perf: reuse glb instead deleting

implements #2

src/unity-to-json/readAndConvertFbxToGltf.ts

@@ -1,12 +1,47 @@
 import convert from 'fbx2gltf';
-import fs from 'fs/promises';
+import fs from 'fs';
+import fsPromises from 'fs/promises';
 import path from 'path';
 import os from 'os';
+import crypto from 'crypto';
+
+const getFileHash = (filepath: string) => {
+  const fd = fs.createReadStream(filepath);
+
+  const hash = crypto.createHash('sha1');
+  hash.setEncoding('hex');
+
+  return new Promise((resolve) => {
+    fd.on('end', () => {
+      hash.end();
+      resolve(hash.read());
+    });
+    fd.on('error', () => resolve(''));
+    fd.pipe(hash);
+  });
+};
+
+const silentlyReadFile = async (filepath: string) => {
+  try {
+    const result = await fsPromises.readFile(filepath, 'base64');
+    return result;
+  } catch (e) {
+    return '';
+  }
+};
 
 export const readAndConvertFbxToGltf = async (filepath: string) => {
-  const glbDestPath = path.resolve(os.tmpdir(), `${filepath}.glb`);
+  const fbxHash = await getFileHash(filepath);
+  const glbDestPath = path.resolve(os.tmpdir(), `${fbxHash}.glb`);
+
+  const recentlyGeneratedGlb = await silentlyReadFile(glbDestPath);
+  if (recentlyGeneratedGlb) {
+    return recentlyGeneratedGlb;
+  }
+
   await convert(filepath, glbDestPath);
-  const glbBase64 = await fs.readFile(glbDestPath, 'base64');
-  await fs.unlink(glbDestPath);
+
+  const glbBase64 = await fsPromises.readFile(glbDestPath, 'base64');
+
   return glbBase64;
 };