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

use std::time::Duration;

use crate::{Sample, Source};

/// Internal function that builds a `PeriodicAccess` object.
pub fn periodic<I, F>(source: I, period: Duration, modifier: F) -> PeriodicAccess<I, F>
where
    I: Source,
    I::Item: Sample,
{
    // TODO: handle the fact that the samples rate can change
    // TODO: generally, just wrong
    let update_ms = period.as_secs() as u32 * 1_000 + period.subsec_millis();
    let update_frequency = (update_ms * source.sample_rate()) / 1000 * source.channels() as u32;

    PeriodicAccess {
        input: source,
        modifier,
        // Can overflow when subtracting if this is 0
        update_frequency: if update_frequency == 0 {
            1
        } else {
            update_frequency
        },
        samples_until_update: 1,
    }
}

/// Calls a function on a source every time a period elapsed.
#[derive(Clone, Debug)]
pub struct PeriodicAccess<I, F> {
    // The inner source.
    input: I,

    // Closure that gets access to `inner`.
    modifier: F,

    // The frequency with which local_volume should be updated by remote_volume
    update_frequency: u32,

    // How many samples remain until it is time to update local_volume with remote_volume.
    samples_until_update: u32,
}

impl<I, F> PeriodicAccess<I, F>
where
    I: Source,
    I::Item: Sample,
    F: FnMut(&mut I),
{
    /// Returns a reference to the inner source.
    #[inline]
    pub fn inner(&self) -> &I {
        &self.input
    }

    /// Returns a mutable reference to the inner source.
    #[inline]
    pub fn inner_mut(&mut self) -> &mut I {
        &mut self.input
    }

    /// Returns the inner source.
    #[inline]
    pub fn into_inner(self) -> I {
        self.input
    }
}

impl<I, F> Iterator for PeriodicAccess<I, F>
where
    I: Source,
    I::Item: Sample,
    F: FnMut(&mut I),
{
    type Item = I::Item;

    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        self.samples_until_update -= 1;
        if self.samples_until_update == 0 {
            (self.modifier)(&mut self.input);
            self.samples_until_update = self.update_frequency;
        }

        self.input.next()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.input.size_hint()
    }
}

impl<I, F> Source for PeriodicAccess<I, F>
where
    I: Source,
    I::Item: Sample,
    F: FnMut(&mut I),
{
    #[inline]
    fn current_frame_len(&self) -> Option<usize> {
        self.input.current_frame_len()
    }

    #[inline]
    fn channels(&self) -> u16 {
        self.input.channels()
    }

    #[inline]
    fn sample_rate(&self) -> u32 {
        self.input.sample_rate()
    }

    #[inline]
    fn total_duration(&self) -> Option<Duration> {
        self.input.total_duration()
    }
}

#[cfg(test)]
mod tests {
    use std::cell::RefCell;
    use std::time::Duration;

    use crate::buffer::SamplesBuffer;
    use crate::source::Source;

    #[test]
    fn stereo_access() {
        // Stereo, 1Hz audio buffer
        let inner = SamplesBuffer::new(2, 1, vec![10i16, -10, 10, -10, 20, -20]);

        let cnt = RefCell::new(0);

        let mut source = inner.periodic_access(Duration::from_millis(1000), |_src| {
            *cnt.borrow_mut() += 1;
        });

        assert_eq!(*cnt.borrow(), 0);
        // Always called on first access!
        assert_eq!(source.next(), Some(10));
        assert_eq!(*cnt.borrow(), 1);
        // Called every 1 second afterwards
        assert_eq!(source.next(), Some(-10));
        assert_eq!(*cnt.borrow(), 1);
        assert_eq!(source.next(), Some(10));
        assert_eq!(*cnt.borrow(), 2);
        assert_eq!(source.next(), Some(-10));
        assert_eq!(*cnt.borrow(), 2);
        assert_eq!(source.next(), Some(20));
        assert_eq!(*cnt.borrow(), 3);
        assert_eq!(source.next(), Some(-20));
        assert_eq!(*cnt.borrow(), 3);
    }

    #[test]
    fn fast_access_overflow() {
        // 1hz is lower than 0.5 samples per 5ms
        let inner = SamplesBuffer::new(1, 1, vec![10i16, -10, 10, -10, 20, -20]);
        let mut source = inner.periodic_access(Duration::from_millis(5), |_src| {});

        source.next();
        source.next(); // Would overflow here.
    }
}