using System.Security.Cryptography;
using System.Text;
using ZstdSharp;

namespace WxAgent.Core;

/// <summary>Database-backed message with stable identity, sender and timestamps.</summary>
public sealed record DbMessage(
    long LocalId,
    long ServerId,
    string ChatId,
    string? SenderWxId,
    string? SenderName,
    string? SenderAvatarUrl,
    long Type,
    string Content,
    DateTimeOffset Timestamp,
    bool? IsSelf);

public static class WechatDbMessage
{
    // WeChat 4.x stores message_content as hex; rows with WCDB_CT_message_content=1 are zstd-compressed (magic 28 b5 2f fd).
    public static string TableNameFor(string chatId) =>
        "Msg_" + Convert.ToHexString(MD5.HashData(Encoding.UTF8.GetBytes(chatId))).ToLowerInvariant();

    public static string DecodeContent(string hexContent, bool compressed)
    {
        if (string.IsNullOrEmpty(hexContent)) return string.Empty;
        if (hexContent.Length > WechatMergedChatParser.MaxXmlCharacters * 2)
            throw new InvalidDataException("Database message content exceeds the decoding limit.");
        byte[] bytes;
        try
        {
            bytes = Convert.FromHexString(hexContent);
        }
        catch (FormatException)
        {
            return string.Empty;
        }

        if (compressed && bytes.Length >= 4 && bytes[0] == 0x28 && bytes[1] == 0xb5 && bytes[2] == 0x2f && bytes[3] == 0xfd)
        {
            try
            {
                using var source = new MemoryStream(bytes);
                using var decompressor = new DecompressionStream(source);
                using var reader = new StreamReader(decompressor, Encoding.UTF8);
                var decoded = new StringBuilder();
                var buffer = new char[4096];
                int read;
                while ((read = reader.Read(buffer, 0, buffer.Length)) != 0)
                {
                    if (decoded.Length + read > WechatMergedChatParser.MaxXmlCharacters)
                        throw new InvalidDataException("Decompressed message exceeds the decoding limit.");
                    decoded.Append(buffer, 0, read);
                }
                return decoded.ToString();
            }
            catch (Exception exception) when (exception is not (OutOfMemoryException or InvalidDataException))
            {
                return string.Empty;
            }
        }

        return compressed ? string.Empty : Encoding.UTF8.GetString(bytes);
    }

    /// <summary>The account root directory name is &lt;wxid&gt;_&lt;random&gt;; the reference project treats the wxid prefix as self.</summary>
    public static bool? IsSelf(string? senderWxId, string? accountRootDirectoryName)
    {
        if (string.IsNullOrEmpty(senderWxId) || string.IsNullOrEmpty(accountRootDirectoryName)) return null;
        return accountRootDirectoryName.StartsWith(senderWxId + "_", StringComparison.Ordinal);
    }
}