From 65622ac96110927b42053f34511aa42d068f17d6 Mon Sep 17 00:00:00 2001
From: Andre Staltz <andre@staltz.com>
Date: Thu, 27 Apr 2023 15:51:31 +0300
Subject: [PATCH] Tangle.precedes(a,b) API

---
 lib/feed-v1/tangle.js  | 17 +++++++++++++++++
 lib/index.js           |  1 +
 test/getTangle.test.js | 22 ++++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/lib/feed-v1/tangle.js b/lib/feed-v1/tangle.js
index 9e7f1e4..5c48023 100644
--- a/lib/feed-v1/tangle.js
+++ b/lib/feed-v1/tangle.js
@@ -222,6 +222,23 @@ class Tangle {
     return path
   }
 
+  precedes(a, b) {
+    if (!this.#rootMsg) {
+      console.warn('Tangle is missing root message')
+      return false
+    }
+    if (a === b) return false
+    if (b === this.#rootHash) return false
+    let toCheck = [b]
+    while (toCheck.length > 0) {
+      const prev = this.#prev.get(toCheck.shift())
+      if (!prev) continue
+      if (prev.includes(a)) return true
+      toCheck.push(...prev)
+    }
+    return false
+  }
+
   size() {
     return this.#depth.size
   }
diff --git a/lib/index.js b/lib/index.js
index 9f21b38..b7e25d3 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -191,6 +191,7 @@ exports.init = function initDB(peer, config) {
     const msgHash = FeedV1.getMsgHash(msg)
 
     // TODO: optimize this. Perhaps have a Map() of msgHash -> record
+    // Or even better, a bloom filter. If you just want to answer no/perhaps.
     let rec
     if ((rec = getRecord(msgHash))) return cb(null, rec)
 
diff --git a/test/getTangle.test.js b/test/getTangle.test.js
index d33cde7..507dd6c 100644
--- a/test/getTangle.test.js
+++ b/test/getTangle.test.js
@@ -125,6 +125,28 @@ test('Tangle.topoSort', (t) => {
   t.end()
 })
 
+test('Tangle.precedes', (t) => {
+  t.true(tangle.precedes(rootPost, reply1Lo), 'rootPost precedes reply1Lo')
+  t.true(tangle.precedes(rootPost, reply1Hi), 'rootPost precedes reply1Hi')
+  t.false(
+    tangle.precedes(reply1Hi, rootPost),
+    'reply1Hi doesnt precede rootPost'
+  )
+  t.false(
+    tangle.precedes(reply1Lo, reply1Hi),
+    'reply1Lo doesnt precede reply1Hi'
+  )
+  t.false(tangle.precedes(reply1Lo, reply1Lo), 'reply1Lo doesnt precede itself')
+  t.true(tangle.precedes(reply1Lo, reply3Hi), 'reply1Lo precedes reply3Hi')
+  t.true(tangle.precedes(reply1Hi, reply2A), 'reply1Hi precedes reply2A')
+  t.false(
+    tangle.precedes(reply3Lo, reply1Hi),
+    'reply3Lo doesnt precede reply1Hi'
+  )
+
+  t.end()
+})
+
 test('Tangle.getTips', (t) => {
   const tips = tangle.getTips()