"""Preprocessor for email HTML files.

Handles:
- HTML stripping via BeautifulSoup
- Metadata extraction (Subject, From, To, Date)
- Thread splitting — isolates the latest reply
"""

from __future__ import annotations

import re
from typing import TYPE_CHECKING

from app.core.preprocessors.base import PreprocessResult

if TYPE_CHECKING:
    pass

# ── Thread split markers ──────────────────────────────────────────────

# Matches patterns like:
#   "On Mon, Apr 7, 2026 at 10:00 AM, Alice <alice@co.com> wrote:"
#   "-----Original Message-----"
#   "> " (plain-text quote prefix)
_THREAD_PATTERNS = [
    re.compile(r"^On\s+.+wrote\s*:", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^-{3,}\s*(original message|forwarded message)\s*-{3,}", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^>{1,}\s+\S", re.MULTILINE),
    re.compile(r"^From:\s+.+\nSent:\s+", re.IGNORECASE | re.MULTILINE),
]

# ── Metadata patterns (applied on raw HTML / plain fallback) ──────────

_META_PATTERNS: dict[str, list[re.Pattern]] = {
    "subject": [
        re.compile(r"<title>(.+?)</title>", re.IGNORECASE | re.DOTALL),
        re.compile(r"Subject:\s*(.+)", re.IGNORECASE),
    ],
    "from": [
        re.compile(r'<meta[^>]+name=["\']?from["\']?[^>]+content=["\']([^"\']+)["\']', re.IGNORECASE),
        re.compile(r"From:\s*(.+)", re.IGNORECASE),
    ],
    "to": [
        re.compile(r'<meta[^>]+name=["\']?to["\']?[^>]+content=["\']([^"\']+)["\']', re.IGNORECASE),
        re.compile(r"To:\s*(.+)", re.IGNORECASE),
    ],
    "date": [
        re.compile(r'<meta[^>]+name=["\']?date["\']?[^>]+content=["\']([^"\']+)["\']', re.IGNORECASE),
        re.compile(r"Date:\s*(.+)", re.IGNORECASE),
        re.compile(r"Sent:\s*(.+)", re.IGNORECASE),
    ],
}


def _extract_metadata(raw_html: str, text: str) -> dict:
    """Extract Subject/From/To/Date from raw HTML or plain text."""
    metadata: dict[str, str] = {}
    for field, patterns in _META_PATTERNS.items():
        for pat in patterns:
            m = pat.search(raw_html) or pat.search(text)
            if m:
                metadata[field] = m.group(1).strip()
                break
    return metadata


def _split_thread(text: str) -> str:
    """Return only the latest message in a threaded email."""
    earliest_pos: int | None = None
    for pat in _THREAD_PATTERNS:
        m = pat.search(text)
        if m and (earliest_pos is None or m.start() < earliest_pos):
            earliest_pos = m.start()

    if earliest_pos is not None and earliest_pos > 0:
        return text[:earliest_pos].strip()
    return text.strip()


def preprocess_email_html(raw_content: str) -> PreprocessResult:
    """Strip HTML, extract metadata, split thread from an email HTML file."""
    try:
        from bs4 import BeautifulSoup  # lazy import — optional dep
    except ImportError as exc:
        raise ImportError(
            "beautifulsoup4 is required for email_html preprocessing. "
            "Install it with: pip install beautifulsoup4"
        ) from exc

    # Parse with lxml if available, fall back to html.parser
    try:
        soup = BeautifulSoup(raw_content, "lxml")
    except Exception:
        soup = BeautifulSoup(raw_content, "html.parser")

    # Remove noise tags
    for tag in soup(["style", "script", "head", "noscript"]):
        tag.decompose()

    clean_text = soup.get_text(separator="\n")
    # Collapse excessive blank lines
    clean_text = re.sub(r"\n{3,}", "\n\n", clean_text).strip()

    metadata = _extract_metadata(raw_content, clean_text)
    latest_message = _split_thread(clean_text)

    return PreprocessResult(
        content_type="email_html",
        clean_text=latest_message,
        metadata=metadata,
    )