local function newNode (posX, posY, distance, priority)
    node = {}
    node.posX = posX
    node.posY = posY
    node.distance = distance
    node.priority = priority
    -- Estimation function for the remaining distance to the goal.
    function node:estimate(destX, destY)
        local dx = destX - self.posX
        local dy = destY - self.posY
        -- Manhattan distance
        -- abs(dx) + abs(dy)
        --Euclidian Distance
        return math.sqrt(dx * dx + dy * dy)
    end
    function node:updatePriority(destX, destY)
        self.priority = self.distance + self:estimate(destX, destY) * 10
    end
    function node:nextMove()
        self.distance = self.distance + 10
    end
    mt = { __lt =   function (a, b)
                        return { value = a.priority < b.priority }
                    end }
    setmetatable(node, mt)

    return node
end