package com.crossbowffs.nekosms.widget;

import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import androidx.viewpager.widget.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;

/**
 * An implementation of the support library FragmentPagerAdapter
 * class for the native Android {@link Fragment} class.
 */
public abstract class FragmentPagerAdapter extends PagerAdapter {
    private final FragmentManager mFragmentManager;
    private FragmentTransaction mCurTransaction;
    private Fragment mCurrentPrimaryItem;

    public FragmentPagerAdapter(FragmentManager fragmentManager) {
        mFragmentManager = fragmentManager;
    }

    public abstract Fragment getItem(int position);

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        if (mCurTransaction == null) {
            mCurTransaction = mFragmentManager.beginTransaction();
        }

        String name = makeFragmentName(container.getId(), position);
        Fragment fragment = mFragmentManager.findFragmentByTag(name);
        if (fragment != null) {
            mCurTransaction.attach(fragment);
        } else {
            fragment = getItem(position);
            mCurTransaction.add(container.getId(), fragment, name);
        }

        if (fragment != mCurrentPrimaryItem) {
            fragment.setMenuVisibility(false);
            fragment.setUserVisibleHint(false);
        }

        return fragment;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        if (mCurTransaction == null) {
            mCurTransaction = mFragmentManager.beginTransaction();
        }
        mCurTransaction.detach((Fragment)object);
    }

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        Fragment fragment = (Fragment)object;
        if (fragment != mCurrentPrimaryItem) {
            if (mCurrentPrimaryItem != null) {
                mCurrentPrimaryItem.setMenuVisibility(false);
                mCurrentPrimaryItem.setUserVisibleHint(false);
            }
            if (fragment != null) {
                fragment.setMenuVisibility(true);
                fragment.setUserVisibleHint(true);
            }
            mCurrentPrimaryItem = fragment;
        }
    }

    @Override
    public void finishUpdate(ViewGroup container) {
        if (mCurTransaction != null) {
            mCurTransaction.commitAllowingStateLoss();
            mCurTransaction = null;
            mFragmentManager.executePendingTransactions();
        }
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return ((Fragment)object).getView() == view;
    }

    private static String makeFragmentName(int viewId, long id) {
        return "android:switcher:" + viewId + ":" + id;
    }
}