Scale down cover images

This brings memory usage (for my music library) down from 2+GB to less
than 300MB. 👍🏼

Persephone/Extensions/NSImage.swift

@@ -13,4 +13,24 @@ extension NSImage {
   static let pauseIcon = NSImage(named: "pauseButton")
 
   static let defaultCoverArt = NSImage(named: "blankAlbum")
+
+  func toFitBox(size: NSSize) -> NSImage {
+    let newImage = NSImage(size: size)
+    newImage.lockFocus()
+    self.draw(in: newImage.alignmentRect)
+    newImage.unlockFocus()
+    return newImage
+  }
+
+  func jpegData(compressionQuality: CGFloat) -> Data? {
+    guard let image = cgImage(forProposedRect: nil, context: nil, hints: nil)
+      else { return nil }
+
+    let bitmapImageRep = NSBitmapImageRep(cgImage: image)
+
+    return bitmapImageRep.representation(
+      using: .jpeg,
+      properties: [.compressionFactor: compressionQuality]
+    )
+  }
 }

Persephone/Services/AlbumArtService.swift

@@ -76,8 +76,15 @@ class AlbumArtService: NSObject {
           if FileManager.default.fileExists(atPath: coverArtURI),
             let data = FileManager.default.contents(atPath: coverArtURI),
             let image = NSImage(data: data) {
-            self.cacheArtwork(for: album, data: data)
+
-            callback(image)
+            let imageThumb = image.toFitBox(
+              size: NSSize(width: 180, height: 180)
+            )
+            self.cacheArtwork(
+              for: album,
+              data: imageThumb.jpegData(compressionQuality: 0.5)
+            )
+            callback(imageThumb)
             break
           }
         }
@@ -85,7 +92,7 @@ class AlbumArtService: NSObject {
     )
   }
 
-  func cacheArtwork(for album: AlbumItem, data: Data) {
+  func cacheArtwork(for album: AlbumItem, data: Data?) {
     guard let bundleIdentifier = Bundle.main.bundleIdentifier,
       let cacheDir = try? FileManager.default.url(for: .cachesDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
         .appendingPathComponent(bundleIdentifier)