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

use super::*;

use std::marker::PhantomData;

pub struct DeferredBucket<'a, Q, B>
    where Q: Queue<B>,
          B: Bucket,
{
    queue: &'a mut Q,
    priority: usize,
    consumed: bool,
    phantom: PhantomData<B>,
}

impl<'a, Q, B> DeferredBucket<'a, Q, B>
    where Q: Queue<B>,
          B: Bucket,
{
    pub fn new(queue: &'a mut Q, priority: usize) -> Self {
        Self { queue, priority, consumed: false, phantom: PhantomData }
    }

    pub fn len(&self) -> usize {
        self.peeking().map_or(0, |b| b.len_bucket())
    }

    pub fn is_empty(&self) -> bool {
        self.peeking().map_or(true, |b| b.is_empty_bucket())
    }

    pub fn adding(&mut self) -> &mut B {
        self.panic_if_consumed();
        self.queue.bucket_for_adding(self.priority)
    }

    pub fn removing(&mut self) -> Option<&mut B> {
        self.panic_if_consumed();
        self.queue.bucket_for_removing(self.priority)
    }

    pub fn peeking(&self) -> Option<&B> {
        self.queue.bucket_for_peeking(self.priority)
    }

    pub fn replacing(&mut self) -> &mut B {
        self.queue.bucket_for_replacing(self.priority)
            .get_or_insert_with(|| B::new_bucket())
    }

    // Updates queue's index to record how many items were replaced.
    pub fn replaced(&mut self, old_size: usize, new_size: usize) {
        self.queue.items_replaced(self.priority, old_size, new_size);
    }

    fn panic_if_consumed(&mut self) {
        if self.consumed {
            panic!("You may only add or remove a single item from the bucket.")
        }

        self.consumed = true
    }
}

impl<'a, Q, B> Bucket for DeferredBucket<'a, Q, B>
    where Q: Queue<B>,
          B: Bucket,
{
    type Item = B::Item;

    fn new_bucket() -> Self {
        panic!("DeferredBucket should not be initialized this way.");
    }

    fn len_bucket(&self) -> usize {
        self.queue.len_queue()
    }

    fn is_empty_bucket(&self) -> bool {
        self.queue.is_empty_queue()
    }

    fn clear(&mut self) {
        self.queue.replace(self.priority, None);
    }
}

// ----------------------------------------------------------------------
// Implement Queue for DeferredBucket if the Bucket type is also a Queue:
// ----------------------------------------------------------------------

impl<'a, Q, B, C> Queue<C> for DeferredBucket<'a, Q, B>
    where Q: Queue<B>,
          B: Bucket + Queue<C>,
          C: Bucket,
{
    fn new_queue() -> Self {
        panic!("DeferredBucket should not be initialized this way.");
    }

    fn min_priority(&self) -> Option<usize> {
        self.peeking()?.min_priority()
    }

    fn max_priority(&self) -> Option<usize> {
        self.peeking()?.max_priority()
    }

    fn bucket_for_adding(&mut self, priority: usize) -> &mut C {
        self.adding().bucket_for_adding(priority)
    }

    fn bucket_for_removing(&mut self, priority: usize) -> Option<&mut C> {
        self.removing()?.bucket_for_removing(priority)
    }

    fn bucket_for_peeking(&self, priority: usize) -> Option<&C> {
        self.peeking()?.bucket_for_peeking(priority)
    }

    fn bucket_for_replacing(&mut self, priority: usize) -> &mut Option<C> {
        self.replacing().bucket_for_replacing(priority)
    }

    fn items_replaced(&mut self, priority: usize, old_size: usize, new_size: usize) {
        // Update the parent queue's index.
        self.replaced(old_size, new_size);

        // Update the current queue's index.
        self.replacing().items_replaced(priority, old_size, new_size);
    }

    fn len_queue(&self) -> usize {
        self.peeking().map_or(0, |q| q.len_queue())
    }

    fn is_empty_queue(&self) -> bool {
        self.peeking().map_or(true, |q| q.is_empty_queue())
    }

    fn replace(&mut self, priority: usize, replacement: Option<C>) -> Option<C> {
        let queue = self.replacing();
        let existing = queue.bucket_for_replacing(priority);

        let old_size = existing.as_ref().map_or(0, |b| b.len_bucket());
        let new_size = replacement.as_ref().map_or(0, |b| b.len_bucket());

        let replaced = queue.replace(priority, replacement);
        self.replaced(old_size, new_size);

        replaced
    }
}