public class AllUsersFragment extends Fragment {

    private View mView;
    private RecyclerView mDCUserList;

    private FirebaseRecyclerAdapter<Users, UsersViewHolders> mUserAdapter;

    private FirebaseUser mCurrentUser;
    private DatabaseReference mUsersDatabase;

    private LinearLayoutManager mLinearLayoutManager;

    public DCUsersFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        initUiViews(inflater, container);
        initObjects();
        setUpRecyclerAdapter();
        return mView;
    }

    private void initUiViews(LayoutInflater inflater, ViewGroup container) {
        mView = inflater.inflate(R.layout.fragment_dcusers, container, false);
        mDCUserList = mView.findViewById(R.id.rv_dcusers_list);

//        mDCUserList.setHasFixedSize(true);
        mDCUserList.setLayoutManager(new LinearLayoutManager(getContext()));
    }

    private void initObjects() {
        mUsersDatabase = FirebaseDatabase.getInstance().getReference().child("users");
        mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();

        mUsersDatabase.keepSynced(true);
    }

    private void setUpRecyclerAdapter() {
        Query usersQuery = mUsersDatabase.orderByKey();
        FirebaseRecyclerOptions usersOptions = new FirebaseRecyclerOptions.Builder<Users>()
                .setQuery(usersQuery, Users.class).build();

        mUserAdapter = new FirebaseRecyclerAdapter<Users, UsersViewHolders>(usersOptions) {

            @Override
            protected void onBindViewHolder(@NonNull UsersViewHolders holder, int position, @NonNull Users model) {
                final String user_id = getRef(position).getKey();

                if (user_id.equals(mCurrentUser.getUid())) {
                    holder.layoutHide();
                    return;
                }

                if (model.getStudent() != null) {
                    String desc = model.getStudent().getYear() + " " + model.getStudent().getCourse();

                    holder.setDesc(desc);

                } else {

                    holder.setDesc("Teacher");
                }

                holder.setName(model.getName());
                holder.setImage(model.getThumbnail());

                holder.mView.setOnClickListener(new View.OnClickListener() {

                    @Override
                    public void onClick(View v) {

                        Intent profileIntent = new Intent(getContext(), ProfileActivity.class);
                        profileIntent.putExtra("user_id", user_id);
                        startActivity(profileIntent);

                    }
                });

            }

            @NonNull
            @Override
            public UsersViewHolders onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View mView = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.row_item_dc_users, parent, false);
                return new UsersViewHolders(mView);
            }
        };

        mUserAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {

            @Override
            public void onItemRangeInserted(int positionStart, int itemCount) {
                super.onItemRangeInserted(positionStart, itemCount);
                int dcUsersCount = mUserAdapter.getItemCount();
                int lastVisiblePosition = mLinearLayoutManager
                        .findLastCompletelyVisibleItemPosition();

                // If the recycler view is initially being loaded or the
                // user is at the bottom of the list, scroll to the bottom
                // of the list to show the newly added message.

                if (lastVisiblePosition == -1 || (positionStart >= (dcUsersCount -1)) &&
                        lastVisiblePosition == (positionStart - 1)) {
                    mDCUserList.scrollToPosition(positionStart);
                }
            }
        });

        mDCUserList.setAdapter(mUserAdapter);
    }

    public static class UsersViewHolders extends RecyclerView.ViewHolder {

        private View mView;
        private RelativeLayout mRootLayout;
        private RelativeLayout.LayoutParams mParams;

        public UsersViewHolders(View mView) {
            super(mView);
            this.mView = mView;
        }

        public void setName(String name) {
            TextView display_name = mView.findViewById(R.id.item_search_user_name);
            display_name.setText(name);
        }

        public void setImage(String image) {
            RoundedImageView display_image = mView.findViewById(R.id.item_search_user_picture);
            Picasso.get().load(image).placeholder(R.drawable.user).transform(new CircleTransform())
                    .into(display_image);
        }

        public void setDesc(String desc) {
            TextView display_desc = mView.findViewById(R.id.item_search_user_desc);
            display_desc.setText(desc);
        }

        public void layoutHide() {
            mRootLayout = mView.findViewById(R.id.item_dc_users_layout);
            mParams = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);

            mParams.height = 0;
            mRootLayout.setLayoutParams(mParams);
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        mUserAdapter.startListening();
    }

    @Override
    public void onPause() {
        super.onPause();
        mUserAdapter.stopListening();
    }
}