"""Document content streaming endpoint.

Endpoints:
  GET /{doc_id}/content — stream document bytes from any backend (MinIO or cloud)

Sub-router carries NO prefix — prefix="/api/documents" lives in __init__.py (D-04).

Security:
  T-04-05-01: uses get_regular_user — admin role → 403 (critical security invariant).
  T-04-05-02: bytes fetched via get_object() ONLY — presigned_get_url() never called.
  T-04-05-03: Range header validated via _parse_range(); invalid range → 416.
  T-04-05-04: access gated on ownership OR active Share.recipient_id.
  DOC-04 / SEC-04: ownership assertion before serving bytes.
"""
from __future__ import annotations

import urllib.parse
import uuid

from fastapi import APIRouter, Depends, HTTPException, Request, status
from fastapi.responses import StreamingResponse
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from db.models import Document, Share, User
from deps.auth import get_regular_user
from deps.db import get_db
from services.rate_limiting import account_limiter
from storage.exceptions import CloudConnectionError

router = APIRouter()


# ── Range header parsing helper ───────────────────────────────────────────────

def _parse_range(range_header: str, file_size: int) -> tuple:
    """Parse a 'bytes=X-Y' Range header and return (start, end).

    Returns (start, end) where both are inclusive byte offsets.
    Raises HTTP 416 on any invalid or out-of-bounds range.

    T-04-05-03: validates start <= end, start >= 0, end < file_size.
    """
    try:
        h = range_header.replace("bytes=", "").split("-")
        start = int(h[0]) if h[0] != "" else 0
        end = int(h[1]) if h[1] != "" else file_size - 1
    except (ValueError, IndexError):
        raise HTTPException(status.HTTP_416_RANGE_NOT_SATISFIABLE)
    if start > end or start < 0 or end >= file_size:
        raise HTTPException(status.HTTP_416_RANGE_NOT_SATISFIABLE)
    return start, end


# ── GET /api/documents/{doc_id}/content ──────────────────────────────────────

@router.get("/{doc_id}/content")
@account_limiter.limit("100/minute")
async def stream_document_content(
    doc_id: str,
    request: Request,
    session: AsyncSession = Depends(get_db),
    current_user: User = Depends(get_regular_user),
):
    """Stream document bytes directly from MinIO (DOC-02).

    T-04-05-01: uses get_regular_user — admin role → 403 (critical security invariant).
    T-04-05-02: bytes fetched via get_object() ONLY — presigned_get_url() never called.
    T-04-05-03: Range header validated via _parse_range(); invalid range → 416.
    T-04-05-04: access gated on ownership OR active Share.recipient_id.

    Returns 200 (or 206 for Range requests) with:
      Content-Type: doc.content_type
      Content-Disposition: inline; filename="<filename>"
      Accept-Ranges: bytes
      Content-Length: <size>
    """
    request.state.current_user = current_user
    try:
        uid = uuid.UUID(doc_id)
    except ValueError:
        raise HTTPException(status_code=404, detail="Document not found")

    doc = await session.get(Document, uid)
    if doc is None:
        raise HTTPException(status_code=404, detail="Document not found")

    # Access control: owner OR share recipient (T-04-05-04)
    if doc.user_id != current_user.id:
        result = await session.execute(
            select(Share).where(
                Share.document_id == doc.id,
                Share.recipient_id == current_user.id,
            )
        )
        share = result.scalar_one_or_none()
        if share is None:
            raise HTTPException(status_code=404, detail="Document not found")

    # Fetch bytes from the correct backend — get_storage_backend_for_document handles
    # all backends (MinIO, Google Drive, OneDrive, Nextcloud, WebDAV) transparently
    # (D-15, T-04-05-02). NEVER via presigned URL for cloud backends (D-14).
    try:
        import api.documents as _doc_pkg  # late import allows test monkeypatching via api.documents
        storage_backend = await _doc_pkg.get_storage_backend_for_document(doc, current_user, session)
        file_bytes = await storage_backend.get_object(doc.object_key)
    except CloudConnectionError as exc:
        raise HTTPException(
            status_code=503,
            detail="Cloud connection requires re-authentication. Please reconnect in Settings.",
        ) from exc
    except HTTPException:
        raise
    except Exception as exc:
        raise HTTPException(
            status_code=502,
            detail="Cloud backend unreachable. Please try again or reconnect in Settings.",
        ) from exc
    file_size = len(file_bytes)

    safe_name = urllib.parse.quote(doc.filename, safe='')
    headers = {
        "content-type": doc.content_type,
        "content-disposition": f"inline; filename*=UTF-8''{safe_name}",
        "accept-ranges": "bytes",
        "content-length": str(file_size),
    }

    range_header = request.headers.get("range")
    if range_header:
        start, end = _parse_range(range_header, file_size)
        chunk = file_bytes[start : end + 1]
        headers["content-range"] = f"bytes {start}-{end}/{file_size}"
        headers["content-length"] = str(len(chunk))
        return StreamingResponse(
            iter([chunk]),
            status_code=206,
            headers=headers,
        )

    return StreamingResponse(
        iter([file_bytes]),
        status_code=200,
        headers=headers,
    )