Refactor to allow previews without WebKit

- Add `PreviewVC` protocol which can be implemented by any
`ViewController` to generate previews for a specific file type
- Re-implement CSV previews with `NSTableView`
- Update code style: Capitalize acronyms, abbreviate "ViewController"
with "VC"
- Rename `Asset` protocol to `WebAsset`

QLPlugin/Info.plist

@@ -191,7 +191,7 @@
  <key>NSExtensionPointIdentifier</key>
  <string>com.apple.quicklook.preview</string>
  <key>NSExtensionPrincipalClass</key>
- <string>$(PRODUCT_MODULE_NAME).PreviewViewController</string>
+ <string>$(PRODUCT_MODULE_NAME).MainVC</string>
  </dict>
  <key>NSHumanReadableCopyright</key>
  <string>Copyright © 2020 Samuel Meuli. All rights reserved.</string>

QLPlugin/MainVC.swift

@@ -0,0 +1,96 @@
+import Cocoa
+import os.log
+import Quartz
+
+enum PreviewError: Error {
+ case fileSizeError(path: String)
+}
+
+extension PreviewError: LocalizedError {
+ public var errorDescription: String? {
+ switch self {
+ case let .fileSizeError(path):
+ return NSLocalizedString("File \(path) is too large to preview", comment: "")
+ }
+ }
+}
+
+class MainVC: NSViewController, QLPreviewingController {
+ /// Max size of files to render
+ let maxFileSize = 100_000 // 100000 B = 100 KB
+
+ let stats = Stats()
+
+ override var nibName: NSNib.Name? {
+ NSNib.Name("MainVC")
+ }
+
+ override func viewDidLoad() {
+ super.viewDidLoad()
+ configureView()
+ }
+
+ private func configureView() {
+ // Draw border around previews, in similar style to macOS's default previews
+ view.wantsLayer = true
+ view.layer?.borderWidth = 1
+ view.layer?.borderColor = NSColor.tertiaryLabelColor.cgColor
+ }
+
+ /// Function responsible for generating file previews. It's called for previews in Finder,
+ /// Spotlight, Quick Look and any other UI elements which implement the API
+ func preparePreviewOfFile(
+ at fileUrl: URL,
+ completionHandler handler: @escaping (Error?) -> Void
+ ) {
+ // Read information about the file to preview
+ var file: File
+ do {
+ file = try File(url: fileUrl)
+ } catch {
+ handler(error)
+ return
+ }
+
+ // Skip preview if the file is too large
+ if !file.isDirectory, file.size > maxFileSize {
+ // Log error and fall back to default preview (by calling the completion handler with
+ // the error)
+ handler(PreviewError.fileSizeError(path: file.path))
+ return
+ }
+
+ // Render file preview
+ os_log("Generating preview for file %s", type: .debug, fileUrl.path)
+ do {
+ try previewFile(file: file)
+ } catch {
+ // Log error and fall back to default preview (by calling the completion handler with
+ // the error)
+ handler(error)
+ return
+ }
+
+ // Update stats
+ stats.increaseStatsCounts(fileExtension: file.url.pathExtension)
+
+ // Hide preview loading spinner
+ handler(nil)
+ }
+
+ /// Generates a preview of the selected file and adds the corresponding child view controller
+ private func previewFile(file: File) throws {
+ // Initialize `PreviewVC` for the file type
+ let previewVCType = PreviewVCFactory.getView(fileExtension: file.url.pathExtension)
+ let previewVC = previewVCType.init(file: file)
+
+ // Generate file preview
+ try previewVC.loadPreview()
+
+ // Add `PreviewVC` as a child view controller
+ addChild(previewVC)
+ previewVC.view.autoresizingMask = [.height, .width]
+ previewVC.view.frame = view.frame
+ view.addSubview(previewVC.view)
+ }
+}

QLPlugin/MainVC.xib

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="16096" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
+ <dependencies>
+ <deployment identifier="macosx"/>
+ <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="16096"/>
+ <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
+ </dependencies>
+ <objects>
+ <customObject id="-2" userLabel="File's Owner" customClass="MainVC" customModule="QLPlugin" customModuleProvider="target">
+ <connections>
+ <outlet property="view" destination="c22-O7-iKe" id="NRM-P4-wb6"/>
+ </connections>
+ </customObject>
+ <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
+ <customObject id="-3" userLabel="Application" customClass="NSObject"/>
+ <customView translatesAutoresizingMaskIntoConstraints="NO" id="c22-O7-iKe" userLabel="Preview View">
+ <rect key="frame" x="0.0" y="0.0" width="480" height="272"/>
+ <point key="canvasLocation" x="139" y="154"/>
+ </customView>
+ </objects>
+</document>