PluralKit/PluralKit.Bot/Utils/GroupMemberUtils.cs

using System;

using PluralKit.Core;

namespace PluralKit.Bot
{
    public static class GroupMemberUtils
    {
        public static string GenerateResponse(Groups.AddRemoveOperation action, int memberCount, int groupCount, int actionedOn, int notActionedOn)
        {
            var op = action;

            var actionStr = action == Groups.AddRemoveOperation.Add ? "added to" : "removed from";
            var containStr = action == Groups.AddRemoveOperation.Add ? "in" : "not in";
            var emojiStr = actionedOn > 0 ? Emojis.Success : Emojis.Error;

            var memberPlural = memberCount > 1;
            var groupPlural = groupCount > 1;

            // sanity checking: we can't add multiple groups to multiple members (at least for now)
            if (memberPlural && groupPlural)
                throw new ArgumentOutOfRangeException();

            // sanity checking: we can't act/not act on a different number of entities than we have
            if (memberPlural && (actionedOn + notActionedOn) != memberCount)
                throw new ArgumentOutOfRangeException();
            if (groupPlural && (actionedOn + notActionedOn) != groupCount)
                throw new ArgumentOutOfRangeException();

            // name generators
            string MemberString(int count, bool capitalize = false)
                => capitalize
                    ? (count == 1 ? "Member" : "Members")
                    : (count == 1 ? "member" : "members");

            string GroupString(int count)
                => count == 1 ? "group" : "groups";

            // string generators

            string ResponseString()
            {
                if (actionedOn > 0 && notActionedOn > 0 && memberPlural)
                    return $"{actionedOn} {MemberString(actionedOn)} {actionStr} {GroupString(groupCount)}";
                if (actionedOn > 0 && notActionedOn > 0 && groupPlural)
                    return $"{MemberString(memberCount, capitalize: true)} {actionStr} {actionedOn} {GroupString(actionedOn)}";
                if (notActionedOn == 0)
                    return $"{MemberString(memberCount, capitalize: true)} {actionStr} {GroupString(groupCount)}";
                if (actionedOn == 0)
                    return $"{MemberString(memberCount, capitalize: true)} not {actionStr} {GroupString(groupCount)}";

                throw new ArgumentOutOfRangeException();
            }

            string InfoMessage()
            {
                if (notActionedOn == 0) return $"";

                var msg = "";
                if (actionedOn > 0 && memberPlural)
                    msg += $"{notActionedOn} {MemberString(notActionedOn)}";
                else
                    msg += $"{MemberString(memberCount)}";

                msg += $" already {containStr}";

                if (actionedOn > 0 && groupPlural)
                    msg += $" {notActionedOn} {GroupString(notActionedOn)}";
                else
                    msg += $" {GroupString(groupCount)}";

                return $" ({msg})";
            }

            return $"{emojiStr} {ResponseString()}{InfoMessage()}.";
        }
    }
}