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use std::time::Duration;

use crate::{Sample, Source};

/// Internal function that builds a `FadeIn` object.
pub fn fadein<I>(input: I, duration: Duration) -> FadeIn<I>
where
    I: Source,
    I::Item: Sample,
{
    let duration = duration.as_secs() * 1000000000 + duration.subsec_nanos() as u64;

    FadeIn {
        input,
        remaining_ns: duration as f32,
        total_ns: duration as f32,
    }
}

/// Filter that modifies raises the volume from silence over a time period.
#[derive(Clone, Debug)]
pub struct FadeIn<I> {
    input: I,
    remaining_ns: f32,
    total_ns: f32,
}

impl<I> FadeIn<I>
where
    I: Source,
    I::Item: Sample,
{
    /// 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> Iterator for FadeIn<I>
where
    I: Source,
    I::Item: Sample,
{
    type Item = I::Item;

    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        if self.remaining_ns <= 0.0 {
            return self.input.next();
        }

        let factor = 1.0 - self.remaining_ns / self.total_ns;
        self.remaining_ns -=
            1000000000.0 / (self.input.sample_rate() as f32 * self.channels() as f32);
        self.input.next().map(|value| value.amplify(factor))
    }

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

impl<I> ExactSizeIterator for FadeIn<I>
where
    I: Source + ExactSizeIterator,
    I::Item: Sample,
{
}

impl<I> Source for FadeIn<I>
where
    I: Source,
    I::Item: Sample,
{
    #[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()
    }
}