using UnityEngine;
using UnityEditor;

public class SetPivot : EditorWindow
{

    Vector3 p; //Pivot value -1..1, calculated from Mesh bounds
    Vector3 last_p; //Last used pivot

    GameObject obj; //Selected object in the Hierarchy
    MeshFilter meshFilter; //Mesh Filter of the selected object
    Mesh mesh; //Mesh of the selected object
    Collider col; //Collider of the selected object

    bool pivotUnchanged; //Flag to decide when to instantiate a copy of the mesh

    [MenuItem("GameObject/Set Pivot")] //Place the Set Pivot menu item in the GameObject menu
    static void Init()
    {
        SetPivot window = (SetPivot)EditorWindow.GetWindow(typeof(SetPivot));
        window.RecognizeSelectedObject(); //Initialize the variables by calling RecognizeSelectedObject on the class instance
        window.Show();
    }

    void OnGUI()
    {
        if (obj)
        {
            if (mesh)
            {
                p.x = EditorGUILayout.Slider("X", p.x, -11.0f, 11.0f);
                p.y = EditorGUILayout.Slider("Y", p.y, -1.0f, 1.0f);
                p.z = EditorGUILayout.Slider("Z", p.z, -1.0f, 1.0f);
                if (p != last_p)
                { //Detects user input on any of the three sliders
                  //Only create instance of mesh when user changes pivot
                    if (pivotUnchanged) mesh = meshFilter.sharedMesh; pivotUnchanged = false;
                    UpdatePivot();
                    last_p = p;
                }
                if (GUILayout.Button("Center"))
                { //Set pivot to the center of the mesh bounds
                  //Only create instance of mesh when user changes pivot
                    if (pivotUnchanged) mesh = meshFilter.sharedMesh; pivotUnchanged = false;
                    p = Vector3.zero;
                    UpdatePivot();
                    last_p = p;
                }
                GUILayout.Label("Bounds " + mesh.bounds.ToString());
            }
            else
            {
                GUILayout.Label("Selected object does not have a Mesh specified.");
            }
        }
        else
        {
            GUILayout.Label("No object selected in Hierarchy.");
        }
    }

    //Achieve the movement of the pivot by moving the transform position in the specified direction
    //and then moving all vertices of the mesh in the opposite direction back to where they were in world-space
    void UpdatePivot()
    {
        Vector3 diff = Vector3.Scale(mesh.bounds.extents, last_p - p); //Calculate difference in 3d position
        obj.transform.position -= Vector3.Scale(diff, obj.transform.localScale); //Move object position
                                                                                 //Iterate over all vertices and move them in the opposite direction of the object position movement
        Vector3[] verts = mesh.vertices;
        for (int i = 0; i < verts.Length; i++)
        {
            verts[i] += diff;
        }
        mesh.vertices = verts; //Assign the vertex array back to the mesh
        mesh.RecalculateBounds(); //Recalculate bounds of the mesh, for the renderer's sake
                                  //The 'center' parameter of certain colliders needs to be adjusted
                                  //when the transform position is modified
        if (col)
        {
            if (col is BoxCollider)
            {
                ((BoxCollider)col).center += diff;
            }
            else if (col is CapsuleCollider)
            {
                ((CapsuleCollider)col).center += diff;
            }
            else if (col is SphereCollider)
            {
                ((SphereCollider)col).center += diff;
            }
        }
    }

    //Look at the object's transform position in comparison to the center of its mesh bounds
    //and calculate the pivot values for xyz
    void UpdatePivotVector()
    {
        Bounds b = mesh.bounds;
        Vector3 offset = -1 * b.center;
        p = last_p = new Vector3(offset.x / b.extents.x, offset.y / b.extents.y, offset.z / b.extents.z);
    }

    //When a selection change notification is received
    //recalculate the variables and references for the new object
    void OnSelectionChange()
    {
        RecognizeSelectedObject();
    }

    //Gather references for the selected object and its components
    //and update the pivot vector if the object has a Mesh specified
    void RecognizeSelectedObject()
    {
        Transform t = Selection.activeTransform;
        obj = t ? t.gameObject : null;
        if (obj)
        {
            meshFilter = obj.GetComponent(typeof(MeshFilter)) as MeshFilter;
            mesh = meshFilter ? meshFilter.sharedMesh : null;
            if (mesh)
                UpdatePivotVector();
            col = obj.GetComponent(typeof(Collider)) as Collider;
            pivotUnchanged = true;
        }
        else
        {
            mesh = null;
        }
    }
}