package collision

import fl "common:container/freelist"

Octree :: struct {
	elements:           fl.Free_List(Element),
	element_nodes:      fl.Free_List(Element_Node),
	root:               Octree_Node,
	nodes:              fl.Free_List(Octree_Node_Children),
	free_node_plus_one: int,
	root_aabb:          Aabb,
	max_depth:          int,
}

// You insert elements
Element :: struct {
	id:   i32,
	aabb: Aabb,
}

// Elements may spawn multiple element nodes
Element_Node :: struct {
	next:    i32,
	element: i32,
}

Octree_Node_Children :: struct {
	children: [8]Octree_Node,
}

Octree_Node :: struct {
	// Index of children if this node is a branch or first element if this node is a leaf
	children_or_first_element: i32,

	// Number of elements in a leaf or -1 if not a leaf
	len:                       i32,
}

is_leaf :: proc(node: Octree_Node) -> bool {
	return node.len != -1
}

add_element_to_leaf :: #force_inline proc(octree: ^Octree, node: ^Octree_Node, el_index: i32) {
	new_elem_node_idx := fl.insert(
		&octree.element_nodes,
		Element_Node{element = el_index, next = node.children_or_first_element},
	)
	node.children_or_first_element = i32(new_elem_node_idx)
}

insert :: proc(octree: ^Octree, el: Element) {
	el_index := i32(fl.insert(&octree.elements, el))

	if is_leaf(octree.root) {
		add_element_to_leaf(octree, &octree.root, el_index)
	}
}