Refactoring.

Source/ID3TagEditor.swift

@@ -68,46 +68,9 @@ public class ID3TagEditor {
      ID3 tag).
      */
     public func write(tag: ID3Tag, to path: String, andSaveTo newPath: String? = nil) throws {
-        guard let newPath else {
-            let mp3 = try mp3FileReader.readFileFrom(path: path)
-            let currentTag = try self.id3TagParser.parse(mp3: mp3)
-            let mp3WithId3Tag = try mp3WithID3TagBuilder.build(mp3: mp3, newId3Tag: tag, currentId3Tag: currentTag)
-            try mp3FileWriter.write(mp3: mp3WithId3Tag, path: path)
-            return
-        }
-
-        let currentTag = try read(from: path)
-        let newTag = try ID3TagCreatorFactory.make().create(id3Tag: tag)
-        try mp3FileWriter.write(mp3: newTag, path: newPath)
-
-        // Create file handles
-        let readHandle = try FileHandle(forReadingFrom: URL(fileURLWithPath: path))
-        defer {
-            readHandle.closeFile()
-        }
-
-        let writeHandle = try FileHandle(forWritingTo: URL(fileURLWithPath: newPath))
-        defer {
-            writeHandle.closeFile()
-        }
-
-        // Seek over the tag of the existing file, then copy the rest in chunks
-        readHandle.seek(toFileOffset: 0)
-        writeHandle.seekToEndOfFile()
-
-        if let currentTag {
-            let tagSizeWithHeader = UInt64(currentTag.properties.size) + UInt64(ID3TagConfiguration().headerSize())
-            readHandle.seek(toFileOffset: tagSizeWithHeader)
-        }
-
-        var isFinished = false
-        while !isFinished {
-            autoreleasepool {
-                let chunk = readHandle.readData(ofLength: 65536) // 64 KB
-                writeHandle.write(chunk)
-                isFinished = chunk.isEmpty
-            }
-        }
+        let newId3TagData = try mp3WithID3TagBuilder.build(mp3: Data(), newId3Tag: tag, currentId3Tag: nil)
+        let currentId3Tag = try read(from: path)
+        try mp3FileWriter.write(newId3TagData: newId3TagData, currentId3Tag: currentId3Tag, fromPath: path, toPath: newPath ?? path)
     }
 
     /**

Source/Mp3/Mp3FileWriter.swift

@@ -8,9 +8,59 @@
 import Foundation
 
 class Mp3FileWriter {
-    func write(mp3: Data, path: String) throws {
-        try eventuallyCreateIntermediatesDirectoriesFor(path: path)
-        try mp3.write(to: URL(fileURLWithPath: path))
+    func write(newId3TagData: Data, currentId3Tag: ID3Tag?, fromPath: String, toPath: String) throws {
+        // Create a temporary file for the new mp3
+        let temporaryPath = {
+            if toPath != fromPath {
+                return toPath
+            }
+
+            return FileManager.default.temporaryDirectory.appendingPathComponent("\(UUID().uuidString).mp3").path
+        }()
+
+        defer {
+            if temporaryPath != toPath {
+                try? FileManager.default.removeItem(atPath: temporaryPath)
+            }
+        }
+
+        try eventuallyCreateIntermediatesDirectoriesFor(path: temporaryPath)
+        try newId3TagData.write(to: URL(fileURLWithPath: temporaryPath))
+
+        // Create file handles
+        let readHandle = try FileHandle(forReadingFrom: URL(fileURLWithPath: fromPath))
+        defer {
+            readHandle.closeFile()
+        }
+
+        let writeHandle = try FileHandle(forWritingTo: URL(fileURLWithPath: temporaryPath))
+        defer {
+            writeHandle.closeFile()
+        }
+
+        // Seek over the tag of the existing file, then copy the rest in chunks
+        writeHandle.seekToEndOfFile()
+
+        if let validCurrentId3Tag = currentId3Tag {
+            let tagSizeWithHeader = UInt64(validCurrentId3Tag.properties.size) + UInt64(ID3TagConfiguration().headerSize())
+            readHandle.seek(toFileOffset: tagSizeWithHeader)
+        } else {
+            readHandle.seek(toFileOffset: 0)
+        }
+
+        var isFinished = false
+        while !isFinished {
+            autoreleasepool {
+                let chunk = readHandle.readData(ofLength: 65536) // 64 KB
+                writeHandle.write(chunk)
+                isFinished = chunk.isEmpty
+            }
+        }
+
+        // Replace the file
+        if temporaryPath != toPath {
+            _ = try FileManager.default.replaceItemAt(URL(fileURLWithPath: toPath), withItemAt: URL(fileURLWithPath: temporaryPath))
+        }
     }
 
     private func eventuallyCreateIntermediatesDirectoriesFor(path: String) throws {

Source/Mp3/Mp3WithID3TagBuilder.swift

@@ -22,7 +22,9 @@ class Mp3WithID3TagBuilder {
             tagSizeWithHeader = Int(validCurrentId3Tag.properties.size) + ID3TagConfiguration().headerSize()
         }
         var mp3WithTag = try id3TagCreator.create(id3Tag: newId3Tag)
-        mp3WithTag.append(mp3.subdata(in: tagSizeWithHeader..<mp3.count))
+        if !mp3.isEmpty {
+            mp3WithTag.append(mp3.subdata(in: tagSizeWithHeader..<mp3.count))
+        }
         return mp3WithTag
     }
 }