from __future__ import annotations

import uuid
from datetime import UTC, datetime

from sqlalchemy import select
from sqlalchemy.exc import IntegrityError
from sqlalchemy.orm import Session

from app.core.errors import AppError
from app.models.booking import Booking
from app.models.data_quality import DataQualityIssue
from app.models.idempotency import IdempotencyRecord
from app.models.inspection import Inspection
from app.models.outbox import OutboxEvent
from app.models.vehicle import Vehicle
from app.schemas import CurrentUser, RegisterReturnRequest
from app.services.audit import record_audit_event

REF_PREFIX = "INSP"


def _next_public_ref(db: Session) -> str:
    existing = db.execute(select(Inspection.public_ref)).scalars().all()
    return f"{REF_PREFIX}-{len(existing) + 1:04d}"


def _derive_vehicle_status(body: RegisterReturnRequest, vehicle: Vehicle, new_odometer: int) -> str:
    if body.damage_reported or body.technical_warning:
        return "blocked"
    if new_odometer >= vehicle.next_service_km:
        return "maintenance"
    return "cleaning"


def register_vehicle_return(
    db: Session,
    booking_ref: str,
    body: RegisterReturnRequest,
    idempotency_key: str,
    actor: CurrentUser,
) -> tuple[int, dict]:
    existing = db.scalar(
        select(IdempotencyRecord).where(IdempotencyRecord.idempotency_key == idempotency_key)
    )
    if existing is not None:
        booking = db.get(Booking, existing.booking_id)
        if booking is None or booking.public_ref != booking_ref:
            raise AppError(
                "IDEMPOTENCY_KEY_REUSED",
                "This idempotency key was already used for a different booking.",
                status_code=409,
            )
        return existing.response_status, existing.response_body

    booking = db.scalar(select(Booking).where(Booking.public_ref == booking_ref).with_for_update())
    if booking is None:
        raise AppError("BOOKING_NOT_FOUND", "Booking not found.", status_code=404)
    vehicle = db.scalar(select(Vehicle).where(Vehicle.id == booking.vehicle_id).with_for_update())

    # Re-check after acquiring the row lock: a concurrent identical-key request may have
    # just committed while we were waiting.
    existing = db.scalar(
        select(IdempotencyRecord).where(IdempotencyRecord.idempotency_key == idempotency_key)
    )
    if existing is not None:
        return existing.response_status, existing.response_body

    if booking.status != "active":
        raise AppError(
            "INVALID_BOOKING_STATE",
            f"Booking is '{booking.status}', not 'active'; it cannot be returned.",
            status_code=409,
        )

    now = datetime.now(UTC)
    correlation_id = uuid.uuid4()

    inspection = Inspection(
        public_ref=_next_public_ref(db),
        booking_id=booking.id,
        vehicle_id=vehicle.id,
        type="return",
        fuel_level_percent=body.fuel_level_percent,
        cleanliness_ok=body.cleanliness_ok,
        damage_reported=body.damage_reported,
        technical_warning=body.technical_warning,
        notes=body.notes,
        odometer_km=body.end_odometer_km,
        completed_at=now,
        completed_by=actor.display_name,
    )
    db.add(inspection)

    before_vehicle = {
        "operational_status": vehicle.operational_status,
        "odometer_km": vehicle.odometer_km,
    }

    booking.status = "returned"
    booking.end_odometer_km = body.end_odometer_km

    odometer_regression = body.end_odometer_km < vehicle.odometer_km
    quality_issue_ref: str | None = None
    canonical_odometer = vehicle.odometer_km
    if not odometer_regression:
        canonical_odometer = body.end_odometer_km
        vehicle.odometer_km = canonical_odometer
    else:
        issue = DataQualityIssue(
            public_ref=f"DQ-RET-{str(inspection.public_ref).split('-')[-1]}",
            rule_type="odometer_regression",
            entity_type="vehicle",
            entity_id=vehicle.id,
            severity="medium",
            status="open",
            evidence_json={
                "summary": (
                    f"Return submitted {body.end_odometer_km} km, below canonical "
                    f"{vehicle.odometer_km} km."
                ),
                "entity_ref": vehicle.public_ref,
                "related_refs": [booking.public_ref, inspection.public_ref],
            },
            proposed_action_json={},
            detected_at=now,
        )
        db.add(issue)
        db.flush()
        quality_issue_ref = issue.public_ref

    resulting_status = _derive_vehicle_status(body, vehicle, canonical_odometer)
    vehicle.operational_status = resulting_status
    vehicle.version += 1

    record_audit_event(
        db,
        actor_type="user",
        actor_label=actor.display_name,
        action="return_registered",
        entity_type="booking",
        entity_id=booking.id,
        correlation_id=correlation_id,
        before={"status": "active"},
        after={"status": "returned", "end_odometer_km": body.end_odometer_km},
        metadata={"idempotency_key": idempotency_key},
    )
    record_audit_event(
        db,
        actor_type="user",
        actor_label=actor.display_name,
        action="vehicle_status_changed",
        entity_type="vehicle",
        entity_id=vehicle.id,
        correlation_id=correlation_id,
        before=before_vehicle,
        after={
            "operational_status": vehicle.operational_status,
            "odometer_km": vehicle.odometer_km,
        },
    )

    attention_reasons = []
    if body.damage_reported:
        attention_reasons.append("damage_reported")
    if body.technical_warning:
        attention_reasons.append("technical_warning")
    if odometer_regression:
        attention_reasons.append("odometer_regression")

    event = OutboxEvent(
        event_id=uuid.uuid4(),
        event_type="vehicle.returned.v1",
        aggregate_type="booking",
        aggregate_id=booking.id,
        payload_json={
            "event_type": "vehicle.returned.v1",
            "correlation_id": str(correlation_id),
            "aggregate": {
                "type": "booking",
                "id": str(booking.id),
                "public_ref": booking.public_ref,
            },
            "data": {
                "vehicle_ref": vehicle.public_ref,
                "inspection_ref": inspection.public_ref,
                "resulting_vehicle_status": resulting_status,
                "attention_reasons": attention_reasons,
            },
            "aggregate_ref": booking.public_ref,
        },
        occurred_at=now,
        delivery_status="pending",
        attempts=0,
    )
    db.add(event)

    next_booking = db.scalar(
        select(Booking)
        .where(
            Booking.vehicle_id == vehicle.id,
            Booking.status == "reserved",
            Booking.starts_at > now,
        )
        .order_by(Booking.starts_at.asc())
    )
    next_booking_risk = None
    if next_booking is not None:
        hours_until = (next_booking.starts_at - now).total_seconds() / 3600
        next_booking_risk = {
            "booking_ref": next_booking.public_ref,
            "starts_at": next_booking.starts_at.isoformat(),
            "at_risk": resulting_status != "cleaning" or hours_until < 4,
        }

    response_body = {
        "booking_ref": booking.public_ref,
        "vehicle_ref": vehicle.public_ref,
        "inspection_ref": inspection.public_ref,
        "resulting_vehicle_status": resulting_status,
        "odometer_regression": odometer_regression,
        "quality_issue_ref": quality_issue_ref,
        "workflow_event_id": str(event.event_id),
        "next_booking_risk": next_booking_risk,
    }

    db.add(
        IdempotencyRecord(
            idempotency_key=idempotency_key,
            booking_id=booking.id,
            response_status=201,
            response_body=response_body,
        )
    )

    try:
        db.commit()
    except IntegrityError:
        db.rollback()
        existing = db.scalar(
            select(IdempotencyRecord).where(IdempotencyRecord.idempotency_key == idempotency_key)
        )
        if existing is not None:
            return existing.response_status, existing.response_body
        raise

    return 201, response_body