import asyncio
import email
import imaplib
import os
from datetime import datetime
from email.header import decode_header
from pathlib import Path
from typing import Any, Dict, List, Tuple

from backend.app.db import SessionLocal
from backend.app.models import FinanceRecord


FINANCE_BASE_DIR = Path("data/finance")


def _decode_header_value(value: str | None) -> str:
    if not value:
        return ""
    parts = decode_header(value)
    decoded = ""
    for text, enc in parts:
        if isinstance(text, bytes):
            decoded += text.decode(enc or "utf-8", errors="ignore")
        else:
            decoded += text
    return decoded


def _classify_type(subject: str) -> str:
    """
    Classify finance document type based on subject keywords.
    """
    subject_lower = subject.lower()
    # 发票 / 开票类
    if any(k in subject for k in ["发票", "开票", "票据", "invoice"]):
        return "invoices"
    # 银行流水 / 账户明细 / 对公活期等
    if any(
        k in subject
        for k in [
            "流水",
            "活期",
            "活期明细",
            "对公",
            "明细",
            "回单",
            "bank",
            "对账单",
            "statement",
        ]
    ):
        return "bank_records"
    if any(k in subject for k in ["回执", "receipt"]):
        return "receipts"
    return "others"


def _ensure_month_dir(month_str: str, doc_type: str) -> Path:
    month_dir = FINANCE_BASE_DIR / month_str / doc_type
    month_dir.mkdir(parents=True, exist_ok=True)
    return month_dir


def _parse_email_date(msg: email.message.Message) -> datetime:
    date_tuple = email.utils.parsedate_tz(msg.get("Date"))
    if date_tuple:
        dt = datetime.fromtimestamp(email.utils.mktime_tz(date_tuple))
    else:
        dt = datetime.utcnow()
    return dt


def _save_attachment(
    msg: email.message.Message,
    month_str: str,
    doc_type: str,
) -> List[Tuple[str, str]]:
    """
    Save PDF/image attachments and return list of (file_name, file_path).
    """
    saved: List[Tuple[str, str]] = []
    base_dir = _ensure_month_dir(month_str, doc_type)

    for part in msg.walk():
        content_disposition = part.get("Content-Disposition", "")
        if "attachment" not in content_disposition:
            continue

        filename = part.get_filename()
        filename = _decode_header_value(filename)
        if not filename:
            continue

        content_type = part.get_content_type()
        maintype = part.get_content_maintype()

        # Accept pdf and common images
        if maintype not in ("application", "image"):
            continue

        data = part.get_payload(decode=True)
        if not data:
            continue

        file_path = base_dir / filename
        # Ensure unique filename
        counter = 1
        while file_path.exists():
            stem = file_path.stem
            suffix = file_path.suffix
            file_path = base_dir / f"{stem}_{counter}{suffix}"
            counter += 1

        with open(file_path, "wb") as f:
            f.write(data)

        saved.append((filename, str(file_path)))

    return saved


async def sync_finance_emails() -> List[Dict[str, Any]]:
    """
    Connect to IMAP, fetch unread finance-related emails, download attachments,
    save to filesystem and record FinanceRecord entries.
    """

    def _sync() -> List[Dict[str, Any]]:
        host = os.getenv("IMAP_HOST")
        user = os.getenv("IMAP_USER")
        password = os.getenv("IMAP_PASSWORD")
        port = int(os.getenv("IMAP_PORT", "993"))
        mailbox = os.getenv("IMAP_MAILBOX", "INBOX")

        if not all([host, user, password]):
            raise RuntimeError("IMAP_HOST, IMAP_USER, IMAP_PASSWORD must be set.")

        results: List[Dict[str, Any]] = []

        with imaplib.IMAP4_SSL(host, port) as imap:
            imap.login(user, password)
            imap.select(mailbox)

            # Search for UNSEEN emails with finance related keywords in subject.
            # Note: IMAP SEARCH is limited; here we search UNSEEN first then filter in Python.
            status, data = imap.search(None, "UNSEEN")
            if status != "OK":
                return results

            id_list = data[0].split()
            db = SessionLocal()
            try:
                for msg_id in id_list:
                    status, msg_data = imap.fetch(msg_id, "(RFC822)")
                    if status != "OK":
                        continue

                    raw_email = msg_data[0][1]
                    msg = email.message_from_bytes(raw_email)

                    subject = _decode_header_value(msg.get("Subject"))
                    doc_type = _classify_type(subject)

                    # Filter by keywords first
                    if doc_type == "others":
                        continue

                    dt = _parse_email_date(msg)
                    month_str = dt.strftime("%Y-%m")

                    saved_files = _save_attachment(msg, month_str, doc_type)
                    for file_name, file_path in saved_files:
                        record = FinanceRecord(
                            month=month_str,
                            type=doc_type,
                            file_name=file_name,
                            file_path=file_path,
                        )
                            # NOTE: created_at defaults at DB layer
                        db.add(record)
                        db.flush()

                        results.append(
                            {
                                "id": record.id,
                                "month": record.month,
                                "type": record.type,
                                "file_name": record.file_name,
                                "file_path": record.file_path,
                            }
                        )

                    # Mark email as seen and flagged to avoid re-processing
                    imap.store(msg_id, "+FLAGS", "\\Seen \\Flagged")

                db.commit()
            finally:
                db.close()

        return results

    return await asyncio.to_thread(_sync)


async def create_monthly_zip(month_str: str) -> str:
    """
    Zip the finance folder for a given month (YYYY-MM) and return the zip path.
    """
    import zipfile

    def _zip() -> str:
        month_dir = FINANCE_BASE_DIR / month_str
        if not month_dir.exists():
            raise FileNotFoundError(f"Finance directory for {month_str} not found.")

        FINANCE_BASE_DIR.mkdir(parents=True, exist_ok=True)
        zip_path = FINANCE_BASE_DIR / f"{month_str}.zip"

        with zipfile.ZipFile(zip_path, "w", compression=zipfile.ZIP_DEFLATED) as zf:
            for root, _, files in os.walk(month_dir):
                for file in files:
                    full_path = Path(root) / file
                    rel_path = full_path.relative_to(FINANCE_BASE_DIR)
                    zf.write(full_path, arcname=rel_path)

        return str(zip_path)

    return await asyncio.to_thread(_zip)