# all files / diagram-js/lib/command/ CommandStack.js

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     import {
      uniqueBy,
      isArray
    } from 'min-dash';

    /**
     * A service that offers un- and redoable execution of commands.
     *
     * The command stack is responsible for executing modeling actions
     * in a un- and redoable manner. To do this it delegates the actual
     * command execution to {@link CommandHandler}s.
     *
     * Command handlers provide {@link CommandHandler#execute(ctx)} and
     * {@link CommandHandler#revert(ctx)} methods to un- and redo a command
     * identified by a command context.
     *
     *
     * ## Life-Cycle events
     *
     * In the process the command stack fires a number of life-cycle events
     * that other components to participate in the command execution.
     *
     *    * preExecute
     *    * preExecuted
     *    * execute
     *    * executed
     *    * postExecute
     *    * postExecuted
     *    * revert
     *    * reverted
     *
     * A special event is used for validating, whether a command can be
     * performed prior to its execution.
     *
     *    * canExecute
     *
     * Each of the events is fired as `commandStack.{eventName}` and
     * `commandStack.{commandName}.{eventName}`, respectively. This gives
     * components fine grained control on where to hook into.
     *
     * The event object fired transports `command`, the name of the
     * command and `context`, the command context.
     *
     *
     * ## Creating Command Handlers
     *
     * Command handlers should provide the {@link CommandHandler#execute(ctx)}
     * and {@link CommandHandler#revert(ctx)} methods to implement
     * redoing and undoing of a command.
     *
     * A command handler _must_ ensure undo is performed properly in order
     * not to break the undo chain. It must also return the shapes that
     * got changed during the `execute` and `revert` operations.
     *
     * Command handlers may execute other modeling operations (and thus
     * commands) in their `preExecute` and `postExecute` phases. The command
     * stack will properly group all commands together into a logical unit
     * that may be re- and undone atomically.
     *
     * Command handlers must not execute other commands from within their
     * core implementation (`execute`, `revert`).
     *
     *
     * ## Change Tracking
     *
     * During the execution of the CommandStack it will keep track of all
     * elements that have been touched during the command's execution.
     *
     * At the end of the CommandStack execution it will notify interested
     * components via an 'elements.changed' event with all the dirty
     * elements.
     *
     * The event can be picked up by components that are interested in the fact
     * that elements have been changed. One use case for this is updating
     * their graphical representation after moving / resizing or deletion.
     *
     * @see CommandHandler
     *
     * @param {EventBus} eventBus
     * @param {Injector} injector
     */
    export default function CommandStack(eventBus, injector) {

      /**
       * A map of all registered command handlers.
       *
       * @type {Object}
       */
      this._handlerMap = {};

      /**
       * A stack containing all re/undoable actions on the diagram
       *
       * @type {Array<Object>}
       */
      this._stack = [];

      /**
       * The current index on the stack
       *
       * @type {Number}
       */
      this._stackIdx = -1;

      /**
       * Current active commandStack execution
       *
       * @type {Object}
       */
      this._currentExecution = {
        actions: [],
        dirty: []
      };

      this._injector = injector;
      this._eventBus = eventBus;

      this._uid = 1;

      eventBus.on([
        'diagram.destroy',
        'diagram.clear'
      ], function() {
        this.clear(false);
      }, this);
    }

    CommandStack.$inject = [ 'eventBus', 'injector' ];

    /**
     * Execute a command
     *
     * @param {String} command the command to execute
     * @param {Object} context the environment to execute the command in
     */
    CommandStack.prototype.execute = function(command, context) {
      Iif (!command) {
        throw new Error('command required');
      }

      var action = { command: command, context: context };

      this._pushAction(action);
      this._internalExecute(action);
      this._popAction(action);
    };

    /**
     * Ask whether a given command can be executed.
     *
     * Implementors may hook into the mechanism on two ways:
     *
     *   * in event listeners:
     *
     *     Users may prevent the execution via an event listener.
     *     It must prevent the default action for `commandStack.(<command>.)canExecute` events.
     *
     *   * in command handlers:
     *
     *     If the method {@link CommandHandler#canExecute} is implemented in a handler
     *     it will be called to figure out whether the execution is allowed.
     *
     * @param  {String} command the command to execute
     * @param  {Object} context the environment to execute the command in
     *
     * @return {Boolean} true if the command can be executed
     */
    CommandStack.prototype.canExecute = function(command, context) {

      var action = { command: command, context: context };

      var handler = this._getHandler(command);

      var result = this._fire(command, 'canExecute', action);

      // handler#canExecute will only be called if no listener
      // decided on a result already
      if (result === undefined) {
        Iif (!handler) {
          return false;
        }

        Iif (handler.canExecute) {
          result = handler.canExecute(context);
        }
      }

      return result;
    };

    /**
     * Clear the command stack, erasing all undo / redo history
     */
    CommandStack.prototype.clear = function(emit) {
      this._stack.length = 0;
      this._stackIdx = -1;

      Iif (emit !== false) {
        this._fire('changed');
      }
    };

    /**
     * Undo last command(s)
     */
    CommandStack.prototype.undo = function() {
      var action = this._getUndoAction(),
          next;

      Eif (action) {
        this._pushAction(action);

        while (action) {
          this._internalUndo(action);
          next = this._getUndoAction();

          if (!next || next.id !== action.id) {
            break;
          }

          action = next;
        }

        this._popAction();
      }
    };

    /**
     * Redo last command(s)
     */
    CommandStack.prototype.redo = function() {
      var action = this._getRedoAction(),
          next;

      Eif (action) {
        this._pushAction(action);

        while (action) {
          this._internalExecute(action, true);
          next = this._getRedoAction();

          if (!next || next.id !== action.id) {
            break;
          }

          action = next;
        }

        this._popAction();
      }
    };

    /**
     * Register a handler instance with the command stack
     *
     * @param {String} command
     * @param {CommandHandler} handler
     */
    CommandStack.prototype.register = function(command, handler) {
      this._setHandler(command, handler);
    };

    /**
     * Register a handler type with the command stack
     * by instantiating it and injecting its dependencies.
     *
     * @param {String} command
     * @param {Function} a constructor for a {@link CommandHandler}
     */
    CommandStack.prototype.registerHandler = function(command, handlerCls) {

      Iif (!command || !handlerCls) {
        throw new Error('command and handlerCls must be defined');
      }

      var handler = this._injector.instantiate(handlerCls);
      this.register(command, handler);
    };

    CommandStack.prototype.canUndo = function() {
      return !!this._getUndoAction();
    };

    CommandStack.prototype.canRedo = function() {
      return !!this._getRedoAction();
    };

    // stack access  //////////////////////

    CommandStack.prototype._getRedoAction = function() {
      return this._stack[this._stackIdx + 1];
    };

    CommandStack.prototype._getUndoAction = function() {
      return this._stack[this._stackIdx];
    };

    // internal functionality //////////////////////

    CommandStack.prototype._internalUndo = function(action) {
      var self = this;

      var command = action.command,
          context = action.context;

      var handler = this._getHandler(command);

      // guard against illegal nested command stack invocations
      this._atomicDo(function() {
        self._fire(command, 'revert', action);

        if (handler.revert) {
          self._markDirty(handler.revert(context));
        }

        self._revertedAction(action);

        self._fire(command, 'reverted', action);
      });
    };

    CommandStack.prototype._fire = function(command, qualifier, event) {
      if (arguments.length < 3) {
        event = qualifier;
        qualifier = null;
      }

      var names = qualifier ? [ command + '.' + qualifier, qualifier ] : [ command ],
          i, name, result;

      event = this._eventBus.createEvent(event);

      for (i = 0; (name = names[i]); i++) {
        result = this._eventBus.fire('commandStack.' + name, event);

        if (event.cancelBubble) {
          break;
        }
      }

      return result;
    };

    CommandStack.prototype._createId = function() {
      return this._uid++;
    };

    CommandStack.prototype._atomicDo = function(fn) {

      var execution = this._currentExecution;

      execution.atomic = true;

      try {
        fn();
      } finally {
        execution.atomic = false;
      }
    };

    CommandStack.prototype._internalExecute = function(action, redo) {
      var self = this;

      var command = action.command,
          context = action.context;

      var handler = this._getHandler(command);

      Iif (!handler) {
        throw new Error('no command handler registered for <' + command + '>');
      }

      this._pushAction(action);

      if (!redo) {
        this._fire(command, 'preExecute', action);

        if (handler.preExecute) {
          handler.preExecute(context);
        }

        this._fire(command, 'preExecuted', action);
      }

      // guard against illegal nested command stack invocations
      this._atomicDo(function() {

        self._fire(command, 'execute', action);

        if (handler.execute) {
          // actual execute + mark return results as dirty
          self._markDirty(handler.execute(context));
        }

        // log to stack
        self._executedAction(action, redo);

        self._fire(command, 'executed', action);
      });

      if (!redo) {
        this._fire(command, 'postExecute', action);

        if (handler.postExecute) {
          handler.postExecute(context);
        }

        this._fire(command, 'postExecuted', action);
      }

      this._popAction(action);
    };

    CommandStack.prototype._pushAction = function(action) {

      var execution = this._currentExecution,
          actions = execution.actions;

      var baseAction = actions[0];

      Iif (execution.atomic) {
        throw new Error('illegal invocation in <execute> or <revert> phase (action: ' + action.command + ')');
      }

      if (!action.id) {
        action.id = (baseAction && baseAction.id) || this._createId();
      }

      actions.push(action);
    };

    CommandStack.prototype._popAction = function() {
      var execution = this._currentExecution,
          actions = execution.actions,
          dirty = execution.dirty;

      actions.pop();

      if (!actions.length) {
        this._eventBus.fire('elements.changed', { elements: uniqueBy('id', dirty) });

        dirty.length = 0;

        this._fire('changed');
      }
    };

    CommandStack.prototype._markDirty = function(elements) {
      var execution = this._currentExecution;

      if (!elements) {
        return;
      }

      elements = isArray(elements) ? elements : [ elements ];

      execution.dirty = execution.dirty.concat(elements);
    };

    CommandStack.prototype._executedAction = function(action, redo) {
      var stackIdx = ++this._stackIdx;

      if (!redo) {
        this._stack.splice(stackIdx, this._stack.length, action);
      }
    };

    CommandStack.prototype._revertedAction = function(action) {
      this._stackIdx--;
    };

    CommandStack.prototype._getHandler = function(command) {
      return this._handlerMap[command];
    };

    CommandStack.prototype._setHandler = function(command, handler) {
      Iif (!command || !handler) {
        throw new Error('command and handler required');
      }

      Iif (this._handlerMap[command]) {
        throw new Error('overriding handler for command <' + command + '>');
      }

      this._handlerMap[command] = handler;
    };