using UnityEngine;
using UnityEngine.UI;

using System;
using System.Collections;

public enum LocatePos
{
    Left,
    Right,
    Center,

    Up,
    Down,
    Middle,
}

public static class ExtensionScrollRect
{
    public static MoveRoot Locate(this ScrollRect scrollRect, int index, float duration, Curve curve, LocatePos locatePos)
    {
        float scaleFactor = scrollRect.GetComponent<Image>().canvas.scaleFactor;
        
        LayoutGroup layoutGroup = scrollRect.content.GetComponent<LayoutGroup>();

        RectTransform tra1 = scrollRect.GetComponent<RectTransform>();

        Rect rect1 = tra1.rect;

        RectTransform tra2 = scrollRect.content.GetChild(index).GetComponent<RectTransform>();

        Rect rect2 = tra2.rect;

        if (locatePos == LocatePos.Up)
        {
            Vector3 itemPos = tra2.position + new Vector3(0, rect2.yMax, 0) * scaleFactor;
            Vector3 targetPos = tra1.position + new Vector3(0, rect1.yMax - layoutGroup.padding.top, 0) * scaleFactor;

            Vector3 offset = targetPos - itemPos;
            offset.x = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }
        if (locatePos == LocatePos.Down)
        {
            Vector3 itemPos = tra2.position + new Vector3(0, rect2.yMin, 0) * scaleFactor;
            Vector3 targetPos = tra1.position + new Vector3(0, rect1.yMin  + layoutGroup.padding.bottom, 0) * scaleFactor;

            Vector3 offset = targetPos - itemPos;
            offset.x = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }
        else if (locatePos == LocatePos.Middle)
        {
            Vector3 itemPos = tra2.position + new Vector3(rect2.center.x, rect2.center.y, 0);
            Vector3 targetPos = tra1.position + new Vector3(rect1.center.x, rect1.center.y, 0);

            Vector3 offset = targetPos - itemPos;
            offset.x = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }
        if (locatePos == LocatePos.Left)
        {
            Vector3 itemPos = tra2.position + new Vector3(rect2.xMin, 0, 0) * scaleFactor;
            Vector3 targetPos = tra1.position + new Vector3(rect1.xMin + layoutGroup.padding.left, 0, 0) * scaleFactor;

            Vector3 offset = targetPos - itemPos;
            offset.y = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }
        if (locatePos == LocatePos.Right)
        {
            Vector3 itemPos = tra2.position + new Vector3(rect2.xMax, 0, 0) * scaleFactor;
            Vector3 targetPos = tra1.position + new Vector3(rect1.xMax - layoutGroup.padding.right, 0, 0) * scaleFactor;

            Vector3 offset = targetPos - itemPos;
            offset.y = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }
        if (locatePos == LocatePos.Center)
        {
            Vector3 itemPos = tra2.position + new Vector3(rect2.center.x, rect2.center.y, 0);
            Vector3 targetPos = tra1.position + new Vector3(rect1.center.x, rect1.center.y, 0);

            Vector3 offset = targetPos - itemPos;
            offset.y = 0;

            return scrollRect.content.MoveOffset2D(offset, duration, false, curve);
        }

        throw new Exception();
    }

    public static MoveRoot Locate(this ScrollRect scrollRect, Transform item, float duration, Curve curve, LocatePos locatePos)
    {
        return scrollRect.Locate(item.GetSiblingIndex(), duration, curve, locatePos);
    }
}