using System;
using Server.Network;
using Xunit;

namespace Server.Tests.Network;

/// <summary>
/// Known-answer test for outgoing huffman compression.
/// The table is a contract with the client's hard-coded decompression tree, so a single wrong
/// entry -- or a subtle bit-packing error in a future rewrite of <see cref="NetworkCompression.Compress"/> --
/// silently corrupts every affected packet and desyncs the client's framing with no error.
/// A round-trip test cannot catch that, since encoder and decoder would share the same mistake.
/// The expected bytes below were generated from the canonical table, not from the implementation.
/// </summary>
public class NetworkCompressionTests
{
    // Every symbol 0x00-0xFF exactly once. Any single wrong table entry changes these bytes, so this
    // pins all 256 entries plus the terminal code, and exercises the encoder end to end.
    private static ReadOnlySpan<byte> AllSymbolsCompressed =>
    [
        0x3F, 0x13, 0x4E, 0xB4, 0x76, 0xCB, 0x81, 0x8A, 0xB3, 0xCE, 0x76, 0x5E,
        0xAA, 0xEE, 0x2B, 0x7C, 0xCA, 0x74, 0xB3, 0xD9, 0x9F, 0x72, 0x3C, 0xE7,
        0xE9, 0x05, 0x97, 0xB9, 0x1C, 0x6B, 0x70, 0xCD, 0xE9, 0x37, 0x31, 0x69,
        0xAE, 0x70, 0x29, 0x14, 0xA4, 0x13, 0x3F, 0x71, 0x90, 0x39, 0xDF, 0x3A,
        0x5C, 0x03, 0x20, 0x9D, 0x86, 0x4B, 0x33, 0xCA, 0xDC, 0xF9, 0x48, 0x6F,
        0x4B, 0x6F, 0xD8, 0x8B, 0x42, 0xAA, 0x5A, 0x73, 0x87, 0x9C, 0x47, 0xE3,
        0xD2, 0x28, 0x76, 0x35, 0xDD, 0x12, 0xD6, 0x46, 0x7B, 0xBD, 0x68, 0x4B,
        0x25, 0xD7, 0x9A, 0xBC, 0x88, 0x95, 0xDC, 0xA1, 0x48, 0xD9, 0xD4, 0x71,
        0xE1, 0x78, 0x30, 0xEE, 0xE3, 0xBF, 0xD3, 0x3F, 0x1B, 0xC9, 0xE5, 0xD4,
        0xE1, 0x40, 0x83, 0x0B, 0x58, 0x35, 0x60, 0xF1, 0xF1, 0x63, 0x4C, 0x86,
        0xED, 0x9A, 0x6A, 0x2A, 0xFC, 0x96, 0x75, 0x26, 0xC0, 0xDD, 0x33, 0xDC,
        0xFB, 0x97, 0x29, 0x84, 0x93, 0x30, 0x6C, 0x90, 0xFA, 0x1C, 0x14, 0x75,
        0x63, 0xE1, 0x7D, 0xB5, 0xF5, 0x06, 0xE5, 0xE4, 0xE5, 0xD3, 0x19, 0xE6,
        0x5C, 0xF4, 0xAF, 0xFD, 0xF7, 0x77, 0x2D, 0xBB, 0x70, 0xB4, 0x1E, 0xE8,
        0xF7, 0x92, 0x57, 0xA1, 0xD2, 0xE6, 0xB6, 0xB6, 0x58, 0xCA, 0xE1, 0x75,
        0xCF, 0x19, 0xF1, 0x40, 0xB4, 0xD4, 0x91, 0x66, 0xC7, 0x6F, 0x16, 0x51,
        0xBA, 0x65, 0x2F, 0x53, 0xA0, 0x72, 0x31, 0xE3, 0x92, 0x7A, 0xB1, 0x9D,
        0x98, 0xE4, 0x1B, 0xB7, 0x42, 0xF1, 0x21, 0x18, 0x0E, 0x55, 0x18, 0xBE,
        0x0A, 0x6D, 0xEB, 0xC0, 0x4E, 0xB6, 0x13, 0x94, 0xF2, 0xC8, 0xF6, 0x3F,
        0xCB, 0xD1, 0xCE, 0x13, 0x1C, 0x5F, 0x30, 0xAB, 0x82, 0x76, 0x94, 0x1F,
        0x1F, 0x2C, 0xC7, 0xC0, 0x90, 0x34, 0x61, 0x32, 0xC2, 0x51, 0xF3, 0xAC,
        0x72, 0x6F, 0x85, 0xDE, 0x7A, 0xD8, 0xEB, 0xE5, 0x7C, 0x90, 0x3B, 0xC7,
        0x9D, 0xDE, 0xA6, 0x02, 0xC5, 0xED, 0x24, 0x8D, 0xA4, 0xC9, 0x9E, 0xBA,
        0x2D, 0x7F, 0x3D, 0x27, 0xB7, 0x39, 0x25, 0xB9, 0x59, 0xE1, 0x08, 0xE9,
        0xB8, 0x75, 0xEC, 0x75, 0xD9, 0x8B, 0x40
    ];

    [Fact]
    public void Compress_EncodesEverySymbol_MatchingCanonicalTable()
    {
        Span<byte> input = stackalloc byte[256];
        for (var i = 0; i < input.Length; i++)
        {
            input[i] = (byte)i;
        }

        Span<byte> output = stackalloc byte[512];
        var length = NetworkCompression.Compress(input, output);

        Assert.Equal(AllSymbolsCompressed.Length, length);

        var expected = AllSymbolsCompressed;
        for (var i = 0; i < expected.Length; i++)
        {
            Assert.True(expected[i] == output[i], $"Byte {i}: expected 0x{expected[i]:X2}, got 0x{output[i]:X2}");
        }
    }
}