Attempt to implement back stack manager wrapper

NavigationManager.java

package com.lifeslice.app.navigation;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import java.util.WeakHashMap;

public class NavigationManager {
    private static final String TAG = NavigationManager.class.getSimpleName();
    private static NavigationManager mInstance = null;
    private WeakHashMap<String, Fragment> mFragmentsWeakHashMap;

    private final int MAIN_ACTIVITY_CONTAINER = R.id.mainactivity_fragment_container;

    protected NavigationManager() {
        mFragmentsWeakHashMap = new WeakHashMap<>();
    }

    public static synchronized NavigationManager get() {
        if (mInstance == null) {
            mInstance = new NavigationManager();
        }

        return mInstance;
    }

    // custom back press handlings
    public boolean proceedOnBackPress() {
        return true;
    }


    /**
     * Navigate to fragment by tag if default fragment instance will satisfy and store it's instance
     *
     * @param fragmentManager SupporFragmentManager instance
     * @param tag             Tag of the fragment to replace
     * @param addToBackStack  True if fragment should be added to backstack
     */
    public void navigateToFragment(FragmentManager fragmentManager,
                                   String tag, boolean addToBackStack) {

        if (mFragmentsWeakHashMap.get(tag) == null) {
            setFragmentByTag(tag, getDefaultFragmentInstance(tag));
        }

        if (getFragmentByTag(tag).isVisible() || getFragmentByTag(tag).isAdded()) return;

        replaceFragment(fragmentManager, getFragmentByTag(tag), tag, addToBackStack);
    }

    /**
     * Navigate to specified fragment and store it by tag
     *
     * @param fragmentManager SupporFragmentManager instance
     * @param fragment        Fragment to replace and store
     * @param tag             Tag of the fragment to replace
     * @param addToBackStack  True if fragment should be added to backstack
     */
    public void navigateToFragment(FragmentManager fragmentManager, Fragment fragment,
                                   String tag, boolean addToBackStack) {

        setFragmentByTag(tag, fragment);

        if (getFragmentByTag(tag).isVisible() || getFragmentByTag(tag).isAdded()) return;

        replaceFragment(fragmentManager, getFragmentByTag(tag), tag, addToBackStack);
    }

    /**
     * Pop backstack to the bottom
     *
     * @param fragmentManager
     */
    public void clearBackstackInclusive(FragmentManager fragmentManager) {
        fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
        fragmentManager.executePendingTransactions();
    }

    /**
     * Pop backstack to the specified fragment. Fragments above the found by tag fragment will be popped up
     *
     * @param fragmentManager
     * @param fragmentTag
     */
    public void popBackStackToFragment(FragmentManager fragmentManager, String fragmentTag) {
        int count = fragmentManager.getBackStackEntryCount();
        while (count > 0) {
            String name = fragmentManager.getBackStackEntryAt(count - 1).getName();
            if (name.equals(fragmentTag)) return;
            count--;

            fragmentManager.popBackStack();
            fragmentManager.executePendingTransactions();
        }
    }

    private Fragment getFragmentByTag(String tag) {
        return mFragmentsWeakHashMap.get(tag);
    }

    private void setFragmentByTag(String tag, Fragment fragment) {
        mFragmentsWeakHashMap.put(tag, fragment);
    }

    private void replaceFragment(FragmentManager fm, Fragment fragment,
                                 String tag, boolean addToBackStack) {

        FragmentTransaction transaction = fm.beginTransaction();
        transaction.replace(MAIN_ACTIVITY_CONTAINER, fragment);
        if (addToBackStack) transaction.addToBackStack(tag);
        transaction.commit();

        fm.executePendingTransactions();
    }

    // default fragments instances handling
    private Fragment getDefaultFragmentInstance(String tag) {
        return new Fragment();
    }
}