using System;
using System.Buffers.Binary;
using System.Text;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Inbound <c>0x02BB HearSpeech</c> + <c>0x02BC HearRangedSpeech</c>
/// GameMessages. Local-area / shout chat heard by the player. These
/// do NOT ride the 0xF7B0 GameEvent envelope — they're standalone
/// GameMessages dispatched the same way as CreateObject / UpdateMotion.
///
/// <para>
/// Wire layout:
/// <code>
///   u32 opcode               // 0x02BB or 0x02BC
///   string16L text
///   string16L senderName
///   u32 senderGuid
///   u32 chatType
/// </code>
/// </para>
///
/// <para>
/// ChatType (from ACE):
/// <list type="bullet">
///   <item><description>0x01 = Broadcast</description></item>
///   <item><description>0x02 = Combat</description></item>
///   <item><description>0x0B = Speech</description></item>
///   <item><description>0x0F = Emote</description></item>
///   <item><description>0x10 = Tell</description></item>
///   <item><description>0x11 = Syllables (spell casting)</description></item>
///   <item><description>other values in ACE ChatMessageType.cs</description></item>
/// </list>
/// </para>
/// </summary>
public static class HearSpeech
{
    public const uint LocalOpcode  = 0x02BBu;
    public const uint RangedOpcode = 0x02BCu;

    public readonly record struct Parsed(
        string Text,
        string SenderName,
        uint SenderGuid,
        uint ChatType,
        bool IsRanged);

    public static Parsed? TryParse(byte[] body)
    {
        if (body is null || body.Length < 16) return null;

        uint opcode = BinaryPrimitives.ReadUInt32LittleEndian(body);
        bool isRanged;
        if (opcode == LocalOpcode)       isRanged = false;
        else if (opcode == RangedOpcode) isRanged = true;
        else return null;

        int pos = 4;
        try
        {
            string text   = ReadString16L(body, ref pos);
            string sender = ReadString16L(body, ref pos);
            if (body.Length - pos < 8) return null;
            uint senderGuid = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(pos));  pos += 4;
            uint chatType   = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(pos));  pos += 4;
            return new Parsed(text, sender, senderGuid, chatType, isRanged);
        }
        catch { return null; }
    }

    private static string ReadString16L(ReadOnlySpan<byte> source, ref int pos)
    {
        if (source.Length - pos < 2) throw new FormatException("truncated String16L length");
        ushort length = BinaryPrimitives.ReadUInt16LittleEndian(source.Slice(pos));
        pos += 2;
        if (source.Length - pos < length) throw new FormatException("truncated String16L body");
        string result = Encoding.ASCII.GetString(source.Slice(pos, length));
        pos += length;
        int recordSize = 2 + length;
        int padding = (4 - (recordSize & 3)) & 3;
        pos += padding;
        return result;
    }
}