main.py

from email.mime.multipart import MIMEMultipart
from email.mime.image import MIMEImage
from email.mime.text import MIMEText
import smtplib
import ssl
import os

from flask import Flask, abort, request
import jinja2

import config


app = Flask(__name__)

TEMPLATES = os.path.abspath("./templates")
LOGO_CID = "logo"
LOGO = "logo.png"


def format_template(template, context):
    return jinja2.Environment(
        loader=jinja2.FileSystemLoader(TEMPLATES)
    ).get_template(template).render(context)


def format_email(template, params):
    html_p = os.path.expanduser(os.path.abspath(os.path.join(TEMPLATES, template + ".html")))
    text_p = os.path.expanduser(os.path.abspath(os.path.join(TEMPLATES, template + ".txt")))

    if not html_p.startswith(TEMPLATES) or not text_p.startswith(TEMPLATES):
        return None, 400
    
    if not os.path.exists(html_p) or not os.path.exists(text_p):
        return None, 404

    html = format_template(template + ".html", params)
    text = format_template(template + ".txt", params)

    return html, text


def build_email(html, text, from_, to, subject):
    """
    Multipart(mixed)
        Multipart(related)
            Multipart(alternative)
                Text(plain)
                Text(html)
            Image
    """
    mixed = MIMEMultipart("mixed")
    mixed["Subject"] = subject
    mixed["From"] = from_
    mixed["To"] = to
    mixed.preamble = "This is a multi-part message in MIME format."

    related = MIMEMultipart("related")

    alt = MIMEMultipart("alternative")
    alt.attach(MIMEText(text, "plain"))
    alt.attach(MIMEText(html, "html"))
    related.attach(alt)

    with open(LOGO, "rb") as f:
        logo = MIMEImage(f.read())
    logo.add_header("Content-ID", f"<{LOGO_CID}>")
    related.attach(logo)

    mixed.attach(related)

    return mixed.as_string()


def send_email(mime, recipient):
    if config.MODE == "SSL":
        context = ssl.create_default_context()

        with smtplib.SMTP_SSL(*config.SMTP, context=context) as server:
            server.login(*config.LOGIN)

            server.sendmail(config.EMAIL, recipient, mime)
        return True
    elif config.MODE == "STARTTLS":
        with smtplib.SMTP(*config.SMTP) as server:
            server.ehlo()
            server.starttls()
            server.ehlo()
            server.login(*config.LOGIN)

            server.sendmail(config.EMAIL, recipient, mime)
        return True
    else:
        return False


@app.route("/")
def index():
    return "", 200


@app.route("/send", methods=["POST"])
def send():
    if not all(i in request.form for i in ("template", "to", "subject")):
        return abort(400)

    context = {k: request.form[k] for k in request.form if request.form[k] and k != "template"}
    context["logo_cid"] = "cid:" + LOGO_CID

    email = format_email(request.form["template"], context)
    if email[0] is None:
        return abort(email[1])
    
    html, txt = email

    email = build_email(email[0], email[1], config.FROM_NAME, context["to"], context["subject"])

    if send_email(email, context["to"]):
        return "", 200
    return abort(500)


if __name__ == "__main__":
    app.run(debug=True)