"""The knowledge library: documents a person has collected.

Ingestion is deliberately **not** written here. A knowledge document and a chat
attachment are the same processing problem -- sniff the bytes, downscale the
image, extract the PDF once -- so both go through
``services.files.prepare``. Keeping one pipeline is what guarantees the same
PDF produces the same text whichever way it arrived, and it is why `Document`
carries the same content columns as `Attachment`.
"""

from __future__ import annotations

import logging
import secrets
from pathlib import Path

from sqlalchemy import select
from sqlalchemy.orm import Session as DBSession

from lembas.config import settings
from lembas.db.models import SOURCE_LINK, SOURCE_UPLOAD, Document, KnowledgeBase, User
from lembas.services import files as files_service
from lembas.services import sharing
from lembas.services.fetch import Fetched
from lembas.services.library.fts import search_ids

log = logging.getLogger(__name__)

INDEX = "documents_fts"

# What a first base is called when one has to be invented -- on the first
# upload, or for documents that predate bases existing.
DEFAULT_BASE_NAME = "My documents"

# How much of a document's text a search result carries back to the model. A
# whole 100-page extract would swallow the context window; this is enough to
# judge relevance and to answer from, and `knowledge_get` fetches the rest.
SNIPPET_CHARS = 1200


def library_dir() -> Path:
    """Where library files live, beside but separate from chat attachments."""
    path = settings.uploads_dir / "library"
    path.mkdir(parents=True, exist_ok=True)
    return path


def stored_path(stored_name: str) -> Path | None:
    """Resolve a stored name, refusing anything outside the library directory.

    The same check as ``services.files.stored_path``, against a different root.
    """
    if not stored_name or "/" in stored_name or "\\" in stored_name or stored_name.startswith("."):
        return None
    base = library_dir().resolve()
    path = (base / stored_name).resolve()
    try:
        path.relative_to(base)
    except ValueError:
        return None
    return path if path.is_file() else None


# --- Bases -------------------------------------------------------------------
def visible_bases(db: DBSession, user: User | None):
    return select(KnowledgeBase).where(sharing.visible_to(KnowledgeBase, user))


def get_base(db: DBSession, base_id: str, user: User | None) -> KnowledgeBase | None:
    base = db.get(KnowledgeBase, base_id)
    if base is None or not sharing.can_read(db, base, user):
        return None
    return base


def create_base(
    db: DBSession, *, owner: User, name: str, description: str = ""
) -> KnowledgeBase:
    name = " ".join((name or "").split())[:200] or DEFAULT_BASE_NAME
    existing = db.scalar(
        select(KnowledgeBase).where(
            KnowledgeBase.owner_id == owner.id, KnowledgeBase.name == name
        )
    )
    if existing is not None:
        raise ValueError(f"You already have a knowledge base called {name!r}.")

    base = KnowledgeBase(owner_id=owner.id, name=name, description=description.strip()[:2000])
    db.add(base)
    db.commit()
    return base


def default_base(db: DBSession, owner: User) -> KnowledgeBase:
    """The base a document goes into when none was chosen.

    Made on demand rather than at registration, so an account that never uses
    the library never grows an empty one.
    """
    base = db.scalar(
        select(KnowledgeBase)
        .where(KnowledgeBase.owner_id == owner.id)
        .order_by(KnowledgeBase.created_at)
    )
    if base is not None:
        return base
    base = KnowledgeBase(owner_id=owner.id, name=DEFAULT_BASE_NAME)
    db.add(base)
    db.commit()
    return base


def delete_base(db: DBSession, base: KnowledgeBase) -> None:
    """Delete a base and everything in it.

    The documents go too -- a base is a place, not a label, and leaving its
    contents behind with nowhere to live would need an "unfiled" concept that
    exists only to hold the wreckage of deletes.
    """
    for document in list(base.documents):
        path = stored_path(document.stored_name)
        if path is not None:
            path.unlink(missing_ok=True)
    sharing.forget_resource(db, base)
    db.delete(base)
    db.commit()


def sweep_unfiled(db: DBSession) -> int:
    """File documents that predate knowledge bases into their owner's default.

    `Document.base_id` is nullable only because the column had to be added to a
    table that already had rows. This is what makes "always set" true in
    practice, and it runs at startup beside the orphaned-upload sweep.
    """
    # Empty string as well as NULL: an earlier release added the column with a
    # type-derived default, so a deployment that upgraded through it has rows
    # holding "" rather than NULL. Both mean the same thing here.
    unfiled = list(
        db.scalars(select(Document).where((Document.base_id.is_(None)) | (Document.base_id == "")))
    )
    if not unfiled:
        return 0

    bases: dict[str, KnowledgeBase] = {}
    for document in unfiled:
        owner = db.get(User, document.owner_id)
        if owner is None:
            continue
        if owner.id not in bases:
            bases[owner.id] = default_base(db, owner)
        document.base_id = bases[owner.id].id

    db.commit()
    log.info("filed %d document(s) that predated knowledge bases", len(unfiled))
    return len(unfiled)


# --- Creating ----------------------------------------------------------------
def store_upload(
    db: DBSession,
    *,
    owner: User,
    payload: bytes,
    filename: str,
    title: str = "",
    base: KnowledgeBase | None = None,
) -> Document:
    """Add an uploaded file to the library. Raises files.FileError if unusable."""
    prepared = files_service.prepare(payload, filename)
    base = base or default_base(db, owner)

    stored_name = f"{secrets.token_hex(16)}{prepared.extension}"
    (library_dir() / stored_name).write_bytes(prepared.payload)

    display = files_service.safe_display_name(filename)
    document = Document(
        owner_id=owner.id,
        base_id=base.id,
        title=(title.strip() or display)[:300],
        source=SOURCE_UPLOAD,
        filename=display,
        stored_name=stored_name,
        media_type=prepared.media_type,
        size_bytes=len(prepared.payload),
        kind=prepared.kind,
        width=prepared.width,
        height=prepared.height,
        extracted_text=prepared.extracted_text,
        pages=prepared.pages,
        truncated=prepared.truncated,
        extraction_error=prepared.extraction_error,
    )
    db.add(document)
    db.commit()
    log.info("library: stored %r (%s) for %s", document.title, document.kind, owner.email)
    return document


def store_page(
    db: DBSession, *, owner: User, page: Fetched, base: KnowledgeBase | None = None
) -> Document:
    """Add a fetched web page to the library.

    Saved as text rather than as the original HTML: the point of keeping it is
    what it said, and the markup would have to be reduced again on every read.
    """
    base = base or default_base(db, owner)
    document = Document(
        owner_id=owner.id,
        base_id=base.id,
        title=page.title[:300] or page.url[:300],
        source=SOURCE_LINK,
        source_url=page.url,
        filename="",
        media_type="text/plain",
        size_bytes=len(page.text.encode("utf-8")),
        kind="text",
        extracted_text=page.text,
        truncated=page.truncated,
    )
    db.add(document)
    db.commit()
    log.info("library: saved page %r for %s", document.title, owner.email)
    return document


# --- Reading -----------------------------------------------------------------
def visible(db: DBSession, user: User | None, *, base_ids: list[str] | None = None):
    """Documents this user may see, optionally narrowed to some bases.

    Visibility comes from the base, not the document: a document is readable by
    whoever can read the base it lives in. That is the whole reason bases are
    shareable and documents are not.
    """
    condition = Document.base_id.in_(
        select(KnowledgeBase.id).where(sharing.visible_to(KnowledgeBase, user))
    )
    query = select(Document).where(condition)
    if base_ids:
        # Still filtered by visibility above, so naming a base you cannot see
        # returns nothing rather than granting access to it.
        query = query.where(Document.base_id.in_(base_ids))
    return query


def get(db: DBSession, document_id: str, user: User | None) -> Document | None:
    document = db.get(Document, document_id)
    if document is None:
        return None
    base = db.get(KnowledgeBase, document.base_id) if document.base_id else None
    if base is None or not sharing.can_read(db, base, user):
        return None
    return document


def search(
    db: DBSession,
    user: User | None,
    needle: str,
    *,
    limit: int = 10,
    base_ids: list[str] | None = None,
) -> list[Document]:
    """Documents matching `needle` that this user may see, best match first.

    The index is searched first and the visibility filter applied to the rows
    it returned. That order matters: filtering afterwards is what makes it
    impossible for a hit on somebody else's document to leak, even as a count.
    """
    hits = search_ids(db, INDEX, needle, limit=limit * 4)
    if not hits:
        return []

    order = {hit.id: position for position, hit in enumerate(hits)}
    rows = list(
        db.scalars(
            visible(db, user, base_ids=base_ids).where(Document.id.in_(list(order)))
        )
    )
    rows.sort(key=lambda document: order.get(document.id, len(order)))
    return rows[:limit]


def snippet(document: Document) -> str:
    """The part of a document a search result carries."""
    text = (document.extracted_text or "").strip()
    if len(text) <= SNIPPET_CHARS:
        return text
    return text[:SNIPPET_CHARS].rstrip() + "…"


# --- Removing ----------------------------------------------------------------
def delete(db: DBSession, document: Document) -> None:
    path = stored_path(document.stored_name)
    if path is not None:
        path.unlink(missing_ok=True)
    db.delete(document)
    db.commit()