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use randomize::{formulas, PCG32};
use std::{cell::RefCell, f32::consts::PI};

const PI2: f32 = PI * 2.0;

/// Possible values for the duty cycle of the square wave.
#[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
pub enum DutyCycle {
    /// A duty cycle of 12.5%.
    Eight,
    /// A duty cycle of 25%.
    Quarter,
    /// A duty cycle of 33%.
    Third,
    /// A duty cycle of 50%.
    Half,
}

impl DutyCycle {
    /// Convert it to a number we can compare with.
    pub fn to_frac(self) -> f32 {
        match self {
            DutyCycle::Eight => 0.125,
            DutyCycle::Quarter => 0.25,
            DutyCycle::Third => 0.33,
            DutyCycle::Half => 0.5,
        }
    }
}

impl Default for DutyCycle {
    /// The default cycle is half.
    fn default() -> Self {
        DutyCycle::Half
    }
}

/// Wave form generation type.
#[derive(Debug, Copy, Clone, Hash, Eq, PartialEq)]
pub enum OscillatorType {
    /// A continuus tone.
    Sine,
    /// Strong, clear, buzzing sound.
    Saw,
    /// Smooth sound, between sine & square.
    Triangle,
    /// Rich sound, between sine & saw.
    ///
    /// This wave type uses `osc_duty_cycle` from `Sample`.
    Square,
    /// White noise, very noisy.
    ///
    /// `osc_frequency` is the seed for the RNG.
    Noise,
}

impl OscillatorType {
    /// Build a lookup table from this type.
    ///
    /// The table will be twice the size of the sample rate so we can use the whole size with an
    /// offset in it.
    pub(crate) fn build_lut(
        self,
        frequency: usize,
        duty_cycle: DutyCycle,
        sample_rate: usize,
    ) -> Vec<f32> {
        if self == OscillatorType::Noise {
            // We handle noise differently because it needs a generator
            let mut pcg = PCG32::seed(frequency as u64, 5);

            (0..sample_rate * 2)
                .map(|_| formulas::f32_closed_neg_pos(pcg.next_u32()))
                .collect()
        } else {
            let wave_func = self.wave_function();

            // Create a table twice the size so we don't have to use modulo on every frame
            (0..sample_rate * 2)
                .map(|i| {
                    wave_func(
                        i as f32,
                        frequency as f32,
                        // Convert the duty cycle enum to the fractional number
                        duty_cycle.to_frac(),
                        sample_rate as f32,
                    )
                })
                .collect()
        }
    }

    /// The way the oscillator calculates the output wave.
    ///
    /// Used to build the lookup table.
    fn wave_function(self) -> Box<dyn Fn(f32, f32, f32, f32) -> f32> {
        match self {
            OscillatorType::Sine => Box::new(
                |index: f32, frequency: f32, _duty_cycle: f32, sample_rate: f32| {
                    (index * frequency * PI2 / sample_rate).sin()
                },
            ),
            OscillatorType::Saw => Box::new(
                |index: f32, frequency: f32, _duty_cycle: f32, sample_rate: f32| {
                    let steps = sample_rate / frequency;

                    1.0 - ((index / steps) % 1.0) * 2.0
                },
            ),
            OscillatorType::Triangle => Box::new(
                |index: f32, frequency: f32, _duty_cycle: f32, sample_rate: f32| {
                    let steps = sample_rate / frequency;

                    let slope = (index / steps) % 1.0 * 2.0;
                    if slope < 1.0 {
                        -1.0 + slope * 2.0
                    } else {
                        3.0 - slope * 2.0
                    }
                },
            ),
            OscillatorType::Square => Box::new(
                |index: f32, frequency: f32, duty_cycle: f32, sample_rate: f32| {
                    let steps = sample_rate / frequency;

                    if (index / steps) % 1.0 < duty_cycle {
                        1.0
                    } else {
                        -1.0
                    }
                },
            ),
            // Implemented buffer-wide.
            OscillatorType::Noise => unreachable!(),
        }
    }
}

/// The oscillator just loops through the already populated lookup table.
#[derive(Debug)]
pub(crate) struct Oscillator {
    /// The lookup table is a reference owned by the Mixer struct.
    lut: RefCell<Vec<f32>>,
    /// The sample rate, also half the size of the lookup table.
    sample_rate: usize,
}

impl Oscillator {
    /// Instantiate a new oscillator that uses the passed lookup table.
    pub(crate) fn new(lut: RefCell<Vec<f32>>, sample_rate: usize) -> Self {
        Self { lut, sample_rate }
    }

    /// Fill the output buffer with generated sound.
    pub(crate) fn generate(&mut self, output: &mut [f32], offset: usize) {
        let rotating_index = offset % self.sample_rate;

        // Combine the size of the output buffer with the size of the cached frequencies buffer and
        // add the frequencies to the output
        output
            .iter_mut()
            .zip(self.lut.borrow()[rotating_index..].iter())
            .for_each(|(old, new)| *old += *new);
    }
}