using UnityEngine;
using System;

public class SmartInput : MonoBehaviour
{
    // Fixed size array for hit testing to avoid repeated memory allocation
    //  If you might have more than 10 overlapping colliders, you may need to increase array size
    Collider2D[] Hits = new Collider2D[10];

    void Update()
    {
        // Get all 2D colliders under the mouse/finger
        Vector3 v3 = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        int hitCount = Physics2D.OverlapPointNonAlloc(new Vector2(v3.x, v3.y), Hits);

        // If none, do nothing.
        if (hitCount == 0)
            return;

        // This will be set to front-most collider
        Collider2D frontMostHit = null;

        // Keep track of highest sort order found so far
        uint highestSortOrder = 0;

        // For each collider hit...
        for(int x=0;x<hitCount;x++)
        {
            Collider2D hit = Hits[x];

            // Get sprite render
            SpriteRenderer sr = hit.GetComponent<SpriteRenderer>();

            // Convert sorting order to unsigned value by adding the minimum (negative) value it can possibly have
            uint uSortingOrder = (uint)(sr.sortingOrder + short.MinValue);

            // In my game I use 3 sorting layers, you will need to adjust this.  SortingLayerOrder needs to have
            //  a value of 0 for your first layer, 1 for second, 2 for third, and so on.  This code
            uint sortingLayerOrder;
            if (sr.sortingLayerID == 0) // Default
                sortingLayerOrder = 1;
            else if (sr.sortingLayerID == 1) // Background
                sortingLayerOrder = 0;
            else
            {
                if (sr.sortingLayerID != 2) // Foreground
                    throw new Exception("You updated sorting layers but forgot to update this code!");
                sortingLayerOrder = 2;
            }

            // Assign base value for layer based on layer order
            //  1st layer = 0 to 65535
            //  2nd layer = 65536 to 131,070
            //  3rd layer = 131,070 to 196,605
            //  Each value increases by ushort.MaxValue to ensure that the highest value in a prior layer can never be
            //   greater than the lowest value in the next layer.
            uint sortingLayerBase = sortingLayerOrder * ushort.MaxValue;

            // Actual sort order is layer base value + object order
            uint sortOrder = sortingLayerBase + uSortingOrder;

            // If sort order is same (mostly to ensure we always have something) or higher than our highest so far...
            if (sortOrder >= highestSortOrder)
            {
                // Save new high value
                highestSortOrder = sortOrder;

                // This hit is our current front-most collider
                frontMostHit = hit;
            }
        }

        // If left mouse or finger just went down between last frame and this one...
        if (Input.GetMouseButtonDown(0))
        {
            // Fire OnLeftDown event if this object has one
            frontMostHit.SendMessage("OnLeftDown", SendMessageOptions.DontRequireReceiver);
        }

        // If left mouse or finger is down...
        if (Input.GetMouseButton(0))
        {
            // Fire OnLeftHoverDown event if this object has one
            frontMostHit.SendMessage("OnLeftHoverDown", SendMessageOptions.DontRequireReceiver);
        }

        // Always fire OnHover if this object has one
        frontMostHit.SendMessage("OnHover", SendMessageOptions.DontRequireReceiver);
    }
}