GridSpacingItemDecoration

package ui.widget;

import android.content.Context;
import android.graphics.Rect;
import android.support.annotation.DimenRes;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.View;

/**
 * grid space item decorator
 */
public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration {
    private static final int VERTICAL = 1;
    private int halfSpacing;
    private int orientation;
    private int spacing;
    private int spanCount;

    public GridSpacingItemDecoration(final int spacing) {
        this.orientation = -1;
        this.spanCount = -1;
        this.spacing = spacing;
        this.halfSpacing = this.spacing / 2;
    }

    public GridSpacingItemDecoration(final Context context, @DimenRes final int i) {
        this(Math.round(context.getResources().getDimension(i) / context.getResources().getDisplayMetrics().density));
    }

    @Override
    public void getItemOffsets(final Rect rect, final View view, final RecyclerView recyclerView, final RecyclerView.State state) {
        super.getItemOffsets(rect, view, recyclerView, state);
        if (this.orientation == -1) {
            this.orientation = this.getOrientation(recyclerView);
        }
        if (this.spanCount == -1) {
            this.spanCount = this.getTotalSpan(recyclerView);
        }
        final int itemCount = recyclerView.getLayoutManager().getItemCount();
        final int childAdapterPosition = recyclerView.getChildAdapterPosition(view);
        final int itemSpanSize = this.getItemSpanSize(recyclerView, childAdapterPosition);
        final int itemSpanIndex = this.getItemSpanIndex(recyclerView, childAdapterPosition);
        if (this.spanCount < 1) {
            return;
        }
        this.setSpacings(rect, recyclerView, itemCount, childAdapterPosition, itemSpanSize, itemSpanIndex);
    }

    protected int getItemSpanIndex(final RecyclerView recyclerView, final int n) {
        final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            return ((GridLayoutManager) layoutManager).getSpanSizeLookup().getSpanIndex(n, this.spanCount);
        }
        if (layoutManager instanceof StaggeredGridLayoutManager) {
            return n % this.spanCount;
        }
        if (layoutManager instanceof LinearLayoutManager) {
            return 0;
        }
        return -1;
    }

    protected int getItemSpanSize(final RecyclerView recyclerView, int spanSize) {
        final int n = VERTICAL;
        final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            spanSize = ((GridLayoutManager) layoutManager).getSpanSizeLookup().getSpanSize(spanSize);
        } else {
            spanSize = n;
            if (!(layoutManager instanceof StaggeredGridLayoutManager)) {
                spanSize = n;
                if (!(layoutManager instanceof LinearLayoutManager)) {
                    return -1;
                }
            }
        }
        return spanSize;
    }

    protected int getOrientation(final RecyclerView recyclerView) {
        final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        if (layoutManager instanceof LinearLayoutManager) {
            return ((LinearLayoutManager) layoutManager).getOrientation();
        }
        if (layoutManager instanceof GridLayoutManager) {
            return ((GridLayoutManager) layoutManager).getOrientation();
        }
        if (layoutManager instanceof StaggeredGridLayoutManager) {
            return ((StaggeredGridLayoutManager) layoutManager).getOrientation();
        }
        return 1;
    }

    protected int getTotalSpan(final RecyclerView recyclerView) {
        final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            return ((GridLayoutManager) layoutManager).getSpanCount();
        }
        if (layoutManager instanceof StaggeredGridLayoutManager) {
            return ((StaggeredGridLayoutManager) layoutManager).getSpanCount();
        }
        if (layoutManager instanceof LinearLayoutManager) {
            return VERTICAL;
        }
        return -1;
    }

    protected boolean isBottomEdge(final RecyclerView recyclerView, final int n, final int n2, final int n3, final int n4) {
        final boolean b = true;
        boolean b2 = true;
        boolean lastItemEdgeValid;
        if (this.orientation == VERTICAL) {
            if (n2 < n - this.spanCount) {
                b2 = false;
            }
            lastItemEdgeValid = this.isLastItemEdgeValid(b2, recyclerView, n, n2, n4);
        } else {
            lastItemEdgeValid = b;
            if (n4 + n3 != this.spanCount) {
                return false;
            }
        }
        return lastItemEdgeValid;
    }

    protected boolean isFirstItemEdgeValid(final boolean b, final RecyclerView recyclerView, int n) {
        int n2 = 0;
        final int n3 = 0;
        if (b) {
            int n4 = n;
            n = n3;
            while (true) {
                n2 = n;
                if (n4 < 0) {
                    break;
                }
                n += this.getItemSpanSize(recyclerView, n4);
                --n4;
            }
        }
        return b && n2 <= this.spanCount;
    }

    protected boolean isLastItemEdgeValid(final boolean b, final RecyclerView recyclerView, final int n, int n2, final int n3) {
        int n4 = 0;
        final int n5 = 0;
        if (b) {
            int n6 = n2;
            n2 = n5;
            while (true) {
                n4 = n2;
                if (n6 >= n) {
                    break;
                }
                n2 += this.getItemSpanSize(recyclerView, n6);
                ++n6;
            }
        }
        return b && n4 <= this.spanCount - n3;
    }

    protected boolean isLeftEdge(final RecyclerView recyclerView, final int n, final int n2, final int n3, final int n4) {
        boolean b = false;
        if (this.orientation == 1) {
            return n4 == 0;
        }
        if (n2 == 0 || this.isFirstItemEdgeValid(n2 < this.spanCount, recyclerView, n2)) {
            b = true;
        }
        return b;
    }

    protected boolean isRightEdge(final RecyclerView recyclerView, final int n, final int n2, final int n3, final int n4) {
        boolean b = false;
        if (this.orientation == VERTICAL) {
            return n4 + n3 == this.spanCount;
        }
        if (n2 >= n - this.spanCount) {
            b = true;
        }
        return this.isLastItemEdgeValid(b, recyclerView, n, n2, n4);
    }

    protected boolean isTopEdge(final RecyclerView recyclerView, final int n, final int n2, final int n3, final int n4) {
        boolean b = false;
        boolean b2 = true;
        if (this.orientation == 1) {
            if (n2 == 0 || this.isFirstItemEdgeValid(n2 < this.spanCount, recyclerView, n2)) {
                b = true;
            }
            return b;
        }
        if (n4 != 0) {
            b2 = false;
        }
        return b2;
    }

    protected void setSpacings(final Rect rect, final RecyclerView recyclerView, final int n, final int n2, final int n3, final int n4) {
        rect.top = this.halfSpacing;
        rect.bottom = this.halfSpacing;
        rect.left = this.halfSpacing;
        rect.right = this.halfSpacing;
        if (this.isTopEdge(recyclerView, n, n2, n3, n4)) {
            rect.top = this.spacing;
        }
        if (this.isLeftEdge(recyclerView, n, n2, n3, n4)) {
            rect.left = this.spacing;
        }
        if (this.isRightEdge(recyclerView, n, n2, n3, n4)) {
            rect.right = this.spacing;
        }
        if (this.isBottomEdge(recyclerView, n, n2, n3, n4)) {
            rect.bottom = this.spacing;
        }
    }
}