using SharpChat.SockChat.S2CPackets;
using System.Globalization;
using System.Text;

namespace SharpChat.ClientCommands {
    public class NickClientCommand : ClientCommand {
        private const int MAX_GRAPHEMES = 16;
        private const int MAX_BYTES = MAX_GRAPHEMES * 10;

        public bool IsMatch(ClientCommandContext ctx) {
            return ctx.NameEquals("nick");
        }

        public async Task Dispatch(ClientCommandContext ctx) {
            long msgId = ctx.Chat.RandomSnowflake.Next();
            bool setOthersNick = ctx.User.Can(UserPermissions.SetOthersNickname);

            if(!setOthersNick && !ctx.User.Can(UserPermissions.SetOwnNickname)) {
                await ctx.Chat.SendTo(ctx.User, new CommandResponseS2CPacket(msgId, LCR.COMMAND_NOT_ALLOWED, true, $"/{ctx.Name}"));
                return;
            }

            User? targetUser = null;
            int offset = 0;

            if(setOthersNick && long.TryParse(ctx.Args.FirstOrDefault(), out long targetUserId) && targetUserId > 0) {
                targetUser = ctx.Chat.Users.FirstOrDefault(u => u.UserId == targetUserId.ToString());
                ++offset;
            }

            targetUser ??= ctx.User;

            if(ctx.Args.Length < offset) {
                await ctx.Chat.SendTo(ctx.User, new CommandResponseS2CPacket(msgId, LCR.COMMAND_FORMAT_ERROR));
                return;
            }

            string nickStr = string.Join('_', ctx.Args.Skip(offset))
                .Replace("\n", string.Empty).Replace("\r", string.Empty)
                .Replace("\f", string.Empty).Replace("\t", string.Empty)
                .Replace(' ', '_').Trim();

            if(nickStr == targetUser.UserName)
                nickStr = string.Empty;
            else if(string.IsNullOrEmpty(nickStr))
                nickStr = string.Empty;
            else {
                StringInfo nsi = new(nickStr);
                if(Encoding.UTF8.GetByteCount(nickStr) > MAX_BYTES
                    || nsi.LengthInTextElements > MAX_GRAPHEMES)
                    nickStr = nsi.SubstringByTextElements(0, Math.Min(nsi.LengthInTextElements, MAX_GRAPHEMES)).Trim();
            }

            if(!string.IsNullOrWhiteSpace(nickStr) && ctx.Chat.Users.Any(u => u.NameEquals(nickStr))) {
                await ctx.Chat.SendTo(ctx.User, new CommandResponseS2CPacket(msgId, LCR.NAME_IN_USE, true, nickStr));
                return;
            }

            string? previousName = targetUser.UserId == ctx.User.UserId ? (targetUser.NickName ?? targetUser.UserName) : null;
            await ctx.Chat.UpdateUser(targetUser, nickName: nickStr, silent: previousName == null);
        }
    }
}