# -*- coding: utf-8 -*-
"""Semantic RAG engine for Astraea — chunk the law 'books', embed, and retrieve.

stdlib-only (urllib + json + math), no numpy needed. Embeddings and generation
run on the Ollama host (nightmare). The vector index is cached to disk and rebuilt
incrementally only when a book changes.
"""
import json
import math
import os
import re
import threading
import urllib.request

from agents import OLLAMA_URL, EMBED_MODEL, BOOKS_DIR, AGENTS

INDEX_PATH = "/opt/astraea/index.json"


def _post(url, payload, timeout=120):
    """POST JSON to Ollama with a no-proxy opener (safe on LAN)."""
    req = urllib.request.Request(
        url, data=json.dumps(payload).encode("utf-8"),
        headers={"Content-Type": "application/json"},
    )
    opener = urllib.request.build_opener(urllib.request.ProxyHandler({}))
    with opener.open(req, timeout=timeout) as r:
        return json.loads(r.read().decode("utf-8"))


def embed(text):
    """Return a float vector for `text` via the Ollama embeddings endpoint."""
    d = _post(f"{OLLAMA_URL}/api/embeddings", {"model": EMBED_MODEL, "prompt": text})
    v = d.get("embedding") or d.get("embeddings")
    if isinstance(v, list) and v and isinstance(v[0], list):
        v = v[0]
    if not v:
        raise RuntimeError("empty embedding returned")
    return v


def _cosine(a, b):
    dot = sum(x * y for x, y in zip(a, b))
    na = math.sqrt(sum(x * x for x in a))
    nb = math.sqrt(sum(y * y for y in b))
    return dot / (na * nb) if na and nb else 0.0


MAX_CHUNK = 1100  # chars — stay safely under the embedding model's context budget


def _split_long(text, limit):
    """Split text into pieces <= limit chars, preferring sentence boundaries."""
    if len(text) <= limit:
        return [text] if text.strip() else []
    parts = re.split(r"(?<=[.!?])\s+", text)
    out = []
    cur = ""
    for p in parts:
        if cur and len(cur) + len(p) + 1 > limit:
            out.append(cur)
            cur = p
        else:
            cur = (cur + " " + p).strip() if cur else p
        while len(cur) > limit:
            out.append(cur[:limit])
            cur = cur[limit:]
    if cur.strip():
        out.append(cur)
    return out


def _chunk_markdown(text):
    """Split markdown into self-contained (title, body) chunks, each <= MAX_CHUNK chars."""
    lines = text.splitlines()
    chunks = []
    cur_title = None
    cur_buf = []

    def flush():
        nonlocal cur_title, cur_buf
        if not cur_buf:
            return
        body = "\n".join(cur_buf).strip()
        cur_buf = []
        if not body:
            return
        for piece in _split_long(body, MAX_CHUNK):
            chunks.append((cur_title or "Section", piece))

    for line in lines:
        if re.match(r"^#{1,4}\s+", line):
            flush()
            cur_title = re.sub(r"^#{1,4}\s+", "", line).strip()
        else:
            cur_buf.append(line)
    flush()
    return chunks


def build_index():
    """Build (or load from cache) the vector index. Returns list of chunk dicts."""
    index = []
    book_files = []
    for a in AGENTS:
        for b in a["books"]:
            path = os.path.join(BOOKS_DIR, b)
            if os.path.exists(path):
                book_files.append((path, a["id"]))

    # Decide whether to reuse cache: index.json exists, embed model matches, and no book changed.
    if os.path.exists(INDEX_PATH):
        try:
            with open(INDEX_PATH) as f:
                cached = json.load(f)
            if cached.get("embed_model") == EMBED_MODEL:
                newest_book = max(os.path.getmtime(p) for p, _ in book_files) if book_files else 0
                if os.path.getmtime(INDEX_PATH) >= newest_book:
                    return cached["chunks"]
        except Exception:
            pass

    for path, agent_id in book_files:
        try:
            with open(path, encoding="utf-8") as f:
                text = f.read()
        except Exception:
            continue
        base = os.path.basename(path)
        for title, body in _chunk_markdown(text):
            # Embed the title + body together for best semantic match.
            try:
                vec = embed(f"{title}\n{body}")
            except Exception:
                continue  # skip any chunk that fails to embed
            index.append({
                "agent": agent_id,
                "source": base,
                "title": title,
                "text": body,
                "vector": vec,
            })

    if index:
        try:
            with open(INDEX_PATH, "w") as f:
                json.dump({"embed_model": EMBED_MODEL, "chunks": index}, f)
        except Exception:
            pass
    return index


def retrieve(query, agent_id, top_k=5):
    """Return top-k relevant chunks for `agent_id` via cosine similarity."""
    qvec = embed(query)
    scored = []
    for c in _INDEX:
        if c["agent"] != agent_id:
            continue
        scored.append((_cosine(qvec, c["vector"]), c))
    scored.sort(key=lambda x: x[0], reverse=True)
    return [(s, c) for s, c in scored[:top_k]]


# Global index, built lazily once in a background thread.
_INDEX = []
_index_lock = threading.Lock()
_index_ready = False


def start_background_index():
    def _run():
        global _index_ready
        try:
            idx = build_index()
            with _index_lock:
                _INDEX.clear()
                _INDEX.extend(idx)
        finally:
            _index_ready = True
    threading.Thread(target=_run, daemon=True).start()


def index_status():
    return {"ready": _index_ready, "chunks": len(_INDEX)}