adding writeSupport for yUnit fields (#82)

Co-authored-by: magnaw <[email protected]>

src/SpaFileReader/SpaFile.cs

@@ -121,6 +121,12 @@ public static Span<byte> ReadYUnitAsSpanByte(ref Span<byte> bytes)
         return yUnitAsBytes;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Span<byte> WriteYUnitAsSpanByte(Span<byte> bytes, Span<byte> yUnits)
+    {
+        return WriteByteAt(ref bytes, YUnitFlag, yUnits);
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static Span<float> ReadYUnitAsSpanFloat(ref Span<byte> bytes)
     {
@@ -132,6 +138,12 @@ public static Span<float> ReadYUnitAsSpanFloat(ref Span<byte> bytes)
         return yUnitAsFloats;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Span<byte> WriteYUnitAsSpanFloat(Span<byte> bytes, Span<float> yUnit)
+    {
+        return WriteByteAt(ref bytes, YUnitFlag, MemoryMarshal.Cast<float, byte>(yUnit));
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static Span<byte> ReadInterferogramAsSpanByte(ref Span<byte> bytes)
     {
@@ -236,4 +248,15 @@ public static int ReadInt32At(this ref Span<byte> data, int offset)
             ? 0
             : MemoryMarshal.Read<int>(data.Slice(offset, 4));
     }
+    private static Span<byte> WriteByteAt(this ref Span<byte> data, short expectedFlag, Span<byte> bytesToWrite)
+    {
+        var (start, length) = ReadSpecificFlagPositions(ref data, expectedFlag);
+        var n = 0;
+        for (var i = start; start + length > i; i ++)
+        {
+            data[i] = bytesToWrite[n];
+            n++;
+        }
+        return data;
+    }
 }

tests/SpaFileReader.Tests/WriterTest.cs

@@ -0,0 +1,33 @@
+namespace SpaFileReader.Tests;
+
+public class WriterTest
+{
+    private readonly byte[] _bytes;
+    private readonly byte[] _noInterferogramBytes;
+
+    public WriterTest()
+    {
+        _bytes = File.ReadAllBytes(TestFile("test1.spa"));
+        _noInterferogramBytes = File.ReadAllBytes(TestFile("test2.spa"));
+    }
+
+    [Fact]
+    public void WriteYUnitAsBytesTest()
+    {
+        var convertedSpa = SpaFile.WriteYUnitAsSpanByte(_bytes, SpaFile.ReadYUnitAsSpanByte(_noInterferogramBytes));
+        var spaToWrite = SpaFile.ReadYUnitAsFloatArray(_noInterferogramBytes);
+        var writtenSpa = SpaFile.ReadYUnitAsFloatArray(convertedSpa.ToArray());
+        Assert.Equal(spaToWrite, writtenSpa);
+    }
+
+    [Fact]
+    public void WriteYUnitAsFloatsTest()
+    {
+        var convertedSpa = SpaFile.WriteYUnitAsSpanFloat( _bytes, SpaFile.ReadYUnitAsFloatArray(_noInterferogramBytes));
+        var spaToWrite = SpaFile.ReadYUnitAsFloatArray(_noInterferogramBytes);
+        var writtenSpa = SpaFile.ReadYUnitAsFloatArray(convertedSpa.ToArray());
+        Assert.Equal(spaToWrite, writtenSpa);
+    }
+
+
+}