namespace WxAgent.Core;

public sealed record WechatDatabaseContact(string Username, string? NickName, string? Remark, string? AvatarUrl)
{
    public string DisplayName => !string.IsNullOrWhiteSpace(Remark) ? Remark :
        !string.IsNullOrWhiteSpace(NickName) ? NickName : Username;
}

public sealed record WechatContactPage(IReadOnlyList<WechatDatabaseContact> Contacts, int? NextOffset)
{
    public bool HasMore => NextOffset is not null;
}

public static class WechatContactQuery
{
    // Stable IDs, not display names, define ordering and identity. No UI fallback.
    public const string Sql = """
        SELECT username, nick_name, remark, small_head_url FROM contact
        WHERE ($contains IS NULL OR instr(username, $contains) > 0
            OR instr(nick_name, $contains) > 0 OR instr(remark, $contains) > 0)
          AND ($groups IS NULL OR (substr(username, -9) = '@chatroom') = $groups)
        ORDER BY username COLLATE BINARY LIMIT $limit OFFSET $offset;
        """;

    public static IReadOnlyList<KeyValuePair<string, object?>> Parameters(int limit, int offset, string? contains, bool? groupsOnly)
    {
        if (limit is < 1 or > 10000 || offset < 0 || offset > int.MaxValue - limit)
            throw new WxAgentException(WxAgentErrorCode.InvalidArgument, "Contact limit must be 1-10000 and offset must leave room for the next page.");
        return new KeyValuePair<string, object?>[]
        {
            new("$limit", limit + 1), new("$offset", offset), new("$contains", contains),
            new("$groups", groupsOnly is null ? null : groupsOnly.Value ? 1 : 0)
        };
    }

    public static WechatContactPage Page(IReadOnlyList<WechatDatabaseContact> rows, int limit, int offset)
    {
        _ = Parameters(limit, offset, null, null);
        return new(rows.Take(limit).ToArray(), rows.Count > limit ? offset + limit : null);
    }
}