Audinaut-subsonic-app-android/app/src/main/java/net/nullsum/audinaut/view/GridSpacingDecoration.java

/*
  This file is part of Subsonic.
    Subsonic 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.
    Subsonic 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 Subsonic. If not, see <http://www.gnu.org/licenses/>.
    Copyright 2015 (C) Scott Jackson
*/

package net.nullsum.audinaut.view;

import android.graphics.Rect;
import android.util.TypedValue;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.LinearLayout;

import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

public class GridSpacingDecoration extends RecyclerView.ItemDecoration {
    public static final int SPACING = 10;

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        int spacing = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, SPACING, view.getResources().getDisplayMetrics());
        int halfSpacing = spacing / 2;

        int childCount = parent.getChildCount();
        int childIndex = parent.getChildAdapterPosition(view);
        // Not an actual child (ie: during delete event)
        if (childIndex == -1) {
            return;
        }
        int spanCount = getTotalSpan(parent);
        int spanIndex = childIndex % spanCount;

        // If we can, use the SpanSizeLookup since headers screw up the index calculation
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
            GridLayoutManager.SpanSizeLookup spanSizeLookup = gridLayoutManager.getSpanSizeLookup();
            if (spanSizeLookup != null) {
                spanIndex = spanSizeLookup.getSpanIndex(childIndex, spanCount);
            }
        }
        int spanSize = getSpanSize(parent, childIndex);

        /* INVALID SPAN */
        if (spanCount < 1 || spanSize > 1) return;

        int margins = 0;
        if (view instanceof UpdateView) {
            View firstChild = ((ViewGroup) view).getChildAt(0);
            ViewGroup.LayoutParams layoutParams = firstChild.getLayoutParams();
            if (layoutParams instanceof LinearLayout.LayoutParams) {
                margins = ((LinearLayout.LayoutParams) layoutParams).bottomMargin;
            } else if (layoutParams instanceof FrameLayout.LayoutParams) {
                margins = ((FrameLayout.LayoutParams) layoutParams).bottomMargin;
            }
        }
        int doubleMargins = margins * 2;

        outRect.top = halfSpacing - margins;
        outRect.bottom = halfSpacing - margins;
        outRect.left = halfSpacing - margins;
        outRect.right = halfSpacing - margins;

        if (isTopEdge(childIndex, spanIndex, spanCount)) {
            outRect.top = spacing - doubleMargins;
        }

        if (isLeftEdge(spanIndex)) {
            outRect.left = spacing - doubleMargins;
        }

        if (isRightEdge(spanIndex, spanCount)) {
            outRect.right = spacing - doubleMargins;
        }

        if (isBottomEdge(childIndex, childCount, spanCount)) {
            outRect.bottom = spacing - doubleMargins;
        }
    }

    private int getTotalSpan(RecyclerView parent) {
        RecyclerView.LayoutManager mgr = parent.getLayoutManager();
        if (mgr instanceof GridLayoutManager) {
            return ((GridLayoutManager) mgr).getSpanCount();
        }

        return -1;
    }

    private int getSpanSize(RecyclerView parent, int childIndex) {
        RecyclerView.LayoutManager mgr = parent.getLayoutManager();
        if (mgr instanceof GridLayoutManager) {
            GridLayoutManager.SpanSizeLookup lookup = ((GridLayoutManager) mgr).getSpanSizeLookup();
            if (lookup != null) {
                return lookup.getSpanSize(childIndex);
            }
        }

        return 1;
    }

    private boolean isLeftEdge(int spanIndex) {
        return spanIndex == 0;
    }

    private boolean isRightEdge(int spanIndex, int spanCount) {
        return spanIndex == spanCount - 1;
    }

    private boolean isTopEdge(int childIndex, int spanIndex, int spanCount) {
        return childIndex < spanCount && childIndex == spanIndex;
    }

    private boolean isBottomEdge(int childIndex, int childCount, int spanCount) {
        return childIndex >= childCount - spanCount;
    }
}