"""Embedding function for Chroma — Ollama-hosted nomic-embed-text by default.

Swappable: implement the same `embedding_function()` interface returning
a Chroma `EmbeddingFunction` and the rest of the pipeline doesn't care.

Env-configurable (matches the zerto-docs-rag pattern so the same Gitea
runner + GPU-pinned Ollama containers can serve every docs MCP build):

  OLLAMA_URLS   comma-separated list, load-balanced round-robin per batch.
                Preferred — set in the CI workflow to fan out across two
                GPU-pinned Ollama containers on the Gitea host.
  OLLAMA_URL    single endpoint, fallback when OLLAMA_URLS is unset.
                Default http://192.168.0.2:11434 (the host where the GPUs
                live in Justin's lab).
  EMBED_MODEL   model name; default 'nomic-embed-text'
  EMBED_DIM     expected embedding dim; default 768 (nomic-embed-text)
"""
from __future__ import annotations

import os
import logging
import time
from typing import Any

import httpx
from chromadb import EmbeddingFunction, Documents, Embeddings

log = logging.getLogger(__name__)

DEFAULT_OLLAMA_URL = "http://192.168.0.2:11434"


def _resolve_urls() -> list[str]:
    raw = os.environ.get("OLLAMA_URLS", "").strip()
    if raw:
        return [u.strip().rstrip("/") for u in raw.split(",") if u.strip()]
    single = os.environ.get("OLLAMA_URL", DEFAULT_OLLAMA_URL).strip().rstrip("/")
    return [single]


OLLAMA_URLS = _resolve_urls()
EMBED_MODEL = os.environ.get("EMBED_MODEL", "nomic-embed-text")
EMBED_DIM = int(os.environ.get("EMBED_DIM", "768"))


class OllamaEmbeddings(EmbeddingFunction):
    """Calls /api/embed across N Ollama endpoints, round-robin per batch.

    For indexing throughput on multiple GPUs, run one Ollama container
    per GPU (pinned via NVIDIA_VISIBLE_DEVICES) and pass all their URLs
    in OLLAMA_URL — the embedder picks the next endpoint per batch.

    Resilient (ported from zerto-docs PR #45): a failed call rotates to
    the next endpoint and retries with backoff instead of failing the
    whole rebuild. HTTP status errors additionally halve the input —
    the .0.125 Windows Ollama (4090) 400s when its model runner dies on
    an oversized input array, and one endpoint rejecting a batch the
    others accept shouldn't kill a multi-hour index build.
    """

    def __init__(self, urls: list[str] = OLLAMA_URLS, model: str = EMBED_MODEL):
        self.urls = urls
        self.model = model
        self._next = 0

    def __call__(self, input: Documents) -> Embeddings:
        return self._embed(list(input), attempt=1)

    def _embed(self, texts: list, attempt: int) -> Embeddings:
        url = self.urls[self._next % len(self.urls)]
        self._next += 1
        try:
            with httpx.Client(timeout=300) as c:
                r = c.post(f"{url}/api/embed",
                           json={"model": self.model, "input": texts})
                r.raise_for_status()
                return r.json().get("embeddings") or []
        except (httpx.TransportError, httpx.HTTPStatusError) as e:
            if isinstance(e, httpx.HTTPStatusError):
                desc = f"HTTP {e.response.status_code} ({e.response.text[:200]})"
            else:
                desc = f"transport error {type(e).__name__}"
            if attempt >= 5:
                log.error("%s from %s (%d texts) — giving up after %d attempts",
                          desc, url, len(texts), attempt)
                raise
            if isinstance(e, httpx.HTTPStatusError) and len(texts) > 16:
                mid = len(texts) // 2
                log.warning("%s from %s — splitting %d texts into %d+%d (attempt %d)",
                            desc, url, len(texts), mid, len(texts) - mid, attempt)
                return (self._embed(texts[:mid], attempt + 1)
                        + self._embed(texts[mid:], attempt + 1))
            backoff = 0.5 * (2 ** (attempt - 1))  # 0.5, 1, 2, 4
            log.warning("%s (attempt %d, %s) — retrying in %.1fs",
                        desc, attempt, url, backoff)
            time.sleep(backoff)
            return self._embed(texts, attempt + 1)

    def name(self) -> str:                  # newer chromadb requires this
        return f"ollama:{self.model}"

    @staticmethod
    def build_from_config(config: dict) -> "OllamaEmbeddings":  # newer chromadb
        return OllamaEmbeddings(
            urls=config.get("urls", OLLAMA_URLS),
            model=config.get("model", EMBED_MODEL),
        )

    def get_config(self) -> dict:           # newer chromadb
        return {"urls": self.urls, "model": self.model}

    def default_space(self) -> str:
        return "cosine"

    def supported_spaces(self) -> list[str]:
        return ["cosine", "l2", "ip"]


def embedding_function() -> EmbeddingFunction:
    return OllamaEmbeddings()
