#![allow(clippy::excessive_precision)]

/// The number of samples in one full turn.
pub const N: usize = 256;

/// One full turn of sine, sampled N times.
pub const SINE: [f32; 256] = [
    0.0f32,
    0.024541229009628296f32,
    0.049067676067352295f32,
    0.0735645666718483f32,
    0.0980171412229538f32,
    0.12241067737340927f32,
    0.1467304676771164f32,
    0.1709618866443634f32,
    0.19509032368659973f32,
    0.21910123527050018f32,
    0.24298018217086792f32,
    0.2667127549648285f32,
    0.290284663438797f32,
    0.3136817514896393f32,
    0.3368898630142212f32,
    0.3598950505256653f32,
    0.3826834261417389f32,
    0.40524131059646606f32,
    0.4275550842285156f32,
    0.4496113359928131f32,
    0.4713967442512512f32,
    0.49289819598197937f32,
    0.5141027569770813f32,
    0.5349976420402527f32,
    0.5555702447891235f32,
    0.5758081674575806f32,
    0.5956993103027344f32,
    0.6152315735816956f32,
    0.6343932747840881f32,
    0.6531728506088257f32,
    0.6715589761734009f32,
    0.6895405650138855f32,
    0.7071067690849304f32,
    0.7242470979690552f32,
    0.7409511208534241f32,
    0.7572088241577148f32,
    0.7730104327201843f32,
    0.7883464097976685f32,
    0.803207516670227f32,
    0.8175848126411438f32,
    0.8314695954322815f32,
    0.8448535799980164f32,
    0.8577286005020142f32,
    0.8700869679450989f32,
    0.8819212913513184f32,
    0.89322429895401f32,
    0.903989315032959f32,
    0.91420978307724f32,
    0.9238795042037964f32,
    0.9329928159713745f32,
    0.9415440559387207f32,
    0.949528157711029f32,
    0.9569403529167175f32,
    0.9637760519981384f32,
    0.9700312614440918f32,
    0.9757021069526672f32,
    0.9807852506637573f32,
    0.9852776527404785f32,
    0.9891765117645264f32,
    0.9924795627593994f32,
    0.9951847195625305f32,
    0.9972904324531555f32,
    0.9987954497337341f32,
    0.99969881772995f32,
    1.0f32,
    0.99969881772995f32,
    0.9987954497337341f32,
    0.9972904324531555f32,
    0.9951847195625305f32,
    0.9924795627593994f32,
    0.9891765117645264f32,
    0.9852776527404785f32,
    0.9807852506637573f32,
    0.9757021069526672f32,
    0.9700312614440918f32,
    0.9637760519981384f32,
    0.9569403529167175f32,
    0.949528157711029f32,
    0.9415440559387207f32,
    0.9329928159713745f32,
    0.9238795042037964f32,
    0.91420978307724f32,
    0.903989315032959f32,
    0.89322429895401f32,
    0.8819212913513184f32,
    0.8700869679450989f32,
    0.8577286005020142f32,
    0.8448535799980164f32,
    0.8314695954322815f32,
    0.8175848126411438f32,
    0.803207516670227f32,
    0.7883464097976685f32,
    0.7730104327201843f32,
    0.7572088241577148f32,
    0.7409511208534241f32,
    0.7242470979690552f32,
    0.7071067690849304f32,
    0.6895405650138855f32,
    0.6715589761734009f32,
    0.6531728506088257f32,
    0.6343932747840881f32,
    0.6152315735816956f32,
    0.5956993103027344f32,
    0.5758081674575806f32,
    0.5555702447891235f32,
    0.5349976420402527f32,
    0.5141027569770813f32,
    0.49289819598197937f32,
    0.4713967442512512f32,
    0.4496113359928131f32,
    0.4275550842285156f32,
    0.40524131059646606f32,
    0.3826834261417389f32,
    0.3598950505256653f32,
    0.3368898630142212f32,
    0.3136817514896393f32,
    0.290284663438797f32,
    0.2667127549648285f32,
    0.24298018217086792f32,
    0.21910123527050018f32,
    0.19509032368659973f32,
    0.1709618866443634f32,
    0.1467304676771164f32,
    0.12241067737340927f32,
    0.0980171412229538f32,
    0.0735645666718483f32,
    0.049067676067352295f32,
    0.024541229009628296f32,
    1.2246468525851679e-16f32,
    -0.024541229009628296f32,
    -0.049067676067352295f32,
    -0.0735645666718483f32,
    -0.0980171412229538f32,
    -0.12241067737340927f32,
    -0.1467304676771164f32,
    -0.1709618866443634f32,
    -0.19509032368659973f32,
    -0.21910123527050018f32,
    -0.24298018217086792f32,
    -0.2667127549648285f32,
    -0.290284663438797f32,
    -0.3136817514896393f32,
    -0.3368898630142212f32,
    -0.3598950505256653f32,
    -0.3826834261417389f32,
    -0.40524131059646606f32,
    -0.4275550842285156f32,
    -0.4496113359928131f32,
    -0.4713967442512512f32,
    -0.49289819598197937f32,
    -0.5141027569770813f32,
    -0.5349976420402527f32,
    -0.5555702447891235f32,
    -0.5758081674575806f32,
    -0.5956993103027344f32,
    -0.6152315735816956f32,
    -0.6343932747840881f32,
    -0.6531728506088257f32,
    -0.6715589761734009f32,
    -0.6895405650138855f32,
    -0.7071067690849304f32,
    -0.7242470979690552f32,
    -0.7409511208534241f32,
    -0.7572088241577148f32,
    -0.7730104327201843f32,
    -0.7883464097976685f32,
    -0.803207516670227f32,
    -0.8175848126411438f32,
    -0.8314695954322815f32,
    -0.8448535799980164f32,
    -0.8577286005020142f32,
    -0.8700869679450989f32,
    -0.8819212913513184f32,
    -0.89322429895401f32,
    -0.903989315032959f32,
    -0.91420978307724f32,
    -0.9238795042037964f32,
    -0.9329928159713745f32,
    -0.9415440559387207f32,
    -0.949528157711029f32,
    -0.9569403529167175f32,
    -0.9637760519981384f32,
    -0.9700312614440918f32,
    -0.9757021069526672f32,
    -0.9807852506637573f32,
    -0.9852776527404785f32,
    -0.9891765117645264f32,
    -0.9924795627593994f32,
    -0.9951847195625305f32,
    -0.9972904324531555f32,
    -0.9987954497337341f32,
    -0.99969881772995f32,
    -1.0f32,
    -0.99969881772995f32,
    -0.9987954497337341f32,
    -0.9972904324531555f32,
    -0.9951847195625305f32,
    -0.9924795627593994f32,
    -0.9891765117645264f32,
    -0.9852776527404785f32,
    -0.9807852506637573f32,
    -0.9757021069526672f32,
    -0.9700312614440918f32,
    -0.9637760519981384f32,
    -0.9569403529167175f32,
    -0.949528157711029f32,
    -0.9415440559387207f32,
    -0.9329928159713745f32,
    -0.9238795042037964f32,
    -0.91420978307724f32,
    -0.903989315032959f32,
    -0.89322429895401f32,
    -0.8819212913513184f32,
    -0.8700869679450989f32,
    -0.8577286005020142f32,
    -0.8448535799980164f32,
    -0.8314695954322815f32,
    -0.8175848126411438f32,
    -0.803207516670227f32,
    -0.7883464097976685f32,
    -0.7730104327201843f32,
    -0.7572088241577148f32,
    -0.7409511208534241f32,
    -0.7242470979690552f32,
    -0.7071067690849304f32,
    -0.6895405650138855f32,
    -0.6715589761734009f32,
    -0.6531728506088257f32,
    -0.6343932747840881f32,
    -0.6152315735816956f32,
    -0.5956993103027344f32,
    -0.5758081674575806f32,
    -0.5555702447891235f32,
    -0.5349976420402527f32,
    -0.5141027569770813f32,
    -0.49289819598197937f32,
    -0.4713967442512512f32,
    -0.4496113359928131f32,
    -0.4275550842285156f32,
    -0.40524131059646606f32,
    -0.3826834261417389f32,
    -0.3598950505256653f32,
    -0.3368898630142212f32,
    -0.3136817514896393f32,
    -0.290284663438797f32,
    -0.2667127549648285f32,
    -0.24298018217086792f32,
    -0.21910123527050018f32,
    -0.19509032368659973f32,
    -0.1709618866443634f32,
    -0.1467304676771164f32,
    -0.12241067737340927f32,
    -0.0980171412229538f32,
    -0.0735645666718483f32,
    -0.049067676067352295f32,
    -0.024541229009628296f32,
];

/// Returns the sine at a sample index, wrapping past a full turn.
#[inline]
pub fn sin_idx(i: usize) -> f32 {
    SINE[i % N]
}

/// Returns the cosine at a sample index by a quarter-turn shift of the sine table.
#[inline]
pub fn cos_idx(i: usize) -> f32 {
    SINE[(i + N / 4) % N]
}

/// Returns the unit vector of cosine and sine at a sample index.
#[inline]
pub fn unit(i: usize) -> (f32, f32) {
    (cos_idx(i), sin_idx(i))
}

/// A fractional sample index that wraps around the turn.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct FracIndex {
    /// The fractional index within one turn.
    pub value: f32,
}

impl FracIndex {
    /// Builds a fractional index wrapped into the turn.
    #[inline]
    pub fn new(value: f32) -> FracIndex {
        FracIndex { value }.wrapped()
    }

    /// Advances the index by a delta and wraps it back into the turn.
    #[inline]
    pub fn advance(&mut self, delta: f32) {
        self.value += delta;
        *self = self.wrapped();
    }

    /// Rounds to the nearest whole sample index.
    #[inline]
    pub fn index(&self) -> usize {
        let r = (self.value + 0.5).floor();
        (r as usize) % N
    }

    /// Returns the unit vector at the rounded index.
    #[inline]
    pub fn unit(&self) -> (f32, f32) {
        unit(self.index())
    }

    #[inline]
    fn wrapped(self) -> FracIndex {
        let n = N as f32;
        let v = self.value - (self.value / n).floor() * n;
        FracIndex { value: v }
    }
}

/// Scales a count of turns into a fractional sample index.
#[inline]
pub fn index_from_turns(turns: f32) -> f32 {
    turns * N as f32
}

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

    #[test]
    fn quarter_turns_are_exact() {
        assert_eq!(unit(0), (1.0, 0.0));
        assert_eq!(sin_idx(N / 4), 1.0);
        assert!(cos_idx(N / 4).abs() < 1e-6);
        assert!(sin_idx(N / 2).abs() < 1e-6);
        assert_eq!(sin_idx(3 * N / 4), -1.0);
    }

    #[test]
    fn unit_vectors_are_unit_length() {
        for i in 0..N {
            let (c, s) = unit(i);
            let mag = c * c + s * s;
            assert!((mag - 1.0).abs() < 1e-5, "index {i} mag {mag}");
        }
    }

    #[test]
    fn stride_divides_every_count() {
        for &count in &[1usize, 2, 4, 8, 16, 32, 64, 128] {
            assert_eq!(N % count, 0, "N must divide count {count}");
        }
    }

    #[test]
    fn frac_index_wraps_with_floor_only() {
        let mut f = FracIndex::new(0.0);
        f.advance(N as f32 + 3.0);
        assert!(f.value >= 0.0 && f.value < N as f32);
        assert_eq!(f.index(), 3);
    }

    #[test]
    fn frac_index_negative_wraps() {
        let f = FracIndex::new(-1.0);
        assert!(f.value >= 0.0 && f.value < N as f32);
        assert_eq!(f.index(), N - 1);
    }
}