local graph = require "./graph"
type Node<T> = graph.Node<T>
local create_node = graph.create_node
local push_scope = graph.push_scope
local pop_scope = graph.pop_scope
local destroy = graph.destroy
local get_scope = graph.get_scope

local function branch<T>(fn: () -> T): (() -> (), T)
    local current = get_scope()
    if not current then
        error(`cannot use branch() outside a stable or reactive scope`, 0)
    end

    local parent = current.owner
    if not parent or parent.effect then
        error(`current scope is not owned by a stable scope`, 0)
    end

    local node = create_node(parent, false, false)

    local destroy = function()
        destroy(node)
    end

    push_scope(node)

    local ok, result = xpcall(fn, debug.traceback)

    pop_scope()

    if not ok then
        destroy()
        error(`error while running branch():\n\n{result}`, 0)
    end

    return destroy, result
end

return branch