"""Document API router — upload, list, get, delete, preview."""

from __future__ import annotations

import logging

from fastapi import APIRouter, HTTPException, Query, UploadFile
from fastapi.responses import Response

from api.schemas import DocumentResponse
from services import document_service

logger = logging.getLogger(__name__)
router = APIRouter(prefix="/api/documents", tags=["documents"])

_READ_CHUNK_SIZE = 64 * 1024  # 64 KB


def _to_response(doc) -> DocumentResponse:
    return DocumentResponse(
        id=doc.id,
        filename=doc.filename,
        content_type=doc.content_type,
        file_size=doc.file_size,
        page_count=doc.page_count,
        created_at=str(doc.created_at),
    )


@router.post("/upload", response_model=DocumentResponse, status_code=200)
async def upload(file: UploadFile) -> DocumentResponse:
    """Upload a PDF document."""
    if not file.filename:
        raise HTTPException(status_code=400, detail="No filename provided")

    # Reject early if Content-Length exceeds limit (before reading body)
    if file.size and file.size > document_service.MAX_FILE_SIZE:
        raise HTTPException(status_code=413, detail="File too large (max 5 MB)")

    # Read in chunks to avoid holding the full upload in a single allocation
    chunks: list[bytes] = []
    total = 0
    while chunk := await file.read(_READ_CHUNK_SIZE):
        total += len(chunk)
        if total > document_service.MAX_FILE_SIZE:
            raise HTTPException(status_code=413, detail="File too large (max 5 MB)")
        chunks.append(chunk)
    content = b"".join(chunks)

    try:
        doc = await document_service.upload(
            filename=file.filename,
            content_type=file.content_type or "application/pdf",
            file_content=content,
        )
    except ValueError as e:
        raise HTTPException(status_code=400, detail=str(e)) from e

    return _to_response(doc)


@router.get("", response_model=list[DocumentResponse])
async def list_documents() -> list[DocumentResponse]:
    """List all documents."""
    docs = await document_service.find_all()
    return [_to_response(d) for d in docs]


@router.get("/{doc_id}", response_model=DocumentResponse)
async def get_document(doc_id: str) -> DocumentResponse:
    """Get a single document."""
    doc = await document_service.find_by_id(doc_id)
    if not doc:
        raise HTTPException(status_code=404, detail="Document not found")
    return _to_response(doc)


@router.delete("/{doc_id}", status_code=204)
async def delete_document(doc_id: str) -> None:
    """Delete a document and its file."""
    deleted = await document_service.delete(doc_id)
    if not deleted:
        raise HTTPException(status_code=404, detail="Document not found")


@router.get("/{doc_id}/preview")
async def preview(
    doc_id: str,
    page: int = Query(1, ge=1),
    dpi: int = Query(150, ge=72, le=300),
) -> Response:
    """Generate a PNG preview of a specific PDF page."""
    doc = await document_service.find_by_id(doc_id)
    if not doc:
        raise HTTPException(status_code=404, detail="Document not found")

    if doc.page_count and page > doc.page_count:
        raise HTTPException(
            status_code=400,
            detail=f"Page {page} out of range (document has {doc.page_count} pages)",
        )

    try:
        with open(doc.storage_path, "rb") as f:
            file_content = f.read()
        png_bytes = document_service.generate_preview(file_content, page=page, dpi=dpi)
        return Response(content=png_bytes, media_type="image/png")
    except ValueError as e:
        raise HTTPException(status_code=404, detail=str(e)) from e
    except FileNotFoundError as exc:
        raise HTTPException(status_code=404, detail="PDF file not found on disk") from exc
    except OSError as exc:
        logger.exception("I/O error generating preview for %s", doc_id)
        raise HTTPException(status_code=422, detail="Failed to read PDF file") from exc
    except Exception as exc:
        logger.exception("Unexpected error generating preview for %s", doc_id)
        raise HTTPException(status_code=422, detail="Failed to generate preview") from exc