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use math::{Vec3, Mat4};

struct Data {
    parent: Option<Transform>,
    dirty: bool,
    position: Vec3,
    scale: Vec3,
    global: Mat4,
}

#[derive(Copy, Clone)]
pub struct Transform(usize);

pub struct TransformSystem {
    transforms: Vec<Data>,
}

impl TransformSystem {
    pub fn new() -> Self {
        Self { transforms: Vec::new() }
    }

    pub fn add<V1, V2>(&mut self, position: V1, scale: V2) -> Transform
    where Vec3: From<V1> + From<V2> {
        self.add_inner(None, Vec3::from(position), Vec3::from(scale))
    }

    pub fn add_child<V1, V2>(&mut self, parent: Transform, position: V1, scale: V2) -> Transform
    where Vec3: From<V1> + From<V2> {
        self.add_inner(Some(parent), Vec3::from(position), Vec3::from(scale))
    }

    pub fn position(&self, transform: Transform) -> Vec3 {
        self.transforms[transform.0].position
    }

    pub fn global(&self, transform: Transform) -> Mat4 {
        self.transforms[transform.0].global
    }

    pub fn set_position<V>(&mut self, transform: Transform, position: V)
    where Vec3: From<V> {
        self.transforms[transform.0].position = Vec3::from(position);
    }

    pub fn update(&mut self) {
        for transform in self.transforms.iter_mut() {
            transform.dirty = true;
        }
        for index in 0 .. self.transforms.len() {
            self.update_transform(index);
        }
    }

    fn update_transform(&mut self, index: usize) {
        if self.transforms[index].dirty {
            self.transforms[index].dirty = false;
            let local = Mat4::model(self.transforms[index].position, self.transforms[index].scale);
            if let Some(parent) = self.transforms[index].parent {
                self.update_transform(parent.0);
                self.transforms[index].global = self.transforms[parent.0].global * local;
            } else {
                self.transforms[index].global = local;
            }
        }
    }

    fn add_inner(&mut self, parent: Option<Transform>, position: Vec3, scale: Vec3) -> Transform {        
        self.transforms.push(Data {
            parent,
            position,
            scale,
            dirty: false,
            global: Mat4::identity(),
        });
        Transform(self.transforms.len() - 1)
    }
}