"""Author RAG Chatbot SaaS — Email Service (Gmail SMTP).

All outgoing emails go through this service.
RULE: Email sends are always queued as Celery tasks (non-blocking).
RULE: Never call this directly from API handlers — use tasks/email_task.py.
Templates are inline HTML for zero external dependency.
"""

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText

import structlog

from app.config import get_settings

logger = structlog.get_logger(__name__)
cfg = get_settings()


class EmailService:
    """Sends transactional emails via Gmail SMTP (STARTTLS on 587, SSL on 465)."""

    def _smtp_meta(self):
        """Return resolved from/support addresses for outgoing mail."""
        from app.services.smtp_config_service import resolve_smtp_config_sync

        creds = resolve_smtp_config_sync()
        if creds:
            return creds.from_name, creds.from_address, creds.support_email
        return cfg.EMAIL_FROM_NAME, str(cfg.EMAIL_FROM_ADDRESS or cfg.SMTP_USERNAME or ""), str(
            cfg.SUPPORT_EMAIL or cfg.SMTP_USERNAME or "",
        )

    def _send(self, to: str, subject: str, html_body: str, reply_to: str | None = None) -> None:
        """Send a single email.

        Args:
            to: Recipient email address.
            subject: Email subject line.
            html_body: Full HTML body content.
            reply_to: Optional Reply-To header for reader replies.
        """
        msg = MIMEMultipart("alternative")
        msg["Subject"] = subject
        from_name, from_addr, _ = self._smtp_meta()
        msg["From"] = f"{from_name} <{from_addr}>"
        msg["To"] = to
        if reply_to:
            msg["Reply-To"] = reply_to
        msg.attach(MIMEText(html_body, "html"))

        from app.services.smtp_config_service import resolve_smtp_config_sync
        from app.services.smtp_transport import send_raw_message

        creds = resolve_smtp_config_sync()
        if not creds:
            raise smtplib.SMTPException("SMTP is not configured")

        try:
            send_raw_message(creds, from_addr, to, msg.as_string())
            logger.info("Email sent", to=to, subject=subject)
        except smtplib.SMTPException as e:
            logger.error("Failed to send email", to=to, subject=subject, error=str(e))
            raise

    def send_welcome(self, to: str, name: str) -> None:
        """Send welcome email after successful registration.

        Args:
            to: Author's email address.
            name: Author's display name.
        """
        subject = "Welcome to AuthorBot! 🎉"
        body = _render_template("welcome", {"name": name})
        self._send(to, subject, body)

    def send_account_locked(self, to: str) -> None:
        """Notify user their account has been temporarily locked.

        Args:
            to: Author's email address.
        """
        subject = "AuthorBot: Account temporarily locked"
        body = _render_template("account_locked", {"minutes": cfg.LOCKOUT_DURATION_MINUTES})
        self._send(to, subject, body)

    def send_subscription_granted(self, to: str, name: str, plan: str, expires_at: str) -> None:
        """Notify author that access has been granted.

        Args:
            to: Author's email address.
            name: Author's display name.
            plan: Subscription plan name.
            expires_at: Formatted expiry date string.
        """
        subject = "Your AuthorBot chatbot is now active!"
        body = _render_template("subscription_granted", {
            "name": name, "plan": plan, "expires_at": expires_at
        })
        self._send(to, subject, body)

    def send_subscription_revoked(self, to: str, name: str, reason: str) -> None:
        """Notify author that access has been revoked.

        Args:
            to: Author's email address.
            name: Author's display name.
            reason: Revocation reason.
        """
        subject = "AuthorBot: Your chatbot access has been revoked"
        body = _render_template("subscription_revoked", {"name": name, "reason": reason})
        self._send(to, subject, body)

    def send_subscription_expiry_warning(
        self, to: str, name: str, days_remaining: int, expires_at: str
    ) -> None:
        """Send expiry warning email (7 days and 1 day before).

        Args:
            to: Author's email address.
            name: Author's display name.
            days_remaining: Number of days until expiry.
            expires_at: Formatted expiry date string.
        """
        subject = f"AuthorBot: Your subscription expires in {days_remaining} day(s)"
        body = _render_template("expiry_warning", {
            "name": name, "days_remaining": days_remaining, "expires_at": expires_at
        })
        self._send(to, subject, body)

    def send_token_budget_warning(
        self, to: str, name: str, pct_used: int, tokens_used: int,
        tokens_total: int, forecast_date: str
    ) -> None:
        """Send token budget warning email.

        Args:
            to: Author's email address.
            name: Author's display name.
            pct_used: Percentage of budget consumed.
            tokens_used: Raw tokens consumed this month.
            tokens_total: Total monthly budget.
            forecast_date: Estimated date of exhaustion.
        """
        subject = f"AuthorBot: You've used {pct_used}% of your monthly tokens"
        body = _render_template("token_warning", {
            "name": name, "pct_used": pct_used,
            "tokens_used": f"{tokens_used:,}", "tokens_total": f"{tokens_total:,}",
            "forecast_date": forecast_date,
        })
        self._send(to, subject, body)

    def send_weekly_digest(
        self, to: str, name: str, chat_count: int, top_book: str,
        token_pct: int, top_country: str
    ) -> None:
        """Send weekly summary digest email.

        Args:
            to: Author's email address.
            name: Author's display name.
            chat_count: Total chats this week.
            top_book: Title of the most-engaged book.
            token_pct: Token usage percentage this month.
            top_country: Country with most visitors.
        """
        subject = f"AuthorBot Weekly: {chat_count} chats this week 📚"
        body = _render_template("weekly_digest", {
            "name": name, "chat_count": chat_count, "top_book": top_book,
            "token_pct": token_pct, "top_country": top_country,
        })
        self._send(to, subject, body)

    def send_publish_help_request(
        self,
        *,
        author_name: str,
        author_email: str,
        book_title: str,
        platform_names: list[str],
        message: str,
        submitted_at: str,
        book_id: str | None = None,
        isbn: str | None = None,
        book_author: str | None = None,
        source_url: str | None = None,
    ) -> None:
        """Send publish-help request to the support inbox.

        Args:
            author_name: Display name of the requesting author.
            author_email: Author's account email.
            book_title: Title of the book needing distribution help.
            platform_names: Human-readable platform names.
            message: Optional note from the author.
            submitted_at: ISO timestamp of the request.
            book_id: Optional book UUID.
            isbn: Optional ISBN.
            book_author: Optional book author name.
            source_url: Optional source listing URL.
        """
        dest = self._smtp_meta()[2] or cfg.SUPPORT_EMAIL
        if not dest:
            raise ValueError("SUPPORT_EMAIL is not configured")
        subject = f"Publish help: {book_title} ({len(platform_names)} platform(s))"
        body = _render_template("publish_help", {
            "author_name": author_name,
            "author_email": author_email,
            "book_title": book_title,
            "book_id": book_id or "—",
            "isbn": isbn or "—",
            "book_author": book_author or "—",
            "source_url": source_url or "—",
            "platforms": ", ".join(platform_names),
            "message": message or "(no message)",
            "submitted_at": submitted_at,
        })
        self._send(str(dest), subject, body)

    def send_contact_request(
        self,
        author_name: str,
        author_email: str,
        category: str,
        message: str,
        submitted_at: str,
        subject: str | None = None,
    ) -> None:
        """Send a general contact message to the support inbox."""
        dest = self._smtp_meta()[2] or cfg.SUPPORT_EMAIL
        if not dest:
            raise ValueError("SUPPORT_EMAIL is not configured")
        mail_subject = subject or f"Contact: {category} — {author_name}"
        body = _render_template("contact_request", {
            "author_name": author_name,
            "author_email": author_email,
            "category": category,
            "subject": mail_subject,
            "message": message,
            "submitted_at": submitted_at,
        })
        self._send(str(dest), mail_subject, body)

    def send_contact_reply(
        self,
        *,
        author_name: str,
        author_email: str,
        subject: str,
        original_message: str,
        reply_body: str,
        replied_at: str,
    ) -> None:
        """Notify an author that SuperAdmin replied to their support message."""
        mail_subject = f"Re: {subject}"
        body = _render_template("contact_reply", {
            "author_name": author_name,
            "subject": subject,
            "original_message": original_message,
            "reply_body": reply_body,
            "replied_at": replied_at,
        })
        self._send(author_email, mail_subject, body)

    def send_author_reader_email(
        self,
        *,
        to_email: str,
        reader_name: str | None,
        author_name: str,
        author_email: str,
        subject: str,
        message: str,
        sent_at: str,
    ) -> None:
        """Send a personal message from an author to a reader who opted in."""
        import html

        greeting = reader_name or "there"
        body = _render_template("author_reader_email", {
            "greeting": html.escape(greeting),
            "author_name": html.escape(author_name),
            "message": html.escape(message),
            "sent_at": sent_at,
        })
        self._send(to_email, subject, body, reply_to=author_email)

    def send_account_credentials(
        self,
        *,
        to: str,
        name: str,
        login_url: str,
        temp_password: str | None = None,
        user_chose_password: bool = False,
    ) -> None:
        """Send login credentials after Stripe payment or SuperAdmin support action."""
        import html

        subject = "Your AuthorBot account is ready"
        body = _render_template("account_credentials", {
            "name": html.escape(name),
            "login_url": html.escape(login_url),
            "email": html.escape(to),
            "temp_password": html.escape(temp_password) if temp_password else None,
            "user_chose_password": user_chose_password,
            "forgot_url": html.escape(f"{login_url.rstrip('/login')}/reset-password"),
        })
        self._send(to, subject, body)

    def send_payment_failed_notice(self, to: str, name: str, billing_url: str) -> None:
        """Notify author that a subscription payment failed."""
        import html

        subject = "Action required: payment failed"
        body = _render_template("payment_failed", {
            "name": html.escape(name),
            "billing_url": html.escape(billing_url),
        })
        self._send(to, subject, body)

    def send_subscription_cancelled_notice(self, to: str, name: str) -> None:
        """Notify author that their subscription was cancelled."""
        import html

        subject = "Your AuthorBot subscription has ended"
        body = _render_template("subscription_cancelled_notice", {
            "name": html.escape(name),
        })
        self._send(to, subject, body)

    def send_publish_help_confirmation(
        self,
        to: str,
        name: str,
        book_title: str,
        platform_names: list[str],
    ) -> None:
        """Confirm receipt of a publish-help request to the author.

        Args:
            to: Author's email address.
            name: Author's display name.
            book_title: Title of the book.
            platform_names: Platforms requested for help.
        """
        subject = "We received your publishing help request"
        body = _render_template("publish_help_confirmation", {
            "name": name,
            "book_title": book_title,
            "platforms": ", ".join(platform_names),
        })
        self._send(to, subject, body)


# ─── Template Renderer ────────────────────────────────────────────────────────

def _render_template(template_name: str, context: dict) -> str:
    """Render an HTML email template with context variables.

    Args:
        template_name: Name of the template (maps to a function below).
        context: Dictionary of variables to inject.

    Returns:
        Rendered HTML string.
    """
    templates = {
        "welcome": _tpl_welcome,
        "account_locked": _tpl_account_locked,
        "subscription_granted": _tpl_subscription_granted,
        "subscription_revoked": _tpl_subscription_revoked,
        "expiry_warning": _tpl_expiry_warning,
        "token_warning": _tpl_token_warning,
        "weekly_digest": _tpl_weekly_digest,
        "publish_help": _tpl_publish_help,
        "publish_help_confirmation": _tpl_publish_help_confirmation,
        "contact_request": _tpl_contact_request,
        "contact_reply": _tpl_contact_reply,
        "author_reader_email": _tpl_author_reader_email,
        "account_credentials": _tpl_account_credentials,
        "payment_failed": _tpl_payment_failed,
        "subscription_cancelled_notice": _tpl_subscription_cancelled_notice,
    }
    renderer = templates.get(template_name)
    if not renderer:
        raise ValueError(f"Unknown email template: {template_name}")
    return renderer(context)


def _base_html(title: str, content: str) -> str:
    """Wrap content in a branded HTML email shell."""
    return f"""
    <!DOCTYPE html><html><head><meta charset="utf-8">
    <title>{title}</title></head>
    <body style="margin:0;padding:0;background:#f4f4f8;font-family:Inter,Arial,sans-serif;">
    <table width="100%" cellpadding="0" cellspacing="0" style="background:#f4f4f8;padding:40px 0;">
      <tr><td align="center">
        <table width="600" cellpadding="0" cellspacing="0"
               style="background:#ffffff;border-radius:16px;overflow:hidden;box-shadow:0 4px 24px rgba(0,0,0,0.08);">
          <tr><td style="background:linear-gradient(135deg,#6366f1,#8b5cf6);padding:32px;text-align:center;">
            <h1 style="color:#fff;margin:0;font-size:24px;font-weight:700;">✦ AuthorBot</h1>
          </td></tr>
          <tr><td style="padding:40px;">
            {content}
          </td></tr>
          <tr><td style="background:#f9f9fb;padding:24px;text-align:center;color:#9ca3af;font-size:12px;">
            AuthorBot — Intelligent Book Advisor for Authors<br>
            You're receiving this because you have an AuthorBot account.
          </td></tr>
        </table>
      </td></tr>
    </table></body></html>
    """


def _tpl_welcome(ctx: dict) -> str:
    return _base_html("Welcome to AuthorBot", f"""
        <h2 style="color:#1f2937;">Welcome, {ctx['name']}! 🎉</h2>
        <p style="color:#4b5563;line-height:1.6;">Your AuthorBot account is ready.
        Start by uploading your first book and configuring your chatbot.</p>
        <p style="color:#4b5563;line-height:1.6;">Your chatbot will help readers discover
        and fall in love with your books — automatically.</p>
    """)


def _tpl_account_locked(ctx: dict) -> str:
    return _base_html("Account Locked", f"""
        <h2 style="color:#dc2626;">Account Temporarily Locked</h2>
        <p style="color:#4b5563;">Too many failed login attempts.
        Your account is locked for {ctx['minutes']} minutes.</p>
        <p style="color:#4b5563;">If this wasn't you, please contact support immediately.</p>
    """)


def _tpl_subscription_granted(ctx: dict) -> str:
    return _base_html("Subscription Active", f"""
        <h2 style="color:#059669;">Your chatbot is now active! ✓</h2>
        <p style="color:#4b5563;">Hi {ctx['name']}, your <strong>{ctx['plan']}</strong> subscription
        is now active.</p>
        <p style="color:#4b5563;">Access expires: <strong>{ctx['expires_at']}</strong></p>
    """)


def _tpl_subscription_revoked(ctx: dict) -> str:
    return _base_html("Access Revoked", f"""
        <h2 style="color:#dc2626;">Chatbot Access Revoked</h2>
        <p style="color:#4b5563;">Hi {ctx['name']}, your chatbot access has been revoked.</p>
        <p style="color:#4b5563;">Reason: {ctx['reason']}</p>
        <p style="color:#4b5563;">Please contact us to restore access.</p>
    """)


def _tpl_expiry_warning(ctx: dict) -> str:
    return _base_html("Subscription Expiring Soon", f"""
        <h2 style="color:#d97706;">Subscription Expiring in {ctx['days_remaining']} Day(s)</h2>
        <p style="color:#4b5563;">Hi {ctx['name']}, your subscription expires on
        <strong>{ctx['expires_at']}</strong>.</p>
        <p style="color:#4b5563;">Contact us to renew and keep your chatbot running.</p>
    """)


def _tpl_token_warning(ctx: dict) -> str:
    return _base_html("Token Budget Warning", f"""
        <h2 style="color:#d97706;">You've used {ctx['pct_used']}% of your tokens</h2>
        <p style="color:#4b5563;">Hi {ctx['name']},</p>
        <p style="color:#4b5563;">Usage: <strong>{ctx['tokens_used']}</strong> /
        {ctx['tokens_total']} tokens</p>
        <p style="color:#4b5563;">At this pace, budget runs out around
        <strong>{ctx['forecast_date']}</strong>.</p>
    """)


def _tpl_weekly_digest(ctx: dict) -> str:
    return _base_html("Weekly Digest", f"""
        <h2 style="color:#1f2937;">Your week in review 📚</h2>
        <p style="color:#4b5563;">Hi {ctx['name']}, here's what happened this week:</p>
        <ul style="color:#4b5563;line-height:2;">
          <li>💬 <strong>{ctx['chat_count']}</strong> visitor conversations</li>
          <li>📖 Top book: <strong>{ctx['top_book']}</strong></li>
          <li>🔋 Token usage: <strong>{ctx['token_pct']}%</strong> this month</li>
          <li>🌍 Top country: <strong>{ctx['top_country']}</strong></li>
        </ul>
    """)


def _tpl_publish_help(ctx: dict) -> str:
    return _base_html("Publish Help Request", f"""
        <h2 style="color:#1f2937;">New publishing help request</h2>
        <p style="color:#4b5563;line-height:1.6;">
          <strong>Author:</strong> {ctx['author_name']} &lt;{ctx['author_email']}&gt;<br>
          <strong>Book:</strong> {ctx['book_title']}<br>
          <strong>Book author:</strong> {ctx['book_author']}<br>
          <strong>ISBN:</strong> {ctx['isbn']}<br>
          <strong>Book ID:</strong> {ctx['book_id']}<br>
          <strong>Source URL:</strong> {ctx['source_url']}<br>
          <strong>Platforms:</strong> {ctx['platforms']}<br>
          <strong>Submitted:</strong> {ctx['submitted_at']}
        </p>
        <div style="padding:14px 16px;border-radius:12px;background:#f9fafb;border:1px solid #e5e7eb;">
          <strong style="color:#374151;">Message</strong>
          <p style="color:#4b5563;margin:8px 0 0;white-space:pre-wrap;">{ctx['message']}</p>
        </div>
    """)


def _tpl_publish_help_confirmation(ctx: dict) -> str:
    return _base_html("Request Received", f"""
        <h2 style="color:#059669;">We received your request ✓</h2>
        <p style="color:#4b5563;line-height:1.6;">Hi {ctx['name']},</p>
        <p style="color:#4b5563;line-height:1.6;">
          Thanks for reaching out about <strong>{ctx['book_title']}</strong>.
          Our team will help you publish on: <strong>{ctx['platforms']}</strong>.
        </p>
        <p style="color:#4b5563;line-height:1.6;">We aim to reply within 24 hours.</p>
    """)


def _tpl_contact_request(ctx: dict) -> str:
    return _base_html("Contact Request", f"""
        <h2 style="color:#1f2937;">New contact message</h2>
        <p style="color:#4b5563;line-height:1.6;">
          <strong>Author:</strong> {ctx['author_name']} &lt;{ctx['author_email']}&gt;<br>
          <strong>Category:</strong> {ctx['category']}<br>
          <strong>Subject:</strong> {ctx.get('subject', '—')}<br>
          <strong>Submitted:</strong> {ctx['submitted_at']}
        </p>
        <div style="padding:14px 16px;border-radius:12px;background:#f9fafb;border:1px solid #e5e7eb;">
          <strong style="color:#374151;">Message</strong>
          <p style="color:#4b5563;margin:8px 0 0;white-space:pre-wrap;">{ctx['message']}</p>
        </div>
    """)


def _tpl_contact_reply(ctx: dict) -> str:
    return _base_html("Support Reply", f"""
        <h2 style="color:#1f2937;">Hi {ctx['author_name']},</h2>
        <p style="color:#4b5563;line-height:1.6;">
          Our team replied to your message about <strong>{ctx['subject']}</strong>.
        </p>
        <div style="padding:14px 16px;border-radius:12px;background:#f0fdf4;border:1px solid #bbf7d0;margin:16px 0;">
          <strong style="color:#166534;">Our reply</strong>
          <p style="color:#374151;margin:8px 0 0;white-space:pre-wrap;line-height:1.6;">{ctx['reply_body']}</p>
        </div>
        <div style="padding:14px 16px;border-radius:12px;background:#f9fafb;border:1px solid #e5e7eb;">
          <strong style="color:#6b7280;font-size:12px;">Your original message</strong>
          <p style="color:#9ca3af;margin:8px 0 0;white-space:pre-wrap;font-size:13px;">{ctx['original_message']}</p>
        </div>
        <p style="color:#9ca3af;font-size:12px;margin-top:24px;">
          Log in to your AuthorBot dashboard to view this reply in the Messages tab.
        </p>
    """)


def _tpl_author_reader_email(ctx: dict) -> str:
    return _base_html("Message from your author", f"""
        <h2 style="color:#1f2937;">Hi {ctx['greeting']},</h2>
        <p style="color:#4b5563;line-height:1.6;">
          <strong>{ctx['author_name']}</strong> sent you a message via their book chatbot:
        </p>
        <div style="padding:14px 16px;border-radius:12px;background:#f9fafb;border:1px solid #e5e7eb;">
          <p style="color:#374151;margin:0;white-space:pre-wrap;line-height:1.6;">{ctx['message']}</p>
        </div>
        <p style="color:#9ca3af;font-size:12px;margin-top:24px;">
          Reply to this email to reach {ctx['author_name']} directly.
        </p>
    """)


def _tpl_account_credentials(ctx: dict) -> str:
    pwd_block = ""
    if ctx.get("temp_password"):
        pwd_block = f"""
        <p style="color:#4b5563;line-height:1.6;">
          <strong>Email:</strong> {ctx['email']}<br>
          <strong>Temporary password:</strong> <code style="background:#f3f4f6;padding:2px 6px;border-radius:4px;">{ctx['temp_password']}</code>
        </p>
        <p style="color:#d97706;font-size:13px;">Please change this password after your first login.</p>
        """
    elif ctx.get("user_chose_password"):
        pwd_block = f"""
        <p style="color:#4b5563;line-height:1.6;">
          <strong>Email:</strong> {ctx['email']}<br>
          Use the password you set during checkout.
        </p>
        <p style="color:#4b5563;font-size:13px;">
          Forgot it? <a href="{ctx['forgot_url']}" style="color:#6366f1;">Reset your password</a>
        </p>
        """
    else:
        pwd_block = f"""
        <p style="color:#4b5563;line-height:1.6;">
          <strong>Email:</strong> {ctx['email']}
        </p>
        """

    return _base_html("Your Account", f"""
        <h2 style="color:#059669;">Welcome, {ctx['name']}!</h2>
        <p style="color:#4b5563;line-height:1.6;">Your AuthorBot account is active. Sign in to upload books and configure your chatbot.</p>
        {pwd_block}
        <p style="margin-top:24px;">
          <a href="{ctx['login_url']}" style="display:inline-block;background:#6366f1;color:#fff;padding:12px 24px;border-radius:8px;text-decoration:none;font-weight:600;">
            Sign in to your dashboard
          </a>
        </p>
    """)


def _tpl_payment_failed(ctx: dict) -> str:
    return _base_html("Payment Failed", f"""
        <h2 style="color:#dc2626;">Payment failed</h2>
        <p style="color:#4b5563;line-height:1.6;">Hi {ctx['name']}, we could not process your latest subscription payment.</p>
        <p style="color:#4b5563;line-height:1.6;">Update your payment method within 7 days to keep your chatbot running.</p>
        <p style="margin-top:20px;">
          <a href="{ctx['billing_url']}" style="color:#6366f1;font-weight:600;">Manage billing</a>
        </p>
    """)


def _tpl_subscription_cancelled_notice(ctx: dict) -> str:
    return _base_html("Subscription Ended", f"""
        <h2 style="color:#1f2937;">Subscription ended</h2>
        <p style="color:#4b5563;line-height:1.6;">Hi {ctx['name']}, your AuthorBot subscription has been cancelled and your chatbot access has ended.</p>
        <p style="color:#4b5563;line-height:1.6;">Contact support if you'd like to reactivate.</p>
    """)