Added basic data handler for mmap

Sources/SwiftNLP/1. Data Collection/HNSWCorpusDataHandler.swift

@@ -8,8 +8,7 @@
 import Foundation
 
 final class HNSWCorpusDataHandler<Scalar: BinaryFloatingPoint & Codable> {
-    private var corpus: HNSWCorpus<Scalar>
-    private var mmapURL: URL? // set default URL
+    var corpus: HNSWCorpus<Scalar>
     
     init(corpus: HNSWCorpus<Scalar>) {
         self.corpus = corpus
@@ -17,11 +16,55 @@ final class HNSWCorpusDataHandler<Scalar: BinaryFloatingPoint & Codable> {
 }
 
 extension HNSWCorpusDataHandler {
-    func saveMemoryMap() {
-        
+    func saveMemoryMap(url: URL) {
+        let fileManager = FileManager.default
+        if !fileManager.fileExists(atPath: url.path) {
+            fileManager.createFile(atPath: url.path, contents: nil, attributes: nil)
+        }
+        do {
+            let fileHandle = try FileHandle(forWritingTo: url)
+            
+            let count = corpus.count
+            let countData = withUnsafeBytes(of: count) { Data($0) }
+            fileHandle.write(countData)
+            
+            // TODO: We may need to edit the HNSWCorpus iterator to actually iterate over its dictionary as it would be useful here
+            let data = corpus.getDictionary()
+            for (key, documentVectorPair) in data {
+                let documentData = documentVectorPair.untokenizedDocument.utf8CString.withUnsafeBufferPointer { Data(buffer: $0) }
+                fileHandle.write(documentData)
+            }
+            fileHandle.closeFile()
+        } catch {
+            print("Error writing HNSW to file: \(error)")
+        }
     }
     
-    func loadMemoryMap() {
+    // TODO: Change the return from Double to Scalar
+    func loadMemoryMap(url: URL, encoder: any SNLPEncoder) -> HNSWCorpus<Double> {
+        var loadedCorpus = HNSWCorpus(encoder: encoder)
         
+        do {
+            let data = try Data(contentsOf: url, options: .alwaysMapped)
+            let countData = data.prefix(MemoryLayout<Int>.size)
+            let count: Int = countData.withUnsafeBytes { $0.load(as: Int.self) }
+            var index = MemoryLayout<Int>.size
+
+            for _ in 0..<count {
+                if let stringRange = data[index...].range(of: "\0".data(using: .utf8)!) {
+                    let documentData = data[index..<stringRange.lowerBound]
+                    if let document = String(data: documentData, encoding: .utf8) {
+                        // Add the untokenized document to the corpus
+                        loadedCorpus.addUntokenizedDocument(document)
+                        index = stringRange.upperBound
+                    }
+                } else {
+                    break
+                }
+            }
+        } catch {
+            print("Error reading HNSW from file: \(error)")
+        }
+        return loadedCorpus
     }
 }