From 67485e98373de0eaa69d87d16db4f1db5f49dc4c Mon Sep 17 00:00:00 2001
From: zkldi <ktchidev@gmail.com>
Date: Sun, 4 Sep 2022 20:03:31 +0100
Subject: [PATCH] refactor: improve performance of song lookups

use lookup tables to optimise looking up songs; the former solution
was O(n^2), this one is O(1) with a small hit to memory.
---
 common/src/utils/util.ts                               | 10 ++++++++++
 .../api/v1/games/_game/_playtype/content/bms-router.ts | 10 ++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/common/src/utils/util.ts b/common/src/utils/util.ts
index 376c30834..8e6dd1ba5 100644
--- a/common/src/utils/util.ts
+++ b/common/src/utils/util.ts
@@ -253,3 +253,13 @@ export function FormatSieglindePMS(sgl: number): string {
 
 	return `●${(sgl - 12).toFixed(2)}`;
 }
+
+export function CreateSongMap<G extends Game = Game>(songs: Array<SongDocument<G>>) {
+	const songMap = new Map<integer, SongDocument<G>>();
+
+	for (const song of songs) {
+		songMap.set(song.id, song);
+	}
+
+	return songMap;
+}
diff --git a/server/src/server/router/api/v1/games/_game/_playtype/content/bms-router.ts b/server/src/server/router/api/v1/games/_game/_playtype/content/bms-router.ts
index a6427bae1..e3ab53774 100644
--- a/server/src/server/router/api/v1/games/_game/_playtype/content/bms-router.ts
+++ b/server/src/server/router/api/v1/games/_game/_playtype/content/bms-router.ts
@@ -1,6 +1,8 @@
 import { Router } from "express";
 import db from "external/mongo/db";
 import CreateLogCtx from "lib/logger/logger";
+import { CreateSongMap } from "tachi-common";
+import { integer, SongDocument } from "tachi-common/types";
 import { GetFolderCharts, GetFoldersFromTable } from "utils/folder";
 import { GetTachiData } from "utils/req-tachi-data";
 import type { Request, Response } from "express";
@@ -85,10 +87,10 @@ CreateAndMountTable(
 		for (const folder of folders) {
 			const data = await GetFolderCharts(folder, {}, true);
 			const charts = data.charts as Array<ChartDocument<"bms:7K">>;
-			const songs = data.songs;
+			const songMap = CreateSongMap(data.songs);
 
 			for (const chart of charts) {
-				const song = songs.find((song) => song.id === chart.songID);
+				const song = songMap.get(chart.songID);
 
 				if (!song) {
 					response.push({
@@ -146,10 +148,10 @@ CreateAndMountTable(
 		for (const folder of folders) {
 			const data = await GetFolderCharts(folder, {}, true);
 			const charts = data.charts as Array<ChartDocument<"bms:7K">>;
-			const songs = data.songs;
+			const songMap = CreateSongMap(data.songs);
 
 			for (const chart of charts) {
-				const song = songs.find((song) => song.id === chart.songID);
+				const song = songMap.get(chart.songID);
 
 				if (!song) {
 					response.push({