Non-working queue written in Odin

queue.go

// IMPORTANT: THIS IS A NON WORKING EXAMPLE
// ATTENTION: THIS IS NOT WORKING
import "core:fmt.odin";

QueueNode :: struct(T: type) {
	data: T,
	prev: int,
	used: bool = false,
}

Queue :: struct(T: type) {
	nodes: []QueueNode(T),
	cap:   int = -1,
	size:  int,
	head:  int,
	tail:  int,
}

queue_init :: proc(using queue: ^Queue($T)) {
	if cap != -1 do return;

	cap = 16;
	size = 0;
	nodes = make([]QueueNode(T), cap);
	head = 0;
	tail = -1;
}

queue_clear :: proc(using queue: ^Queue($T)) {
	size = 0;
	head = 0;
	tail = -1;
}

queue_expand :: proc(using queue: ^Queue($T)) {
	if size <= cap do return;

	old_cap := cap;
	cap *= 2;
	new_nodes := make([]QueueNode(T), cap);

	if tail < head {
		// The queue has gone full circle
		// so we move everything right of the head to end of the array
		// We have:
		// [1, 1, tail, head, rest of queue]
		// We want:
		// [1, 1, tail, more empty, head, rest of queue]
		for i := 0; i <= tail; i += 1 {
			new_nodes[i] = nodes[i];
		}
		for i := 0; i < old_cap - head; i += 1 {
			new_nodes[cap-1-(old_cap-head)+i] = nodes[head + i];
		}
		head = cap-head;
	} else {
		// The queue has not gone full circle
		// so we dont have to move anything
		// We have:
		// [head, 1, 1, 1, 1, tail]
		// We want:
		// [head, 1, 1, 1, 1, tail, new space]
		for i := 0; i < old_cap; i += 1 {
			new_nodes[i] = nodes[i];
		}
	}

	free(nodes);
	nodes = new_nodes;
}

enqueue :: proc(using queue: ^Queue($T), el: T) {
	if cap == -1 do queue_init(queue);
	size += 1;
	queue_expand(queue);

	prev := tail;
	if tail == cap-1 {
		tail = 0;
	} else {
		tail += 1;
	}
	
	nodes[tail].used = true;
	nodes[tail].data = el;
	nodes[tail].prev = prev;
}

dequeue :: proc(using queue: ^Queue($T)) -> T {
	result := nodes[head].data;
	nodes[head].used = false;
	head += 1;

	if head == cap {
		head = 0;
	}
	size -= 1;

	return result;
}

expand_test :: proc() {
	test: Queue(int);
	for i := 0; i < 16; i += 1 {
		enqueue(&test, i);
	}
	// cause expand
	fmt.println("Before 17th element:", test.cap);
	enqueue(&test, 255);
	fmt.println("After 17th element:", test.cap);

	dequeue(&test);
}

normal_expand_then_wrap_test :: proc() {
	test: Queue(int);
	for i in 0..16 {
		enqueue(&test, i);
	}

	dequeue(&test);
	dequeue(&test);
	dequeue(&test);

	pretty :: proc(using queue: ^Queue($T)) {
		fmt.printf("[");
		for i := 0; i < cap-1; i += 1 {
			val := 0;
			if nodes[i].used do val = 1;
			fmt.printf("%d, ", val);
		}
		val := 0;
		if nodes[cap-1].used do val = 1;
		fmt.printf("%d]\n", val);
	}

	pretty(&test);

	for i in 0..18 {
		enqueue(&test, i);
	}

	pretty(&test);
}

main :: proc() {
	test: Queue(int);
	pretty :: proc(using queue: ^Queue($T)) {
		fmt.printf("[");
		for i := 0; i < cap-1; i += 1 {
			val := 0;
			if nodes[i].used do val = 1;
			fmt.printf("%d, ", val);
		}
		val := 0;
		if nodes[cap-1].used do val = 1;
		fmt.printf("%d]\n", val);
	}

	for i in 0..16 {
		enqueue(&test, i);
	}

	dequeue(&test);
	dequeue(&test);
	dequeue(&test);
	enqueue(&test, 1);
	//enqueue(&test, 2);

	pretty(&test);

	for i in 0..200 {
		enqueue(&test, i);
		fmt.printf("after #%d: ", i);
		pretty(&test);
	}

	pretty(&test);
}