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
168
169
170
171
172

use std::time::Duration;

use crate::{Sample, Source};

/// Builds a source that chains sources provided by an iterator.
///
/// The `iterator` parameter is an iterator that produces a source. The source is then played.
/// Whenever the source ends, the `iterator` is used again in order to produce the source that is
/// played next.
///
/// If the `iterator` produces `None`, then the sound ends.
pub fn from_iter<I>(iterator: I) -> FromIter<I::IntoIter>
where
    I: IntoIterator,
{
    let mut iterator = iterator.into_iter();
    let first_source = iterator.next();

    FromIter {
        iterator,
        current_source: first_source,
    }
}

/// A source that chains sources provided by an iterator.
#[derive(Clone)]
pub struct FromIter<I>
where
    I: Iterator,
{
    // The iterator that provides sources.
    iterator: I,
    // Is only ever `None` if the first element of the iterator is `None`.
    current_source: Option<I::Item>,
}

impl<I> Iterator for FromIter<I>
where
    I: Iterator,
    I::Item: Iterator + Source,
    <I::Item as Iterator>::Item: Sample,
{
    type Item = <I::Item as Iterator>::Item;

    #[inline]
    fn next(&mut self) -> Option<<I::Item as Iterator>::Item> {
        loop {
            if let Some(src) = &mut self.current_source {
                if let Some(value) = src.next() {
                    return Some(value);
                }
            }

            if let Some(src) = self.iterator.next() {
                self.current_source = Some(src);
            } else {
                return None;
            }
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        if let Some(cur) = &self.current_source {
            (cur.size_hint().0, None)
        } else {
            (0, None)
        }
    }
}

impl<I> Source for FromIter<I>
where
    I: Iterator,
    I::Item: Iterator + Source,
    <I::Item as Iterator>::Item: Sample,
{
    #[inline]
    fn current_frame_len(&self) -> Option<usize> {
        // This function is non-trivial because the boundary between the current source and the
        // next must be a frame boundary as well.
        //
        // The current sound is free to return `None` for `current_frame_len()`, in which case
        // we *should* return the number of samples remaining the current sound.
        // This can be estimated with `size_hint()`.
        //
        // If the `size_hint` is `None` as well, we are in the worst case scenario. To handle this
        // situation we force a frame to have a maximum number of samples indicate by this
        // constant.
        const THRESHOLD: usize = 10240;

        // Try the current `current_frame_len`.
        if let Some(src) = &self.current_source {
            if let Some(val) = src.current_frame_len() {
                if val != 0 {
                    return Some(val);
                }
            }
        }

        // Try the size hint.
        if let Some(src) = &self.current_source {
            if let Some(val) = src.size_hint().1 {
                if val < THRESHOLD && val != 0 {
                    return Some(val);
                }
            }
        }

        // Otherwise we use the constant value.
        Some(THRESHOLD)
    }

    #[inline]
    fn channels(&self) -> u16 {
        if let Some(src) = &self.current_source {
            src.channels()
        } else {
            // Dummy value that only happens if the iterator was empty.
            2
        }
    }

    #[inline]
    fn sample_rate(&self) -> u32 {
        if let Some(src) = &self.current_source {
            src.sample_rate()
        } else {
            // Dummy value that only happens if the iterator was empty.
            44100
        }
    }

    #[inline]
    fn total_duration(&self) -> Option<Duration> {
        None
    }
}

#[cfg(test)]
mod tests {
    use crate::buffer::SamplesBuffer;
    use crate::source::{from_iter, Source};

    #[test]
    fn basic() {
        let mut rx = from_iter((0..2).map(|n| {
            if n == 0 {
                SamplesBuffer::new(1, 48000, vec![10i16, -10, 10, -10])
            } else if n == 1 {
                SamplesBuffer::new(2, 96000, vec![5i16, 5, 5, 5])
            } else {
                unreachable!()
            }
        }));

        assert_eq!(rx.channels(), 1);
        assert_eq!(rx.sample_rate(), 48000);
        assert_eq!(rx.next(), Some(10));
        assert_eq!(rx.next(), Some(-10));
        assert_eq!(rx.next(), Some(10));
        assert_eq!(rx.next(), Some(-10));
        /*assert_eq!(rx.channels(), 2);
        assert_eq!(rx.sample_rate(), 96000);*/
        // FIXME: not working
        assert_eq!(rx.next(), Some(5));
        assert_eq!(rx.next(), Some(5));
        assert_eq!(rx.next(), Some(5));
        assert_eq!(rx.next(), Some(5));
        assert_eq!(rx.next(), None);
    }
}