From 04c918d092d8da1f98ef39a8614667ec2249c387 Mon Sep 17 00:00:00 2001
From: Xmader <xmader@outlook.com>
Date: Thu, 5 Nov 2020 16:47:50 -0500
Subject: [PATCH] refactor: anti-detection

---
 src/anti-detection.ts | 25 +++++++++++++++++++++++--
 src/file.ts           | 30 +++++++++++-------------------
 2 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/src/anti-detection.ts b/src/anti-detection.ts
index 65ed729..2e3ee1f 100644
--- a/src/anti-detection.ts
+++ b/src/anti-detection.ts
@@ -7,7 +7,9 @@
 export const makeNative = (() => {
   const l: Set<Function> = new Set()
 
-  const _toString = Function.prototype['toString']
+  const target = Function.prototype
+  const method = 'toString'
+  const _toString = target[method]
   const toString = function () {
     if (l.has(this)) {
       // "function () {\n    [native code]\n}"
@@ -15,7 +17,7 @@ export const makeNative = (() => {
     }
     return _toString.call(this) as string
   }
-  Function.prototype.toString = toString
+  target[method] = toString
 
   // make `Function.prototype.toString` itself "native"
   l.add(toString)
@@ -24,3 +26,22 @@ export const makeNative = (() => {
     l.add(fn)
   }
 })()
+
+export const hookNative = <T extends object, M extends (keyof T)> (
+  target: T,
+  method: M,
+  hook: (originalFn: T[M], detach: () => void) => T[M],
+): void => {
+  // reserve for future hook update
+  const _fn = target[method]
+  const detach = () => {
+    target[method] = _fn // detach
+  }
+
+  // This script can run before anything on the page,  
+  // so setting this function to be non-configurable and non-writable is no use.
+  const hookedFn = hook(_fn, detach)
+  target[method] = hookedFn
+
+  makeNative(hookedFn as any)
+}
diff --git a/src/file.ts b/src/file.ts
index 0d41ca1..c4a8ceb 100644
--- a/src/file.ts
+++ b/src/file.ts
@@ -2,7 +2,7 @@
 
 import scoreinfo from './scoreinfo'
 import { webpackHook } from './webpack-hook'
-import { makeNative } from './anti-detection'
+import { hookNative } from './anti-detection'
 
 const FILE_URL_MODULE_ID = 'iNJA'
 const MAGIC_REG = /^\d+(img|mp3|midi)\d(.+)$/
@@ -18,25 +18,17 @@ const getApiUrl = (id: number, type: FileType, index: number): string => {
  * I know this is super hacky.
  */
 let magic: Promise<string> | string = new Promise((resolve) => {
-  // reserve for future hook update
-  const target = String.prototype
-  const method = 'charCodeAt'
-  const _fn = target[method]
-
-  // This script can run before anything on the page,  
-  // so setting this function to be non-configurable and non-writable is no use.
-  const hookFn = function (i: number) {
-    const m = this.match(MAGIC_REG)
-    if (m) {
-      resolve(m[2])
-      magic = m[2]
-      target[method] = _fn // detach
+  hookNative(String.prototype, 'charCodeAt', (_fn, detach) => {
+    return function (i: number) {
+      const m = this.match(MAGIC_REG)
+      if (m) {
+        resolve(m[2])
+        magic = m[2]
+        detach()
+      }
+      return _fn.call(this, i) as number
     }
-    return _fn.call(this, i) as number
-  }
-  target[method] = hookFn
-
-  makeNative(hookFn)
+  })
 })
 
 export const getFileUrl = async (type: FileType, index = 0): Promise<string> => {