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use alloc::sync::Arc;
use core::sync::atomic::{AtomicU32, Ordering};

use crate::{frame, math::Float, Frame, Seek, Signal, Smoothed};

/// Amplifies a signal by a constant amount
///
/// Unlike [`Gain`], this can implement [`Seek`].
pub struct FixedGain<T: ?Sized> {
    gain: f32,
    inner: T,
}

impl<T> FixedGain<T> {
    /// Amplify `signal` by `db` decibels
    ///
    /// Decibels are perceptually linear. Negative values make the signal quieter.
    pub fn new(signal: T, db: f32) -> Self {
        Self {
            gain: 10.0f32.powf(db / 20.0),
            inner: signal,
        }
    }
}

impl<T: Signal + ?Sized> Signal for FixedGain<T>
where
    T::Frame: Frame,
{
    type Frame = T::Frame;

    fn sample(&mut self, interval: f32, out: &mut [T::Frame]) {
        self.inner.sample(interval, out);
        for x in out {
            *x = frame::scale(x, self.gain);
        }
    }

    fn is_finished(&self) -> bool {
        self.inner.is_finished()
    }
}

impl<T: Seek + ?Sized> Seek for FixedGain<T>
where
    T::Frame: Frame,
{
    fn seek(&mut self, seconds: f32) {
        self.inner.seek(seconds)
    }
}

/// Amplifies a signal dynamically
///
/// To implement a volume control, place a gain combinator near the end of your pipeline where the
/// input amplitude is initially in the range [0, 1] and pass decibels to [`GainControl::set_gain`],
/// mapping the maximum volume to 0 decibels, and the minimum to e.g. -60.
pub struct Gain<T: ?Sized> {
    shared: Arc<AtomicU32>,
    gain: Smoothed<f32>,
    inner: T,
}

impl<T> Gain<T> {
    /// Apply dynamic amplification to `signal`
    pub fn new(signal: T) -> (GainControl, Self) {
        let signal = Gain {
            shared: Arc::new(AtomicU32::new(1.0f32.to_bits())),
            gain: Smoothed::new(1.0),
            inner: signal,
        };
        let handle = GainControl(signal.shared.clone());
        (handle, signal)
    }

    /// Set the initial amplification to `db` decibels
    ///
    /// Perceptually linear. Negative values make the signal quieter.
    ///
    /// Equivalent to `self.set_amplitude_ratio(10.0f32.powf(db / 20.0))`.
    pub fn set_gain(&mut self, db: f32) {
        self.set_amplitude_ratio(10.0f32.powf(db / 20.0));
    }

    /// Set the initial amplitude scaling of the signal directly
    ///
    /// This is nonlinear in terms of both perception and power. Most users should prefer
    /// `set_gain`. Unlike `set_gain`, this method allows a signal to be completely zeroed out if
    /// needed, or even have its phase inverted with a negative factor.
    pub fn set_amplitude_ratio(&mut self, factor: f32) {
        self.shared.store(factor.to_bits(), Ordering::Relaxed);
        self.gain = Smoothed::new(factor);
    }
}

impl<T: Signal> Signal for Gain<T>
where
    T::Frame: Frame,
{
    type Frame = T::Frame;

    #[allow(clippy::float_cmp)]
    fn sample(&mut self, interval: f32, out: &mut [T::Frame]) {
        self.inner.sample(interval, out);
        let shared = f32::from_bits(self.shared.load(Ordering::Relaxed));
        if self.gain.target() != &shared {
            self.gain.set(shared);
        }
        if self.gain.progress() == 1.0 {
            let g = self.gain.get();
            if g != 1.0 {
                for x in out {
                    *x = frame::scale(x, g);
                }
            }
            return;
        }
        for x in out {
            *x = frame::scale(x, self.gain.get());
            self.gain.advance(interval / SMOOTHING_PERIOD);
        }
    }

    fn is_finished(&self) -> bool {
        self.inner.is_finished()
    }
}

/// Thread-safe control for a [`Gain`] filter
pub struct GainControl(Arc<AtomicU32>);

impl GainControl {
    /// Get the current amplification in decibels
    pub fn gain(&self) -> f32 {
        20.0 * self.amplitude_ratio().log10()
    }

    /// Amplify the signal by `db` decibels
    ///
    /// Perceptually linear. Negative values make the signal quieter.
    ///
    /// Equivalent to `self.set_amplitude_ratio(10.0f32.powf(db / 20.0))`.
    pub fn set_gain(&mut self, db: f32) {
        self.set_amplitude_ratio(10.0f32.powf(db / 20.0));
    }

    /// Get the current amplitude scaling factor
    pub fn amplitude_ratio(&self) -> f32 {
        f32::from_bits(self.0.load(Ordering::Relaxed))
    }

    /// Scale the amplitude of the signal directly
    ///
    /// This is nonlinear in terms of both perception and power. Most users should prefer
    /// `set_gain`. Unlike `set_gain`, this method allows a signal to be completely zeroed out if
    /// needed, or even have its phase inverted with a negative factor.
    pub fn set_amplitude_ratio(&mut self, factor: f32) {
        self.0.store(factor.to_bits(), Ordering::Relaxed);
    }
}

/// Number of seconds over which to smooth a change in gain
const SMOOTHING_PERIOD: f32 = 0.1;

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

    #[test]
    fn smoothing() {
        let (mut c, mut s) = Gain::new(Constant(1.0));
        let mut buf = [0.0; 6];
        c.set_amplitude_ratio(5.0);
        s.sample(0.025, &mut buf);
        assert_eq!(buf, [1.0, 2.0, 3.0, 4.0, 5.0, 5.0]);
        s.sample(0.025, &mut buf);
        assert_eq!(buf, [5.0; 6]);
    }
}