"""
Async document/topic/settings storage service for DocuVault.

This module replaces the legacy flat-file + filelock implementation with:
  - Async SQLAlchemy ORM for document and topic persistence (PostgreSQL)
  - MinIO SDK (via asyncio.to_thread) for binary object storage

Public function names are PRESERVED from the old flat-file implementation so
that api/documents.py and api/topics.py can be updated in Plan 05 with minimal
changes (async def + await + session parameter).

Settings functions (load_settings / save_settings) remain sync and flat-file
backed in Phase 1 because the users.ai_provider / users.ai_model schema columns
cannot be populated until Phase 2.
# Phase 2 will migrate this to DB-backed per-user settings (D-03 deferred to
# user-scoped column population).

D-05: Storage service layer switched to PostgreSQL + MinIO.
D-06: Object key schema: {user_id}/{document_id}/{uuid4()}{ext} — human filename in DB only.
D-03: documents.user_id is None (nullable) in Phase 1 — no auth system yet.
"""
from __future__ import annotations

import copy
import json
import sys
import uuid
from datetime import datetime, timezone
from typing import Optional

from sqlalchemy import select, delete, text
from sqlalchemy import func as sql_func
from sqlalchemy.ext.asyncio import AsyncSession

from config import DEFAULT_SETTINGS, SETTINGS_FILE
from db.models import Document, DocumentTopic, Topic
from storage import get_storage_backend


# ── Lazy singleton storage backend ────────────────────────────────────────────

_storage = None


def _backend():
    """Return the lazily-instantiated StorageBackend singleton.

    Mirrors the module-level singleton behaviour of the old filelock objects so
    the MinIO client is created once per process, not once per request.
    """
    global _storage
    _storage = _storage or get_storage_backend()
    return _storage


# ── Private helpers ────────────────────────────────────────────────────────────

def _doc_to_dict(doc: Document, topic_names: list) -> dict:
    """Convert a Document ORM row + resolved topic names to the legacy dict shape."""
    return {
        "id": str(doc.id),
        "original_name": doc.filename,
        "filename": doc.filename,
        "mime_type": doc.content_type,
        "size_bytes": doc.size_bytes,
        "extracted_text": doc.extracted_text or "",
        "topics": topic_names,
        "created_at": doc.created_at.isoformat() if doc.created_at else None,
        "classified_at": doc.updated_at.isoformat() if doc.status == "classified" else None,
    }


async def _load_topic_names(session: AsyncSession, doc_id: uuid.UUID) -> list:
    """Return the list of topic names for a given document UUID."""
    q = await session.execute(
        select(Topic.name)
        .join(DocumentTopic, DocumentTopic.topic_id == Topic.id)
        .where(DocumentTopic.document_id == doc_id)
    )
    return [row[0] for row in q]


# ── Documents ─────────────────────────────────────────────────────────────────


async def save_metadata(session: AsyncSession, meta: dict) -> None:
    """Update a Document row from the legacy metadata dict shape.

    Keys consumed: id, extracted_text, topics (list[str]), classified_at.
    """
    try:
        uid = uuid.UUID(meta["id"])
    except (ValueError, KeyError):
        return

    doc = await session.get(Document, uid)
    if doc is None:
        return

    doc.extracted_text = meta.get("extracted_text", "")

    topics_list = meta.get("topics")
    if topics_list:
        await update_document_topics(session, meta["id"], topics_list)

    doc.status = "classified" if meta.get("classified_at") else "pending"
    await session.commit()


async def get_metadata(session: AsyncSession, doc_id: str) -> Optional[dict]:
    """Return the legacy metadata dict for a document, or None if not found."""
    try:
        uid = uuid.UUID(doc_id)
    except ValueError:
        return None

    doc = await session.get(Document, uid)
    if doc is None:
        return None

    topic_names = await _load_topic_names(session, uid)
    return _doc_to_dict(doc, topic_names)


async def list_metadata(
    session: AsyncSession, topic: Optional[str] = None
) -> list:
    """Return a list of metadata dicts, optionally filtered by topic name."""
    stmt = select(Document).order_by(Document.created_at.desc())
    if topic is not None:
        stmt = (
            stmt.join(DocumentTopic, DocumentTopic.document_id == Document.id)
            .join(Topic, Topic.id == DocumentTopic.topic_id)
            .where(Topic.name == topic)
        )
    result = await session.execute(stmt)
    docs = result.scalars().all()

    rows = []
    for doc in docs:
        topic_names = await _load_topic_names(session, doc.id)
        rows.append(_doc_to_dict(doc, topic_names))
    return rows


async def delete_document(session: AsyncSession, doc_id: str) -> bool:
    """Delete a document's MinIO object and its PostgreSQL row.

    Returns False if the document is not found; True on success.
    MinIO deletion failures are logged to stderr but do not prevent the DB row
    deletion (the bytes may already be gone).
    """
    try:
        uid = uuid.UUID(doc_id)
    except ValueError:
        return False

    doc = await session.get(Document, uid)
    if doc is None:
        return False

    try:
        await _backend().delete_object(doc.object_key)
    except Exception as exc:
        print(f"[storage] WARNING: MinIO delete_object failed for {doc.object_key!r}: {exc}", file=sys.stderr)

    # Atomic quota decrement (STORE-06, D-07).
    # The user_id is None guard is removed in Plan 03-03.
    if doc.user_id is not None:
        await session.execute(
            text(
                "UPDATE quotas "
                "SET used_bytes = GREATEST(0, used_bytes - :delta) "
                "WHERE user_id = :uid"
            ),
            {"delta": doc.size_bytes, "uid": str(doc.user_id)},
        )

    await session.delete(doc)
    await session.commit()
    return True


async def update_document_topics(
    session: AsyncSession, doc_id: str, topics: list
) -> Optional[dict]:
    """Replace all topic associations for a document.

    Auto-creates topics that don't yet exist. Returns the refreshed metadata
    dict, or None if the document is not found.
    """
    try:
        uid = uuid.UUID(doc_id)
    except ValueError:
        return None

    doc = await session.get(Document, uid)
    if doc is None:
        return None

    # Remove all existing associations
    await session.execute(
        delete(DocumentTopic).where(DocumentTopic.document_id == uid)
    )

    # Re-insert, deduplicating by name
    seen: set = set()
    for name in topics:
        if name in seen:
            continue
        seen.add(name)
        topic_dict = await create_topic(session, name)
        session.add(
            DocumentTopic(
                document_id=uid,
                topic_id=uuid.UUID(topic_dict["id"]),
            )
        )

    doc.status = "classified"
    await session.commit()
    return await get_metadata(session, doc_id)


async def remove_topic_from_all_documents(
    session: AsyncSession, topic_name: str
) -> int:
    """Delete all DocumentTopic rows for the named topic.

    Returns the number of rows deleted.
    """
    q = await session.execute(
        select(Topic).where(sql_func.lower(Topic.name) == topic_name.lower())
    )
    topic = q.scalars().first()
    if topic is None:
        return 0

    result = await session.execute(
        delete(DocumentTopic).where(DocumentTopic.topic_id == topic.id)
    )
    await session.commit()
    return result.rowcount


# ── Topics ────────────────────────────────────────────────────────────────────

async def load_topics(session: AsyncSession) -> list:
    """Return all topics ordered by name."""
    q = await session.execute(select(Topic).order_by(Topic.name))
    return [
        {"id": str(t.id), "name": t.name, "description": t.description, "color": t.color}
        for t in q.scalars()
    ]


async def save_topics(session: AsyncSession, topics: list) -> None:
    """Idempotent bulk replace — delete all Topic rows then insert the list.

    # legacy: not used by current endpoints; preserved for API compatibility.
    """
    await session.execute(delete(Topic))
    for t in topics:
        session.add(
            Topic(
                id=uuid.UUID(t["id"]) if t.get("id") else uuid.uuid4(),
                name=t["name"],
                description=t.get("description", ""),
                color=t.get("color", "#6366f1"),
            )
        )
    await session.commit()


async def get_topic(session: AsyncSession, topic_id: str) -> Optional[dict]:
    """Return a topic dict by UUID string, or None if not found."""
    try:
        uid = uuid.UUID(topic_id)
    except ValueError:
        return None
    t = await session.get(Topic, uid)
    if t is None:
        return None
    return {"id": str(t.id), "name": t.name, "description": t.description, "color": t.color}


async def create_topic(
    session: AsyncSession,
    name: str,
    description: str = "",
    color: str = "#6366f1",
) -> dict:
    """Create a topic, or return the existing one (case-insensitive deduplication)."""
    q = await session.execute(
        select(Topic).where(sql_func.lower(Topic.name) == name.lower())
    )
    existing = q.scalars().first()
    if existing is not None:
        return {
            "id": str(existing.id),
            "name": existing.name,
            "description": existing.description,
            "color": existing.color,
        }

    topic = Topic(name=name, description=description, color=color)
    session.add(topic)
    await session.commit()
    return {
        "id": str(topic.id),
        "name": topic.name,
        "description": topic.description,
        "color": topic.color,
    }


async def update_topic(
    session: AsyncSession,
    topic_id: str,
    name: Optional[str] = None,
    description: Optional[str] = None,
    color: Optional[str] = None,
) -> Optional[dict]:
    """Update non-None fields on a topic. Returns updated dict or None."""
    try:
        uid = uuid.UUID(topic_id)
    except ValueError:
        return None
    t = await session.get(Topic, uid)
    if t is None:
        return None
    if name is not None:
        t.name = name
    if description is not None:
        t.description = description
    if color is not None:
        t.color = color
    await session.commit()
    return {"id": str(t.id), "name": t.name, "description": t.description, "color": t.color}


async def delete_topic(session: AsyncSession, topic_id: str) -> Optional[str]:
    """Delete a topic and cascade-remove its DocumentTopic rows.

    Returns the deleted topic name, or None if not found.
    """
    try:
        uid = uuid.UUID(topic_id)
    except ValueError:
        return None
    t = await session.get(Topic, uid)
    if t is None:
        return None
    name = t.name
    await session.delete(t)  # ondelete="CASCADE" removes DocumentTopic rows
    await session.commit()
    return name


async def topic_doc_counts(session: AsyncSession) -> dict:
    """Return a mapping of topic name -> document count."""
    q = await session.execute(
        select(Topic.name, sql_func.count(DocumentTopic.document_id))
        .join(DocumentTopic, DocumentTopic.topic_id == Topic.id, isouter=True)
        .group_by(Topic.name)
    )
    return {name: count for name, count in q}


# ── Settings ──────────────────────────────────────────────────────────────────
# Phase 2 will move per-user settings to users.ai_provider / users.ai_model
# (D-03 deferred to user-scoped column population).
# For now these remain as flat-file JSON — single-writer, no filelock needed.

def load_settings() -> dict:
    """Read app settings from the flat-file SETTINGS_FILE.

    Falls back to DEFAULT_SETTINGS if the file is missing.
    # Phase 2 will move per-user settings to users.ai_provider / users.ai_model.
    """
    try:
        return json.loads(SETTINGS_FILE.read_text())
    except (FileNotFoundError, json.JSONDecodeError):
        return copy.deepcopy(DEFAULT_SETTINGS)


def save_settings(settings: dict) -> None:
    """Write app settings to the flat-file SETTINGS_FILE.

    No filelock — Phase 1 settings file is single-writer.
    # Phase 2 will move per-user settings to users.ai_provider / users.ai_model.
    """
    SETTINGS_FILE.write_text(json.dumps(settings, indent=2))


def mask_api_key(key: str) -> str:
    if not key or len(key) <= 4:
        return "****"
    return "****" + key[-4:]


def settings_masked(settings: dict) -> dict:
    s = copy.deepcopy(settings)
    for prov in ("anthropic", "openai"):
        key = s.get("providers", {}).get(prov, {}).get("api_key", "")
        if key:
            s["providers"][prov]["api_key"] = mask_api_key(key)
    return s


# ── Public surface ─────────────────────────────────────────────────────────────

__all__ = [
    "save_metadata",
    "get_metadata",
    "list_metadata",
    "delete_document",
    "update_document_topics",
    "remove_topic_from_all_documents",
    "load_topics",
    "save_topics",
    "get_topic",
    "create_topic",
    "update_topic",
    "delete_topic",
    "topic_doc_counts",
    "load_settings",
    "save_settings",
    "mask_api_key",
    "settings_masked",
]