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>
/// The two opcodes do NOT share a payload: ranged speech carries an extra
/// <c>f32 range</c> between the sender guid and the chat type. Both oracles
/// agree — ACE's
/// <c>GameMessages/Messages/GameMessageHearRangedSpeech.cs</c> writes
/// <c>senderID, range, chatMessageType</c> where
/// <c>GameMessageHearSpeech.cs</c> writes only <c>senderID,
/// chatMessageType</c>, and holtburger's
/// <c>crates/holtburger-protocol/src/messages/chat/types.rs</c> declares
/// <c>HearRangedSpeechData</c> with a <c>range: f32</c> that
/// <c>HearSpeechData</c> lacks.
/// </para>
///
/// <para>
/// Wire layout:
/// <code>
///   u32 opcode               // 0x02BB or 0x02BC
///   string16L text
///   string16L senderName
///   u32 senderGuid
///   f32 range                // 0x02BC ONLY
///   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;

    /// <param name="Range">
    /// Audible radius carried only by <c>0x02BC HearRangedSpeech</c>. Local
    /// speech (<c>0x02BB</c>) has no such field on the wire and reports 0.
    /// </param>
    public readonly record struct Parsed(
        string Text,
        string SenderName,
        uint SenderGuid,
        uint ChatType,
        bool IsRanged,
        float Range);

    public static Parsed? TryParse(ReadOnlySpan<byte> body)
    {
        if (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);

            // 0x02BB: guid + chatType. 0x02BC: guid + range + chatType.
            int tailSize = isRanged ? 12 : 8;
            if (body.Length - pos < tailSize) return null;

            uint senderGuid = BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(pos));  pos += 4;

            float range = 0f;
            if (isRanged)
            {
                range = BinaryPrimitives.ReadSingleLittleEndian(body.Slice(pos));
                pos += 4;
            }

            uint chatType = BinaryPrimitives.ReadUInt32LittleEndian(body.Slice(pos));  pos += 4;
            return new Parsed(text, sender, senderGuid, chatType, isRanged, range);
        }
        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");
        // Windows-1252 matches retail (and holtburger's encoding_rs::WINDOWS_1252).
        // ASCII would munge any non-ASCII byte into a '?' which corrupts player
        // names and chat with accented characters (e.g. "Café").
        string result = Encoding.GetEncoding(1252).GetString(source.Slice(pos, length));
        pos += length;
        int recordSize = 2 + length;
        int padding = (4 - (recordSize & 3)) & 3;
        pos += padding;
        return result;
    }
}