Method InviteMemberAsync

backend/Services/BoardService.cs:400–473

(int boardId, string username, string role, int inviterId)

    }

    public async Task<BoardMemberDto?> InviteMemberAsync(int boardId, string username, string role, int inviterId)
    {
        // Only the owner or an admin can invite
        var board = await _db.Boards.Include(b => b.Members).FirstOrDefaultAsync(b => b.Id == boardId);
        if (board == null) return null;

        // Only Workspace Owners or Admins can invite to boards
        var workspace = await _db.Workspaces
            .Include(w => w.Members)
            .FirstOrDefaultAsync(w => w.Id == board.WorkspaceId);

        if (workspace == null) return null;

        var isWsAdmin = workspace.OwnerId == inviterId ||
                        workspace.Members.Any(m => m.UserId == inviterId && m.Role == "Admin" && m.Status == "Accepted");

        var isBoardAdmin = board.OwnerId == inviterId ||
                          board.Members.Any(m => m.UserId == inviterId && m.Role == "Admin" && m.Status == "Accepted");

        if (!isWsAdmin && !isBoardAdmin) return null;

        var user = await _db.Users.FirstOrDefaultAsync(u => u.Username == username);
        if (user == null) return null;

        // Cannot invite yourself
        if (user.Id == inviterId) return null;

        // Check if already a member or invited
        var existing = await _db.BoardMembers
            .FirstOrDefaultAsync(bm => bm.BoardId == boardId && bm.UserId == user.Id);

        if (existing != null)
        {
            // Update role and set back to Pending so they can accept/be notified
            existing.Role = role;
            existing.Status = "Pending";
            await _db.SaveChangesAsync();

            return new BoardMemberDto
            {
                Id = existing.Id,
                UserId = user.Id,
                Username = user.Username,
                Email = user.Email,
                Role = existing.Role,
                JoinedAt = existing.JoinedAt,
                AvatarUrl = user.AvatarUrl,
                BoardId = boardId
            };
        }

        var member = new BoardMember
        {
            UserId = user.Id,
            BoardId = boardId,
            Role = role,
            Status = "Pending"
        };