From 2ee01cbeaa9019b7ee46da43a78448d7e62c4a8b Mon Sep 17 00:00:00 2001
From: Jared Grippe <jared@deadlyicon.com>
Date: Thu, 4 Aug 2022 14:45:50 -0700
Subject: [PATCH] added core.update({ minLength: n }) and core.waitForLength(n)

---
 index.js          | 17 ++++++++++++++++
 test/replicate.js | 52 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/index.js b/index.js
index 2117088..2169880 100644
--- a/index.js
+++ b/index.js
@@ -626,11 +626,28 @@ module.exports = class Hypercore extends EventEmitter {
       if (!upgraded) upgraded = this.contiguousLength !== contig
     }
 
+    if (opts && typeof opts.minLength === 'number') {
+      await this.waitForLength(opts.minLength)
+    }
+
     if (!upgraded) return false
     if (this.snapshotted) return this._updateSnapshot()
     return true
   }
 
+  waitForLength (minLength = 0) {
+    return new Promise(resolve => {
+      if (this.length >= minLength) return resolve(this.length)
+      const onAppend = () => {
+        if (this.length >= minLength) {
+          this.removeListener('append', onAppend)
+          resolve(this.length)
+        }
+      }
+      this.on('append', onAppend)
+    })
+  }
+
   async seek (bytes, opts) {
     if (this.opened === false) await this.opening
 
diff --git a/test/replicate.js b/test/replicate.js
index 2234ad6..de700bf 100644
--- a/test/replicate.js
+++ b/test/replicate.js
@@ -840,3 +840,55 @@ test('sparse replication without gossiping', async function (t) {
     t.alike(await c.seek(4), [4, 0])
   })
 })
+
+test('sparse update with minLength', async function (t) {
+  const a = await create()
+  const b = await create(a.key)
+  replicate(a, b, t)
+
+  await a.append(['1', '2'])
+  await b.update()
+  t.is(b.length, 2)
+
+  const updateLength5 = t.test('updateLength5')
+  updateLength5.plan(1)
+
+  b.update({ minLength: 5 }).then(() => {
+    updateLength5.pass()
+  })
+
+  await a.append(['3'])
+  await eventFlush()
+  await a.append(['4'])
+  await eventFlush()
+  await a.append(['5'])
+
+  await updateLength5
+  t.is(b.length, 5)
+})
+
+test('non-sparse update with minLength', async function (t) {
+  const a = await create()
+  const b = await create(a.key, { sparse: false })
+  replicate(a, b, t)
+
+  await a.append(['1', '2'])
+  await b.update()
+  t.is(b.length, 2)
+
+  const updateLength5 = t.test('updateLength5')
+  updateLength5.plan(1)
+
+  b.update({ minLength: 5 }).then(() => {
+    updateLength5.pass()
+  })
+
+  await a.append(['3'])
+  await eventFlush()
+  await a.append(['4'])
+  await eventFlush()
+  await a.append(['5'])
+
+  await updateLength5
+  t.is(b.length, 5)
+})