Tangle can be built from randomly ordered msgs

lib/msg-v4/tangle.js

@@ -93,6 +93,7 @@ class Tangle {
    * @param {Msg} msg
    */
   add(msgID, msg) {
+    // Add the root msg
     if (msgID === this.#rootID && !this.#rootMsg) {
       this.#tips.add(msgID)
       this.#perDepth.set(0, [msgID])
@@ -101,10 +102,20 @@ class Tangle {
       return
     }
 
+    // Add affix msg
     const tangles = msg.metadata.tangles
     if (msgID !== this.#rootID && tangles[this.#rootID]) {
       if (this.#depth.has(msgID)) return
-      this.#tips.add(msgID)
+      let hasSuccessor = false
+      for (const prevs of this.#prev.values()) {
+        if (prevs.includes(msgID)) {
+          hasSuccessor = true
+          break
+        }
+      }
+      if (!hasSuccessor) {
+        this.#tips.add(msgID)
+      }
       const prev = tangles[this.#rootID].prev
       for (const p of prev) {
         this.#tips.delete(p)

test/msg-v4/tangles.test.js

@@ -192,3 +192,49 @@ test('MsgV4.Tangle lipmaa in multi-author tangle', (t) => {
     'A:msg4 points to A:msg1,B:msg3'
   )
 })
+
+test('MsgV4.Tangle can add msgs in random order', (t) => {
+  const keypairA = Keypair.generate('ed25519', 'alice')
+  const accountA = MsgV4.getMsgID(
+    MsgV4.createAccount(keypairA, 'person', 'alice')
+  )
+  const mootA = MsgV4.createMoot(accountA, 'post', keypairA)
+  const mootAID = MsgV4.getMsgID(mootA)
+
+  const tangleBuilder = new MsgV4.Tangle(mootAID)
+  tangleBuilder.add(mootAID, mootA)
+
+  const msg1 = MsgV4.create({
+    account: accountA,
+    accountTips: [accountA],
+    domain: 'post',
+    data: { text: 'Hello world!' },
+    tangles: {
+      [mootAID]: tangleBuilder,
+    },
+    keypair: keypairA,
+  })
+  const msgID1 = MsgV4.getMsgID(msg1)
+  tangleBuilder.add(msgID1, msg1)
+
+  const msg2 = MsgV4.create({
+    account: accountA,
+    accountTips: [accountA],
+    domain: 'post',
+    data: { text: 'Hello world!' },
+    tangles: {
+      [mootAID]: tangleBuilder,
+    },
+    keypair: keypairA,
+  })
+  const msgID2 = MsgV4.getMsgID(msg2)
+  tangleBuilder.add(msgID1, msg1)
+
+  const tangle = new MsgV4.Tangle(mootAID)
+  tangle.add(mootAID, mootA)
+  tangle.add(msgID2, msg2)
+  tangle.add(msgID1, msg1)
+
+  assert.deepEqual(tangle.topoSort(), [mootAID, msgID1, msgID2]);
+  assert.deepEqual([...tangle.tips], [msgID2], 'tangle tips')
+})