// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Linq;
using System.Numerics;
using Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure;
using Microsoft.AspNetCore.InternalTesting;
using Xunit;
 
namespace Microsoft.AspNetCore.Server.Kestrel.Core.Tests;
 
public class AsciiDecodingTests
{
    [Fact]
    private void FullAsciiRangeSupported()
    {
        var byteRange = Enumerable.Range(1, 127).Select(x => (byte)x);
 
        var byteArray = byteRange
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .ToArray();
 
        var span = new Span<byte>(byteArray);
 
        for (var i = 0; i <= byteArray.Length; i++)
        {
            // Test all the lengths to hit all the different length paths e.g. Vector, long, short, char
            Test(span.Slice(i));
        }
 
        static void Test(Span<byte> asciiBytes)
        {
            var s = asciiBytes.GetAsciiString();
 
            Assert.True(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, asciiBytes));
            Assert.Equal(s.Length, asciiBytes.Length);
 
            for (var i = 0; i < asciiBytes.Length; i++)
            {
                var sb = (byte)s[i];
                var b = asciiBytes[i];
 
                Assert.Equal(sb, b);
            }
        }
    }
 
    [Fact]
    private void ExceptionThrownForNonAscii()
    {
        byte b = 0x80;
        for (var length = 1; length < Vector<sbyte>.Count * 4; length++)
        {
            for (var position = 0; position < length; position++)
            {
                var byteRange = Enumerable.Range(1, length).Select(x => (byte)x).ToArray();
                byteRange[position] = b;
 
                Assert.Throws<InvalidOperationException>(() => new Span<byte>(byteRange).GetAsciiString());
            }
        }
    }
 
    [Fact]
    private void LargeAllocationProducesCorrectResults()
    {
        var byteRange = Enumerable.Range(0, 16384 + 64).Select(x => (byte)((x & 0x7f) | 0x01)).ToArray();
        var expectedByteRange = byteRange.Concat(byteRange).ToArray();
 
        var span = new Span<byte>(expectedByteRange);
        var s = span.GetAsciiString();
 
        Assert.Equal(expectedByteRange.Length, s.Length);
 
        for (var i = 0; i < expectedByteRange.Length; i++)
        {
            var sb = (byte)((s[i] & 0x7f) | 0x01);
            var b = expectedByteRange[i];
        }
 
        Assert.True(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, span));
    }
 
    [Fact]
    private void DifferentLengthsAreNotEqual()
    {
        var byteRange = Enumerable.Range(0, 4096).Select(x => (byte)((x & 0x7f) | 0x01)).ToArray();
        var expectedByteRange = byteRange.Concat(byteRange).ToArray();
 
        for (var i = 1; i < byteRange.Length; i++)
        {
            var span = new Span<byte>(expectedByteRange);
            var s = span.GetAsciiString();
 
            Assert.True(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, span));
 
            // One off end
            Assert.False(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, span.Slice(0, span.Length - 1)));
            Assert.False(StringUtilities.BytesOrdinalEqualsStringAndAscii(s.Substring(0, s.Length - 1), span));
 
            // One off start
            Assert.False(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, span.Slice(1, span.Length - 1)));
            Assert.False(StringUtilities.BytesOrdinalEqualsStringAndAscii(s.Substring(1, s.Length - 1), span));
        }
    }
 
    [Fact]
    private void AsciiBytesEqualAsciiStrings()
    {
        var byteRange = Enumerable.Range(1, 127).Select(x => (byte)x);
 
        var byteArray = byteRange
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .Concat(byteRange)
            .ToArray();
 
        var span = new Span<byte>(byteArray);
 
        for (var i = 0; i <= byteArray.Length; i++)
        {
            // Test all the lengths to hit all the different length paths e.g. Vector, long, short, char
            Test(span.Slice(i));
        }
 
        static void Test(Span<byte> asciiBytes)
        {
            var s = asciiBytes.GetAsciiString();
 
            // Should start as equal
            Assert.True(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, asciiBytes));
 
            for (var i = 0; i < asciiBytes.Length; i++)
            {
                var b = asciiBytes[i];
 
                // Change one byte, ensure is not equal
                asciiBytes[i] = (byte)(b + 1);
                Assert.False(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, asciiBytes));
 
                // Change byte back for next iteration, ensure is equal again
                asciiBytes[i] = b;
                Assert.True(StringUtilities.BytesOrdinalEqualsStringAndAscii(s, asciiBytes), s);
            }
        }
    }
}