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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) {
if (!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) {
if (!handler) {
return false;
}
if (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;
if (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;
if (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);
if (!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];
if (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;
};
|