using System;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor.Experimental.SceneManagement;
#endif

[ExecuteAlways, DisallowMultipleComponent]
public abstract class MeshInstanceBehaviour : MonoBehaviour
{
	public const string meshInstanceSuffix = "(MeshInstance)";

	[HideInInspector]
	public Mesh meshAsset;
	[NonSerialized]
	public Mesh meshInstance;

	protected virtual void OnMeshInstanceCreated() { }
	protected virtual void OnMeshInstanceDeleted() { }

	public void EnsureMeshInstance()
	{
		var smr = GetComponent<SkinnedMeshRenderer>();
		if (smr != null)
		{
			if (smr.sharedMesh == null || (smr.sharedMesh.GetInstanceID() < 0 && smr.sharedMesh != meshInstance))
				smr.sharedMesh = meshAsset;

			if (smr.sharedMesh != null && smr.sharedMesh.GetInstanceID() >= 0)
				smr.sharedMesh = EnsureMeshInstanceAux(smr.sharedMesh);

			return;
		}

		var mf = GetComponent<MeshFilter>();
		if (mf != null)
		{
			if (mf.sharedMesh == null || (mf.sharedMesh.GetInstanceID() < 0 && mf.sharedMesh != meshInstance))
				mf.sharedMesh = meshAsset;

			if (mf.sharedMesh != null && mf.sharedMesh.GetInstanceID() >= 0)
				mf.sharedMesh = EnsureMeshInstanceAux(mf.sharedMesh);

			return;
		}
	}

	Mesh EnsureMeshInstanceAux(Mesh mesh)
	{
		if (meshInstance != null)
		{
			Mesh.DestroyImmediate(meshInstance);
			meshInstance = null;
		}

		meshAsset = mesh;
		meshInstance = Mesh.Instantiate(meshAsset);
		meshInstance.name = meshAsset.name + meshInstanceSuffix;
		meshInstance.hideFlags = HideFlags.HideAndDontSave & ~HideFlags.DontUnloadUnusedAsset;
		meshInstance.MarkDynamic();

		//Debug.Log("ensureMeshInstance " + meshAsset.name + " -> " + meshInstance.name);

		OnMeshInstanceCreated();

		return meshInstance;
	}

	public void RemoveMeshInstance()
	{
		var smr = GetComponent<SkinnedMeshRenderer>();
		if (smr != null)
		{
			if (smr.sharedMesh == null || smr.sharedMesh.GetInstanceID() < 0)
				smr.sharedMesh = meshAsset;

			RemoveMeshInstanceAux();
			return;
		}

		var mf = GetComponent<MeshFilter>();
		if (mf != null)
		{
			if (mf.sharedMesh == null || mf.sharedMesh.GetInstanceID() < 0)
				mf.sharedMesh = meshAsset;

			RemoveMeshInstanceAux();
			return;
		}
	}

	void RemoveMeshInstanceAux()
	{
		if (meshInstance != null)
		{
			Mesh.DestroyImmediate(meshInstance);
			meshInstance = null;
		}

		OnMeshInstanceDeleted();
	}

#if UNITY_EDITOR
	static MeshInstanceBehaviour()
	{
		PrefabStage.prefabSaving += (GameObject prefab) =>
		{
			var prefabStage = PrefabStageUtility.GetCurrentPrefabStage();
			if (prefabStage != null)
			{
				var meshInstanceBehaviours = prefab.GetComponentsInChildren<MeshInstanceBehaviour>(includeInactive: true);
				foreach (var meshInstanceBehaviour in meshInstanceBehaviours)
				{
					meshInstanceBehaviour.RemoveMeshInstance();
					//Debug.Log("reverted mesh instance for " + meshInstanceBehaviour.ToString());
				}
			}
		};

		PrefabStage.prefabSaved += (GameObject prefab) =>
		{
			var prefabStage = PrefabStageUtility.GetCurrentPrefabStage();
			if (prefabStage != null)
			{
				var meshInstanceBehaviours = prefab.GetComponentsInChildren<MeshInstanceBehaviour>(includeInactive: false);
				foreach (var meshInstanceBehaviour in meshInstanceBehaviours)
				{
					meshInstanceBehaviour.EnsureMeshInstance();
					//Debug.Log("reinstated mesh instance for " + meshInstanceBehaviour.ToString());
				}
			}
		};
	}
#endif
}