import SwiftUI

/// 顶部带“内凹”弧形的连续圆角矩形
struct ScoopRoundedRect: Shape {
    var cornerRadius: CGFloat = 20
    /// 凹凸的“深度”：>0 向下凸（更接近你截图的效果），<0 为向上凹
    var scoopDepth: CGFloat = 10
    /// 半宽：控制水平占据范围（越大越“平缓”）
    var scoopHalfWidth: CGFloat = 18
    /// 相对位置（0~1，0.5 正中）
    var scoopCenterX: CGFloat = 0.33
    /// 是否向下凸；为 false 时表现为向上“凹”（与 notch 类似）
    var convexDown: Bool = true
    /// 凹陷/鼓包底部的“平底”半宽（0 为无平底）
    var flatHalfWidth: CGFloat = 8

    func path(in rect: CGRect) -> Path {
        let r = min(cornerRadius, min(rect.width, rect.height) * 0.5)
        let topY = rect.minY

        // 约束中心与范围，避免穿出圆角
        let minX = rect.minX + r
        let maxX = rect.maxX - r
        let centerX = rect.minX + rect.width * scoopCenterX
        let hw = min(scoopHalfWidth, (maxX - minX) * 0.45)
        let flatHW = max(0, min(flatHalfWidth, hw * 0.8))
        let shoulder = max(1, hw - flatHW) // 两侧曲线的水平长度
        let startX = max(minX, centerX - (flatHW + shoulder))
        let endX = min(maxX, centerX + (flatHW + shoulder))
        let leftFlatX = max(minX, centerX - flatHW)
        let rightFlatX = min(maxX, centerX + flatHW)
        let depth = (convexDown ? 1 : -1) * scoopDepth

        // 左曲线：P0 -> Lf（水平）；右曲线：Rf -> P3（水平）；Lf~Rf 之间是一段水平直线
        let P0 = CGPoint(x: startX, y: topY)
        let Lf = CGPoint(x: leftFlatX, y: topY + depth)
        let Rf = CGPoint(x: rightFlatX, y: topY + depth)
        let P3 = CGPoint(x: endX, y: topY)

        // 使用圆角近似系数控制手柄长度（基于 shoulder）
        let k = shoulder * 0.5522847498
        let C1 = CGPoint(x: P0.x + k, y: P0.y)   // P0 水平切线
        let C2 = CGPoint(x: Lf.x - k, y: Lf.y)   // Lf 水平切线
        let C3 = CGPoint(x: Rf.x + k, y: Rf.y)   // Rf 水平切线
        let C4 = CGPoint(x: P3.x - k, y: P3.y)   // P3 水平切线

        var p = Path()
        // 顶部从左上圆角起
        p.move(to: CGPoint(x: rect.minX + r, y: topY))
        // 左侧直线到凹/凸开始
        p.addLine(to: P0)
        // 左侧进入曲线
        p.addCurve(to: Lf, control1: C1, control2: C2)
        // 平底水平直线
        p.addLine(to: Rf)
        // 右侧离开曲线
        p.addCurve(to: P3, control1: C3, control2: C4)
        // 顶部到右上圆角
        p.addLine(to: CGPoint(x: rect.maxX - r, y: topY))
        // 右上圆角
        p.addQuadCurve(to: CGPoint(x: rect.maxX, y: rect.minY + r),
                       control: CGPoint(x: rect.maxX, y: rect.minY))
        // 右侧直线到右下圆角
        p.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY - r))
        // 右下圆角
        p.addQuadCurve(to: CGPoint(x: rect.maxX - r, y: rect.maxY),
                       control: CGPoint(x: rect.maxX, y: rect.maxY))
        // 底边到左下圆角
        p.addLine(to: CGPoint(x: rect.minX + r, y: rect.maxY))
        // 左下圆角
        p.addQuadCurve(to: CGPoint(x: rect.minX, y: rect.maxY - r),
                       control: CGPoint(x: rect.minX, y: rect.maxY))
        // 左侧到左上圆角
        p.addLine(to: CGPoint(x: rect.minX, y: rect.minY + r))
        // 左上圆角
        p.addQuadCurve(to: CGPoint(x: rect.minX + r, y: rect.minY),
                       control: CGPoint(x: rect.minX, y: rect.minY))
        p.closeSubpath()
        return p
    }
}

struct ScoopRoundedRect_Previews: PreviewProvider {
    static var previews: some View {
        VStack(spacing: 30) {
            // 向下“鼓包”且底部有平直段
            ScoopRoundedRect(cornerRadius: 24, scoopDepth: 8, scoopHalfWidth: 26, scoopCenterX: 0.25, convexDown: true, flatHalfWidth: 12)
                .fill(Color.orange)
                .frame(height: 140)
                .shadow(color: .black.opacity(0.08), radius: 12, y: 6)
                .padding()

            // 中央更深、更宽，平底更宽
            ScoopRoundedRect(cornerRadius: 28, scoopDepth: 12, scoopHalfWidth: 36, scoopCenterX: 0.5, convexDown: true, flatHalfWidth: 18)
                .fill(Color.orange)
                .frame(height: 140)
                .shadow(color: .black.opacity(0.08), radius: 12, y: 6)
                .padding()

            // 作为对比：向上“凹陷”的 notch，带平底
            ScoopRoundedRect(cornerRadius: 24, scoopDepth: 10, scoopHalfWidth: 22, scoopCenterX: 0.6, convexDown: false, flatHalfWidth: 10)
                .fill(Color.orange)
                .frame(height: 140)
                .shadow(color: .black.opacity(0.08), radius: 12, y: 6)
                .padding()
        }
        .background(Color(white: 0.96))
        .previewLayout(.sizeThatFits)
    }
}