debt-pirate/api/src/services/mailer/service.rs

use std::{
    fs::File,
    io::Read,
    path::Path,
    sync::{mpsc::Receiver, LazyLock},
    thread,
};

use lettre::{
    message::{header::ContentType, Mailbox},
    transport::smtp::{
        authentication::{Credentials, Mechanism},
        PoolConfig,
    },
    AsyncSmtpTransport, AsyncTransport, Message, Tokio1Executor,
};
use tokio::runtime::Handle;

use super::UserConfirmationMessage;

static CREDENTIALS: LazyLock<Credentials> = LazyLock::new(|| {
    Credentials::new(
        "donotreply@mail.dziura.cloud".to_owned(),
        "hunter2".to_owned(),
    )
});

static NUM_CPUS: LazyLock<u32> = LazyLock::new(|| num_cpus::get() as u32);

static FROM_MAILBOX: LazyLock<Mailbox> = LazyLock::new(|| {
    "No Not Reply Auth-Test <donotreply@mail.dziura.cloud>"
        .parse()
        .unwrap()
});

pub fn start_emailer_service(
    runtime: Handle,
    assets_dir: &Path,
    email_message_rx: Receiver<UserConfirmationMessage>,
) {
    let new_user_confirmation_template_path = assets_dir.join("new-user-confirmation.html");
    // TODO: Validate that the new user confirmation template exists

    let mut new_user_confirmation_template_text = String::with_capacity(8000);
    File::open(new_user_confirmation_template_path)
        .and_then(|mut file| file.read_to_string(&mut new_user_confirmation_template_text))
        .unwrap();

    thread::spawn(move || {
        while let Some(message) = email_message_rx.iter().next() {
            let new_user_confirmation_template_text = new_user_confirmation_template_text.clone();
            let UserConfirmationMessage {
                email: recipient_email,
                name,
                user_id,
                verification_token,
            } = message;

            runtime.spawn(async move {
                send_new_user_confirmation_email(
                    recipient_email.as_str(),
                    new_user_confirmation_template_text.as_str(),
                    name.as_str(),
                    user_id,
                    verification_token.as_str(),
                )
                .await;
            });
        }
    });
}

async fn send_new_user_confirmation_email(
    recipient_email: &str,
    new_user_confirmation_template_text: &str,
    name: &str,
    user_id: i32,
    verification_token: &str,
) {
    let body = new_user_confirmation_template_text
        .replace("$NAME", name)
        .replace("$USER_ID", user_id.to_string().as_str())
        .replace("$VERIFICATION_TOKEN", verification_token);

    let message = Message::builder()
        .from(FROM_MAILBOX.clone())
        .reply_to(FROM_MAILBOX.clone())
        .to(recipient_email.parse().unwrap())
        .subject(format!(
            "You're registered, {name}, please confirm your email address"
        ))
        .header(ContentType::TEXT_HTML)
        .body(body)
        .unwrap();

    let sender: AsyncSmtpTransport<Tokio1Executor> =
        AsyncSmtpTransport::<Tokio1Executor>::starttls_relay("mail.dziura.cloud")
            .unwrap()
            .credentials(CREDENTIALS.clone())
            .authentication(vec![Mechanism::Plain])
            .pool_config(PoolConfig::new().max_size(*NUM_CPUS))
            .build();

    let _ = sender.send(message).await;
}