class vectorAngle():
    def __init__(self, vec):
        self.x, self.y = vec[0], vec[1]

    def vecAttr(self):
        # 判斷點所在的象限
        #     N
        #  W  O  E
        #     S
        ref = 0.
        x, y = self.x, self.y
        if x == ref:
            if y == ref:
                res = 'OO'
            elif y > ref:
                res = 'ON'
            else:
                res = 'OS'
        elif x > ref:
            if y == ref:
                res = 'OE'
            elif y > ref:
                res = 'EN'
            else:
                res = "ES"
        else:
            if y == ref:
                res = "OW"
            elif y > ref:
                res = "WN"
            else:
                res = "WS"
        return res

    def vecAngle(self):
        flag = self.vecAttr()
        x, y = self.x, self.y
        if flag == "OO":
            angle = 0.
        elif flag == "OE":
            angle = 0.
        elif flag == "EN":
            angle = np.arctan(y/x)
        elif flag == "ON":
            angle = np.pi / 2
        elif flag == "WN":
            angle = np.pi - np.arctan(abs(y/x))
        elif flag == "OW":
            angle = np.pi
        elif flag == "WS":
            angle = np.pi + np.arctan(abs(y/x))
        elif flag == "OS":
            angle = np.pi * 1.5
        else:
            angle = np.pi * 2.0 - np.arctan(abs(y/x))

        return round(angle, 3)