--- States stack
--- @class StateManager
StateManager = {
    states = {},
    ---
    ---@param self StateManager
    new = function(self, o)
        o = o or {}
        setmetatable(o, self)
        self.__index = self
        return o
    end,
    ---
    ---@param self StateManager
    ---@return unknown
    _get_current_state = function(self)
        return self.states[#self.states]
    end,
    ---
    ---@param self StateManager
    ---@param state any
    _set_current_state = function(self, state)
        if #self.states == 0 then
            self.states = { state }
        else
            local last = self.states[#self.states]
            if last._leave then last:_leave() end
            self.states[#self.states] = state
        end
    end,
    ---
    ---@param self StateManager
    ---@param state any
    change_state = function(self, state, ...)
        local current = self:_get_current_state()
        if current and current._leave then current:_leave() end
        self:_set_current_state(state)
        if state._enter then state:_enter(...) end
    end,
    ---
    ---@param self StateManager
    push_state = function(self, state, data)
        table.insert(self.states, state)
        if state._enter then state:_enter(data) end
    end,
    ---
    ---@param self StateManager
    pop_state = function(self)
        local state = table.remove(self.states)
        if #self.states == 0 then trace("No state left", 2) end
        if state._leave then state:_leave() end
    end,
    ---
    ---@param self StateManager
    update = function(self)
        local current = self:_get_current_state()
        if not current then return end
        if current.update then current:update() end
    end,
}