From 3a7930088713a66c84ff3d276fb0da2ba3762d6f Mon Sep 17 00:00:00 2001
From: yoshikazu <yoshikazu@yfox.jp>
Date: Mon, 27 Jul 2026 15:41:29 +0000
Subject: [PATCH] Add thumbnail loader

---
 .../Photochk/Services/ThumbnailLoader.swift   | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 Sources/Photochk/Services/ThumbnailLoader.swift

diff --git a/Sources/Photochk/Services/ThumbnailLoader.swift b/Sources/Photochk/Services/ThumbnailLoader.swift
new file mode 100644
index 0000000..829d6d9
--- /dev/null
+++ b/Sources/Photochk/Services/ThumbnailLoader.swift
@@ -0,0 +1,46 @@
+import AppKit
+import Foundation
+import QuickLookThumbnailing
+
+/// サムネイル生成。QuickLook 任せなので HEIC や RAW もそのまま扱える。
+@MainActor
+final class ThumbnailLoader {
+    static let shared = ThumbnailLoader()
+
+    private let cache = NSCache<NSString, NSImage>()
+
+    private init() {
+        cache.countLimit = 600
+    }
+
+    /// すでに読み込み済みなら即座に返す。スクロールで戻ってきたときに
+    /// 一瞬プレースホルダが出るのを防ぐために使う。
+    func cached(for url: URL, size: CGFloat) -> NSImage? {
+        cache.object(forKey: Self.key(url, size))
+    }
+
+    func thumbnail(for url: URL, size: CGFloat) async -> NSImage? {
+        let key = Self.key(url, size)
+        if let cached = cache.object(forKey: key) { return cached }
+
+        let scale = NSScreen.main?.backingScaleFactor ?? 2
+        let request = QLThumbnailGenerator.Request(
+            fileAt: url,
+            size: CGSize(width: size, height: size),
+            scale: scale,
+            representationTypes: .thumbnail
+        )
+
+        guard let representation = try? await QLThumbnailGenerator.shared
+            .generateBestRepresentation(for: request)
+        else { return nil }
+
+        let image = NSImage(cgImage: representation.cgImage, size: representation.contentRect.size)
+        cache.setObject(image, forKey: key)
+        return image
+    }
+
+    private static func key(_ url: URL, _ size: CGFloat) -> NSString {
+        "\(url.path)|\(Int(size))" as NSString
+    }
+}