import hashlib
from pathlib import Path
from typing import Any, Dict, List, Optional

import chromadb
from chromadb.errors import NotFoundError

from app.observability import retrieval as _obs_retrieval
from app.observability.contracts import RetrievalOutcome
from app.observability.operation import observe_operation
from app.rag.embeddings import Embedder
from app.rag.pipeline_version import get_pipeline_version

_FILE_INDEX_COLLECTION = "file-index"
_COLLECTION_ROLES = {
    "paper_evidence": "paper_evidence",
    "project_memory": "project_memory",
}


def _collection_role(collection: str) -> str:
    """Return the finite role name safe to attach to retrieval spans."""
    return _COLLECTION_ROLES.get(collection, "other")


def _safe_count(col: Any) -> Optional[int]:
    """Read a collection's size without ever raising into product code."""
    try:
        return col.count()
    except Exception:
        return None


class ChromaDBClient:
    """In-memory ChromaDB wrapper for the web demo deployment.

    State is persistent across process restarts. Files are deduplicated by
    SHA-256 content hash.
    """

    def __init__(
        self,
        embedder: Optional[Embedder] = None,
        *,
        path: str | Path | None = None,
        client: Any | None = None,
    ) -> None:
        import os
        if client is not None:
            self._client = client
        else:
            db_path = Path(path).expanduser() if path is not None else Path(os.path.expanduser("~/.studybuddy/chroma"))
            db_path.mkdir(parents=True, exist_ok=True)
            self._client = chromadb.PersistentClient(path=str(db_path))
        self.embedder = embedder or Embedder()

    # ------------------------------------------------------------------ #
    # Internal                                                             #
    # ------------------------------------------------------------------ #

    def _get_or_create(self, name: str):
        return self._client.get_or_create_collection(name)

    # ------------------------------------------------------------------ #
    # File dedup                                                           #
    # ------------------------------------------------------------------ #

    @staticmethod
    def file_hash(content: bytes) -> str:
        return hashlib.sha256(content).hexdigest()

    def is_indexed(self, content_hash: str) -> bool:
        try:
            col = self._client.get_or_create_collection(_FILE_INDEX_COLLECTION)
            r = col.get(ids=[content_hash])
            return len(r["ids"]) > 0
        except Exception:
            return False

    def mark_indexed(self, content_hash: str, filename: str) -> None:
        col = self._client.get_or_create_collection(_FILE_INDEX_COLLECTION)
        col.upsert(
            ids=[content_hash],
            documents=[filename],
            metadatas=[{"filename": filename}],
        )

    # ------------------------------------------------------------------ #
    # Public API                                                           #
    # ------------------------------------------------------------------ #

    def upsert(
        self,
        collection: str,
        documents: List[str],
        metadatas: List[Dict[str, Any]],
        ids: List[str],
    ) -> None:
        col = self._get_or_create(collection)
        with observe_operation("embedding.batch", subsystem="embedding") as op:
            op.add_count("embedding_batch_size", len(documents))
            embeddings = self.embedder.embed(documents)
        with observe_operation("chroma.upsert", subsystem="chroma") as op:
            before = _safe_count(col)
            if before is not None:
                op.set("collection_count_before", before)
            col.upsert(documents=documents, embeddings=embeddings, metadatas=metadatas, ids=ids)
            after = _safe_count(col)
            if after is not None:
                op.set("collection_count_after", after)

    def query_observed(
        self,
        collection: str,
        query_embedding: List[float],
        n_results: int = 5,
        where: Optional[Dict[str, Any]] = None,
        *,
        consumer: Optional[str] = None,
        pipeline_version: Optional[str] = None,
    ) -> RetrievalOutcome:
        """Vector search that preserves the *cause* of an empty result.

        Behaviourally identical to :meth:`query` (same clamping, same
        fallbacks), but returns a :class:`RetrievalOutcome` so a caller can
        tell a genuinely-empty successful search (``success_empty``) apart from
        a collection-lookup / vector-search failure that fell back to ``[]``
        (``error_fallback``). :meth:`query` delegates here and unwraps
        ``.candidates`` so every existing caller stays byte-for-byte compatible.

        ``pipeline_version`` (default ``None``) gates the over-fetch + dedup +
        truncate mechanism -- see ``app.rag.pipeline_version``. ``None`` (every
        ordinary product call site) and the explicit ``"rag-naive-v1"`` both
        resolve to the exact same frozen, unmodified behavior this method has
        always had: request exactly ``n_results``, no over-fetch, no dedup.
        Only an explicit ``"rag-dedup-v2"`` (driven by the benchmark runner)
        changes anything.
        """
        pv = get_pipeline_version(pipeline_version)
        requested_n = n_results  # what the caller actually wants back, unchanged by over-fetch

        with observe_operation("chroma.collection_lookup", subsystem="chroma", consumer=consumer) as op:
            try:
                col = self._client.get_collection(collection)
            except Exception as exc:
                op.mark_error(_obs_retrieval.COLLECTION_UNAVAILABLE)
                return RetrievalOutcome.failure(_obs_retrieval.COLLECTION_UNAVAILABLE)

        # Over-fetch a larger raw pool when dedup is enabled, so removing
        # near-duplicates below can still backfill up to `requested_n` from
        # alternate candidates instead of only ever shrinking the naive
        # top-k in place. `fetch_n == requested_n` whenever dedup is
        # disabled (v1's overfetch_factor is pinned to 1), which is what
        # keeps v1 byte-identical to its pre-Task-8 behavior.
        fetch_n = requested_n * pv.overfetch_factor

        # Clamp fetch_n to actual collection size (a count failure is
        # non-fatal here, exactly as before). `requested_top_k` is always the
        # caller's original ask, never the inflated over-fetch amount, so
        # this attribute means the same thing across both pipeline versions.
        with observe_operation("chroma.collection_count", subsystem="chroma", consumer=consumer) as op:
            try:
                actual = col.count()
                op.set("collection_size", actual)
                op.set("requested_top_k", requested_n)
                fetch_n = min(fetch_n, actual) if actual > 0 else 1
            except Exception:
                pass

        kwargs: Dict[str, Any] = {
            "query_embeddings": [query_embedding],
            "n_results": fetch_n,
        }
        if where:
            kwargs["where"] = where

        with observe_operation("chroma.vector_search", subsystem="chroma", consumer=consumer) as op:
            try:
                results = col.query(**kwargs)
            except Exception as exc:
                op.mark_error(_obs_retrieval.VECTOR_SEARCH_FAILED)
                return RetrievalOutcome.failure(_obs_retrieval.VECTOR_SEARCH_FAILED)

        with observe_operation("rag.result_prepare", subsystem="retrieval", consumer=consumer) as op:
            out = []
            for doc, meta in zip(results["documents"][0], results["metadatas"][0]):
                out.append({"text": doc, **meta})
            # Pool-level removed count, captured *before* truncation to
            # `requested_n` -- this is direct evidence of what the dedup
            # mechanism actually did to the raw over-fetched pool. It is
            # deliberately distinct from `duplicate_candidate_ratio` below,
            # which is computed on the final, already-deduplicated/truncated
            # list `candidate_stats()` receives: a post-dedup set is ~0.0 by
            # construction whether or not anything was removed, so it alone
            # cannot tell "removed nothing" apart from "removed something and
            # truncated it away". `duplicates_removed_from_pool` closes that
            # gap. Always 0 for v1 (dedup disabled -- there is no pool step to
            # remove anything from), which is itself the correct, honest value.
            duplicates_removed_from_pool = 0
            if pv.dedup_enabled:
                dup_indices = _obs_retrieval.find_duplicate_indices(out)
                duplicates_removed_from_pool = len(dup_indices)
                out = [c for i, c in enumerate(out) if i not in dup_indices]
                out = out[:requested_n]
            op.set("duplicates_removed_from_pool", duplicates_removed_from_pool)
            for key, value in _obs_retrieval.candidate_stats(out).items():
                op.set(key, value)

        outcome = RetrievalOutcome.success(out)
        return outcome

    def query(
        self,
        collection: str,
        query_embedding: List[float],
        n_results: int = 5,
        where: Optional[Dict[str, Any]] = None,
        *,
        pipeline_version: Optional[str] = None,
    ) -> List[Dict[str, Any]]:
        return self.query_observed(
            collection,
            query_embedding,
            n_results=n_results,
            where=where,
            pipeline_version=pipeline_version,
        ).candidates

    def query_raw(
        self,
        collection: str,
        query_embedding: List[float],
        n_results: int = 20,
        where: Optional[Dict[str, Any]] = None,
        *,
        consumer: Optional[str] = None,
        raise_on_failure: bool = False,
    ) -> List[Dict[str, Any]]:
        """Return stable IDs and distances for repository-level retrieval.

        Product consumers should use ``PaperEvidenceService`` or the project
        memory repository. This low-level method exists so rank fusion retains
        Chroma's identity and score instead of flattening results into text.
        ``raise_on_failure`` lets the structured source-retrieval boundary
        distinguish an unavailable dense index from a genuinely empty one;
        legacy callers retain the established empty-list fallback.
        """

        collection_role = _collection_role(collection)
        with observe_operation(
            "chroma.collection_lookup",
            subsystem="chroma",
            consumer=consumer,
            attributes={"collection_role": collection_role},
        ) as op:
            try:
                col = self._client.get_collection(collection)
            except NotFoundError:
                return []
            except Exception:
                op.mark_error(_obs_retrieval.COLLECTION_UNAVAILABLE)
                if raise_on_failure:
                    raise
                return []
        try:
            actual = col.count()
        except Exception:
            actual = n_results
        if actual <= 0:
            return []
        kwargs: Dict[str, Any] = {
            "query_embeddings": [query_embedding],
            "n_results": min(max(1, n_results), actual),
            "include": ["documents", "metadatas", "distances"],
        }
        if where:
            kwargs["where"] = where
        with observe_operation(
            "chroma.vector_search",
            subsystem="chroma",
            consumer=consumer,
            attributes={"collection_role": collection_role},
        ) as op:
            try:
                result = col.query(**kwargs)
            except Exception:
                op.mark_error(_obs_retrieval.VECTOR_SEARCH_FAILED)
                if raise_on_failure:
                    raise
                return []
        ids = (result.get("ids") or [[]])[0]
        documents = (result.get("documents") or [[]])[0]
        metadatas = (result.get("metadatas") or [[]])[0]
        distances = (result.get("distances") or [[]])[0]
        rows: List[Dict[str, Any]] = []
        for index, item_id in enumerate(ids):
            rows.append(
                {
                    "id": item_id,
                    "text": documents[index] if index < len(documents) else "",
                    "metadata": metadatas[index] if index < len(metadatas) else {},
                    "distance": distances[index] if index < len(distances) else None,
                }
            )
        return rows

    def delete_where(self, collection: str, where: Dict[str, Any]) -> None:
        """Delete matching rows, treating only an absent collection as empty.

        Derived-state deletion is a correctness operation.  Authentication,
        storage, or filter failures must reach the caller so source files are
        not removed while stale vectors remain searchable.
        """
        try:
            col = self._client.get_collection(collection)
        except NotFoundError:
            return
        col.delete(where=where)

    def get_where(
        self,
        collection: str,
        where: Dict[str, Any],
        *,
        include: List[str] | None = None,
    ) -> Dict[str, Any]:
        try:
            col = self._client.get_collection(collection)
        except NotFoundError:
            return {"ids": [], "metadatas": [], "documents": []}
        return col.get(where=where, include=include or ["metadatas"])

    def delete_ids(self, collection: str, ids: List[str]) -> None:
        if not ids:
            return
        try:
            col = self._client.get_collection(collection)
        except NotFoundError:
            return
        col.delete(ids=ids)

    def collection_count(self, collection: str) -> int:
        try:
            return self._client.get_collection(collection).count()
        except Exception:
            return 0

    def count_where(self, collection: str, where: Dict[str, Any]) -> int:
        try:
            result = self._client.get_collection(collection).get(where=where, include=[])
            return len(result.get("ids") or [])
        except Exception:
            return 0

    def delete_collection(self, name: str) -> None:
        try:
            self._client.delete_collection(name)
        except Exception:
            pass