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;

package-lock.json

@@ -1043,6 +1043,11 @@
       "integrity": "sha512-1nh45deeb5olNY7eX82BkPO7SSxR5SSYJiPTrTdFUVYwAl8CKMA5N9PjTYkHiRjisVcxcQ1HXdLhx2qxxJzLNQ==",
       "dev": true
     },
+    "node-fetch": {
+      "version": "2.6.0",
+      "resolved": "https://registry.npmjs.org/node-fetch/-/node-fetch-2.6.0.tgz",
+      "integrity": "sha512-8dG4H5ujfvFiqDmVu9fQ5bOHUC15JMjMY/Zumv26oOvvVJjM67KF8koCWIabKQ1GJIa9r2mMZscBq/TbdOcmNA=="
+    },
     "normalize-package-data": {
       "version": "2.5.0",
       "resolved": "https://registry.npmjs.org/normalize-package-data/-/normalize-package-data-2.5.0.tgz",

package.json

@@ -5,7 +5,8 @@
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
-    "lint": "./node_modules/.bin/eslint ."
+    "lint": "./node_modules/.bin/eslint .",
+    "lintfix": "./node_modules/.bin/eslint . --fix"
   },
   "repository": {
     "type": "git",
@@ -28,5 +29,8 @@
     "eslint": "^6.8.0",
     "eslint-config-airbnb-base": "^14.1.0",
     "eslint-plugin-import": "^2.20.2"
+  },
+  "dependencies": {
+    "node-fetch": "*"
   }
 }