"""Zip(.eml) extraction, parsing, cleaning, and date filtering."""

from __future__ import annotations

import email
import email.policy
import re
import zipfile
from collections.abc import Callable
from dataclasses import dataclass, field
from datetime import date, datetime, timezone
from email.header import decode_header, make_header
from email.message import EmailMessage
from email.utils import parsedate_to_datetime
from html.parser import HTMLParser
from pathlib import Path
from zoneinfo import ZoneInfo

KST = ZoneInfo("Asia/Seoul")

_SUBJECT_PREFIX_RE = re.compile(
    r"^\s*((re|fw|fwd|답장|전달|회신)\s*[:：]|\[?\s*(re|fw|fwd)\s*\]?\s*:)\s*",
    re.IGNORECASE,
)
_QUOTE_MARKERS = (
    "-----original message-----",
    "----- 원본 메시지 -----",
    "-----원본 메시지-----",
    "________________________________",
    "begin forwarded message",
    "보낸 사람:",
    "보내는 사람:",
    "보내는사람:",
    "보내는사람 :",
    "from:",
)
_SIG_MARKERS = (
    "\n-- \n",
    "\n--\n",
    "\n감사합니다.\n",
    "\nthanks,\n",
    "\nbest regards,\n",
    "\ncustomer centric agility\n",
    "\ntel :",
    "\ntel:",
)


@dataclass
class ParsedMail:
    mailbox: str
    message_id: str
    thread_key: str
    subject: str
    from_addr: str
    to_addrs: str
    cc_addrs: str
    mailed_at: datetime | None
    attachment_names: list[str] = field(default_factory=list)
    body_text: str = ""
    source_path: str = ""


class _HTMLTextExtractor(HTMLParser):
    def __init__(self) -> None:
        super().__init__()
        self._parts: list[str] = []
        self._skip = False

    def handle_starttag(self, tag: str, attrs) -> None:  # noqa: ANN001
        if tag in {"script", "style"}:
            self._skip = True
        elif tag in {"br", "p", "div", "tr", "li"}:
            self._parts.append("\n")

    def handle_endtag(self, tag: str) -> None:
        if tag in {"script", "style"}:
            self._skip = False
        elif tag in {"p", "div", "tr", "li"}:
            self._parts.append("\n")

    def handle_data(self, data: str) -> None:
        if not self._skip:
            self._parts.append(data)

    def text(self) -> str:
        return "".join(self._parts)


def decode_mime_header(value: str | None) -> str:
    if not value:
        return ""
    try:
        return str(make_header(decode_header(value))).strip()
    except Exception:  # noqa: BLE001
        return value.strip()


def normalize_thread_key(subject: str) -> str:
    text = decode_mime_header(subject)
    prev = None
    while prev != text:
        prev = text
        text = _SUBJECT_PREFIX_RE.sub("", text).strip()
    text = re.sub(r"\s+", " ", text).strip().lower()
    return text or "(no-subject)"


def html_to_text(html: str) -> str:
    parser = _HTMLTextExtractor()
    try:
        parser.feed(html)
        parser.close()
    except Exception:  # noqa: BLE001
        return re.sub(r"<[^>]+>", " ", html)
    return parser.text()


def clean_body(text: str) -> str:
    if not text:
        return ""
    normalized = text.replace("\r\n", "\n").replace("\r", "\n")
    lower = normalized.lower()
    cut = len(normalized)
    for marker in _QUOTE_MARKERS:
        idx = lower.find(marker)
        if idx != -1:
            cut = min(cut, idx)
    body = normalized[:cut]
    for marker in _SIG_MARKERS:
        idx = body.lower().find(marker.lower())
        if idx != -1 and idx > 40:
            body = body[:idx]
            break

    lines: list[str] = []
    for line in body.split("\n"):
        stripped = line.strip()
        if stripped.startswith(">"):
            continue
        if re.match(
            r"^(from|sent|to|cc|subject|보내는\s*사람|보내는사람)\s*:",
            stripped,
            re.IGNORECASE,
        ):
            # Likely start of an inline quoted header block.
            break
        if re.match(r"^customer centric agility$", stripped, re.IGNORECASE):
            break
        if re.match(r"^tel\s*:", stripped, re.IGNORECASE):
            break
        lines.append(line.rstrip())

    cleaned = "\n".join(lines)
    cleaned = re.sub(r"\n{3,}", "\n\n", cleaned).strip()
    return cleaned


def _addresses(msg: EmailMessage, header: str) -> str:
    raw = msg.get_all(header, [])
    if not raw:
        return ""
    values = [decode_mime_header(str(item)) for item in raw]
    return ", ".join(v for v in values if v)


def _parse_date(msg: EmailMessage) -> datetime | None:
    raw = msg.get("Date")
    if not raw:
        return None
    try:
        dt = parsedate_to_datetime(raw)
    except Exception:  # noqa: BLE001
        return None
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)
    return dt.astimezone(KST)


def _extract_body(msg: EmailMessage) -> str:
    text_part = ""
    html_part = ""
    if msg.is_multipart():
        for part in msg.walk():
            ctype = part.get_content_type()
            disp = str(part.get("Content-Disposition") or "")
            if "attachment" in disp.lower():
                continue
            try:
                payload = part.get_content()
            except Exception:  # noqa: BLE001
                continue
            if not isinstance(payload, str):
                continue
            if ctype == "text/plain" and not text_part:
                text_part = payload
            elif ctype == "text/html" and not html_part:
                html_part = payload
    else:
        try:
            payload = msg.get_content()
        except Exception:  # noqa: BLE001
            payload = ""
        if isinstance(payload, str):
            if msg.get_content_type() == "text/html":
                html_part = payload
            else:
                text_part = payload

    raw = text_part if text_part.strip() else html_to_text(html_part)
    return clean_body(raw)


def _attachment_names(msg: EmailMessage) -> list[str]:
    names: list[str] = []
    for part in msg.walk():
        filename = part.get_filename()
        if filename:
            names.append(decode_mime_header(filename))
    return names


def parse_eml_bytes(data: bytes, mailbox: str, source_name: str) -> ParsedMail | None:
    try:
        msg = email.message_from_bytes(data, policy=email.policy.default)
    except Exception:  # noqa: BLE001
        return None

    subject = decode_mime_header(msg.get("Subject"))
    message_id = decode_mime_header(msg.get("Message-ID")) or Path(source_name).name
    return ParsedMail(
        mailbox=mailbox,
        message_id=message_id,
        thread_key=normalize_thread_key(subject),
        subject=subject,
        from_addr=_addresses(msg, "From"),
        to_addrs=_addresses(msg, "To"),
        cc_addrs=_addresses(msg, "Cc"),
        mailed_at=_parse_date(msg),
        attachment_names=_attachment_names(msg),
        body_text=_extract_body(msg),
        source_path=source_name,
    )


def parse_eml_file(path: Path, mailbox: str) -> ParsedMail | None:
    try:
        return parse_eml_bytes(path.read_bytes(), mailbox, str(path))
    except Exception:  # noqa: BLE001
        return None


def find_zip(job_dir: Path, prefix: str) -> Path | None:
    matches = sorted(job_dir.glob(f"{prefix}_*.zip"))
    return matches[0] if matches else None


def iter_eml_members(zip_path: Path) -> list[zipfile.ZipInfo]:
    members: list[zipfile.ZipInfo] = []
    with zipfile.ZipFile(zip_path, "r") as zf:
        for info in zf.infolist():
            if info.is_dir():
                continue
            name = info.filename.replace("\\", "/")
            if name.startswith("/") or ".." in Path(name).parts:
                continue
            if not name.lower().endswith(".eml"):
                continue
            members.append(info)
    return members


def load_mailbox_from_zip(
    zip_path: Path,
    mailbox: str,
    *,
    date_from: date | None = None,
    date_to: date | None = None,
    on_progress: Callable[[int, int, int], None] | None = None,
) -> tuple[list[ParsedMail], int]:
    """Stream-parse .eml entries inside zip. Optionally keep only mails in date range.

    Returns (mails, total_eml_count). Avoids extracting multi-GB archives to disk.
    on_progress(scanned, total, matched) is called periodically.
    """
    members = iter_eml_members(zip_path)
    total = len(members)
    mails: list[ParsedMail] = []
    scanned = 0

    if on_progress:
        on_progress(0, total, 0)

    with zipfile.ZipFile(zip_path, "r") as zf:
        for info in members:
            scanned += 1
            name = info.filename.replace("\\", "/")
            try:
                with zf.open(info) as src:
                    data = src.read()
            except Exception:  # noqa: BLE001
                data = b""
            if data:
                parsed = parse_eml_bytes(data, mailbox, name)
                if parsed:
                    keep = True
                    if date_from and date_to:
                        if parsed.mailed_at is None:
                            keep = False
                        else:
                            day = parsed.mailed_at.astimezone(KST).date()
                            keep = date_from <= day <= date_to
                    if keep:
                        mails.append(parsed)

            if on_progress and (scanned == total or scanned % 25 == 0):
                on_progress(scanned, total, len(mails))

    mails.sort(key=lambda m: m.mailed_at or datetime.min.replace(tzinfo=KST))
    if on_progress:
        on_progress(total, total, len(mails))
    return mails, total

def filter_by_date(mails: list[ParsedMail], date_from: date, date_to: date) -> list[ParsedMail]:
    filtered: list[ParsedMail] = []
    for mail in mails:
        if mail.mailed_at is None:
            continue
        local_day = mail.mailed_at.astimezone(KST).date()
        if date_from <= local_day <= date_to:
            filtered.append(mail)
    filtered.sort(key=lambda m: m.mailed_at or datetime.min.replace(tzinfo=KST))
    return filtered


def group_by_thread(mails: list[ParsedMail]) -> dict[str, list[ParsedMail]]:
    groups: dict[str, list[ParsedMail]] = {}
    for mail in mails:
        groups.setdefault(mail.thread_key, []).append(mail)
    for key in groups:
        groups[key].sort(key=lambda m: m.mailed_at or datetime.min.replace(tzinfo=KST))
    return groups