[feat]: image comparison

Author: DanielCech

Sources/ScriptToolkit/DataExtension.swift

@@ -0,0 +1,31 @@
+//
+//  DataExtension.swift
+//  ScriptToolkit
+//
+//  Created by Daniel Cech on 20/07/2020.
+//
+
+import Foundation
+
+extension Data {
+    func indexOf(data: Data) -> Data.Index? {
+        var selfIndex = self.startIndex
+        var dataIndex = data.startIndex
+        
+        while selfIndex <= self.endIndex && dataIndex <= data.endIndex {
+            if dataIndex == data.endIndex {
+                return selfIndex - data.count
+            }
+            
+            if self[selfIndex] == data[dataIndex] {
+                dataIndex += 1
+            }
+            else {
+                dataIndex = data.startIndex
+            }
+            selfIndex += 1
+        }
+        
+        return nil
+    }
+}

Sources/ScriptToolkit/NSImageExtension.swift

@@ -58,20 +58,26 @@ public extension NSImage {
         // Return nil in case something went wrong.
         throw ScriptError.generalError(message: "Unable to resize image")
     }
+    
+    func areImagesSame(firstPNGData: Data, secondPNGData: Data) -> Bool {
+        let sequence = Data([0x6C, 0x65, 0x58, 0x49, 0x66])
+
+        let firstOffset = firstPNGData.indexOf(data: sequence)!
+        let firstSubdata = firstPNGData.subdata(in: firstOffset ..< firstPNGData.endIndex)
+
+        let secondOffset = secondPNGData.indexOf(data: sequence)!
+        let secondSubdata = secondPNGData.subdata(in: secondOffset ..< secondPNGData.endIndex)
+        
+        return firstSubdata == secondSubdata
+    }
 
     ///  Saves the PNG representation of the current image to the HD.
     ///
     /// - parameter url: The location url to which to write the png file.
     func savePNGRepresentationToURL(url: URL, onlyChange: Bool = true) throws {
         if let pngData = self.PNGRepresentation {
             if let originalData = try? Data(contentsOf: url) {
-                
-                // The beginning of PNG contains some data that may differ - a header
-                let originalSubdata = originalData.subdata(in: 175 ..< originalData.endIndex)
-                let pngSubdata = pngData.subdata(in: 175 ..< pngData.endIndex)
-                
-                
-                if onlyChange && (pngSubdata == originalSubdata) {
+                if onlyChange && areImagesSame(firstPNGData: pngData, secondPNGData: originalData) {
                     return
                 }
             }