from manim import *


class ParabolaLesson(Scene):
    # 坐标常量定义
    LEFT_MARGIN = 3.2
    AXIS_CENTER = LEFT * LEFT_MARGIN
    TITLE_POS = UP * 3.2
    FORMULA_POS = UP * 2.2
    SLIDER_POS = UP * 1.2
    GRAPH_POS = LEFT * LEFT_MARGIN

    def construct(self):
        self._intro()
        self._discovery()
        self._proof()
        self._practice()

    def _intro(self):
        # 创建坐标轴
        axes = Axes(
            x_range=[-3, 3, 1],
            y_range=[0, 8, 2],
            axis_config={"color": BLUE},
            tips=False
        ).shift(self.GRAPH_POS)

        # 初始曲线 y=x²
        curve = axes.plot(lambda x: x ** 2, color=YELLOW)

        # 标题和公式
        title = Tex("$a$是正数，开口向上", color=GREEN).to_edge(self.TITLE_POS)
        formula = MathTex("y = x^2", color=RED).to_edge(self.FORMULA_POS)

        # 动画序列
        self.play(Create(axes), run_time=1.5)
        self.play(Create(curve), Write(formula), run_time=2)
        self.play(Write(title), run_time=1.5)
        self.wait(1)

        # 保存对象
        self.axes = axes
        self.curve = curve
        self.formula = formula
        self.title = title

    def _discovery(self):
        # 创建滑杆数值显示
        a_value = DecimalNumber(1.0, num_decimal_places=1)
        a_text = Tex("$a = $").next_to(a_value, LEFT)
        a_display = VGroup(a_text, a_value).to_edge(self.SLIDER_POS)

        # 更新公式为 y=ax²
        new_formula = MathTex("y = a x^2", color=RED).to_edge(self.FORMULA_POS)
        self.play(Transform(self.formula, new_formula), FadeIn(a_display))

        # 创建滑杆
        slider = NumberLine(x_range=[0.5, 2.5], length=4, include_numbers=True)
        slider.to_edge(self.SLIDER_POS).shift(DOWN * 0.6)
        dot = Dot(color=RED).move_to(slider.n2p(1))

        # 添加滑杆动画
        self.play(Create(slider), Create(dot))

        # 定义曲线更新函数
        def update_curve(mob):
            a = a_value.get_value()
            new_curve = self.axes.plot(lambda x: a * x ** 2, color=YELLOW)
            mob.become(new_curve)

        # 设置数值更新器
        self.curve.add_updater(update_curve)

        # 参数变化动画序列
        a_values = [0.5, 1.0, 2.0]
        for a in a_values:
            self.play(
                a_value.animate.set_value(a),
                dot.animate.move_to(slider.n2p(a)),
                run_time=3
            )
            self.wait(0.5)

        # 移除更新器
        self.curve.remove_updater(update_curve)

        # 保持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=GREEN).to_edge(self.TITLE_POS)
        self.play(Transform(self.title, new_title))

        # 更新公式
        new_formula = MathTex("y = a x^2", color=RED).to_edge(self.FORMULA_POS)
        self.play(Transform(self.formula, new_formula))

        # 创建新的滑杆数值显示
        a_value = DecimalNumber(-0.5, num_decimal_places=1)
        a_text = Tex("$a = $").next_to(a_value, LEFT)
        a_display = VGroup(a_text, a_value).to_edge(self.SLIDER_POS)

        # 创建新滑杆
        slider = NumberLine(x_range=[-2.5, -0.5], length=4, include_numbers=True)
        slider.to_edge(self.SLIDER_POS).shift(DOWN * 0.6)
        dot = Dot(color=RED).move_to(slider.n2p(-0.5))

        # 添加滑杆动画
        self.play(FadeIn(a_display), Create(slider), Create(dot))

        # 定义曲线更新函数
        def update_curve(mob):
            a = a_value.get_value()
            new_curve = self.axes.plot(lambda x: a * x ** 2, color=YELLOW)
            mob.become(new_curve)

        # 设置数值更新器
        self.curve.add_updater(update_curve)

        # 参数变化动画序列
        a_values = [-0.5, -1.0, -2.0]
        for a in a_values:
            self.play(
                a_value.animate.set_value(a),
                dot.animate.move_to(slider.n2p(a)),
                run_time=3
            )
            self.wait(0.5)

        # 移除更新器
        self.curve.remove_updater(update_curve)

        # 保持5秒静止帧
        self.wait(5)

    def _practice(self):
        # 练习环节留空
        pass


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({"preview": True, "quality": "high_quality"}):
        # 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()