A Simple SelectionHistory manager for Unity

SelectionHistoryWindow.cs

/*The MIT License (MIT)
Copyright (c) 2016 Red Blue Games, LLC. Author Edward Rowe (@edwardlrowe)
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine;

/// <summary>
/// Selection history window watches the selection and adds Forward and Back buttons to navigate previous selections.
/// </summary>
public class SelectionHistoryWindow : EditorWindow, IHasCustomMenu
{
    private const string BackMenuPath = "Edit/Select Previous #F1";
    private const string ForwardMenuPath = "Edit/Select Next #F2";
    private const string WindowMenuPath = "Window/Selection History Window";
    private const int HistorySize = 10;

    private bool ignoreSelectionChange;

    private int[] currentSelection;
    private Stack<int[]> selectionHistory;
    private Stack<int[]> poppedSelections;

    /// <summary>
    /// Implements IHasCutomMenu callback to add items into the right click menu and context menu on the window.
    /// </summary>
    /// <param name="menu">Menu to add into.</param>
    public virtual void AddItemsToMenu(GenericMenu menu)
    {
        menu.AddItem(new GUIContent("Clear History"), false, new GenericMenu.MenuFunction(this.ClearHistory));
    }

    [MenuItem(WindowMenuPath)]
    private static SelectionHistoryWindow OpenSelectionHistoryWindow()
    { 
        var window = EditorWindow.GetWindow<SelectionHistoryWindow>(false, "History");
        return window;
    }

    [MenuItem(BackMenuPath, false, 50)]
    private static void BackMenuItem()
    {
        var window = OpenSelectionHistoryWindow();
        window.MoveSelectionBack();
    }

    [MenuItem(ForwardMenuPath, false, 51)]
    private static void ForwardMenuItem()
    {
        var window = OpenSelectionHistoryWindow();
        window.MoveSelectionForward();
    }

    private void OnEnable()
    {
        this.minSize = new Vector2(minSize.x, 25.0f);

        // Note this clears selection every time the game recompiles.
        this.poppedSelections = new Stack<int[]>(HistorySize);
        this.selectionHistory = new Stack<int[]>(HistorySize);
    }

    private void ClearHistory()
    {
        this.selectionHistory.Clear();
        this.poppedSelections.Clear();
    }

    private void OnGUI()
    {
        EditorGUILayout.BeginHorizontal();

        EditorGUI.BeginDisabledGroup(!this.IsBackEnabled());

        var leftArrowCode = "\u2190";
        if (GUILayout.Button(leftArrowCode, GUILayout.MinWidth(35)))
        {
            this.MoveSelectionBack();
        }

        EditorGUI.EndDisabledGroup();

        this.GUIDrawLabelForStack(this.selectionHistory, true);

        GUILayout.FlexibleSpace();

        this.GUIDrawLabelForStack(this.poppedSelections, false);

        EditorGUI.BeginDisabledGroup(!this.IsForwardEnabled());

        var rightArrowCode = "\u2192";
        if (GUILayout.Button(rightArrowCode, GUILayout.MinWidth(35)))
        {
            this.MoveSelectionForward();
        }

        EditorGUI.EndDisabledGroup();

        EditorGUILayout.EndHorizontal();
    }

    private bool IsBackEnabled()
    {
        if (this.selectionHistory == null)
        {
            return false;
        }

        return this.selectionHistory.Count > 0;
    }

    private void MoveSelectionBack()
    {
        if (this.IsBackEnabled())
        {
            this.PushCurrentSelectionAndPopNext(this.poppedSelections, this.selectionHistory);
        }
    }

    private bool IsForwardEnabled()
    {
        if (this.poppedSelections == null)
        {
            return false;
        }

        return this.poppedSelections.Count > 0;
    }

    private void MoveSelectionForward()
    {
        if (this.IsForwardEnabled())
        {
            this.PushCurrentSelectionAndPopNext(this.selectionHistory, this.poppedSelections);
        }
    }

    private void PushCurrentSelectionAndPopNext(Stack<int[]> pushToStack, Stack<int[]> popFromStack)
    {
        // Set flag so that this selection change is ignored during the selection callback
        this.ignoreSelectionChange = true;

        // Add current selection to a stack that maintains history
        pushToStack.Push(this.currentSelection);

        this.currentSelection = popFromStack.Pop();

        // Selected the popped value
        Selection.instanceIDs = this.currentSelection;
    }

    private void GUIDrawLabelForStack(Stack<int[]> stack, bool alignLeft)
    {
        var itemName = string.Empty;
        if (stack.Count > 0)
        {
            var nextItems = stack.Peek();
            itemName = this.GetStringForInstanceIDs(nextItems);
        }

        GUIStyle textStyle = new GUIStyle(EditorStyles.label);
        textStyle.alignment = alignLeft ? TextAnchor.MiddleLeft : TextAnchor.MiddleRight;

        EditorGUILayout.LabelField(itemName, textStyle, GUILayout.MinWidth(40), GUILayout.ExpandWidth(true));
    }

    private void OnSelectionChange()
    {
        if (this.ignoreSelectionChange)
        {
            this.ignoreSelectionChange = false;
            return;
        }

        // Push old selection onto the history, unless there is no selection (first selection ever)
        if (this.currentSelection != null)
        {
            // This is the same group. do not affect history
            if (!this.IsSelectionAddative())
            {
                // Selection represents a new selection. 
                this.selectionHistory.Push(this.currentSelection);
            }
        }

        this.currentSelection = Selection.instanceIDs;

        // Clear forward history whenever any selection change is made
        this.poppedSelections.Clear();

        this.Repaint();
    }

    private bool IsSelectionAddative()
    {
        var selectedIDs = Selection.instanceIDs;

        // Can't be addative if only one thing is selected
        if (selectedIDs.Length > 1)
        {
            // If current (previous) selection contains one of the newly selected IDs, this must be a shift+select or drag select
            for (int i = 0; i < this.currentSelection.Length; ++i)
            {
                var currentSelectionID = this.currentSelection[i];
                for (int idIndex = 0; idIndex < selectedIDs.Length; ++idIndex)
                {
                    var id = selectedIDs[idIndex];
                    if (id == currentSelectionID)
                    {
                        return true;
                    }
                }
            }
        }

        return false;
    }

    private string GetStringForInstanceIDs(int[] ids)
    {
        string name = string.Empty;
        if (ids.Length > 0)
        {
            var instanceID = ids[0];
            UnityEngine.Object firstObject = EditorUtility.InstanceIDToObject(instanceID);
            if (firstObject != null)
            {
                name = firstObject.name;
            }
            else
            {
                name = "[Destroyed]";
            }

            if (ids.Length > 1)
            {
                name = string.Concat("[", ids.Length, "]", name);
            }
        }
        else
        {
            name = "[None]";
        }

        return name;
    }
}