from __future__ import annotations

import logging
import re
from html import unescape

logger = logging.getLogger(__name__)

try:
    from bs4 import BeautifulSoup

    HAS_BS4 = True
except ImportError:
    HAS_BS4 = False
    logger.warning("beautifulsoup4 not installed — Help Scout HTML parsing will use fallback regex")

_EMAIL_QUOTE_PATTERNS = [
    re.compile(r"^On\s+.*wrote:\s*$", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^>{1,}\s?", re.MULTILINE),
    re.compile(r"^-{2,}\s*Original Message\s*-{2,}", re.IGNORECASE),
    re.compile(r"^From:\s+.*$", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^Sent:\s+.*$", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^To:\s+.*$", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^Subject:\s+.*$", re.IGNORECASE | re.MULTILINE),
    re.compile(r"^Date:\s+.*$", re.IGNORECASE | re.MULTILINE),
]


def html_to_text(html_body: str) -> str:
    if not html_body:
        return ""

    if HAS_BS4:
        return _bs4_html_to_text(html_body)
    return _regex_html_to_text(html_body)


def _bs4_html_to_text(html_body: str) -> str:
    soup = BeautifulSoup(html_body, "html.parser")

    for tag in soup(["style", "script", "head"]):
        tag.decompose()

    for a_tag in soup.find_all("a", href=True):
        text = a_tag.get_text(strip=True)
        url = a_tag["href"]
        if text and url:
            a_tag.replace_with(f"[{text}]({url})")

    for br in soup.find_all("br"):
        br.replace_with("\n")

    for p in soup.find_all("p"):
        p.insert_before("\n")
        p.insert_after("\n")
        p.unwrap()

    for tag in soup.find_all(["strong", "b"]):
        if tag.string:
            tag.string.replace_with(f"**{tag.string}**")
        tag.unwrap()

    for tag in soup.find_all(["em", "i"]):
        if tag.string:
            tag.string.replace_with(f"*{tag.string}*")
        tag.unwrap()

    for li in soup.find_all("li"):
        li.insert_before("- ")
        li.insert_after("\n")
        li.unwrap()

    text = soup.get_text(separator="\n")
    text = unescape(text)
    text = strip_email_quote(text)
    text = re.sub(r"\n{3,}", "\n\n", text)

    return text.strip()


def _regex_html_to_text(html_body: str) -> str:
    import html

    text = html_body

    for tag in ("style", "script", "head"):
        text = re.sub(
            f"<{tag}[^>]*>.*?</{tag}>",
            "",
            text,
            flags=re.DOTALL | re.IGNORECASE,
        )

    text = re.sub(
        r'<a\s[^>]*href=["\']([^"\']*)["\'][^>]*>(.*?)</a>',
        r"[\2](\1)",
        text,
        flags=re.DOTALL,
    )
    text = re.sub(r"<br\s*/?>", "\n", text, flags=re.IGNORECASE)
    text = re.sub(r"<p[^>]*>", "\n", text, flags=re.IGNORECASE)
    text = re.sub(r"</p>", "\n", text, flags=re.IGNORECASE)
    text = re.sub(
        r"<(?:strong|b)[^>]*>(.*?)</(?:strong|b)>",
        r"**\1**",
        text,
        flags=re.DOTALL,
    )
    text = re.sub(r"<(?:em|i)[^>]*>(.*?)</(?:em|i)>", r"*\1*", text, flags=re.DOTALL)
    text = re.sub(r"<li[^>]*>(.*?)</li>", r"- \1\n", text, flags=re.DOTALL)
    text = re.sub(r"<[^>]+>", "", text)
    text = html.unescape(text)
    text = strip_email_quote(text)
    text = re.sub(r"\n{3,}", "\n\n", text)
    text = re.sub(r"[ \t]{2,}", " ", text)

    return text.strip()


def strip_email_quote(text: str) -> str:
    lines = text.split("\n")
    cleaned_lines = []

    for line in lines:
        is_quote = False
        for pattern in _EMAIL_QUOTE_PATTERNS:
            if pattern.match(line.strip()):
                is_quote = True
                break

        if not is_quote:
            cleaned_lines.append(line)
        else:
            break

    return "\n".join(cleaned_lines)


def extract_plain_text(text: str, max_length: int = 500) -> str:
    plain = re.sub(r"[#*_>\-\[\]\(\)]", "", text)
    plain = re.sub(r"\s+", " ", plain).strip()
    if len(plain) > max_length:
        plain = plain[: max_length - 3] + "..."
    return plain