feat: add WeChat sharing and invite flow

suixinkan/Core/WeChat/WeChatThumbImageProcessor.swift

@@ -0,0 +1,47 @@
+//
+//  WeChatThumbImageProcessor.swift
+//  suixinkan
+//
+
+import UIKit
+
+/// 微信分享缩略图处理器，将图片压缩到微信 32KB 限制内。
+enum WeChatThumbImageProcessor {
+    /// 微信缩略图最大字节数。
+    static let maxThumbBytes = 32 * 1024
+
+    /// 将图片压缩为符合微信要求的缩略图数据。
+    static func makeThumbData(from image: UIImage, maxBytes: Int = maxThumbBytes) -> Data? {
+        guard maxBytes > 0 else { return nil }
+
+        let resized = resize(image, maxPixel: 120)
+        var quality: CGFloat = 0.82
+        var data = resized.jpegData(compressionQuality: quality)
+
+        while let current = data, current.count > maxBytes, quality > 0.12 {
+            quality -= 0.1
+            data = resized.jpegData(compressionQuality: quality)
+        }
+
+        guard let result = data, result.count <= maxBytes else { return nil }
+        return result
+    }
+
+    /// 等比缩放图片，使最长边不超过指定像素。
+    static func resize(_ image: UIImage, maxPixel: CGFloat) -> UIImage {
+        let sourceSize = image.size
+        guard sourceSize.width > 0, sourceSize.height > 0 else { return image }
+
+        let maxSide = max(sourceSize.width, sourceSize.height)
+        guard maxSide > maxPixel else { return image }
+
+        let scale = maxPixel / maxSide
+        let targetSize = CGSize(width: sourceSize.width * scale, height: sourceSize.height * scale)
+        let format = UIGraphicsImageRendererFormat.default()
+        format.scale = 1
+        let renderer = UIGraphicsImageRenderer(size: targetSize, format: format)
+        return renderer.image { _ in
+            image.draw(in: CGRect(origin: .zero, size: targetSize))
+        }
+    }
+}