"""
Celery tasks for asynchronous report generation.
Also provides a synchronous fallback for demo/dev environments.
"""
import logging
from datetime import date, datetime

from sqlalchemy import select, create_engine
from sqlalchemy.orm import Session as SyncSession, sessionmaker

from app.core.config import get_settings
from app.models.report import ReportTemplate, ReportTask

logger = logging.getLogger(__name__)

settings = get_settings()

# Synchronous DB engine for Celery workers (Celery cannot use async)
_sync_url = settings.DATABASE_URL_SYNC
if not _sync_url:
    # Derive sync URL from async URL
    _sync_url = settings.DATABASE_URL.replace("+aiosqlite", "").replace("+asyncpg", "").replace("+aiomysql", "")

_sync_engine = create_engine(_sync_url, echo=False)
SyncSessionLocal = sessionmaker(bind=_sync_engine)


# Report type -> generator method name mapping
REPORT_TYPE_METHODS = {
    "daily": "generate_energy_daily_report",
    "monthly": "generate_monthly_summary",
    "device_status": "generate_device_status_report",
    "alarm": "generate_alarm_report",
    "carbon": "generate_carbon_report",
}


def _run_report_sync(task_id: int) -> str:
    """
    Synchronous report generation logic.
    Used both by Celery tasks and by the synchronous fallback in the API.
    Returns the generated file path.
    """
    db: SyncSession = SyncSessionLocal()
    try:
        task = db.execute(select(ReportTask).where(ReportTask.id == task_id)).scalar_one_or_none()
        if not task:
            raise ValueError(f"ReportTask {task_id} not found")

        task.status = "running"
        db.commit()

        template = db.execute(
            select(ReportTemplate).where(ReportTemplate.id == task.template_id)
        ).scalar_one_or_none()
        if not template:
            task.status = "failed"
            db.commit()
            raise ValueError(f"ReportTemplate {task.template_id} not found")

        # Determine date range from template filters
        filters = template.filters or {}
        today = date.today()
        start_date = _parse_date(filters.get("start_date"), default=today.replace(day=1))
        end_date = _parse_date(filters.get("end_date"), default=today)
        device_ids = filters.get("device_ids")
        export_format = task.export_format or "xlsx"
        report_type = template.report_type

        method_name = REPORT_TYPE_METHODS.get(report_type)
        if not method_name:
            task.status = "failed"
            db.commit()
            raise ValueError(f"Unknown report type: {report_type}")

        # Use synchronous wrapper around async generator
        import asyncio
        from app.core.database import async_session
        from app.services.report_generator import ReportGenerator

        async def _generate():
            async with async_session() as adb:
                gen = ReportGenerator(adb)
                method = getattr(gen, method_name)
                if report_type == "monthly":
                    month = filters.get("month", today.month)
                    year = filters.get("year", today.year)
                    return await method(month=month, year=year, export_format=export_format)
                elif report_type == "device_status":
                    return await method(export_format=export_format)
                else:
                    return await method(
                        start_date=start_date, end_date=end_date,
                        export_format=export_format,
                        **({"device_ids": device_ids} if device_ids and report_type == "daily" else {}),
                    )

        loop = asyncio.new_event_loop()
        try:
            filepath = loop.run_until_complete(_generate())
        finally:
            loop.close()

        task.status = "completed"
        task.file_path = filepath
        task.last_run = datetime.now()
        db.commit()

        logger.info(f"Report task {task_id} completed: {filepath}")
        return filepath

    except Exception as e:
        logger.error(f"Report task {task_id} failed: {e}")
        try:
            task = db.execute(select(ReportTask).where(ReportTask.id == task_id)).scalar_one_or_none()
            if task:
                task.status = "failed"
                db.commit()
        except Exception:
            pass
        raise
    finally:
        db.close()


def _parse_date(val, default: date) -> date:
    if not val:
        return default
    if isinstance(val, date):
        return val
    try:
        return date.fromisoformat(str(val))
    except (ValueError, TypeError):
        return default


# ---------- Celery task ---------- #

try:
    from app.tasks.celery_app import celery_app

    @celery_app.task(name="app.tasks.report_tasks.generate_report_task", bind=True, max_retries=2)
    def generate_report_task(self, task_id: int) -> str:
        try:
            return _run_report_sync(task_id)
        except Exception as exc:
            logger.error(f"Celery report task failed: {exc}")
            raise self.retry(exc=exc, countdown=10)

    CELERY_AVAILABLE = True
except Exception:
    CELERY_AVAILABLE = False


def run_report_sync(task_id: int) -> str:
    """Public synchronous entry point for fallback mode."""
    return _run_report_sync(task_id)