add MediaHash. Step1

Azaion.Common/Services/HashExtensions.cs

@@ -0,0 +1,63 @@
+using System.IO;
+using System.IO.Hashing;
+using System.Text;
+
+namespace Azaion.Common.Services;
+
+public static class HashExtensions
+{
+    private const int SampleSize = 1024;
+    private const int HashLength = 9;
+    private const string VirtualHashPrefix = "V";
+
+    public static string CalcHash(this FileInfo file)
+    {
+        if (!file.Exists)
+            return CalcVirtualHash(file.Name);
+
+        var fileSize = file.Length;
+        if (fileSize < SampleSize * 8)
+            return CalcHashInner(File.ReadAllBytes(file.FullName));
+        
+        var combinedData = new byte[8 + SampleSize * 3];
+        var offset = 0;
+
+        var fileSizeBytes = BitConverter.GetBytes(fileSize);
+        Array.Copy(fileSizeBytes, 0, combinedData, offset, 8);
+        offset += 8;
+
+        using var stream = new FileStream(file.FullName, FileMode.Open, FileAccess.Read, FileShare.Read);
+
+        stream.ReadExactly(combinedData, offset, SampleSize);
+        offset += SampleSize;
+
+        stream.Position = (fileSize - SampleSize) / 2;
+        stream.ReadExactly(combinedData, offset, SampleSize);
+        offset += SampleSize;
+
+        stream.Position = fileSize - SampleSize;
+        stream.ReadExactly(combinedData, offset, SampleSize);
+
+        return CalcHashInner(combinedData);
+    }
+
+    public static string CalcVirtualHash(string filename)
+    {
+        var bytes = Encoding.UTF8.GetBytes($"VIRTUAL:{filename}");
+        var hash = XxHash64.HashToUInt64(bytes);
+        var hashBytes = BitConverter.GetBytes(hash);
+        var base64 = Convert.ToBase64String(hashBytes);
+        return VirtualHashPrefix + base64[..HashLength];
+    }
+
+    public static bool IsVirtualHash(this string? hash) => 
+        !string.IsNullOrEmpty(hash) && hash.StartsWith(VirtualHashPrefix);
+
+    private static string CalcHashInner(byte[] data)
+    {
+        var hash = XxHash64.HashToUInt64(data);
+        var hashBytes = BitConverter.GetBytes(hash);
+        var base64 = Convert.ToBase64String(hashBytes);
+        return base64[..HashLength];
+    }
+}