implemented undo 🙌

src/Util/UndoManager.js

@@ -0,0 +1,92 @@
+import ID from './ID.js'
+
+class ReverseOperation {
+  constructor (y) {
+    const beforeState = y._transaction.beforeState
+    this.toState = new ID(y.userID, y.ss.getState(y.userID) - 1)
+    if (beforeState.has(y.userID)) {
+      this.fromState = new ID(y.userID, beforeState.get(y.userID))
+    } else {
+      this.fromState = this.toState
+    }
+    this.deletedStructs = y._transaction.deletedStructs
+  }
+}
+
+function isStructInScope (y, struct, scope) {
+  while (struct !== y) {
+    if (struct === scope) {
+      return true
+    }
+    struct = struct._parent
+  }
+  return false
+}
+
+export default class UndoManager {
+  constructor (scope) {
+    this._undoBuffer = []
+    this._redoBuffer = []
+    this._scope = scope
+    this._undoing = false
+    this._redoing = false
+    const y = scope._y
+    this.y = y
+    y.on('afterTransaction', (y, remote) => {
+      if (!remote && (y._transaction.beforeState.has(y.userID) || y._transaction.deletedStructs.size > 0)) {
+        let reverseOperation = new ReverseOperation(y)
+        if (!this._undoing) {
+          this._undoBuffer.push(reverseOperation)
+          if (!this._redoing) {
+            this._redoBuffer = []
+          }
+        } else {
+          this._redoBuffer.push(reverseOperation)
+        }
+      }
+    })
+  }
+  undo () {
+    this._undoing = true
+    this._applyReverseOperation(this._undoBuffer)
+    this._undoing = false
+  }
+  redo () {
+    this._redoing = true
+    this._applyReverseOperation(this._redoBuffer)
+    this._redoing = false
+  }
+  _applyReverseOperation (reverseBuffer) {
+    this.y.transact(() => {
+      let performedUndo = false
+      while (!performedUndo && reverseBuffer.length > 0) {
+        let undoOp = reverseBuffer.pop()
+        // make sure that it is possible to iterate {from}-{to}
+        this.y.os.getItemCleanStart(undoOp.fromState)
+        this.y.os.getItemCleanEnd(undoOp.toState)
+        this.y.os.iterate(undoOp.fromState, undoOp.toState, op => {
+          if (!op._deleted && isStructInScope(this.y, op, this._scope)) {
+            performedUndo = true
+            op._delete(this.y)
+          }
+        })
+        for (let op of undoOp.deletedStructs) {
+          if (
+            isStructInScope(this.y, op, this._scope) &&
+            op._parent !== this.y &&
+            !op._parent._deleted &&
+            (
+              op._parent._id.user !== this.y.userID ||
+              op._parent._id.clock < undoOp.fromState.clock ||
+              op._parent._id.clock > undoOp.fromState.clock
+            )
+          ) {
+            performedUndo = true
+            op = op._copy(undoOp.deletedStructs)
+            op._integrate(this.y)
+          }
+        }
+      }
+    })
+  }
+}