# A tiny SMTP server for Omnara's API that hands each message to exe.dev's
# email gateway (https://exe.dev/docs/send-email). It listens on
# 127.0.0.1:2525 inside the api container's network only.
import json, socketserver, sys, urllib.request
from email import message_from_bytes, policy

GATEWAY = "http://169.254.169.254/gateway/email/send"

def send(rcpts, data):
    msg = message_from_bytes(data, policy=policy.default)
    part = msg.get_body(("plain",))
    body = part.get_content() if part else ""
    for to in rcpts:
        req = urllib.request.Request(GATEWAY, method="POST",
            headers={"Content-Type": "application/json"},
            data=json.dumps({"to": to, "subject": str(msg["subject"] or ""), "body": body}).encode())
        try:
            with urllib.request.urlopen(req, timeout=20) as r:
                print("sent", repr(msg["subject"]), "to", to, flush=True)
        except urllib.error.HTTPError as e:
            err = e.read().decode(errors="replace")[:300]
            print("exe.dev refused mail to", to, ":", err, "\n--- message ---\n" + body + "\n---", flush=True)
            return "550 exe.dev refused: " + " ".join(err.split())
    return "250 sent"

class SMTP(socketserver.StreamRequestHandler):
    def reply(self, line):
        self.wfile.write(line.encode() + b"\r\n")

    def handle(self):
        self.reply("220 exe-mail ESMTP")
        rcpts = []
        while line := self.rfile.readline(65536):
            cmd = line.decode(errors="replace").strip()
            verb = cmd[:4].upper()
            if verb in ("EHLO", "HELO"):
                self.reply("250 exe-mail")
            elif verb == "MAIL":
                rcpts = []
                self.reply("250 ok")
            elif verb == "RCPT":
                rcpts.append(cmd.split(":", 1)[1].strip().strip("<>").split(">")[0])
                self.reply("250 ok")
            elif verb == "DATA":
                self.reply("354 end with .")
                lines = []
                while (l := self.rfile.readline(1 << 20)) not in (b".\r\n", b".\n", b""):
                    lines.append(l[1:] if l.startswith(b".") else l)
                self.reply(send(rcpts, b"".join(lines)))
                rcpts = []
            elif verb == "QUIT":
                self.reply("221 bye")
                return
            elif verb in ("RSET", "NOOP"):
                self.reply("250 ok")
            else:
                self.reply("502 not implemented")

socketserver.ThreadingTCPServer.allow_reuse_address = True
with socketserver.ThreadingTCPServer(("127.0.0.1", 2525), SMTP) as server:
    print("exe-mail listening on 127.0.0.1:2525", flush=True)
    server.serve_forever()