START GUIDE

• Create a new firebase project from firebase console
• Initialize a new Free Database, Must be in the Realtime database service
• Claim your Firebase credentials (Settings>Services Accounts> Go > Create New Credentials) and replace it in the serviceAccountKey.example.go
• Rename the file as serviceAccountKey.go
• In the same file replace your DB Url
• Execute Docker docker-compose -f docker-compose.yml up
• Access to the API from http://localhost:8080

The nex you will see it's a docker instance with 5 replicas of the API this will help for improve the performance in the Encrypt process

How I solve the different tasks:

• For save the logs in the Database I use a middleware for save the request before all the software execute the endpoint, very important for debug if you wanna determinate the complete error path.
• For cache system I use a simple Library permit me store the data as a "localstorage" and I create a logic for the number of times the key is saved
• Work with the Async call to a external API, I use for that a Package to Simulate the Async/Await behavior of other languages
• I decide use firebase because the facility for deploy and maintain
• Also I decided use Docker not only for make the deploy more easy, even for increase the performance implementing a load balancer with 5 replicas, every replica can make part of the request send it to the principal server (Important: That means every Api will have a independent key and a independent counter, but every key will be only used 3 times until the expiration)

Your database will looks like this:

{
  "log" : {
    "-MaCG3sW9Q4nXOdHHjjP" : {
      "Method" : "POST",
      "URL" : "/v1/encrypt"
    },
    "-MaCGFCaJriPjOVWCOpw" : {
      "Method" : "GET",
      "URL" : "/v1/decrypt/-MaCG4-7Ngf9tfEDqcKf"
    },
   
  },
  "text" : {
    "-MaCG4-7Ngf9tfEDqcKf" : {
      "EncryptedText" : "2c1b47f08f09d55eb0f167783f4f885ddff746eb44fd8d67e245ee4377e1510da8ddd4ed5ada4e9528d16164a310e2da997fbcc24ae2ce48542de5758f763b7ecec1e9ab3bc771a800f4f56542cfa1fa5856df9b4b6643ce0917",
      "EncryptionKey" : "25c0aca4-0a0d-44c4-a573-946f2cbdab75"
    },
  }
}