FlipClockSaver/FlipClockSaver/FlipDigit.swift

import AppKit

// MARK: - 单个翻页数字（Core Graphics 绘制，无 layer 拼接，彻底无黑缝）
@MainActor
final class FlipDigit {
    var current: Int = -1
    private var previous: Int = -1
    private var animStart: TimeInterval = 0
    private var animating = false
    let duration: TimeInterval = 0.55

    func set(_ newValue: Int, at time: TimeInterval, animated: Bool) {
        guard newValue != current else { return }
        previous = current < 0 ? newValue : current
        current = newValue
        if animated {
            animStart = time
            animating = true
        } else {
            animating = false
        }
    }

    func advance(to time: TimeInterval) {
        if animating && (time - animStart) >= duration {
            animating = false
        }
    }

    func draw(in ctx: CGContext,
              rect: CGRect,
              radius: CGFloat,
              font: NSFont,
              cardBg: NSColor,
              textColor: NSColor,
              now: TimeInterval) {
        let t01 = animating ? min(max((now - animStart) / duration, 0), 1) : 1
        let midY = rect.midY
        let topRect = CGRect(x: rect.minX, y: midY, width: rect.width, height: rect.height / 2)
        let botRect = CGRect(x: rect.minX, y: rect.minY, width: rect.width, height: rect.height / 2)

        let topDigit = current
        let botDigit = animating ? previous : current

        // 先铺整卡底色：中缝处底色即卡片色，彻底消除抗锯齿透出的黑缝
        ctx.saveGState()
        let basePath = CGMutablePath()
        basePath.addRoundedRect(in: rect, cornerWidth: radius, cornerHeight: radius)
        ctx.addPath(basePath); ctx.clip()
        ctx.setFillColor(cardBg.cgColor)
        ctx.fill(rect)
        ctx.restoreGState()

        drawCard(in: ctx, half: topRect, full: rect, digit: topDigit,
                 radius: radius, font: font, cardBg: cardBg, textColor: textColor)
        drawCard(in: ctx, half: botRect, full: rect, digit: botDigit,
                 radius: radius, font: font, cardBg: cardBg, textColor: textColor)

        if animating && t01 < 1 {
            if t01 < 0.5 {
                // 上半翻片：旧值从直立翻走（0 → -90°），用 cos 模拟 3D 压缩
                let a = -t01 * 2 * (CGFloat.pi / 2)
                let sy = max(cos(a), 0.0001)
                ctx.saveGState()
                ctx.beginPath(); ctx.addRect(topRect); ctx.clip()
                ctx.translateBy(x: 0, y: midY)
                ctx.scaleBy(x: 1, y: sy)
                ctx.translateBy(x: 0, y: -midY)
                drawCard(in: ctx, half: topRect, full: rect, digit: previous,
                         radius: radius, font: font, cardBg: cardBg, textColor: textColor)
                ctx.setFillColor(CGColor(gray: 0, alpha: CGFloat(t01) * 0.40))
                ctx.fill(topRect)
                ctx.restoreGState()
            } else {
                // 下半翻片：新值从水平翻下（90° → 0°）
                let t2 = (t01 - 0.5) * 2
                let a = (1 - t2) * (CGFloat.pi / 2)
                let sy = max(cos(a), 0.0001)
                ctx.saveGState()
                ctx.beginPath(); ctx.addRect(botRect); ctx.clip()
                ctx.translateBy(x: 0, y: midY)
                ctx.scaleBy(x: 1, y: sy)
                ctx.translateBy(x: 0, y: -midY)
                drawCard(in: ctx, half: botRect, full: rect, digit: current,
                         radius: radius, font: font, cardBg: cardBg, textColor: textColor)
                ctx.setFillColor(CGColor(gray: 1, alpha: CGFloat(1 - t2) * 0.30))
                ctx.fill(botRect)
                ctx.restoreGState()
            }
        }

        // 翻页钟铰链：一条细而自然的中缝分割线（位于翻片转轴处，始终可见）
        drawHinge(in: ctx, rect: rect, midY: midY)
    }

    // 细而自然的中缝：主线为柔和阴影，下方一抹微弱高光模拟折边受光
    private func drawHinge(in ctx: CGContext, rect: CGRect, midY: CGFloat) {
        ctx.saveGState()
        ctx.setFillColor(CGColor(gray: 0, alpha: 0.45))
        ctx.fill(CGRect(x: rect.minX, y: midY - 0.75, width: rect.width, height: 1.5))
        ctx.setFillColor(CGColor(gray: 1, alpha: 0.06))
        ctx.fill(CGRect(x: rect.minX, y: midY + 0.75, width: rect.width, height: 1))
        ctx.restoreGState()
    }

    // 整卡圆角 + 半区域双重裁剪：外缘圆角、接缝直边，且上下连续绘制 → 无黑缝
    private func drawCard(in ctx: CGContext,
                          half: CGRect,
                          full: CGRect,
                          digit: Int,
                          radius: CGFloat,
                          font: NSFont,
                          cardBg: NSColor,
                          textColor: NSColor) {
        ctx.saveGState()
        let path = CGMutablePath()
        path.addRoundedRect(in: full, cornerWidth: radius, cornerHeight: radius)
        ctx.addPath(path); ctx.clip()
        ctx.beginPath(); ctx.addRect(half); ctx.clip()

        ctx.setFillColor(cardBg.cgColor)
        ctx.fill(full)

        // 数字在整卡内水平 + 垂直精确居中：先测量文字尺寸，再把绘制框对齐卡片中线
        let str = "\(digit)" as NSString
        let size = str.size(withAttributes: [.font: font])
        let textRect = CGRect(x: full.minX,
                              y: full.midY - size.height / 2,
                              width: full.width,
                              height: size.height)
        let ps = NSMutableParagraphStyle()
        ps.alignment = .center
        let attrs: [NSAttributedString.Key: Any] = [
            .font: font,
            .foregroundColor: textColor,
            .paragraphStyle: ps
        ]
        str.draw(in: textRect, withAttributes: attrs)
        ctx.restoreGState()
    }
}