add persistence decoder

.gitignore

@@ -3,3 +3,5 @@ bower_components
 docs
 /y.*
 /examples/yjs-dist.js*
+.vscode
+.yjsPersisted

src/Persistences/decodePersisted.mjs

@@ -0,0 +1,55 @@
+import { integrateRemoteStructs } from '../MessageHandler/integrateRemoteStructs.mjs'
+import { writeStructs } from '../MessageHandler/syncStep1.mjs'
+import { writeDeleteSet, readDeleteSet } from '../MessageHandler/deleteSet.mjs'
+
+const PERSIST_UPDATE = 0
+/**
+ * Write an update to an encoder.
+ *
+ * @param {Yjs} y A Yjs instance
+ * @param {BinaryEncoder} updateEncoder I.e. transaction.encodedStructs
+ */
+export function encodeUpdate (y, updateEncoder, encoder) {
+  encoder.writeVarUint(PERSIST_UPDATE)
+  encoder.writeBinaryEncoder(updateEncoder)
+}
+
+const PERSIST_STRUCTS_DS = 1
+
+/**
+ * Write the current Yjs data model to an encoder.
+ *
+ * @param {Yjs} y A Yjs instance
+ * @param {BinaryEncoder} encoder An encoder to write to
+ */
+export function encodeStructsDS (y, encoder) {
+  encoder.writeVarUint(PERSIST_STRUCTS_DS)
+  writeStructs(y, encoder, new Map())
+  writeDeleteSet(y, encoder)
+}
+
+/**
+ *Feed the Yjs instance with the persisted state
+ * @param {Yjs} y A Yjs instance.
+ * @param {BinaryDecoder} decoder A Decoder instance that holds the file content.
+ */
+export function decodePersisted (y, decoder) {
+  y.transact(() => {
+    while (decoder.hasContent()) {
+      const contentType = decoder.readVarUint()
+      switch (contentType) {
+        case PERSIST_UPDATE:
+          y.transact(() => {
+            integrateRemoteStructs(y, decoder)
+          })
+          break
+        case PERSIST_STRUCTS_DS:
+          y.transact(() => {
+            integrateRemoteStructs(y, decoder)
+            readDeleteSet(y, decoder)
+          })
+          break
+      }
+    }
+  })
+}