import os
import uuid
from pathlib import Path

from fastapi import APIRouter, Depends, HTTPException, UploadFile, status
from fastapi.responses import FileResponse
from sqlalchemy.orm import Session

from ..database import get_db
from ..dependencies import get_current_user
from ..models import PDF, User
from ..schemas import PDFOut, PDFUploadResult

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

UPLOAD_DIR = Path(os.getenv("UPLOAD_DIR", "/uploads"))
MAX_FILE_SIZE = 500 * 1024 * 1024  # 500 MB


def _user_dir(user_id: int) -> Path:
    d = UPLOAD_DIR / str(user_id)
    d.mkdir(parents=True, exist_ok=True)
    return d


def _own_or_404(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_or_404(db: Session, pdf_id: int) -> PDF:
    """Return PDF if it exists — any authenticated user may read it."""
    pdf = db.get(PDF, pdf_id)
    if not pdf:
        raise HTTPException(status_code=404, detail="PDF not found.")
    return pdf


def _pdf_out(pdf: PDF, db: Session):
    """Build PDFOut including owner_username."""
    from ..schemas import PDFOut as _PDFOut
    owner = db.get(User, pdf.user_id)
    data = {
        "id": pdf.id,
        "user_id": pdf.user_id,
        "owner_username": owner.username if owner else "unknown",
        "title": pdf.title,
        "total_pages": pdf.total_pages,
        "created_at": pdf.created_at,
    }
    return _PDFOut.model_validate(data)


# ── GET /api/pdfs ─────────────────────────────────────────────────────────────

@router.get("", response_model=list[PDFOut])
def list_pdfs(
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    pdfs = db.query(PDF).order_by(PDF.created_at.desc()).all()
    return [_pdf_out(p, db) for p in pdfs]


# ── POST /api/pdfs/upload ─────────────────────────────────────────────────────

@router.post("/upload", response_model=list[PDFUploadResult], status_code=status.HTTP_201_CREATED)
async def upload_pdfs(
    files: list[UploadFile],
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    """Accept one or more PDF files in a single multipart request."""
    results: list[PDFUploadResult] = []

    for file in files:
        # ── Validate MIME type ────────────────────────────────────────────────
        if file.content_type not in ("application/pdf", "application/octet-stream"):
            results.append(PDFUploadResult(filename=file.filename or "", success=False, error="Not a PDF file."))
            continue

        # ── Read & check magic bytes (PDF header: %PDF) ───────────────────────
        header = await file.read(5)
        if not header.startswith(b"%PDF-"):
            results.append(PDFUploadResult(filename=file.filename or "", success=False, error="File is not a valid PDF."))
            continue

        # ── Size guard ────────────────────────────────────────────────────────
        body = header + await file.read()
        if len(body) > MAX_FILE_SIZE:
            results.append(PDFUploadResult(filename=file.filename or "", success=False, error="File exceeds 500 MB limit."))
            continue

        # ── Save to disk with UUID filename (prevents path traversal) ─────────
        safe_name = f"{uuid.uuid4()}.pdf"
        dest = _user_dir(current_user.id) / safe_name
        dest.write_bytes(body)

        # ── Persist metadata ──────────────────────────────────────────────────
        original_title = Path(file.filename or "Untitled").stem or "Untitled"
        pdf = PDF(
            user_id=current_user.id,
            title=original_title,
            file_path=str(dest),
        )
        db.add(pdf)
        db.commit()
        db.refresh(pdf)

        results.append(PDFUploadResult(filename=file.filename or "", success=True, pdf=_pdf_out(pdf, db)))

    return results


# ── DELETE /api/pdfs/{pdf_id} ─────────────────────────────────────────────────

@router.delete("/{pdf_id}", status_code=status.HTTP_204_NO_CONTENT)
def delete_pdf(
    pdf_id: int,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    pdf = _own_or_404(db, pdf_id, current_user.id)
    file_path = Path(pdf.file_path)

    db.delete(pdf)
    db.commit()

    if file_path.exists():
        file_path.unlink()


# ── GET /api/pdfs/{pdf_id}/file ───────────────────────────────────────────────

@router.get("/{pdf_id}/file")
def serve_pdf(
    pdf_id: int,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db),
):
    """Serve the raw PDF bytes — any authenticated user may read."""
    pdf = _any_or_404(db, pdf_id)
    file_path = Path(pdf.file_path)

    if not file_path.exists():
        raise HTTPException(status_code=404, detail="File not found on disk.")

    return FileResponse(
        path=str(file_path),
        media_type="application/pdf",
        filename=f"{pdf.title}.pdf",
    )