App.js

const express = require("express");
const fs = require("fs");
const { fileURLToPath } = require("url");
const app = express();
const AWS = require("aws-sdk");

const DAILY_CARACTE_SYNTHESIZE_LIMIT = 161290;
var counterDate = new Date().getDate();
var dailyCounter = 0;

AWS.config.loadFromPath("./awscreds.json");

const Polly = new AWS.Polly({
  signatureVersion: "v4",
  region: "us-east-1",
});

const port = 3000;
const key = "a188022f2dc551fdb37e8a844c01dc1b";
const file_path = "./public/{name}.mp3";

app.get("/requestaudio/:name", (req, res) => {
  if (req.query.key !== key) {
    // Senha incorreta.
    res
      .status(401)
      .json({ error: "Not authorized! Check if the password is correct." });
    return;
  }

  let name = req.params["name"].trim().toLowerCase();
  let audio_filename = file_path.replace("{name}", encodeURIComponent(name));

  if (name == "" || name.length > 42) {
    res.status(404).json({ error: "Not Found! Name must have 1 - 41 caracteres" });
    return;
  }

  if (!fs.existsSync(audio_filename)) {
    // Arquivo não existe, temos que baixar ele da AWS.
    // res.status(404).json({'error': 'Not Found! This audio does not exist, and we could not download it from AWS at this time...'});

    // TODO: baixar da AWS (lembrete: checar limites diários/mensais antes de baixar).

    // polly settup
    let pollyparams = {
      Text: name,
      TextType: "text",
      OutputFormat: "mp3",
      VoiceId: "Camila",
      Engine: "neural",
      LanguageCode: "pt-BR",
    };


    if(counterDate !=  (new Date().getDate())){
      dailyCounter = 0;
      counterDate =  new Date().getDate();
    }
    if(dailyCounter > DAILY_CARACTE_SYNTHESIZE_LIMIT){
      res
      .status(503)
      .json({
        error:
          "Daily limit of speech synthesis reached! We could not download this audio from AWS at this time...",
      });
    return;
    }

    dailyCounter += name.length;

    Polly.synthesizeSpeech(pollyparams, (err, data) => {
      if (err) {
        res
          .status(404)
          .json({
            error:
              "Not Found! This audio does not exist, and we could not download it from AWS at this time...",
          });
        console.log(err.message);
        return;
      }

      if (!(data.AudioStream instanceof Buffer)) {
        res
          .status(404)
          .json({
            error:
              "Not Found! This audio does not exist, and we could not download it from AWS at this time...",
          });
        return;
      }

      fs.writeFile(audio_filename, data.AudioStream, function (err) {
        if (err) {
          res
            .status(404)
            .json({
              error:
                "Not Found! This audio does not exist, and we could not download it from AWS at this time...",
            });
          console.log(err);
          return;
        }
        console.log("The file was saved!");
        res.download(audio_filename);
      });
    });
    
    return;
  }

  //Enviar arquivo, que agora já existe.
  res.download(audio_filename);
});

app.get("/", (req, res) => {
  res
    .status(400)
    .json({
      error:
        "Bad request! Use this format for the URL instead: " +
        req.protocol +
        "://" +
        req.headers.host +
        "/requestaudio/NAME?key=PASSWORD",
    });
  // Alternativamente, se você não quiser deixar claro como usa a API, descomente o de baixo e comente o de cima.
  //res.status(400).json({'error': 'Bad request!'});
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});