text(), json(), buffer() work

index.js

@@ -0,0 +1,70 @@
+const fetch = require('node-fetch');
+const fs = require('fs');
+const crypto = require('crypto');
+const path = require('path');
+
+function md5(str) {
+  return crypto.createHash('md5').update(str).digest('hex');
+}
+
+async function getResponse(cacheDirPath, requestArguments, bodyFunctionName) {
+  const cacheHash = md5(JSON.stringify(requestArguments) + bodyFunctionName);
+  const cachedFilePath = path.join(cacheDirPath, `${cacheHash}.json`);
+
+  try {
+    const body = JSON.parse(await fs.promises.readFile(cachedFilePath));
+    if (bodyFunctionName === 'buffer') {
+      return Buffer.from(body);
+    }
+
+    return body;
+  } catch (err) {
+    const fetchResponse = await fetch(...requestArguments);
+    const bodyResponse = await fetchResponse[bodyFunctionName]();
+    await fs.promises.writeFile(cachedFilePath, JSON.stringify(bodyResponse));
+    return bodyResponse;
+  }
+}
+
+class ResponseWrapper {
+  constructor(cacheDirPath, requestArguments) {
+    this.cacheDirPath = cacheDirPath;
+    this.requestArguments = requestArguments;
+  }
+
+  text() {
+    return getResponse(this.cacheDirPath, this.requestArguments, this.text.name);
+  }
+
+  json() {
+    return getResponse(this.cacheDirPath, this.requestArguments, this.json.name);
+  }
+
+  buffer() {
+    return getResponse(this.cacheDirPath, this.requestArguments, this.buffer.name);
+  }
+
+  textConverted() {
+    return getResponse(this.cacheDirPath, this.requestArguments, this.textConverted.name);
+  }
+}
+
+function createFetch(cacheDirPath) {
+  let madeDir = false;
+
+  return async (...args) => {
+    if (!madeDir) {
+      try {
+        await fs.promises.mkdir(cacheDirPath);
+      } catch (err) {
+        // Ignore.
+      }
+
+      madeDir = true;
+    }
+
+    return new ResponseWrapper(cacheDirPath, args);
+  };
+}
+
+module.exports = createFetch;