Next.js App Route for getting the current playing song on Spotify (or a cached version)

route.ts

import redis from '@/lib/redis'
import { tap } from '@/lib/utils'
import { NextResponse } from 'next/server'
import { NowPlaying } from '@/types/activities'
import { base64_encode, use } from '@/lib/utils'

type SpotifyResponse = {
	is_playing: boolean
	progress_ms: number
	item: {
		name: string
		external_urls: {
			spotify: string
		}
		duration_ms: number
		artists: {
			name: string
		}[]
		album: {
			images: {
				url: string
			}[]
		}
	}
}

export const revalidate = 60 // seconds

export async function GET(): Promise<NextResponse> {
	const token = await redis.get('spotify:token')
	if (!token) return NextResponse.json({ error: "Couldn't connect to Spotify." }, { status: 401 })

	const response = await fetch('https://api.spotify.com/v1/me/player/currently-playing', {
		headers: { Authorization: `Bearer ${token}` },
	})

	if (response.status == 401) {
		await refreshToken()
		return GET()
	}

	if (response.status == 204) {
		const cachedPlaying = (await redis.hgetall<NowPlaying>('spotify:now-playing')) ?? {}

		return NextResponse.json({ ...cachedPlaying, live: false } satisfies NowPlaying)
	}

	const nowPlaying = tap(
		use<SpotifyResponse, NowPlaying>(await response.json(), data => ({
			title: data.item.name,
			live: data.is_playing,
			url: data.item.external_urls.spotify,
			cover_img: data.item.album.images[0].url,
			artist: data.item.artists.map(artist => artist.name).join(', '),
		})),
		data => redis.hset('spotify:now-playing', data)
	)

	return NextResponse.json(nowPlaying satisfies NowPlaying)
}

const refreshToken = async () => {
	const refreshToken = await redis.get('spotify:refresh')

	const { access_token } = await fetch(
		`https://accounts.spotify.com/api/token?grant_type=refresh_token&refresh_token=${refreshToken}`,
		{
			method: 'POST',
			headers: {
				'Content-Type': 'application/x-www-form-urlencoded',
				Authorization: `Basic ${base64_encode(`${process.env.SPOTIFY_ID}:${process.env.SPOTIFY_SECRET}`)}`,
			},
		}
	).then(res => res.json())

	await redis.set('spotify:token', access_token)
}