fixed merging and adapted writeStructs to write end of message

src/structs/AbstractItem.js

@@ -168,6 +168,7 @@ export class AbstractItem extends AbstractStruct {
     } else {
       o = parent._start
     }
+    // TODO: use something like DeleteSet here (a tree implementation would be best)
     /**
      * @type {Set<AbstractItem>}
      */
@@ -391,6 +392,20 @@ export class AbstractItem extends AbstractStruct {
     throw new Error('unimplemented')
   }
 
+  /**
+   * @param {AbstractItem} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (compareIDs(right.origin, this.lastId) && this.right === right && compareIDs(this.rightOrigin, right.rightOrigin)) {
+      this.right = right.right
+      if (right.right !== null) {
+        right.right = this
+      }
+      return true
+    }
+    return false
+  }
   /**
    * Mark this Item as deleted.
    *

src/structs/ItemDeleted.js

@@ -13,7 +13,6 @@ import {
   changeItemRefOffset,
   GC,
   splitItem,
-  compareIDs,
   addToDeleteSet,
   StructStore, Transaction, ID, AbstractType // eslint-disable-line
 } from '../internals.js'
@@ -80,7 +79,7 @@ export class ItemDeleted extends AbstractItem {
    * @return {boolean}
    */
   mergeWith (right) {
-    if (compareIDs(right.origin, this.lastId) && this.right === right && compareIDs(this.rightOrigin, right.rightOrigin)) {
+    if (super.mergeWith(right)) {
       this._len += right._len
       return true
     }

src/structs/ItemJSON.js

@@ -10,7 +10,6 @@ import {
   getItemType,
   splitItem,
   changeItemRefOffset,
-  compareIDs,
   GC,
   ItemDeleted,
   StructStore, Transaction, ID, AbstractType // eslint-disable-line
@@ -75,7 +74,7 @@ export class ItemJSON extends AbstractItem {
    * @return {boolean}
    */
   mergeWith (right) {
-    if (compareIDs(right.origin, this.lastId) && this.right === right && compareIDs(this.rightOrigin, right.rightOrigin)) {
+    if (super.mergeWith(right)) {
       this.content = this.content.concat(right.content)
       return true
     }

src/structs/ItemString.js

@@ -9,7 +9,6 @@ import {
   getItemType,
   splitItem,
   changeItemRefOffset,
-  compareIDs,
   ItemDeleted,
   GC,
   StructStore, Transaction, ID, AbstractType // eslint-disable-line
@@ -76,7 +75,7 @@ export class ItemString extends AbstractItem {
    * @return {boolean}
    */
   mergeWith (right) {
-    if (compareIDs(right.origin, this.lastId) && this.right === right && compareIDs(this.rightOrigin, right.rightOrigin)) {
+    if (super.mergeWith(right)) {
       this.string += right.string
       return true
     }