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use get_input_index;
use primitive::InterpolationPrimitive;

/// Do linear interpolation.
///
/// `f(t) = p0 + (p1 - p0) * d`
/// `d = (t - t0) / (t1 - t0)`
/// `p0 = output at left keyframe`
/// `p1 = output at right keyframe`
/// `t0 = input at left keyframe`
/// `t1 = input at right keyframe`
///
/// ## Parameters:
///
/// - `input`: the input value to the function
/// - `inputs`: list of discrete input values for each keyframe
/// - `outputs`: list of output values to interpolate between, for linear interpolation this should
///              be the same size as `inputs`
/// - `normalize`: if true, normalize the interpolated value before returning it
pub fn linear_interpolate<T>(input: f32, inputs: &[f32], outputs: &[T], normalize: bool) -> T
where
    T: InterpolationPrimitive + Clone,
{
    let input_index = match get_input_index(input, inputs) {
        Some(index) => index,
        None => return outputs[0].clone(),
    };
    if input_index >= (inputs.len() - 1) {
        outputs[outputs.len() - 1].clone()
    } else {
        let d = (input - inputs[input_index]) / (inputs[input_index + 1] - inputs[input_index]);
        let left = &outputs[input_index];
        let right = &outputs[input_index + 1];
        let v = left.add(&right.sub(&left).mul(d));
        if normalize {
            v.normalize()
        } else {
            v
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use mint::{Quaternion, Vector3};

    #[test]
    fn test_linear_arr3() {
        let input = vec![0., 1., 2., 3., 4.];
        let output = vec![
            [0., 0., 0.],
            [1., 0., 0.],
            [0., 0., 0.],
            [-1., 0., 0.],
            [0., 0., 0.],
        ];
        assert_eq!(
            [0.5, 0., 0.],
            linear_interpolate(0.5, &input, &output, false)
        );
    }

    #[test]
    fn test_linear_arr4() {
        let input = vec![0., 1., 2., 3., 4.];
        let output = vec![
            [0., 0., 0., 0.],
            [1., 0., 0., 0.],
            [0., 0., 0., 0.],
            [-1., 0., 0., 0.],
            [0., 0., 0., 0.],
        ];
        assert_eq!(
            [1., 0., 0., 0.],
            linear_interpolate(0.5, &input, &output, true)
        );
    }

    #[test]
    fn test_linear_vec3() {
        let input = vec![0., 1., 2., 3., 4.];
        let output = vec![
            Vector3::from([0., 0., 0.]),
            Vector3::from([1., 0., 0.]),
            Vector3::from([0., 0., 0.]),
            Vector3::from([-1., 0., 0.]),
            Vector3::from([0., 0., 0.]),
        ];
        assert_eq!(
            Vector3::from([0.5, 0., 0.]),
            linear_interpolate(0.5, &input, &output, false)
        );
    }

    #[test]
    fn test_linear_quat() {
        let input = vec![0., 1., 2., 3., 4.];
        let output = vec![
            Quaternion::from([0., 0., 0., 0.]),
            Quaternion::from([1., 0., 0., 0.]),
            Quaternion::from([0., 0., 0., 0.]),
            Quaternion::from([-1., 0., 0., 0.]),
            Quaternion::from([0., 0., 0., 0.]),
        ];
        assert_eq!(
            Quaternion::from([1., 0., 0., 0.]),
            linear_interpolate(0.5, &input, &output, true)
        );
    }
}