from __future__ import annotations

import uuid
from dataclasses import dataclass
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_with_reason(
    body: RegisterReturnRequest, vehicle: Vehicle, new_odometer: int
) -> tuple[str, str]:
    if body.damage_reported and body.technical_warning:
        return "blocked", "Damage and a technical warning were both reported on return."
    if body.damage_reported:
        return "blocked", "Damage was reported on return."
    if body.technical_warning:
        return "blocked", "A technical warning was reported on return."
    if new_odometer >= vehicle.next_service_km:
        return (
            "maintenance",
            f"Odometer reached the {vehicle.next_service_km:,} km service threshold.",
        )
    return "cleaning", "No damage, technical warning or service threshold; routed to cleaning."


@dataclass
class ReturnEvaluation:
    canonical_odometer_km: int
    submitted_odometer_km: int
    odometer_regression: bool
    resulting_odometer_km: int
    resulting_vehicle_status: str
    status_reason: str
    would_create_quality_issue: bool
    attention_reasons: list[str]
    next_booking_risk: dict | None


def evaluate_return(
    db: Session, booking: Booking, vehicle: Vehicle, body: RegisterReturnRequest, *, now: datetime
) -> ReturnEvaluation:
    """Pure evaluation of what a return would do. No writes; safe to call from a
    non-mutating preview endpoint. `register_vehicle_return` uses the same function so
    preview and commit can never drift apart."""
    odometer_regression = body.end_odometer_km < vehicle.odometer_km
    resulting_odometer_km = vehicle.odometer_km if odometer_regression else body.end_odometer_km
    resulting_status, status_reason = _derive_vehicle_status_with_reason(
        body, vehicle, resulting_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")

    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,
        }

    return ReturnEvaluation(
        canonical_odometer_km=vehicle.odometer_km,
        submitted_odometer_km=body.end_odometer_km,
        odometer_regression=odometer_regression,
        resulting_odometer_km=resulting_odometer_km,
        resulting_vehicle_status=resulting_status,
        status_reason=status_reason,
        would_create_quality_issue=odometer_regression,
        attention_reasons=attention_reasons,
        next_booking_risk=next_booking_risk,
    )


def _load_active_booking_and_vehicle(
    db: Session, booking_ref: str, *, lock: bool
) -> tuple[Booking, Vehicle]:
    stmt = select(Booking).where(Booking.public_ref == booking_ref)
    if lock:
        stmt = stmt.with_for_update()
    booking = db.scalar(stmt)
    if booking is None:
        raise AppError("BOOKING_NOT_FOUND", "Booking not found.", status_code=404)

    vehicle_stmt = select(Vehicle).where(Vehicle.id == booking.vehicle_id)
    if lock:
        vehicle_stmt = vehicle_stmt.with_for_update()
    vehicle = db.scalar(vehicle_stmt)
    if vehicle is None:
        raise AppError(
            "VEHICLE_NOT_FOUND", "The vehicle for this booking could not be found.", status_code=404
        )
    return booking, vehicle


def preview_vehicle_return(
    db: Session, booking_ref: str, body: RegisterReturnRequest
) -> tuple[Booking, Vehicle, ReturnEvaluation]:
    booking, vehicle = _load_active_booking_and_vehicle(db, booking_ref, lock=False)
    if booking.status != "active":
        raise AppError(
            "INVALID_BOOKING_STATE",
            f"Booking is '{booking.status}', not 'active'; it cannot be returned.",
            status_code=409,
        )
    evaluation = evaluate_return(db, booking, vehicle, body, now=datetime.now(UTC))
    return booking, vehicle, evaluation


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, vehicle = _load_active_booking_and_vehicle(db, booking_ref, lock=True)

    # 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()
    evaluation = evaluate_return(db, booking, vehicle, body, now=now)

    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

    quality_issue_ref: str | None = None
    if evaluation.odometer_regression:
        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"{evaluation.canonical_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 = evaluation.resulting_vehicle_status
    vehicle.odometer_km = evaluation.resulting_odometer_km
    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,
        },
    )

    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": evaluation.attention_reasons,
            },
            "aggregate_ref": booking.public_ref,
        },
        occurred_at=now,
        delivery_status="pending",
        attempts=0,
    )
    db.add(event)

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