From d4ef0dc34e0613db9c4a333ea73f792b2dd70fae Mon Sep 17 00:00:00 2001
From: Alex Macocian <amacocian@yahoo.com>
Date: Sun, 8 Sep 2024 18:37:38 +0200
Subject: [PATCH] Base32 conversions

---
 .../SystemExtensions.NetCore.csproj           |   2 +-
 .../Encoding/Base32.cs                        | 128 ++++++++++++++++++
 .../SystemExtensions.NetStandard.csproj       |   2 +-
 3 files changed, 130 insertions(+), 2 deletions(-)
 create mode 100644 SystemExtensions.NetStandard/Encoding/Base32.cs

diff --git a/SystemExtensions.NetCore/SystemExtensions.NetCore.csproj b/SystemExtensions.NetCore/SystemExtensions.NetCore.csproj
index ebc91b2..cd68814 100644
--- a/SystemExtensions.NetCore/SystemExtensions.NetCore.csproj
+++ b/SystemExtensions.NetCore/SystemExtensions.NetCore.csproj
@@ -8,7 +8,7 @@
     <RootNamespace>System</RootNamespace>
 	  <PackageLicenseFile>LICENSE</PackageLicenseFile>
 	  <PackageRequireLicenseAcceptance>true</PackageRequireLicenseAcceptance>
-	  <Version>1.6.7</Version>
+	  <Version>1.6.8</Version>
 	  <Authors>Alexandru Macocian</Authors>
 	  <RepositoryUrl>https://github.com/AlexMacocian/SystemExtensions</RepositoryUrl>
 	  <Description>Extensions for the System namespace</Description>
diff --git a/SystemExtensions.NetStandard/Encoding/Base32.cs b/SystemExtensions.NetStandard/Encoding/Base32.cs
new file mode 100644
index 0000000..f6779f6
--- /dev/null
+++ b/SystemExtensions.NetStandard/Encoding/Base32.cs
@@ -0,0 +1,128 @@
+namespace System.Extensions;
+
+/// <summary>
+/// https://stackoverflow.com/questions/641361/base32-decoding
+/// </summary>
+public static partial class Convert
+{
+    public static byte[] FromBase32String(string input)
+    {
+        if (string.IsNullOrEmpty(input))
+        {
+            throw new ArgumentNullException("input");
+        }
+
+        input = input.TrimEnd('='); //remove padding characters
+        var byteCount = input.Length * 5 / 8; //this must be TRUNCATED
+        var returnArray = new byte[byteCount];
+
+        byte curByte = 0, bitsRemaining = 8;
+        int arrayIndex = 0;
+
+        foreach (var c in input)
+        {
+            var cValue = CharToValue(c);
+            int mask;
+            if (bitsRemaining > 5)
+            {
+                mask = cValue << (bitsRemaining - 5);
+                curByte = (byte)(curByte | mask);
+                bitsRemaining -= 5;
+            }
+            else
+            {
+                mask = cValue >> (5 - bitsRemaining);
+                curByte = (byte)(curByte | mask);
+                returnArray[arrayIndex++] = curByte;
+                curByte = (byte)(cValue << (3 + bitsRemaining));
+                bitsRemaining += 3;
+            }
+        }
+
+        //if we didn't end with a full byte
+        if (arrayIndex != byteCount)
+        {
+            returnArray[arrayIndex] = curByte;
+        }
+
+        return returnArray;
+    }
+
+    public static string ToBase32String(byte[] input)
+    {
+        if (input == null || input.Length == 0)
+        {
+            throw new ArgumentNullException("input");
+        }
+
+        var charCount = (int)Math.Ceiling(input.Length / 5d) * 8;
+        var returnArray = new char[charCount];
+
+        byte nextChar = 0, bitsRemaining = 5;
+        var arrayIndex = 0;
+
+        foreach (var b in input)
+        {
+            nextChar = (byte)(nextChar | (b >> (8 - bitsRemaining)));
+            returnArray[arrayIndex++] = ValueToChar(nextChar);
+
+            if (bitsRemaining < 4)
+            {
+                nextChar = (byte)((b >> (3 - bitsRemaining)) & 31);
+                returnArray[arrayIndex++] = ValueToChar(nextChar);
+                bitsRemaining += 5;
+            }
+
+            bitsRemaining -= 3;
+            nextChar = (byte)((b << bitsRemaining) & 31);
+        }
+
+        //if we didn't end with a full char
+        if (arrayIndex != charCount)
+        {
+            returnArray[arrayIndex++] = ValueToChar(nextChar);
+            while (arrayIndex != charCount) returnArray[arrayIndex++] = '='; //padding
+        }
+
+        return new string(returnArray);
+    }
+
+    private static int CharToValue(char c)
+    {
+        var value = (int)c;
+
+        //65-90 == uppercase letters
+        if (value < 91 && value > 64)
+        {
+            return value - 65;
+        }
+        //50-55 == numbers 2-7
+        if (value < 56 && value > 49)
+        {
+            return value - 24;
+        }
+        //97-122 == lowercase letters
+        if (value < 123 && value > 96)
+        {
+            return value - 97;
+        }
+
+        throw new ArgumentException($"Character {c} is not a Base32 character.");
+    }
+
+    private static char ValueToChar(byte b)
+    {
+        if (b < 26)
+        {
+            return (char)(b + 65);
+        }
+
+        if (b < 32)
+        {
+            return (char)(b + 24);
+        }
+
+        throw new ArgumentException($"Byte {b} is not a value Base32 value.");
+    }
+
+}
diff --git a/SystemExtensions.NetStandard/SystemExtensions.NetStandard.csproj b/SystemExtensions.NetStandard/SystemExtensions.NetStandard.csproj
index 0347364..6e1456a 100644
--- a/SystemExtensions.NetStandard/SystemExtensions.NetStandard.csproj
+++ b/SystemExtensions.NetStandard/SystemExtensions.NetStandard.csproj
@@ -7,7 +7,7 @@
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <PackageRequireLicenseAcceptance>true</PackageRequireLicenseAcceptance>
     <RootNamespace>System</RootNamespace>
-    <Version>1.6.7</Version>
+    <Version>1.6.8</Version>
     <Authors>Alexandru Macocian</Authors>
     <RepositoryUrl>https://github.com/AlexMacocian/SystemExtensions</RepositoryUrl>
     <Description>Extensions for the System namespace</Description>