from datetime import datetime, timezone

from fastapi import APIRouter, Depends, HTTPException
from sqlalchemy.orm import Session

from ..database import get_db
from ..dependencies import get_current_user
from ..models import Annotation, PDF, User
from ..schemas import AnnotationIn, AnnotationOut

router = APIRouter(prefix="/annotations", tags=["annotations"])


def _verify_pdf_ownership(db: Session, pdf_id: int, user_id: int) -> PDF:
    pdf = db.get(PDF, pdf_id)
    if not pdf or pdf.user_id != user_id:
        raise HTTPException(status_code=404, detail="PDF not found.")
    return pdf


def _any_pdf_or_404(db: Session, pdf_id: int) -> PDF:
    """Return PDF regardless of owner — any authenticated user may read annotations."""
    pdf = db.get(PDF, pdf_id)
    if not pdf:
        raise HTTPException(status_code=404, detail="PDF not found.")
    return pdf


# ── GET /api/annotations/{pdf_id}/{page_number} ───────────────────────────────

@router.get("/{pdf_id}/{page_number}", response_model=AnnotationOut)
def get_annotation(
    pdf_id: int,
    page_number: int,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    _any_pdf_or_404(db, pdf_id)

    ann = (
        db.query(Annotation)
        .filter(
            Annotation.pdf_id == pdf_id,
            Annotation.user_id == current_user.id,
            Annotation.page_number == page_number,
        )
        .first()
    )

    # Return empty canvas if no annotation exists yet — not an error
    if ann is None:
        return AnnotationOut(
            id=0,
            pdf_id=pdf_id,
            page_number=page_number,
            canvas_data={},
            updated_at=datetime.now(timezone.utc),
        )

    return ann


# ── GET /api/annotations/{pdf_id}/{page_number}/all ───────────────────────────
# Returns a merged canvas_data whose "objects" array contains annotations from
# ALL users for the given page. Any authenticated user may call this.

@router.get("/{pdf_id}/{page_number}/all", response_model=AnnotationOut)
def get_all_annotations(
    pdf_id: int,
    page_number: int,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    _any_pdf_or_404(db, pdf_id)

    rows = (
        db.query(Annotation)
        .filter(
            Annotation.pdf_id == pdf_id,
            Annotation.page_number == page_number,
        )
        .all()
    )

    if not rows:
        return AnnotationOut(
            id=0,
            pdf_id=pdf_id,
            page_number=page_number,
            canvas_data={},
            updated_at=datetime.now(timezone.utc),
        )

    # Merge all objects arrays; use canvas metadata (background etc.) from latest record
    latest = max(rows, key=lambda r: r.updated_at)
    base: dict = dict(latest.canvas_data) if latest.canvas_data else {}
    merged_objects: list = []
    for row in rows:
        for obj in (row.canvas_data or {}).get("objects", []):
            # Tag each object with its owner so the frontend can avoid re-saving
            # other users' objects under the current user's record (prevents duplicates).
            obj_copy = dict(obj)
            obj_copy["_owner_id"] = row.user_id
            merged_objects.append(obj_copy)
    base["objects"] = merged_objects

    return AnnotationOut(
        id=latest.id,
        pdf_id=pdf_id,
        page_number=page_number,
        canvas_data=base,
        updated_at=latest.updated_at,
    )


# ── PUT /api/annotations/{pdf_id}/{page_number} ───────────────────────────────

@router.put("/{pdf_id}/{page_number}", response_model=AnnotationOut)
def upsert_annotation(
    pdf_id: int,
    page_number: int,
    body: AnnotationIn,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    _any_pdf_or_404(db, pdf_id)

    ann = (
        db.query(Annotation)
        .filter(
            Annotation.pdf_id == pdf_id,
            Annotation.user_id == current_user.id,
            Annotation.page_number == page_number,
        )
        .first()
    )

    if ann is None:
        ann = Annotation(
            pdf_id=pdf_id,
            user_id=current_user.id,
            page_number=page_number,
            canvas_data=body.canvas_data,
        )
        db.add(ann)
    else:
        ann.canvas_data = body.canvas_data
        ann.updated_at = datetime.now(timezone.utc)

    db.commit()
    db.refresh(ann)
    return ann