From 9893ad22c6abd7634c1976d6bc0745a107b557b7 Mon Sep 17 00:00:00 2001
From: Michele Riva <ciao@micheleriva.it>
Date: Mon, 16 Sep 2024 11:06:05 -0700
Subject: [PATCH] fix: fixes zero division when computing scores after removing
 all documents from an index (#792)

Co-authored-by: Braden <braden.herndon@gmail.com>, @kushuh
---
 packages/orama/src/components/index.ts |  7 +++++--
 packages/orama/tests/remove.test.ts    | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/packages/orama/src/components/index.ts b/packages/orama/src/components/index.ts
index 372dc5d04..06505a967 100644
--- a/packages/orama/src/components/index.ts
+++ b/packages/orama/src/components/index.ts
@@ -162,8 +162,11 @@ export async function removeDocumentScoreParameters(
 ): Promise<void> {
   const internalId = getInternalDocumentId(index.sharedInternalDocumentStore, id)
 
-  index.avgFieldLength[prop] =
-    (index.avgFieldLength[prop] * docsCount - index.fieldLengths[prop][internalId]!) / (docsCount - 1)
+  if (docsCount > 1) {
+    index.avgFieldLength[prop] = (index.avgFieldLength[prop] * docsCount - index.fieldLengths[prop][internalId]!) / (docsCount - 1);
+  } else {
+    index.avgFieldLength[prop] = undefined as unknown as number;
+  }
   index.fieldLengths[prop][internalId] = undefined
   index.frequencies[prop][internalId] = undefined
 }
diff --git a/packages/orama/tests/remove.test.ts b/packages/orama/tests/remove.test.ts
index 2b4784069..48263e536 100644
--- a/packages/orama/tests/remove.test.ts
+++ b/packages/orama/tests/remove.test.ts
@@ -353,3 +353,20 @@ async function createSimpleDB() {
 
   return [db, id1, id2, id3, id4] as const
 }
+
+t.test('test case for #766: Zero division when computing scores after removing all documents from an index.', async (t) => {
+  const db = await create({
+    schema: {
+      name: 'string'
+    } as const
+  })
+
+  const id = await insert(db, { name: 'test' })
+
+  const success = await remove(db, id)
+
+  await insert(db, { name: 'foo' })
+  await insert(db, { name: 'bar' })
+
+  t.ok(success)
+})
\ No newline at end of file