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(function(){
var UndoStack = function(){
this.debug = true
this.stack = []
this.types = {}
this.pointer = -1
}
UndoStack.prototype.push = function(action){
this.pointer++
this.stack[this.pointer] = action
this.purge()
this.debug && console.log("push", action.type)
}
UndoStack.prototype.purge = function(){
if (this.stack.length-1 == this.pointer) return
this.stack.length = this.pointer+1
}
UndoStack.prototype.undo = function(){
if (this.pointer == -1) return false
var action = this.stack[this.pointer]
this.debug && console.log("undo", action.type)
this.types[ action.type ].undo(action.undo)
this.pointer--
return this.pointer > -1
}
UndoStack.prototype.redo = function(){
if (this.pointer == this.stack.length-1) return false
this.pointer++
var action = this.stack[this.pointer]
this.debug && console.log("redo", action.type)
this.types[ action.type ].redo(action.redo)
return this.pointer < this.stack.length-1
}
UndoStack.prototype.register = function(actions){
if (actions.length) {
actions.forEach(this.registerOne.bind(this))
}
else {
this.registerOne(actions)
}
}
UndoStack.prototype.registerOne = function(action){
if (! action.redo) { action.redo = action.undo }
this.types[ action.type ] = action
}
if ('window' in this) {
window.UndoStack = new UndoStack
}
else {
module.exports = new UndoStack
}
})()
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