(ch);
                        let k = match self.composee {
                            None => {
                                if ch_class != 0 {
                                    return Some(ch);
                                }
                                self.composee = Some(ch);
                                continue;
                            }
                            Some(k) => k,
                        };
                        match self.last_ccc {
                            None => match super::char::compose(k, ch) {
                                Some(r) => {
                                    self.composee = Some(r);
                                    continue;
                                }
                                None => {
                                    if ch_class == 0 {
                                        self.composee = Some(ch);
                                        return Some(k);
                                    }
                                    self.buffer.push(ch);
                                    self.last_ccc = Some(ch_class);
                                }
                            },
                            Some(l_class) => {
                                if l_class >= ch_class {
                                    // `ch` is blocked from `composee`
                                    if ch_class == 0 {
                                        self.composee = Some(ch);
                                        self.last_ccc = None;
                                        self.state = Purging(0);
                                        return Some(k);
                                    }
                                    self.buffer.push(ch);
                                    self.last_ccc = Some(ch_class);
                                    continue;
                                }
                                match super::char::compose(k, ch) {
                                    Some(r) => {
                                        self.composee = Some(r);
                                        continue;
                                    }
                                    None => {
                                        self.buffer.push(ch);
                                        self.last_ccc = Some(ch_class);
                                    }
                                }
                            }
                        }
                    }
                    self.state = Finished(0);
                    if self.composee.is_some() {
                        return self.composee.take();
                    }
                }
                Purging(next) => match self.buffer.get(next).cloned() {
                    None => {
                        self.buffer.clear();
                        self.state = Composing;
                    }
                    s => {
                        self.state = Purging(next + 1);
                        return s;
                    }
                },
                Finished(next) => match self.buffer.get(next).cloned() {
                    None => {
                        self.buffer.clear();
                        return self.composee.take();
                    }
                    s => {
                        self.state = Finished(next + 1);
                        return s;
                    }
                },
            }
        }
    }
}

impl<I: Iterator<Item = char> + Clone> fmt::Display for Recompositions<I> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for c in self.clone() {
            f.write_char(c)?;
        }
        Ok(())
    }
}