"""Background extraction processor for handling extraction queue."""

import asyncio
from typing import Set

from sqlmodel.ext.asyncio.session import AsyncSession

from app.core.config import settings
from app.core.database import engine
from app.core.logging import get_logger
from app.services.extraction import ExtractionService

logger = get_logger(__name__)


class ExtractionProcessor:
    """Background processor for handling extraction queue with concurrency control."""

    def __init__(self) -> None:
        """Initialize the extraction processor."""
        self.max_concurrent = settings.EXTRACTION_MAX_CONCURRENT
        self.running_extractions: Set[int] = set()
        self.processing_lock = asyncio.Lock()
        self.shutdown_event = asyncio.Event()
        self.processor_task: asyncio.Task | None = None

        logger.info(
            "Initialized extraction processor with max concurrent: %d",
            self.max_concurrent,
        )

    async def start(self) -> None:
        """Start the background extraction processor."""
        if self.processor_task and not self.processor_task.done():
            logger.warning("Extraction processor is already running")
            return

        self.shutdown_event.clear()
        self.processor_task = asyncio.create_task(self._process_queue())
        logger.info("Started extraction processor")

    async def stop(self) -> None:
        """Stop the background extraction processor."""
        logger.info("Stopping extraction processor...")
        self.shutdown_event.set()

        if self.processor_task and not self.processor_task.done():
            try:
                await asyncio.wait_for(self.processor_task, timeout=30.0)
            except asyncio.TimeoutError:
                logger.warning(
                    "Extraction processor did not stop gracefully, cancelling..."
                )
                self.processor_task.cancel()
                try:
                    await self.processor_task
                except asyncio.CancelledError:
                    pass

        logger.info("Extraction processor stopped")

    async def queue_extraction(self, extraction_id: int) -> None:
        """Queue an extraction for processing."""
        async with self.processing_lock:
            if extraction_id not in self.running_extractions:
                logger.info("Queued extraction %d for processing", extraction_id)
                # The processor will pick it up on the next cycle
            else:
                logger.warning(
                    "Extraction %d is already being processed", extraction_id
                )

    async def _process_queue(self) -> None:
        """Main processing loop that handles the extraction queue."""
        logger.info("Starting extraction queue processor")

        while not self.shutdown_event.is_set():
            try:
                await self._process_pending_extractions()

                # Wait before checking for new extractions
                try:
                    await asyncio.wait_for(self.shutdown_event.wait(), timeout=5.0)
                    break  # Shutdown requested
                except asyncio.TimeoutError:
                    continue  # Continue processing

            except Exception as e:
                logger.exception("Error in extraction queue processor: %s", e)
                # Wait a bit before retrying to avoid tight error loops
                try:
                    await asyncio.wait_for(self.shutdown_event.wait(), timeout=10.0)
                    break  # Shutdown requested
                except asyncio.TimeoutError:
                    continue

        logger.info("Extraction queue processor stopped")

    async def _process_pending_extractions(self) -> None:
        """Process pending extractions up to the concurrency limit."""
        async with self.processing_lock:
            # Check how many slots are available
            available_slots = self.max_concurrent - len(self.running_extractions)

            if available_slots <= 0:
                return  # No available slots

            # Get pending extractions from database
            async with AsyncSession(engine) as session:
                extraction_service = ExtractionService(session)
                pending_extractions = await extraction_service.get_pending_extractions()

                # Filter out extractions that are already being processed
                available_extractions = [
                    ext
                    for ext in pending_extractions
                    if ext["id"] not in self.running_extractions
                ]

                # Start processing up to available slots
                extractions_to_start = available_extractions[:available_slots]

                for extraction_info in extractions_to_start:
                    extraction_id = extraction_info["id"]
                    self.running_extractions.add(extraction_id)

                    # Start processing this extraction in the background
                    task = asyncio.create_task(
                        self._process_single_extraction(extraction_id)
                    )
                    task.add_done_callback(
                        lambda t, eid=extraction_id: self._on_extraction_completed(
                            eid,
                            t,
                        )
                    )

                    logger.info(
                        "Started processing extraction %d (%d/%d slots used)",
                        extraction_id,
                        len(self.running_extractions),
                        self.max_concurrent,
                    )

    async def _process_single_extraction(self, extraction_id: int) -> None:
        """Process a single extraction."""
        try:
            logger.info("Processing extraction %d", extraction_id)

            async with AsyncSession(engine) as session:
                extraction_service = ExtractionService(session)
                result = await extraction_service.process_extraction(extraction_id)

                logger.info(
                    "Completed extraction %d with status: %s",
                    extraction_id,
                    result["status"],
                )

        except Exception as e:
            logger.exception("Error processing extraction %d: %s", extraction_id, e)

    def _on_extraction_completed(self, extraction_id: int, task: asyncio.Task) -> None:
        """Callback when an extraction task is completed."""
        # Remove from running set
        self.running_extractions.discard(extraction_id)

        # Check if the task had an exception
        if task.exception():
            logger.error(
                "Extraction %d completed with exception: %s",
                extraction_id,
                task.exception(),
            )
        else:
            logger.info(
                "Extraction %d completed successfully (%d/%d slots used)",
                extraction_id,
                len(self.running_extractions),
                self.max_concurrent,
            )

    def get_status(self) -> dict:
        """Get the current status of the extraction processor."""
        return {
            "running": self.processor_task is not None
            and not self.processor_task.done(),
            "max_concurrent": self.max_concurrent,
            "currently_processing": len(self.running_extractions),
            "processing_ids": list(self.running_extractions),
            "available_slots": self.max_concurrent - len(self.running_extractions),
        }


# Global extraction processor instance
extraction_processor = ExtractionProcessor()