// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
 
namespace Microsoft.Build.Framework;
 
internal static class StringUtils
{
    /// <summary>
    /// Generates a random string of the specified length.
    /// The generated string is suitable for use in file paths.
    /// The randomness distribution is given by the System.Random.
    /// </summary>
    /// <param name="length"></param>
    /// <returns></returns>
    internal static string GenerateRandomString(int length)
    {
        // Base64, 2^6 = 64
        const int eachStringCharEncodesBites = 6;
        const int eachByteHasBits = 8;
        const double bytesNumNeededForSingleStringChar = eachStringCharEncodesBites / (double)eachByteHasBits;
 
        int randomBytesNeeded = (int)Math.Ceiling(length * bytesNumNeededForSingleStringChar);
        Random random = new();
 
        byte[] randomBytes = new byte[randomBytesNeeded];
        random.NextBytes(randomBytes);
        // Base64: [A-Z], [a-z], [0-9], +, /, =
        // We are replacing '/' to get a valid path
        string randomBase64String = Convert.ToBase64String(randomBytes).Replace('/', '_');
        return randomBase64String.Substring(0, length);
    }
}