Add dots indicator to horizontalGridView in HomeFragment

app/src/main/java/com/cappielloantonio/play/helper/recyclerview/DotsIndicatorDecoration.java

@@ -0,0 +1,112 @@
+package com.cappielloantonio.play.helper.recyclerview;
+
+import android.content.res.Resources;
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.graphics.Rect;
+import android.view.View;
+
+import androidx.annotation.ColorInt;
+import androidx.recyclerview.widget.GridLayoutManager;
+import androidx.recyclerview.widget.LinearLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+
+import org.jetbrains.annotations.NotNull;
+
+public class DotsIndicatorDecoration extends RecyclerView.ItemDecoration {
+    private static final String TAG = "DotsIndicatorDecoration";
+
+    private final int indicatorHeight;
+    private final int indicatorItemPadding;
+    private final int radius;
+
+    private final Paint inactivePaint = new Paint();
+    private final Paint activePaint = new Paint();
+
+    public DotsIndicatorDecoration(int radius, int padding, int indicatorHeight, @ColorInt int colorInactive, @ColorInt int colorActive) {
+        float strokeWidth = Resources.getSystem().getDisplayMetrics().density * 1;
+        this.radius = radius;
+
+        inactivePaint.setStrokeCap(Paint.Cap.ROUND);
+        inactivePaint.setStrokeWidth(strokeWidth);
+        inactivePaint.setStyle(Paint.Style.STROKE);
+        inactivePaint.setAntiAlias(true);
+        inactivePaint.setColor(colorInactive);
+
+        activePaint.setStrokeCap(Paint.Cap.ROUND);
+        activePaint.setStrokeWidth(strokeWidth);
+        activePaint.setStyle(Paint.Style.FILL);
+        activePaint.setAntiAlias(true);
+        activePaint.setColor(colorActive);
+
+        this.indicatorItemPadding = padding;
+        this.indicatorHeight = indicatorHeight;
+    }
+
+    @Override
+    public void onDrawOver(@NotNull Canvas c, @NotNull RecyclerView parent, @NotNull RecyclerView.State state) {
+        super.onDrawOver(c, parent, state);
+
+        if (parent.getAdapter() == null) return;
+
+        int itemCount = (int) Math.ceil((double) parent.getAdapter().getItemCount() / 5);
+
+        // center horizontally, calculate width and subtract half from center
+        float totalLength = this.radius * 2 * itemCount;
+        float paddingBetweenItems = Math.max(0, itemCount - 1) * indicatorItemPadding;
+        float indicatorTotalWidth = totalLength + paddingBetweenItems;
+        float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2f;
+
+        // center vertically in the allotted space
+        float indicatorPosY = parent.getHeight() - indicatorHeight - (float) indicatorItemPadding / 3;
+
+        drawInactiveDots(c, indicatorStartX, indicatorPosY, itemCount);
+
+        final int activePosition;
+
+        if (parent.getLayoutManager() instanceof GridLayoutManager) {
+            activePosition = ((GridLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();
+        } else if (parent.getLayoutManager() instanceof LinearLayoutManager) {
+            activePosition = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();
+        } else {
+            // not supported layout manager
+            return;
+        }
+
+        if (activePosition == RecyclerView.NO_POSITION) {
+            return;
+        }
+
+        // find offset of active page if the user is scrolling
+        final View activeChild = parent.getLayoutManager().findViewByPosition(activePosition);
+        if (activeChild == null) {
+            return;
+        }
+
+        drawActiveDot(c, indicatorStartX, indicatorPosY, activePosition);
+    }
+
+    private void drawInactiveDots(Canvas c, float indicatorStartX, float indicatorPosY, int itemCount) {
+        // width of item indicator including padding
+        final float itemWidth = this.radius * 2 + indicatorItemPadding;
+
+        float start = indicatorStartX + radius;
+        for (int i = 0; i < itemCount; i++) {
+            c.drawCircle(start, indicatorPosY, radius, inactivePaint);
+            start += itemWidth;
+        }
+    }
+
+    private void drawActiveDot(Canvas c, float indicatorStartX, float indicatorPosY, int highlightPosition) {
+        // width of item indicator including padding
+        final float itemWidth = this.radius * 2 + indicatorItemPadding;
+        float highlightStart = (float) Math.ceil(indicatorStartX + radius + itemWidth * highlightPosition / 5);
+        c.drawCircle(highlightStart, indicatorPosY, radius, activePaint);
+    }
+
+    @Override
+    public void getItemOffsets(@NotNull Rect outRect, @NotNull View view, @NotNull RecyclerView parent, @NotNull RecyclerView.State state) {
+        super.getItemOffsets(outRect, view, parent, state);
+        outRect.bottom = indicatorHeight;
+    }
+}