FairEmail/app/src/main/java/eu/faircode/email/ViewModelMessages.java

package eu.faircode.email;

/*
    This file is part of FairEmail.

    FairEmail is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    FairEmail is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with FairEmail.  If not, see <http://www.gnu.org/licenses/>.

    Copyright 2018-2019 by Marcel Bokhorst (M66B)
*/

import java.util.HashMap;
import java.util.Map;

import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.OnLifecycleEvent;
import androidx.lifecycle.ViewModel;
import androidx.paging.PagedList;

public class ViewModelMessages extends ViewModel {
    private Map<AdapterMessage.ViewType, LiveData<PagedList<TupleMessageEx>>> messages = new HashMap<>();

    void setMessages(AdapterMessage.ViewType viewType, LifecycleOwner owner, final LiveData<PagedList<TupleMessageEx>> messages) {
        if (viewType == AdapterMessage.ViewType.UNIFIED)
            viewType = AdapterMessage.ViewType.FOLDER;

        this.messages.put(viewType, messages);

        if (viewType == AdapterMessage.ViewType.FOLDER)
            this.messages.remove(AdapterMessage.ViewType.SEARCH);

        if (viewType == AdapterMessage.ViewType.THREAD)
            owner.getLifecycle().addObserver(new LifecycleObserver() {
                @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
                public void onDestroyed() {
                    Log.i("Removed model thread");
                    ViewModelMessages.this.messages.remove(AdapterMessage.ViewType.THREAD);
                }
            });
        else {
            // Keep list up-to-date for previous/next navigation
            messages.observeForever(new Observer<PagedList<TupleMessageEx>>() {
                @Override
                public void onChanged(PagedList<TupleMessageEx> messages) {
                }
            });
        }
    }

    void observe(AdapterMessage.ViewType viewType, LifecycleOwner owner, Observer<PagedList<TupleMessageEx>> observer) {
        if (viewType == AdapterMessage.ViewType.UNIFIED)
            viewType = AdapterMessage.ViewType.FOLDER;

        if (owner.getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.INITIALIZED))
            messages.get(viewType).observe(owner, observer);
    }

    void removeObservers(AdapterMessage.ViewType viewType, LifecycleOwner owner) {
        if (viewType == AdapterMessage.ViewType.UNIFIED)
            viewType = AdapterMessage.ViewType.FOLDER;

        if (owner.getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.INITIALIZED)) {
            LiveData<PagedList<TupleMessageEx>> list = messages.get(viewType);
            if (list != null)
                list.removeObservers(owner);
        }
    }

    @Override
    protected void onCleared() {
        messages.clear();
    }

    void observePrevNext(LifecycleOwner owner, final long id, boolean found, final IPrevNext intf) {
        AdapterMessage.ViewType viewType =
                (found ? AdapterMessage.ViewType.SEARCH : AdapterMessage.ViewType.FOLDER);

        LiveData<PagedList<TupleMessageEx>> list = messages.get(viewType);
        if (list == null) {
            Log.w("Observe previous/next without list");
            return;
        }

        Log.i("Observe previous/next id=" + id);
        list.observe(owner, new Observer<PagedList<TupleMessageEx>>() {
            @Override
            public void onChanged(PagedList<TupleMessageEx> messages) {
                Log.i("Observe previous/next id=" + id + " messages=" + messages.size());

                for (int pos = 0; pos < messages.size(); pos++) {
                    TupleMessageEx item = messages.get(pos);
                    if (item != null && id == item.id) {
                        boolean load = false;

                        if (pos - 1 >= 0) {
                            TupleMessageEx next = messages.get(pos - 1);
                            if (next == null)
                                load = true;
                            intf.onNext(true, next == null ? null : next.id);
                        } else
                            intf.onNext(false, null);

                        if (pos + 1 < messages.size()) {
                            TupleMessageEx prev = messages.get(pos + 1);
                            if (prev == null)
                                load = true;
                            intf.onPrevious(true, prev == null ? null : prev.id);
                        } else
                            intf.onPrevious(false, null);

                        intf.onFound(pos, messages.size());

                        if (load)
                            messages.loadAround(pos);

                        return;
                    }
                }

                Log.w("Observe previous/next gone id=" + id);
            }
        });
    }

    interface IPrevNext {
        void onPrevious(boolean exists, Long id);

        void onNext(boolean exists, Long id);

        void onFound(int position, int size);
    }
}