from manim import *


class ParabolaLesson(Scene):
    # 坐标常量定义
    LEFT_MARGIN = 3.2
    AXIS_RANGE = [-4, 4, -1, 3]

    # 颜色定义
    BG_COLOR = "#F5F5F5"
    CURVE_COLOR = "#00BFFF"
    FOCUS_COLOR = "#FF4500"
    DIRECTRIX_COLOR = "#AAAAAA"

    def construct(self):
        self.camera.background_color = self.BG_COLOR
        self._intro()
        self._discovery()
        self._proof()
        self._practice()

    def _intro(self):
        # 创建坐标系
        axes = Axes(
            x_range=[-4, 4, 1],
            y_range=[-1, 3, 1],
            axis_config={"color": BLACK},
            tips=False
        )
        axes_labels = axes.get_axis_labels(x_label="x", y_label="y")

        # 初始抛物线 (a=1)
        a_value = ValueTracker(1)
        parabola = always_redraw(lambda: axes.plot(
            lambda x: a_value.get_value() * x ** 2,
            color=self.CURVE_COLOR
        ))

        # 添加所有元素
        self.add(axes, axes_labels, parabola)

    def _discovery(self):
        # 标题
        title = Tex("$a$是正数，开口向上", color=BLUE).to_edge(UP)

        # 公式
        formula = MathTex("y = a x^2", color=BLACK).next_to(title, DOWN)

        # 滑杆
        slider = NumberLine(
            x_range=[0, 2, 0.5],
            length=4,
            color=BLACK,
            include_numbers=True
        ).to_edge(DOWN)
        slider_label = Tex("$a$值:", color=BLACK).next_to(slider, LEFT)

        # 滑杆指示器
        dot = Dot(color=RED).move_to(slider.n2p(1))
        a_value = ValueTracker(1)
        dot.add_updater(lambda d: d.move_to(slider.n2p(
            a_value.get_value()
        )))
        a_text = always_redraw(lambda: DecimalNumber(
            a_value.get_value(),
            color=RED
        ).next_to(dot, UP))

        # 添加元素
        self.play(
            Write(title),
            Write(formula),
            Create(slider),
            Write(slider_label)
        )
        self.add(dot, a_text)

        # 动画：a值变化 (0.5 -> 1 -> 2)
        self.play(
            a_value.animate.set_value(0.5),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )
        self.play(
            a_value.animate.set_value(1),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )
        self.play(
            a_value.animate.set_value(2),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )

        # 5秒静止帧
        self.wait(5)

    def _proof(self):
        # 更新标题
        new_title = Tex("$a$是负数，开口向下", color=BLUE).to_edge(UP)

        # 滑杆范围变为负数
        slider = NumberLine(
            x_range=[-2, 0, 0.5],
            length=4,
            color=BLACK,
            include_numbers=True
        ).to_edge(DOWN)
        slider_label = Tex("$a$值:", color=BLACK).next_to(slider, LEFT)

        # 更新滑杆指示器
        a_value = ValueTracker(-1)
        dot = Dot(color=RED).move_to(slider.n2p(-1))
        dot.add_updater(lambda d: d.move_to(slider.n2p(
            a_value.get_value()
        )))
        a_text = always_redraw(lambda: DecimalNumber(
            a_value.get_value(),
            color=RED
        ).next_to(dot, UP))

        # 更新公式
        formula = MathTex("y = a x^2", color=BLACK).next_to(new_title, DOWN)

        # 焦点和准线
        focus = always_redraw(lambda: Dot(
            color=self.FOCUS_COLOR
        ).move_to([0, 1 / (4 * a_value.get_value()), 0]))

        directrix = always_redraw(lambda: DashedLine(
            start=[-4, -1 / (4 * a_value.get_value()), 0],
            end=[4, -1 / (4 * a_value.get_value()), 0],
            color=self.DIRECTRIX_COLOR
        ))

        # 切换元素
        self.play(
            Transform(self.mobjects[0], new_title),
            Transform(self.mobjects[1], formula),
            Transform(self.mobjects[2], slider),
            Transform(self.mobjects[3], slider_label)
        )
        self.add(focus, directrix)

        # 动画：a值变化 (-0.5 -> -1 -> -2)
        self.play(
            a_value.animate.set_value(-0.5),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )
        self.play(
            a_value.animate.set_value(-1),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )
        self.play(
            a_value.animate.set_value(-2),
            run_time=5,
            rate_func=rate_functions.ease_in_out_sine
        )

        # 5秒静止帧
        self.wait(5)

    def _practice(self):
        # 添加练习题文本
        practice = Tex(
            "思考题：当$a=-1$时，\\\\焦点和准线在哪里？",
            color=BLUE
        ).scale(0.8).to_edge(DOWN)

        # 显示练习题
        self.play(Write(practice))
        self.wait(5)


if __name__ == "__main__":
    # 全局指定 ctex 模板（一次性）
    config.tex_template = TexTemplateLibrary.ctex
    # 使用临时配置渲染场景（配置只在with块内有效）
    with tempconfig({
        "quality": "low_quality",
        "preview": True,
        "output_file": "ParabolaLesson"
    }):
        # 实例化场景类
        scene = ParabolaLesson()
        # 执行渲染流程（包含文件生成和预览）
        scene.render()