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::fmt::Debug;
use std::collections::LinkedList;

#[derive(Debug, Clone)]
struct SplitWhenOutputItem<I: Iterator> {
    items: Vec<I::Item>
    
}

#[derive(Debug, Clone)]
pub struct SplitWhen<I: Iterator> {
    ret_buf: LinkedList<SplitWhenOutputItem<I>>,
    iter: I,
    pred: fn(& I::Item, & I::Item) -> bool,
    maxsplit: i64,
    splited: i64,
    iter_finished: bool
}

impl<I: Iterator> Iterator for SplitWhen<I> 
where I::Item: Debug
{
    type Item = Vec<<I as Iterator>::Item>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.maxsplit == 0 {
            if self.iter_finished {
                return None;
            }
            let mut ret = Vec::new();
            loop {
                let _next = self.iter.next();
                match _next {
                    None => {
                        self.iter_finished = true;
                        return Some(ret);
                    },
                    Some(v) => {
                        ret.push(v);
                    }
                }
            }
        }

        loop {
            if self.iter_finished {
                break;
            }
            let _next = self.iter.next();
            match _next {
                None => {
                    self.iter_finished = true;
                    break;
                },
                Some(v) => {
                    if self.ret_buf.len() > 0 {
                        let items = &self.ret_buf.back_mut().unwrap().items;
                        if items.len() > 0 {
                            if self.maxsplit < 0 {
                                if (self.pred)(& v, & items.get(items.len()-1).unwrap()) {
                                    self.ret_buf.push_back(SplitWhenOutputItem{
                                        items: Vec::new()
                                    });
                                    self.ret_buf.back_mut().unwrap().items.push(v);
                                    break;
                                } else {
                                    self.ret_buf.back_mut().unwrap().items.push(v);
                                }
                            } else {
                                if self.splited < self.maxsplit && (self.pred)(& v, & items.get(items.len()-1).unwrap()) {
                                    self.ret_buf.push_back(SplitWhenOutputItem{
                                        items: Vec::new()
                                    });
                                    self.ret_buf.back_mut().unwrap().items.push(v);

                                    self.splited += 1;
                                    break;
                                } else {
                                    self.ret_buf.back_mut().unwrap().items.push(v);
                                }
                            }
                            
                        } else {
                            self.ret_buf.back_mut().unwrap().items.push(v);
                        }
                        
                    } else {
                        self.ret_buf.push_back(SplitWhenOutputItem{
                            items: Vec::new()
                        });
                        self.ret_buf.back_mut().unwrap().items.push(v);
                    }
                }
            }
        }

        loop {
            let ret = self.ret_buf.pop_front();
            match ret {
                None => { return None; }
                Some(v) => {
                    return Some(v.items);
                }
            }
        }
    }
}

pub fn split_when<I>(iter: I, pred: fn(&I::Item, &I::Item)->bool, maxsplit: i64) -> SplitWhen<I>
where
    I: Iterator,
{
    let mut ret = SplitWhen {
        ret_buf: LinkedList::new(),
        iter: iter,
        pred: pred,
        maxsplit: maxsplit,
        splited: 0,
        iter_finished: false
    };

    ret.ret_buf.push_back(SplitWhenOutputItem {
        items: Vec::new()
    });

    return ret;
}

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

    #[test]
    fn test1() {
        let v = vec![1, 2, 3, 3, 2, 5, 2, 4, 2];
        let sw = split_when(v.into_iter(), |x, y| { y > x }, -1);
        let ret = sw.collect::<Vec<_>>();
        assert_eq!(vec![vec![1, 2, 3, 3], vec![2, 5], vec![2, 4], vec![2]], ret);


        let v = vec![1, 2, 3, 3, 2, 5, 2, 4, 2];
        let sw = split_when(v.into_iter(), |x, y| { y > x }, 2);
        let ret = sw.collect::<Vec<_>>();
        assert_eq!(vec![vec![1, 2, 3, 3], vec![2, 5], vec![2, 4, 2]], ret);

        let v = vec![1, 2, 3, 3, 2, 5, 2, 4, 2];
        let sw = split_when(v.into_iter(), |x, y| { y > x }, 10);
        let ret = sw.collect::<Vec<_>>();
        assert_eq!(vec![vec![1, 2, 3, 3], vec![2, 5], vec![2, 4], vec![2]], ret);
    }
}