From 36c58ff9fdeb08ba24037df6b94e00668bc8289c Mon Sep 17 00:00:00 2001
From: afterlifepro <vielle.dev@proton.me>
Date: Wed, 23 Jul 2025 23:12:13 +0100
Subject: [PATCH] Implement access token generation in spotify.ts

.refreshToken stores the refresh token in plaintext and should not be commited to git by mistake
---
 .gitignore                        |   1 +
 src/components/playing/spotify.ts | 135 +++++++++++++++++++++++++++++-
 2 files changed, 134 insertions(+), 2 deletions(-)

diff --git a/.gitignore b/.gitignore
index 16d54bb..a8ef08a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -22,3 +22,4 @@ pnpm-debug.log*
 
 # jetbrains setting folder
 .idea/
+.refreshToken
diff --git a/src/components/playing/spotify.ts b/src/components/playing/spotify.ts
index e577545..20e5db9 100644
--- a/src/components/playing/spotify.ts
+++ b/src/components/playing/spotify.ts
@@ -1,3 +1,134 @@
+import {
+  SPOTIFY_CLIENT_ID,
+  SPOTIFY_CLIENT_SECRET,
+  SPOTIFY_REDIRECT_URI,
+} from "astro:env/server";
+import fs from "fs/promises";
+
+const throws = (val: unknown) => {
+  throw val;
+};
+
+/** via: https://www.totaltypescript.com/concepts/the-prettify-helper */
+type Prettify<T> = {
+  [K in keyof T]: T[K];
+} & {};
+
+type AuthToken = {
+  access_token: string;
+  token_type: "Bearer";
+  scope: string;
+  expires_in: number;
+  refresh_token: string;
+};
+
+type RefreshToken = Prettify<
+  Omit<AuthToken, "refresh_token"> & { refresh_token?: string }
+>;
+
+const isRefreshToken = (obj: unknown): obj is RefreshToken =>
+  // validate is object
+  typeof obj === "object" &&
+  obj !== null &&
+  // validate properties
+  "access_token" in obj &&
+  typeof obj.access_token === "string" &&
+  "token_type" in obj &&
+  obj.token_type === "Bearer" &&
+  "scope" in obj &&
+  typeof obj.scope === "string" &&
+  "expires_in" in obj &&
+  typeof obj.expires_in === "number" &&
+  // either refresh token exists as string or not at all
+  (("refresh_token" in obj && typeof obj.refresh_token === "string") ||
+    !("refresh_token" in obj));
+
+// auth token is just refresh with a non optional refresh_token
+const isAuthToken = (obj: unknown): obj is AuthToken =>
+  isRefreshToken(obj) && "refresh_token" in obj;
+
 export async function getAccessCode(userAuthCode?: string) {
-  return "Not implemented!"
-}
\ No newline at end of file
+  const refreshToken = await fs
+    .readFile("./.refreshToken", { encoding: "utf-8" })
+    .catch((_) => undefined)
+    .then((x) => (x === "" || x === "REFRESH_TOKEN" ? undefined : x));
+  if (!(userAuthCode || refreshToken))
+    throw new Error(
+      "No auth code or refresh token.\nGenerate an auth code at `/src/pages/_callback`\nA refresh token will be generated from this auth token.",
+    );
+
+  // prefer auth codes over refresh tokens
+  // since the auth code may have updated scopes.
+
+  const accessFrom:
+    | {
+        userAuthCode: string;
+      }
+    | {
+        refreshToken: string;
+      } = userAuthCode
+    ? { userAuthCode }
+    : refreshToken
+      ? { refreshToken }
+      : (undefined as never);
+
+  const req = fetch("https://accounts.spotify.com/api/token", {
+    method: "POST",
+    headers: {
+      "Content-Type": "application/x-www-form-urlencoded",
+      Authorization: `Basic ${Buffer.from(SPOTIFY_CLIENT_ID + ":" + SPOTIFY_CLIENT_SECRET).toString("base64")}`,
+    },
+    body: new URLSearchParams({
+      grant_type:
+        "userAuthCode" in accessFrom ? "authorization_code" : "refresh_token",
+      ...("userAuthCode" in accessFrom
+        ? {
+            code: accessFrom.userAuthCode,
+            redirect_uri: SPOTIFY_REDIRECT_URI,
+          }
+        : {
+            refresh_token: accessFrom.refreshToken,
+          }),
+    }).toString(),
+  });
+
+  return (
+    req
+      // if res isn't 200 handle it in the catch
+      .then((res) => (res.ok ? res : throws(res)))
+      // request is 200-299
+      // json can throw SyntaxError in this case
+      .then((res) => res.json())
+      .then((res) =>
+        "userAuthCode" in accessFrom
+          ? isAuthToken(res)
+            ? { code: res.access_token, refresh: res.refresh_token }
+            : throws({ err: "INVALID_RESPONSE", res })
+          : isRefreshToken(res)
+            ? {
+                code: res.access_token,
+                refresh: res.refresh_token ?? accessFrom.refreshToken,
+              }
+            : throws({ err: "INVALID_RESPONSE", res }),
+      )
+      // res is now an access token and refresh token
+      .then((res) => {
+        fs.writeFile("./.refreshToken", res.refresh, { encoding: "utf-8" });
+        return res.code;
+      })
+      .catch((err) => {
+        // SyntaxError
+        // Response
+        // {err: string, res: Response}
+        if (err instanceof Response) console.error("Request failed:", err);
+        else if (err instanceof SyntaxError)
+          console.error("Response JSON failed", err);
+        else if (err.err === "INVALID_RESPONSE")
+          console.error("Response malformed:", err);
+        else {
+          console.error("Unhandled exception.");
+          throw err;
+        }
+      })
+  );
+}
-- 
2.51.2