"""Shared embedding-based semantic retrieval utilities."""

from __future__ import annotations

import asyncio
import json
import math
import os
from typing import Any
from urllib import request


class EmbeddingRetriever:
    """Use an OpenAI-compatible embeddings API to rank lightweight candidates."""

    def __init__(
        self,
        *,
        api_key_env: str = "OPENAI_API_KEY",
        api_base_env: str = "OPENAI_API_BASE",
        model: str = "text-embedding-v4",
        timeout_seconds: float = 20.0,
    ) -> None:
        self.api_key_env = api_key_env
        self.api_base_env = api_base_env
        self.model = model
        self.timeout_seconds = timeout_seconds

    async def retrieve(
        self,
        *,
        query: str,
        candidates: list[dict[str, str]],
        top_k: int,
        api_key: str | None = None,
        api_base: str | None = None,
        model: str | None = None,
        extra_headers: dict[str, str] | None = None,
        timeout_seconds: float | None = None,
        fallback_top_k: int | None = None,
    ) -> list[dict[str, str]]:
        """Return candidates ordered by embedding similarity.

        If embedding config is missing or the request fails, return the original
        candidate order. This keeps retrieval non-blocking for the main run.
        """

        if not candidates or top_k <= 0:
            return []

        fallback = self._fallback_candidates(candidates, fallback_top_k=fallback_top_k)
        resolved_api_key = api_key or os.getenv(self.api_key_env)
        resolved_api_base = api_base or os.getenv(self.api_base_env)
        if not resolved_api_key or not resolved_api_base:
            return fallback

        try:
            query_embedding = await self._embed_texts(
                api_key=resolved_api_key,
                api_base=resolved_api_base,
                texts=[query],
                model=model or self.model,
                extra_headers=extra_headers,
                timeout_seconds=timeout_seconds,
            )
            candidate_embeddings = await self._embed_texts(
                api_key=resolved_api_key,
                api_base=resolved_api_base,
                texts=[self._candidate_text(item) for item in candidates],
                model=model or self.model,
                extra_headers=extra_headers,
                timeout_seconds=timeout_seconds,
            )
        except Exception:
            return fallback

        if not query_embedding or not query_embedding[0] or len(candidate_embeddings) != len(candidates):
            return fallback

        query_vector = query_embedding[0]
        scored: list[tuple[float, dict[str, str]]] = []
        for candidate, vector in zip(candidates, candidate_embeddings, strict=False):
            if vector:
                scored.append((self._cosine_similarity(query_vector, vector), candidate))

        scored.sort(key=lambda item: item[0], reverse=True)
        return [item[1] for item in scored[:top_k]]

    async def _embed_texts(
        self,
        *,
        api_key: str,
        api_base: str,
        texts: list[str],
        model: str,
        extra_headers: dict[str, str] | None = None,
        timeout_seconds: float | None = None,
    ) -> list[list[float]]:
        all_vectors: list[list[float]] = []
        endpoint = self._normalize_embeddings_endpoint(api_base)
        for start in range(0, len(texts), 10):
            batch = texts[start:start + 10]
            payload = await self._post_embeddings(
                endpoint=endpoint,
                api_key=api_key,
                model=model,
                texts=batch,
                extra_headers=extra_headers,
                timeout_seconds=timeout_seconds,
            )
            embeddings = payload.get("data") or []
            embeddings = sorted(embeddings, key=lambda item: item.get("index", 0))
            all_vectors.extend([list(item.get("embedding") or []) for item in embeddings])
        return all_vectors

    async def _post_embeddings(
        self,
        *,
        endpoint: str,
        api_key: str,
        model: str,
        texts: list[str],
        extra_headers: dict[str, str] | None = None,
        timeout_seconds: float | None = None,
    ) -> dict[str, Any]:
        return await asyncio.to_thread(
            self._post_embeddings_sync,
            endpoint=endpoint,
            api_key=api_key,
            model=model,
            texts=texts,
            extra_headers=extra_headers,
            timeout_seconds=timeout_seconds,
        )

    def _post_embeddings_sync(
        self,
        *,
        endpoint: str,
        api_key: str,
        model: str,
        texts: list[str],
        extra_headers: dict[str, str] | None = None,
        timeout_seconds: float | None = None,
    ) -> dict[str, Any]:
        body = json.dumps(
            {
                "model": model,
                "input": texts if len(texts) > 1 else texts[0],
                "encoding_format": "float",
            }
        ).encode("utf-8")
        req = request.Request(
            endpoint,
            data=body,
            headers={
                "Authorization": f"Bearer {api_key}",
                "Content-Type": "application/json",
                **(extra_headers or {}),
            },
            method="POST",
        )
        with request.urlopen(req, timeout=timeout_seconds or self.timeout_seconds) as response:
            return json.loads(response.read().decode("utf-8"))

    @staticmethod
    def _fallback_candidates(
        candidates: list[dict[str, str]],
        *,
        fallback_top_k: int | None,
    ) -> list[dict[str, str]]:
        if fallback_top_k is None:
            return list(candidates)
        if fallback_top_k <= 0:
            return []
        return candidates[:fallback_top_k]

    @staticmethod
    def _candidate_text(candidate: dict[str, str]) -> str:
        parts = [
            (candidate.get("name") or "").strip(),
            (candidate.get("description") or "").strip(),
            (candidate.get("input_schema") or "").strip(),
        ]
        return "\n".join(part for part in parts if part)

    @staticmethod
    def _normalize_embeddings_endpoint(api_base: str) -> str:
        base = api_base.rstrip("/")
        if base.endswith("/embeddings"):
            return base
        if base.endswith("/v1"):
            return f"{base}/embeddings"
        return f"{base}/v1/embeddings"

    @staticmethod
    def _cosine_similarity(left: list[float], right: list[float]) -> float:
        if not left or not right or len(left) != len(right):
            return -1.0
        dot = sum(a * b for a, b in zip(left, right, strict=False))
        left_norm = math.sqrt(sum(a * a for a in left))
        right_norm = math.sqrt(sum(b * b for b in right))
        if left_norm == 0 or right_norm == 0:
            return -1.0
        return dot / (left_norm * right_norm)