creating API to search the amount of doujins in database

backend/metadata/index.js

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+const app = require("./src/app.js")
+const PORT = Number(process?.env?.APP_PORT?.trim() || 3000); 
+
+app.listen(PORT, function(err){
+    if (err) console.log(err);
+    console.log(`Server listening on http://localhost:${PORT}`);
+});

backend/metadata/package.json

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+{
+  "name": "erohoshi",
+  "version": "1.0.0",
+  "description": "",
+  "main": "./src/app.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "dotenv": "^16.0.1",
+    "express": "^4.18.1",
+    "firebase": "^9.8.3",
+    "firebase-admin": "^11.0.0",
+    "typescript": "^4.7.4"
+  }
+}

backend/metadata/src/app.js

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+const express = require("express");
+const routes = require("./routes/routes.js")
+
+const app = express(); 
+
+app.use(express.json({
+    type: ["application.json"]
+}))
+
+app.use(routes);
+
+module.exports = app;

backend/metadata/src/controller/getTotalDoujins.js

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+const db = require("../firebase/db.js")
+
+async function getTotalDoujins(req, res) {
+
+    // get the document "doujins" in the section "metadata"
+    const collection = db.collection("metadata").doc("doujins"); 
+    // read the document
+    const doujins = await collection.get(); 
+    const amountOfDoujins = doujins.data()
+
+    // return the data from document (in this case, the amount of doujins in database)
+    if (!doujins.exists) {
+        return res
+        .status(404)
+        .send("There's nothing here")
+    } else { 
+        return res
+        .status(200)
+        .json({
+            "total": Number(amountOfDoujins.total)
+        })
+    }
+}
+
+module.exports = getTotalDoujins;

backend/metadata/src/firebase/db.js

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+const { initializeApp, cert, applicationDefault } = require("firebase-admin/app")
+const { getFirestore } = require("firebase-admin/firestore")
+const envName = require("../var.js")
+
+const serviceAccount = require("../../../eroneko-c890a77e5039.json")
+
+initializeApp({
+    credential: envName == "local" ? cert(serviceAccount) : applicationDefault()
+})
+
+const db = getFirestore()
+
+module.exports = db;
+

backend/metadata/src/routes/routes.js

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+const { Router } = require("express")
+const getTotalDoujins = require("../controller/getTotalDoujins.js")
+
+const router = Router(); 
+
+router
+    .get("/metadata/doujins/total", getTotalDoujins)
+    .get("/healthcheck", (req, res) => {
+        res
+        .status(200)
+        .send("Okay")
+    })
+
+module.exports = router; 

backend/metadata/src/var.js

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+require("dotenv").config()
+
+const envName = process.env.NODE_ENV || "qa";
+
+module.exports = envName