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nightshift/perf: cache decoded images to eliminate repeated disk reads #3

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22 changes: 19 additions & 3 deletions Sources/SnippetStore.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,9 @@ class SnippetStore: ObservableObject {

private let fileURL: URL
private let imagesDir: URL
/// In-memory cache — keyed by imageFileName. NSCache evicts automatically
/// under memory pressure, so this never grows unboundedly.
private let imageCache = NSCache<NSString, NSImage>()

init() {
let appSupport = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
Expand Down Expand Up @@ -70,6 +73,9 @@ class SnippetStore: ObservableObject {

do {
try pngData.write(to: fileURL)
// Prime the cache with the already-decoded image so the first
// render after adding doesn't hit disk.
imageCache.setObject(image, forKey: fileName as NSString)
let snippet = Snippet(title: "", value: "[image]", imageFileName: fileName)
snippets.insert(snippet, at: 0)
save()
Expand All @@ -83,8 +89,17 @@ class SnippetStore: ObservableObject {
}

func loadImage(for snippet: Snippet) -> NSImage? {
guard let url = imageURL(for: snippet) else { return nil }
return NSImage(contentsOf: url)
guard let name = snippet.imageFileName else { return nil }
// Return cached copy if available.
if let cached = imageCache.object(forKey: name as NSString) {
return cached
}
// Fall back to disk and populate the cache.
let url = imagesDir.appendingPathComponent(name)
guard FileManager.default.fileExists(atPath: url.path),
let image = NSImage(contentsOf: url) else { return nil }
imageCache.setObject(image, forKey: name as NSString)
return image
}

func update(_ snippet: Snippet) {
Expand All @@ -95,10 +110,11 @@ class SnippetStore: ObservableObject {
}

func delete(_ snippet: Snippet) {
// Clean up image file
// Clean up image file and cache entry.
if let name = snippet.imageFileName {
let url = imagesDir.appendingPathComponent(name)
try? FileManager.default.removeItem(at: url)
imageCache.removeObject(forKey: name as NSString)
}
snippets.removeAll { $0.id == snippet.id }
save()
Expand Down