Recommendation Algorithm for Songs

backend/app/api/songs/recommendations/route.ts

@@ -0,0 +1,65 @@
+import { verifySession } from '@/lib/session';
+import { ErrorResponse } from '@/lib/types';
+import { Song } from '@prisma/client';
+import { NextRequest, NextResponse } from 'next/server';
+import prisma from '@/lib/prisma';
+import { getRandomSegment } from '@/lib/misc';
+
+type GetResponse = {
+  songs: Song[];
+};
+
+export const GET = async (
+  req: NextRequest
+): Promise<NextResponse<GetResponse | ErrorResponse>> => {
+  const session = await verifySession();
+
+  const searchParams = new URL(req.url).searchParams;
+  const size = searchParams.get('size');
+
+  if (!size) {
+    return NextResponse.json({ error: 'Size is required' }, { status: 400 });
+  }
+
+  if (!session.isAuth) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+
+  const user = await prisma.user.findUnique({
+    where: {
+      id: session.uid,
+    },
+    include: {
+      preferences: true,
+    },
+  });
+
+  if (!user) {
+    return NextResponse.json({ error: 'User not found' }, { status: 404 });
+  }
+
+  const songs = await prisma.song.findMany({
+    where: {
+      seenBy: {
+        none: {
+          id: session.uid,
+        },
+      },
+      genre: {
+        value: {
+          in: user.preferences.map((preference) => preference.value),
+        },
+      },
+    },
+    include: {
+      genre: true,
+      seenBy: true,
+    },
+  });
+
+  console.log('Songs found:', songs.length);
+
+  return NextResponse.json({
+    songs: getRandomSegment(songs, parseInt(size)),
+  });
+};

backend/lib/misc.ts

@@ -0,0 +1,11 @@
+export const getRandomSegment = <T>(arr: T[], n: number): T[] => {
+  const result: T[] = [];
+  const indices: Set<number> = new Set();
+
+  while (indices.size < n && indices.size < arr.length) {
+    indices.add(Math.floor(Math.random() * arr.length));
+  }
+
+  indices.forEach((i) => result.push(arr[i]));
+  return result;
+};

backend/prisma/migrations/20250202073122_add_seen_to_songs/migration.sql

@@ -0,0 +1,16 @@
+-- CreateTable
+CREATE TABLE "_SongSeenBy" (
+    "A" INTEGER NOT NULL,
+    "B" INTEGER NOT NULL,
+
+    CONSTRAINT "_SongSeenBy_AB_pkey" PRIMARY KEY ("A","B")
+);
+
+-- CreateIndex
+CREATE INDEX "_SongSeenBy_B_index" ON "_SongSeenBy"("B");
+
+-- AddForeignKey
+ALTER TABLE "_SongSeenBy" ADD CONSTRAINT "_SongSeenBy_A_fkey" FOREIGN KEY ("A") REFERENCES "Song"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "_SongSeenBy" ADD CONSTRAINT "_SongSeenBy_B_fkey" FOREIGN KEY ("B") REFERENCES "User"("id") ON DELETE CASCADE ON UPDATE CASCADE;

backend/prisma/schema.prisma

@@ -23,6 +23,7 @@ model User {
   updatedAt DateTime @updatedAt
   preferences Genre[]
   likedSongs Song[]
+  seenSongs Song[] @relation("SongSeenBy")
 }
 
 model Song {
@@ -32,6 +33,7 @@ model Song {
   likedBy User[]
   genreId Int?
   genre Genre? @relation(fields: [genreId], references: [id])
+  seenBy User[] @relation("SongSeenBy")
 }