return empty array if no candidates for home feed selection

packages/api/src/jobs/update_home.ts

@@ -258,12 +258,13 @@ const rankCandidates = async (
 }
 
 const redisKey = (userId: string) => `home:${userId}`
+const emptyHomeKey = (key: string) => `${key}:empty`
 
 export const getHomeSections = async (
   userId: string,
   limit = 100,
   maxScore?: number
-): Promise<Array<{ member: Section; score: number }>> => {
+): Promise<Array<{ member: Section; score: number }> | null> => {
   const redisClient = redisDataSource.redisClient
   if (!redisClient) {
     throw new Error('Redis client not available')
@@ -285,6 +286,19 @@ export const getHomeSections = async (
     limit
   )
 
+  if (!results.length) {
+    logger.info('No sections found in redis')
+    // check if the feed is empty
+    const isEmpty = await redisClient.exists(emptyHomeKey(key))
+    if (isEmpty) {
+      logger.info('Empty feed')
+      return []
+    }
+
+    logger.info('Feed not found')
+    return null
+  }
+
   const sections = []
   for (let i = 0; i < results.length; i += 2) {
     const member = JSON.parse(results[i]) as Section
@@ -317,6 +331,14 @@ const appendSectionsToHome = async (
   }
 
   const key = redisKey(userId)
+  const emptyKey = emptyHomeKey(key)
+
+  if (!sections.length) {
+    logger.info('No available sections to add')
+    // set expiration to 1 hour
+    await redisClient.set(emptyKey, 'true', 'EX', 60 * 60)
+    return
+  }
 
   // store candidates in redis sorted set
   const pipeline = redisClient.pipeline()
@@ -337,6 +359,8 @@ const appendSectionsToHome = async (
   // add section to the sorted set
   pipeline.zadd(key, ...scoreMembers)
 
+  pipeline.del(emptyKey)
+
   // keep only the new sections and remove the oldest ones
   pipeline.zremrangebyrank(key, 0, -(sections.length + 1))
 
@@ -375,6 +399,10 @@ const mixHomeItems = (
     items: Array<Candidate>,
     batches: Array<Array<Candidate>>
   ) => {
+    if (batches.length === 0) {
+      return
+    }
+
     const batchSize = Math.ceil(items.length / batches.length)
 
     for (const item of items) {
@@ -424,32 +452,36 @@ const mixHomeItems = (
     >,
   }
 
-  distributeItems(shortItems, batches.short)
-  distributeItems(longItems, batches.long)
+  batches.short.length && distributeItems(shortItems, batches.short)
+  batches.long.length && distributeItems(longItems, batches.long)
 
   // convert batches to sections
   const sections = []
   const hiddenCandidates = rankedHomeItems.slice(50)
 
-  sections.push({
-    items: hiddenCandidates.map(candidateToItem),
-    layout: 'hidden',
-  })
+  hiddenCandidates.length &&
+    sections.push({
+      items: hiddenCandidates.map(candidateToItem),
+      layout: 'hidden',
+    })
 
-  sections.push({
-    items: batches.short.flat().map(candidateToItem),
-    layout: 'quick_links',
-  })
+  batches.short.length &&
+    sections.push({
+      items: batches.short.flat().map(candidateToItem),
+      layout: 'quick_links',
+    })
 
-  sections.push({
-    items: batches.long.flat().map(candidateToItem),
-    layout: 'top_picks',
-  })
+  batches.long.length &&
+    sections.push({
+      items: batches.long.flat().map(candidateToItem),
+      layout: 'top_picks',
+    })
 
-  sections.push({
-    items: justAddedCandidates.map(candidateToItem),
-    layout: 'just_added',
-  })
+  justAddedCandidates &&
+    sections.push({
+      items: justAddedCandidates.map(candidateToItem),
+      layout: 'just_added',
+    })
 
   return sections
 }
@@ -495,7 +527,6 @@ export const updateHome = async (data: UpdateHomeJobData) => {
 
     if (!justAddedCandidates.length && !candidates.length) {
       logger.info('No candidates found')
-      return
     }
 
     // TODO: integrity check on candidates

packages/api/src/resolvers/home/index.ts

@@ -41,7 +41,8 @@ export const homeResolver = authorized<
   const sections = await getHomeSections(uid, limit, cursor)
   log.info('Home sections fetched')
 
-  if (sections.length === 0) {
+  if (!sections) {
+    // home feed creation pending
     const existingJob = await getJob(updateHomeJobId(uid))
     if (existingJob) {
       log.info('Update job job already enqueued')
@@ -63,6 +64,17 @@ export const homeResolver = authorized<
     }
   }
 
+  if (sections.length === 0) {
+    // no available candidates
+    return {
+      edges: [],
+      pageInfo: {
+        hasPreviousPage: false,
+        hasNextPage: false,
+      },
+    }
+  }
+
   const endCursor = sections[sections.length - 1].score.toString()
 
   const edges = sections.map((section) => {
@@ -127,7 +139,7 @@ export const hiddenHomeSectionResolver = authorized<
   const sections = await getHomeSections(uid)
   log.info('Home sections fetched')
 
-  if (sections.length === 0) {
+  if (!sections) {
     return {
       errorCodes: [HomeErrorCode.Pending],
     }

packages/api/src/services/score.ts

@@ -79,4 +79,4 @@ class ScoreClientImpl implements ScoreClient {
   }
 }
 
-export const scoreClient = new ScoreClientImpl()
+export const scoreClient = new StubScoreClientImpl()