using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Animations;
using UnityEngine.Assertions;

namespace BITKit
{
	public static class ConstraintExtensions
	{
		public static ParentConstraint SetParentConstraint(this Transform target, Transform parentSource,
			ParentConstraint constraint = null)
		{
			Assert.IsTrue(!constraint || target == constraint.transform);

			if (!constraint)
			{
				if (!parentSource) return null;
				constraint = target.gameObject.GetOrAddComponent<ParentConstraint>();
			}

			// 清空已有约束
			constraint.constraintActive = false;
			for (int i = constraint.sourceCount - 1; i >= 0; i--)
			{
				constraint.RemoveSource(i);
			}

			// 无约束
			if (!parentSource) return constraint;

			// 设置新约束
			constraint.AddSource(new ConstraintSource
			{
				sourceTransform = parentSource,
				weight = 1,
			});

			// 设置 Position offset
			var positionOffset = parentSource.InverseTransformPoint(target.position);
			constraint.SetTranslationOffset(0, positionOffset);

			// 设置 Rotation offset
			var localForward = parentSource.InverseTransformDirection(target.forward);
			var localUpward = parentSource.InverseTransformDirection(target.up);
			var rotationOffset = Quaternion.LookRotation(localForward, localUpward).eulerAngles;
			constraint.SetRotationOffset(0, rotationOffset);

			// 激活约束
			constraint.constraintActive = true;

			return constraint;
		}
	}

}