"""Email channel implementation using IMAP polling + SMTP replies."""

import asyncio
import html
import imaplib
import re
import smtplib
import ssl
from datetime import date
from email import policy
from email.header import decode_header, make_header
from email.message import EmailMessage
from email.parser import BytesParser
from email.utils import parseaddr
from typing import Any

from loguru import logger
from pydantic import Field

from nanobot.bus.events import OutboundMessage
from nanobot.bus.queue import MessageBus
from nanobot.channels.base import BaseChannel
from nanobot.config.schema import Base


class EmailConfig(Base):
    """Email channel configuration (IMAP inbound + SMTP outbound)."""

    enabled: bool = False
    consent_granted: bool = False

    imap_host: str = ""
    imap_port: int = 993
    imap_username: str = ""
    imap_password: str = ""
    imap_mailbox: str = "INBOX"
    imap_use_ssl: bool = True

    smtp_host: str = ""
    smtp_port: int = 587
    smtp_username: str = ""
    smtp_password: str = ""
    smtp_use_tls: bool = True
    smtp_use_ssl: bool = False
    from_address: str = ""

    auto_reply_enabled: bool = True
    poll_interval_seconds: int = 30
    mark_seen: bool = True
    max_body_chars: int = 12000
    subject_prefix: str = "Re: "
    allow_from: list[str] = Field(default_factory=list)

    # Email authentication verification (anti-spoofing)
    verify_dkim: bool = True   # Require Authentication-Results with dkim=pass
    verify_spf: bool = True    # Require Authentication-Results with spf=pass


class EmailChannel(BaseChannel):
    """
    Email channel.

    Inbound:
    - Poll IMAP mailbox for unread messages.
    - Convert each message into an inbound event.

    Outbound:
    - Send responses via SMTP back to the sender address.
    """

    name = "email"
    display_name = "Email"
    _IMAP_MONTHS = (
        "Jan",
        "Feb",
        "Mar",
        "Apr",
        "May",
        "Jun",
        "Jul",
        "Aug",
        "Sep",
        "Oct",
        "Nov",
        "Dec",
    )
    _IMAP_RECONNECT_MARKERS = (
        "disconnected for inactivity",
        "eof occurred in violation of protocol",
        "socket error",
        "connection reset",
        "broken pipe",
        "bye",
    )
    _IMAP_MISSING_MAILBOX_MARKERS = (
        "mailbox doesn't exist",
        "select failed",
        "no such mailbox",
        "can't open mailbox",
        "does not exist",
    )

    @classmethod
    def default_config(cls) -> dict[str, Any]:
        return EmailConfig().model_dump(by_alias=True)

    def __init__(self, config: Any, bus: MessageBus):
        if isinstance(config, dict):
            config = EmailConfig.model_validate(config)
        super().__init__(config, bus)
        self.config: EmailConfig = config
        self._last_subject_by_chat: dict[str, str] = {}
        self._last_message_id_by_chat: dict[str, str] = {}
        self._processed_uids: set[str] = set()  # Capped to prevent unbounded growth
        self._MAX_PROCESSED_UIDS = 100000

    async def start(self) -> None:
        """Start polling IMAP for inbound emails."""
        if not self.config.consent_granted:
            logger.warning(
                "Email channel disabled: consent_granted is false. "
                "Set channels.email.consentGranted=true after explicit user permission."
            )
            return

        if not self._validate_config():
            return

        self._running = True
        if not self.config.verify_dkim and not self.config.verify_spf:
            logger.warning(
                "Email channel: DKIM and SPF verification are both DISABLED. "
                "Emails with spoofed From headers will be accepted. "
                "Set verify_dkim=true and verify_spf=true for anti-spoofing protection."
            )
        logger.info("Starting Email channel (IMAP polling mode)...")

        poll_seconds = max(5, int(self.config.poll_interval_seconds))
        while self._running:
            try:
                inbound_items = await asyncio.to_thread(self._fetch_new_messages)
                for item in inbound_items:
                    sender = item["sender"]
                    subject = item.get("subject", "")
                    message_id = item.get("message_id", "")

                    if subject:
                        self._last_subject_by_chat[sender] = subject
                    if message_id:
                        self._last_message_id_by_chat[sender] = message_id

                    await self._handle_message(
                        sender_id=sender,
                        chat_id=sender,
                        content=item["content"],
                        metadata=item.get("metadata", {}),
                    )
            except Exception as e:
                logger.error("Email polling error: {}", e)

            await asyncio.sleep(poll_seconds)

    async def stop(self) -> None:
        """Stop polling loop."""
        self._running = False

    async def send(self, msg: OutboundMessage) -> None:
        """Send email via SMTP."""
        if not self.config.consent_granted:
            logger.warning("Skip email send: consent_granted is false")
            return

        if not self.config.smtp_host:
            logger.warning("Email channel SMTP host not configured")
            return

        to_addr = msg.chat_id.strip()
        if not to_addr:
            logger.warning("Email channel missing recipient address")
            return

        # Determine if this is a reply (recipient has sent us an email before)
        is_reply = to_addr in self._last_subject_by_chat
        force_send = bool((msg.metadata or {}).get("force_send"))

        # autoReplyEnabled only controls automatic replies, not proactive sends
        if is_reply and not self.config.auto_reply_enabled and not force_send:
            logger.info("Skip automatic email reply to {}: auto_reply_enabled is false", to_addr)
            return

        base_subject = self._last_subject_by_chat.get(to_addr, "nanobot reply")
        subject = self._reply_subject(base_subject)
        if msg.metadata and isinstance(msg.metadata.get("subject"), str):
            override = msg.metadata["subject"].strip()
            if override:
                subject = override

        email_msg = EmailMessage()
        email_msg["From"] = self.config.from_address or self.config.smtp_username or self.config.imap_username
        email_msg["To"] = to_addr
        email_msg["Subject"] = subject
        email_msg.set_content(msg.content or "")

        in_reply_to = self._last_message_id_by_chat.get(to_addr)
        if in_reply_to:
            email_msg["In-Reply-To"] = in_reply_to
            email_msg["References"] = in_reply_to

        try:
            await asyncio.to_thread(self._smtp_send, email_msg)
        except Exception as e:
            logger.error("Error sending email to {}: {}", to_addr, e)
            raise

    def _validate_config(self) -> bool:
        missing = []
        if not self.config.imap_host:
            missing.append("imap_host")
        if not self.config.imap_username:
            missing.append("imap_username")
        if not self.config.imap_password:
            missing.append("imap_password")
        if not self.config.smtp_host:
            missing.append("smtp_host")
        if not self.config.smtp_username:
            missing.append("smtp_username")
        if not self.config.smtp_password:
            missing.append("smtp_password")

        if missing:
            logger.error("Email channel not configured, missing: {}", ', '.join(missing))
            return False
        return True

    def _smtp_send(self, msg: EmailMessage) -> None:
        timeout = 30
        if self.config.smtp_use_ssl:
            with smtplib.SMTP_SSL(
                self.config.smtp_host,
                self.config.smtp_port,
                timeout=timeout,
            ) as smtp:
                smtp.login(self.config.smtp_username, self.config.smtp_password)
                smtp.send_message(msg)
            return

        with smtplib.SMTP(self.config.smtp_host, self.config.smtp_port, timeout=timeout) as smtp:
            if self.config.smtp_use_tls:
                smtp.starttls(context=ssl.create_default_context())
            smtp.login(self.config.smtp_username, self.config.smtp_password)
            smtp.send_message(msg)

    def _fetch_new_messages(self) -> list[dict[str, Any]]:
        """Poll IMAP and return parsed unread messages."""
        return self._fetch_messages(
            search_criteria=("UNSEEN",),
            mark_seen=self.config.mark_seen,
            dedupe=True,
            limit=0,
        )

    def fetch_messages_between_dates(
        self,
        start_date: date,
        end_date: date,
        limit: int = 20,
    ) -> list[dict[str, Any]]:
        """
        Fetch messages in [start_date, end_date) by IMAP date search.

        This is used for historical summarization tasks (e.g. "yesterday").
        """
        if end_date <= start_date:
            return []

        return self._fetch_messages(
            search_criteria=(
                "SINCE",
                self._format_imap_date(start_date),
                "BEFORE",
                self._format_imap_date(end_date),
            ),
            mark_seen=False,
            dedupe=False,
            limit=max(1, int(limit)),
        )

    def _fetch_messages(
        self,
        search_criteria: tuple[str, ...],
        mark_seen: bool,
        dedupe: bool,
        limit: int,
    ) -> list[dict[str, Any]]:
        messages: list[dict[str, Any]] = []
        cycle_uids: set[str] = set()

        for attempt in range(2):
            try:
                self._fetch_messages_once(
                    search_criteria,
                    mark_seen,
                    dedupe,
                    limit,
                    messages,
                    cycle_uids,
                )
                return messages
            except Exception as exc:
                if attempt == 1 or not self._is_stale_imap_error(exc):
                    raise
                logger.warning("Email IMAP connection went stale, retrying once: {}", exc)

        return messages

    def _fetch_messages_once(
        self,
        search_criteria: tuple[str, ...],
        mark_seen: bool,
        dedupe: bool,
        limit: int,
        messages: list[dict[str, Any]],
        cycle_uids: set[str],
    ) -> None:
        """Fetch messages by arbitrary IMAP search criteria."""
        mailbox = self.config.imap_mailbox or "INBOX"

        if self.config.imap_use_ssl:
            client = imaplib.IMAP4_SSL(self.config.imap_host, self.config.imap_port)
        else:
            client = imaplib.IMAP4(self.config.imap_host, self.config.imap_port)

        try:
            client.login(self.config.imap_username, self.config.imap_password)
            try:
                status, _ = client.select(mailbox)
            except Exception as exc:
                if self._is_missing_mailbox_error(exc):
                    logger.warning("Email mailbox unavailable, skipping poll for {}: {}", mailbox, exc)
                    return messages
                raise
            if status != "OK":
                logger.warning("Email mailbox select returned {}, skipping poll for {}", status, mailbox)
                return messages

            status, data = client.search(None, *search_criteria)
            if status != "OK" or not data:
                return messages

            ids = data[0].split()
            if limit > 0 and len(ids) > limit:
                ids = ids[-limit:]
            for imap_id in ids:
                status, fetched = client.fetch(imap_id, "(BODY.PEEK[] UID)")
                if status != "OK" or not fetched:
                    continue

                raw_bytes = self._extract_message_bytes(fetched)
                if raw_bytes is None:
                    continue

                uid = self._extract_uid(fetched)
                if uid and uid in cycle_uids:
                    continue
                if dedupe and uid and uid in self._processed_uids:
                    continue

                parsed = BytesParser(policy=policy.default).parsebytes(raw_bytes)
                sender = parseaddr(parsed.get("From", ""))[1].strip().lower()
                if not sender:
                    continue

                # --- Anti-spoofing: verify Authentication-Results ---
                spf_pass, dkim_pass = self._check_authentication_results(parsed)
                if self.config.verify_spf and not spf_pass:
                    logger.warning(
                        "Email from {} rejected: SPF verification failed "
                        "(no 'spf=pass' in Authentication-Results header)",
                        sender,
                    )
                    continue
                if self.config.verify_dkim and not dkim_pass:
                    logger.warning(
                        "Email from {} rejected: DKIM verification failed "
                        "(no 'dkim=pass' in Authentication-Results header)",
                        sender,
                    )
                    continue

                subject = self._decode_header_value(parsed.get("Subject", ""))
                date_value = parsed.get("Date", "")
                message_id = parsed.get("Message-ID", "").strip()
                body = self._extract_text_body(parsed)

                if not body:
                    body = "(empty email body)"

                body = body[: self.config.max_body_chars]
                content = (
                    f"[EMAIL-CONTEXT] Email received.\n"
                    f"From: {sender}\n"
                    f"Subject: {subject}\n"
                    f"Date: {date_value}\n\n"
                    f"{body}"
                )

                metadata = {
                    "message_id": message_id,
                    "subject": subject,
                    "date": date_value,
                    "sender_email": sender,
                    "uid": uid,
                }
                messages.append(
                    {
                        "sender": sender,
                        "subject": subject,
                        "message_id": message_id,
                        "content": content,
                        "metadata": metadata,
                    }
                )

                if uid:
                    cycle_uids.add(uid)
                if dedupe and uid:
                    self._processed_uids.add(uid)
                    # mark_seen is the primary dedup; this set is a safety net
                    if len(self._processed_uids) > self._MAX_PROCESSED_UIDS:
                        # Evict a random half to cap memory; mark_seen is the primary dedup
                        self._processed_uids = set(list(self._processed_uids)[len(self._processed_uids) // 2:])

                if mark_seen:
                    client.store(imap_id, "+FLAGS", "\\Seen")
        finally:
            try:
                client.logout()
            except Exception:
                pass

    @classmethod
    def _is_stale_imap_error(cls, exc: Exception) -> bool:
        message = str(exc).lower()
        return any(marker in message for marker in cls._IMAP_RECONNECT_MARKERS)

    @classmethod
    def _is_missing_mailbox_error(cls, exc: Exception) -> bool:
        message = str(exc).lower()
        return any(marker in message for marker in cls._IMAP_MISSING_MAILBOX_MARKERS)

    @classmethod
    def _format_imap_date(cls, value: date) -> str:
        """Format date for IMAP search (always English month abbreviations)."""
        month = cls._IMAP_MONTHS[value.month - 1]
        return f"{value.day:02d}-{month}-{value.year}"

    @staticmethod
    def _extract_message_bytes(fetched: list[Any]) -> bytes | None:
        for item in fetched:
            if isinstance(item, tuple) and len(item) >= 2 and isinstance(item[1], (bytes, bytearray)):
                return bytes(item[1])
        return None

    @staticmethod
    def _extract_uid(fetched: list[Any]) -> str:
        for item in fetched:
            if isinstance(item, tuple) and item and isinstance(item[0], (bytes, bytearray)):
                head = bytes(item[0]).decode("utf-8", errors="ignore")
                m = re.search(r"UID\s+(\d+)", head)
                if m:
                    return m.group(1)
        return ""

    @staticmethod
    def _decode_header_value(value: str) -> str:
        if not value:
            return ""
        try:
            return str(make_header(decode_header(value)))
        except Exception:
            return value

    @classmethod
    def _extract_text_body(cls, msg: Any) -> str:
        """Best-effort extraction of readable body text."""
        if msg.is_multipart():
            plain_parts: list[str] = []
            html_parts: list[str] = []
            for part in msg.walk():
                if part.get_content_disposition() == "attachment":
                    continue
                content_type = part.get_content_type()
                try:
                    payload = part.get_content()
                except Exception:
                    payload_bytes = part.get_payload(decode=True) or b""
                    charset = part.get_content_charset() or "utf-8"
                    payload = payload_bytes.decode(charset, errors="replace")
                if not isinstance(payload, str):
                    continue
                if content_type == "text/plain":
                    plain_parts.append(payload)
                elif content_type == "text/html":
                    html_parts.append(payload)
            if plain_parts:
                return "\n\n".join(plain_parts).strip()
            if html_parts:
                return cls._html_to_text("\n\n".join(html_parts)).strip()
            return ""

        try:
            payload = msg.get_content()
        except Exception:
            payload_bytes = msg.get_payload(decode=True) or b""
            charset = msg.get_content_charset() or "utf-8"
            payload = payload_bytes.decode(charset, errors="replace")
        if not isinstance(payload, str):
            return ""
        if msg.get_content_type() == "text/html":
            return cls._html_to_text(payload).strip()
        return payload.strip()

    @staticmethod
    def _check_authentication_results(parsed_msg: Any) -> tuple[bool, bool]:
        """Parse Authentication-Results headers for SPF and DKIM verdicts.

        Returns:
            A tuple of (spf_pass, dkim_pass) booleans.
        """
        spf_pass = False
        dkim_pass = False
        for ar_header in parsed_msg.get_all("Authentication-Results") or []:
            ar_lower = ar_header.lower()
            if re.search(r"\bspf\s*=\s*pass\b", ar_lower):
                spf_pass = True
            if re.search(r"\bdkim\s*=\s*pass\b", ar_lower):
                dkim_pass = True
        return spf_pass, dkim_pass

    @staticmethod
    def _html_to_text(raw_html: str) -> str:
        text = re.sub(r"<\s*br\s*/?>", "\n", raw_html, flags=re.IGNORECASE)
        text = re.sub(r"<\s*/\s*p\s*>", "\n", text, flags=re.IGNORECASE)
        text = re.sub(r"<[^>]+>", "", text)
        return html.unescape(text)

    def _reply_subject(self, base_subject: str) -> str:
        subject = (base_subject or "").strip() or "nanobot reply"
        prefix = self.config.subject_prefix or "Re: "
        if subject.lower().startswith("re:"):
            return subject
        return f"{prefix}{subject}"
