import os
import smtplib
import hashlib
from typing import List, Tuple
from email.mime.text import MIMEText  # ← 修正：email.mime.text

def choose_subject(email: str, subject_a: str, subject_b: str) -> Tuple[str, str]:
    # 受信者ごとにハッシュで安定割当（50/50）
    h = hashlib.sha256(email.encode()).digest()[0]
    variant = "A" if (h % 2 == 0) else "B"
    return (subject_a if variant == "A" else subject_b), variant

def send_email(recipients: List[str], subject_a: str, subject_b: str, body_md: str):
    host = os.getenv("SMTP_HOST", "")
    port = int(os.getenv("SMTP_PORT", "587"))
    user = os.getenv("SMTP_USERNAME", "")
    pwd  = os.getenv("SMTP_PASSWORD", "")
    sender = os.getenv("EMAIL_FROM", user or "no-reply@example.com")

    # 資格情報が未設定ならスキップ（アプリは落とさない）
    if not host:
        return {"status": "skipped", "reason": "SMTP not configured"}

    results = []
    with smtplib.SMTP(host, port) as s:
        s.starttls()
        if user and pwd:
            s.login(user, pwd)
        for rcpt in recipients:
            subject, variant = choose_subject(rcpt, subject_a, subject_b)
            msg = MIMEText(body_md, _subtype="plain", _charset="utf-8")
            msg["Subject"] = subject
            msg["From"] = sender
            msg["To"] = rcpt
            s.sendmail(user or sender, [rcpt], msg.as_string())
            results.append({"to": rcpt, "variant": variant, "subject": subject})
    return results