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

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound social + query GameActions. These share a common pattern:
/// single-target / single-parameter GameActions inside the <c>0xF7B1</c>
/// envelope.
///
/// <para>
/// Wire format:
/// <code>
///   u32 0xF7B1                    envelope
///   u32 gameActionSequence
///   u32 subOpcode
///   &lt;payload&gt;                   per-action
/// </code>
/// </para>
///
/// <para>
/// References: r08 §3 rows for each opcode.
/// </para>
/// </summary>
public static class SocialActions
{
    public const uint GameActionEnvelope = 0xF7B1u;

    // Queries
    public const uint QueryHealthOpcode         = 0x01BFu; // u32 targetGuid
    public const uint PingRequestOpcode         = 0x01E9u; // u32 clientId

    // Fellowship
    public const uint FellowshipCreateOpcode    = 0x00A2u; // string16L name, bool openness, bool shareXP
    public const uint FellowshipQuitOpcode      = 0x00A3u; // bool disband
    public const uint FellowshipDismissOpcode   = 0x00A4u; // u32 guid
    public const uint FellowshipRecruitOpcode   = 0x00A5u; // u32 guid
    public const uint FellowshipUpdateOpcode    = 0x00A6u; // bool open

    // Character options
    public const uint SetCharacterOptionsOpcode = 0x01A1u; // u32 options bitmap

    // Chat channels
    public const uint AddChannelOpcode    = 0x0145u; // string16L channelName
    public const uint RemoveChannelOpcode = 0x0146u; // string16L channelName

    /// <summary>Query a target's health — server replies with UpdateHealth (0x01C0).</summary>
    public static byte[] BuildQueryHealth(uint seq, uint targetGuid)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  QueryHealthOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), targetGuid);
        return body;
    }

    /// <summary>Keepalive ping — server echoes with PingResponse (0x01EA).</summary>
    public static byte[] BuildPingRequest(uint seq, uint clientId)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  PingRequestOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), clientId);
        return body;
    }

    /// <summary>Create a fellowship with a chosen name + options.</summary>
    public static byte[] BuildFellowshipCreate(
        uint seq, string fellowshipName, bool openness, bool shareXp)
    {
        byte[] name = PackString16L(fellowshipName);
        // 2 bools consume 2 bytes + alignment pad to 4.
        int boolBlock = 2;
        int pad = (4 - ((name.Length + boolBlock) & 3)) & 3;
        byte[] body = new byte[12 + name.Length + boolBlock + pad];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipCreateOpcode);
        Array.Copy(name, 0, body, 12, name.Length);
        body[12 + name.Length] = openness ? (byte)1 : (byte)0;
        body[12 + name.Length + 1] = shareXp ? (byte)1 : (byte)0;
        return body;
    }

    /// <summary>Quit your current fellowship (optionally disband if leader).</summary>
    public static byte[] BuildFellowshipQuit(uint seq, bool disband)
    {
        byte[] body = new byte[16]; // envelope + 1 byte bool aligned to 4
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipQuitOpcode);
        body[12] = disband ? (byte)1 : (byte)0;
        return body;
    }

    /// <summary>Dismiss a specific vassal from your fellowship.</summary>
    public static byte[] BuildFellowshipDismiss(uint seq, uint targetGuid)
        => SingleGuid(seq, FellowshipDismissOpcode, targetGuid);

    /// <summary>Recruit a target into your fellowship.</summary>
    public static byte[] BuildFellowshipRecruit(uint seq, uint targetGuid)
        => SingleGuid(seq, FellowshipRecruitOpcode, targetGuid);

    /// <summary>Toggle fellowship open / closed recruiting.</summary>
    public static byte[] BuildFellowshipUpdate(uint seq, bool open)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  FellowshipUpdateOpcode);
        body[12] = open ? (byte)1 : (byte)0;
        return body;
    }

    /// <summary>Push the client's character-options bitmap to the server.</summary>
    public static byte[] BuildSetCharacterOptions(uint seq, uint optionsBitmap)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  SetCharacterOptionsOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), optionsBitmap);
        return body;
    }

    /// <summary>Subscribe to a named chat channel.</summary>
    public static byte[] BuildAddChannel(uint seq, string channelName)
        => SingleString(seq, AddChannelOpcode, channelName);

    /// <summary>Unsubscribe from a named chat channel.</summary>
    public static byte[] BuildRemoveChannel(uint seq, string channelName)
        => SingleString(seq, RemoveChannelOpcode, channelName);

    // ── Helpers ──────────────────────────────────────────────────────────────

    private static byte[] SingleGuid(uint seq, uint sub, uint guid)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  sub);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), guid);
        return body;
    }

    private static byte[] SingleString(uint seq, uint sub, string s)
    {
        byte[] str = PackString16L(s);
        byte[] body = new byte[12 + str.Length];
        BinaryPrimitives.WriteUInt32LittleEndian(body,           GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4), seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8), sub);
        Array.Copy(str, 0, body, 12, str.Length);
        return body;
    }

    private static byte[] PackString16L(string s)
    {
        ArgumentNullException.ThrowIfNull(s);
        // Windows-1252 matches retail (and holtburger's encoding_rs::WINDOWS_1252).
        byte[] data = Encoding.GetEncoding(1252).GetBytes(s);
        if (data.Length > ushort.MaxValue)
            throw new ArgumentException("String too long for 16-bit length prefix.", nameof(s));

        int recordSize = 2 + data.Length;
        int padding = (4 - (recordSize & 3)) & 3;
        byte[] result = new byte[recordSize + padding];
        BinaryPrimitives.WriteUInt16LittleEndian(result, (ushort)data.Length);
        Array.Copy(data, 0, result, 2, data.Length);
        return result;
    }
}