import html
import re
from typing import Any, Dict, List, Optional
from urllib.parse import urljoin

import httpx

from core.config import settings

REPORTS_URL = "https://ntp.niehs.nih.gov/publications/reports"
BASE = "https://ntp.niehs.nih.gov"
INDEX_URL = "https://ntp.niehs.nih.gov/data/tr"

TR_RE = re.compile(r"\bTR-?(\d{3,4})\b", re.IGNORECASE)
HREF_RE = re.compile(r"href=[\"']([^\"']+)[\"']", re.IGNORECASE)
TITLE_RE = re.compile(r"<title[^>]*>(.*?)</title>", re.IGNORECASE | re.DOTALL)
TR_MARKER_RE = re.compile(r">(TR-\d{3,})<", re.IGNORECASE)


def _strip_tags(html_text: str) -> str:
    # crude but robust enough for the NTP index page
    text = re.sub(r"<script[\s\S]*?</script>", " ", html_text, flags=re.IGNORECASE)
    text = re.sub(r"<style[\s\S]*?</style>", " ", text, flags=re.IGNORECASE)
    text = re.sub(r"<[^>]+>", " ", text)
    text = html.unescape(text)
    text = re.sub(r"\s+", " ", text).strip()
    return text


def _extract_title(page_html: str) -> str:
    m = TITLE_RE.search(page_html or "")
    if not m:
        return ""
    t = html.unescape(m.group(1))
    t = re.sub(r"\s+", " ", t).strip()
    # common suffix
    t = re.sub(r"\s*\|\s*NTP.*$", "", t, flags=re.IGNORECASE).strip()
    return t


def _extract_pdf_url(page_html: str, page_url: str) -> Optional[str]:
    # Look for any href ending in .pdf
    hrefs = HREF_RE.findall(page_html or "")
    for href in hrefs:
        if ".pdf" not in href.lower():
            continue
        if href.startswith("#"):
            continue
        return urljoin(page_url, href)
    return None


async def _fetch_tr_page(num: str, http: httpx.AsyncClient) -> Optional[Dict[str, Any]]:
    page_url = f"{BASE}/publications/reports/tr{num}"
    try:
        r = await http.get(
            page_url,
            timeout=25,
            follow_redirects=True,
            headers={"User-Agent": "Mozilla/5.0"},
        )
        if r.status_code >= 400:
            return None
        page_html = r.text
    except Exception:
        return None

    title = _extract_title(page_html)
    pdf_url = _extract_pdf_url(page_html, str(r.url))

    # Try to find a year in the title
    year = None
    if title:
        years = re.findall(r"\b(19\d{2}|20\d{2})\b", title)
        if years:
            year = years[-1]

    item = {
        "num": num,
        "tr": f"TR-{num}",
        "report_page": str(r.url),
        "title": title,
        "year": year,
        "pdf": pdf_url,
    }
    return item


async def search_technical_reports(query: str, http: httpx.AsyncClient, limit: int = 8) -> Dict[str, Any]:
    """Search NTP Technical Reports and return ONLY TR hits relevant to the query.

    Implementation mirrors production (Cloudflare worker):
    - download the NTP reports index HTML
    - locate TR-### occurrences
    - keep a TR if the query appears in the surrounding neighborhood text
    - fetch each TR page to obtain report page + PDF
    """

    q = (query or "").strip()
    if not q:
        return {"ok": False, "error": "Empty query", "items": []}

    # Prefer worker proxy if configured (matches production behavior)
    if settings.worker_base_url:
        try:
            worker_url = settings.worker_base_url.rstrip("/") + "/ntp-tr"
            r = await http.post(worker_url, json={"query": q, "limit": limit}, timeout=25.0)
            if r.status_code < 400:
                data = r.json()
                rows = data.get("results") or []
                items: List[Dict[str, Any]] = []
                for row in rows:
                    if not isinstance(row, dict):
                        continue
                    items.append(
                        {
                            "num": (row.get("tr") or "").replace("TR-", ""),
                            "tr": row.get("tr"),
                            "report_page": row.get("page") or row.get("url"),
                            "title": row.get("title") or "NTP Technical Report",
                            "year": row.get("year"),
                            "pdf": row.get("pdf"),
                        }
                    )
                if items:
                    return {"ok": True, "query": q, "items": items}
        except Exception:
            pass

    try:
        r = await http.get(
            REPORTS_URL,
            timeout=25,
            follow_redirects=True,
            headers={"User-Agent": "Mozilla/5.0"},
        )
        r.raise_for_status()
        index_html = r.text
    except Exception as e:
        return {"ok": False, "error": f"Failed to fetch NTP index: {e}", "items": []}

    lines = index_html.splitlines()
    q_low = q.lower()
    is_cas = bool(re.match(r"^\d{2,7}-\d{2}-\d$", q))
    q_digits = re.sub(r"\D", "", q) if is_cas else ""
    results: List[Dict[str, Any]] = []

    for i, line in enumerate(lines):
        m = TR_MARKER_RE.search(line)
        if not m:
            continue

        snippet = " ".join(lines[i : min(i + 12, len(lines))])
        mini_snippet = " ".join(lines[i : min(i + 3, len(lines))])
        low_text = _strip_tags(snippet).lower()
        mini_text = _strip_tags(mini_snippet)

        if is_cas:
            if q_digits not in re.sub(r"\D", "", mini_text):
                continue
        else:
            if q_low not in low_text:
                continue

        tr_id = m.group(1)
        hrefs = HREF_RE.findall(snippet)

        # Prefer a non-PDF link under /publications/ or /go/
        candidates = [urljoin(REPORTS_URL, h) for h in hrefs if not re.search(r"\.pdf(\?|$)", h, re.I)]

        def score(u: str) -> int:
            s = 0
            if "/publications/" in u:
                s += 3
            if "/go/" in u:
                s += 3
            if tr_id and tr_id.lower() in u.lower():
                s += 2
            if re.search(r"/reports?", u):
                s += 1
            return s

        candidates.sort(key=score, reverse=True)
        page_href = candidates[0] if candidates else None

        pdf_match = re.search(r'href="([^"]+\.pdf)"', snippet, re.I)
        pdf_url = urljoin(REPORTS_URL, pdf_match.group(1)) if pdf_match else None

        text_block = _strip_tags(snippet)
        if is_cas and q_digits not in re.sub(r"\D", "", text_block):
            continue
        title_match = re.search(
            r"TR-\d{3,}\s+PDF\s+(.*?)\s+\b(20\d{2}|19\d{2})\b\s+Technical Report",
            text_block,
            re.I,
        )
        year_match = re.search(r"\b(20\d{2}|19\d{2})\b", text_block)

        results.append(
            {
                "tr": tr_id,
                "title": title_match.group(1) if title_match else "",
                "year": year_match.group(1) if year_match else "",
                "pdf": pdf_url,
                "report_page": page_href or REPORTS_URL,
            }
        )
        if len(results) >= int(limit):
            break

    # Fallback: scan the TR index page (data/tr)
    if not results:
        try:
            r2 = await http.get(
                INDEX_URL,
                timeout=25,
                follow_redirects=True,
                headers={"User-Agent": "Mozilla/5.0"},
            )
            if r2.status_code < 400:
                idx_html = r2.text
            else:
                idx_html = ""
        except Exception:
            idx_html = ""

        if idx_html:
            idx_lines = idx_html.splitlines()
            for i, row in enumerate(idx_lines):
                if not re.search(r"TR-\d{3,}", row, re.I):
                    continue
                block = " ".join(idx_lines[i : min(i + 6, len(idx_lines))])
                block_text = _strip_tags(block)
                low = block_text.lower()
                if q_low not in low:
                    continue

                tr = re.search(r"TR-\d{3,}", block_text, re.I)
                cas = re.search(r"\b\d{2,7}-\d{2}-\d\b", block_text)
                name = block_text
                if tr:
                    name = re.sub(r"TR-\d{3,}", "", name, flags=re.I)
                if cas:
                    name = re.sub(r"\b\d{2,7}-\d{2}-\d\b", "", name)
                name = name.strip()

                results.append(
                    {
                        "tr": tr.group(0) if tr else "",
                        "title": name or "",
                        "year": "",
                        "pdf": None,
                        "report_page": INDEX_URL,
                    }
                )
                if len(results) >= int(limit):
                    break

    return {"ok": True, "query": q, "items": results}