Project Overview

This project is structured around five core components, designed to handle email notifications based on currency exchange rates from the Coinbase service. Below is a brief overview of each component and their functionalities:

Core Components:

• Handler (/internal/handlers/handler.go): Manages incoming requests and interfaces with the EmailService to execute the main logic which includes fetching the current exchange rate, subscribing users to notifications, and sending emails.
• EmailService (/internal/service/email.go): Acts as the central business logic layer, coordinating with Fstorage, CoinbaseClient, and SmtpClient to manage rates, subscriptions, and email notifications.
• Fstorage (/internal/storage/fstorage.go): Handles data persistence by saving email entries to a file, leveraging a hash table for efficient lookup.
• CoinbaseClient (/internal/client/coinbase.go): Fetches the current exchange rate from Coinbase's API.
• SmtpClient (/internal/client/smtp.go): Sends out email notifications using an SMTP server.

Handler Functions:

• getRate(): Retrieves the current rate from the EmailService. In case of an issue, it returns a 400 status code.
• Subscribe(): Registers an email for notifications, checking for duplicates and validating the email format.
• SendEmails(): Triggers the sending of email notifications to all subscribed users, tracking any errors.

EmailService Methods:

• Rate(): Contacts CoinbaseClient for the latest exchange rate.
• SendEmail(): Gathers emails from Fstorage and sends out notifications, collecting any unsent emails due to errors.
• Subscribe(): Adds a new email to the subscription list, ensuring no duplicates.

Fstorage:

• Manages a file and a hash table for storing email addresses.
• Append(): Adds a new email, ensuring uniqueness.
• GetEmails(): Retrieves a list of subscribed emails.
• buildIndex(): Initializes the hash table during startup.

External Communication:

• CoinbaseClient makes a GET request to Coinbase for the latest exchange rate in UAH.
• SmtpClient interfaces with an SMTP server to send emails.

Application Setup and Launch:

1. Clone the repository.
2. Edit config.yml with your SMTP server details (e.g., Gmail).
3. Build a Docker image: docker build --tag go-email .
4. Run the container: docker run -p 1313:1313 go-email (ensure the first port matches bind_ip in the config).