"""Business logic for deals."""

from __future__ import annotations

from collections.abc import Iterable
from dataclasses import dataclass
from decimal import Decimal

from redis.asyncio.client import Redis
from sqlalchemy import func, select

from app.models.activity import Activity, ActivityType
from app.models.contact import Contact
from app.models.deal import Deal, DealCreate, DealStage, DealStatus
from app.models.organization_member import OrganizationRole
from app.repositories.deal_repo import DealRepository
from app.services.analytics_service import invalidate_analytics_cache
from app.services.organization_service import OrganizationContext

STAGE_ORDER = {
    stage: index
    for index, stage in enumerate(
        [
            DealStage.QUALIFICATION,
            DealStage.PROPOSAL,
            DealStage.NEGOTIATION,
            DealStage.CLOSED,
        ],
    )
}


class DealServiceError(Exception):
    """Base class for deal service errors."""


class DealOrganizationMismatchError(DealServiceError):
    """Raised when attempting to use resources from another organization."""


class DealStageTransitionError(DealServiceError):
    """Raised when stage transition violates business rules."""


class DealStatusValidationError(DealServiceError):
    """Raised when invalid status transitions are requested."""


class ContactHasDealsError(DealServiceError):
    """Raised when attempting to delete a contact with active deals."""


@dataclass(slots=True)
class DealUpdateData:
    """Structured container for deal update operations."""

    status: DealStatus | None = None
    stage: DealStage | None = None
    amount: Decimal | None = None
    currency: str | None = None


class DealService:
    """Encapsulates deal workflows and validations."""

    def __init__(
        self,
        repository: DealRepository,
        cache: Redis | None = None,
        *,
        cache_backoff_ms: int = 0,
    ) -> None:
        self._repository = repository
        self._cache = cache
        self._cache_backoff_ms = cache_backoff_ms

    async def create_deal(self, data: DealCreate, *, context: OrganizationContext) -> Deal:
        self._ensure_same_organization(data.organization_id, context)
        await self._ensure_contact_in_organization(data.contact_id, context.organization_id)
        deal = await self._repository.create(data=data, role=context.role, user_id=context.user_id)
        await invalidate_analytics_cache(
            self._cache, context.organization_id, self._cache_backoff_ms
        )
        return deal

    async def update_deal(
        self,
        deal: Deal,
        updates: DealUpdateData,
        *,
        context: OrganizationContext,
    ) -> Deal:
        self._ensure_same_organization(deal.organization_id, context)
        changes: dict[str, object] = {}
        stage_activity: tuple[ActivityType, dict[str, str]] | None = None
        status_activity: tuple[ActivityType, dict[str, str]] | None = None

        if updates.amount is not None:
            changes["amount"] = updates.amount
        if updates.currency is not None:
            changes["currency"] = updates.currency

        if updates.stage is not None and updates.stage != deal.stage:
            self._validate_stage_transition(deal.stage, updates.stage, context.role)
            changes["stage"] = updates.stage
            stage_activity = (
                ActivityType.STAGE_CHANGED,
                {"old_stage": deal.stage, "new_stage": updates.stage},
            )

        if updates.status is not None and updates.status != deal.status:
            self._validate_status_transition(deal, updates)
            changes["status"] = updates.status
            status_activity = (
                ActivityType.STATUS_CHANGED,
                {"old_status": deal.status, "new_status": updates.status},
            )

        if not changes:
            return deal

        updated = await self._repository.update(
            deal, changes, role=context.role, user_id=context.user_id
        )
        await self._log_activities(
            deal_id=deal.id,
            author_id=context.user_id,
            activities=[activity for activity in [stage_activity, status_activity] if activity],
        )
        await invalidate_analytics_cache(
            self._cache, context.organization_id, self._cache_backoff_ms
        )
        return updated

    async def ensure_contact_can_be_deleted(self, contact_id: int) -> None:
        stmt = select(func.count()).select_from(Deal).where(Deal.contact_id == contact_id)
        count = await self._repository.session.scalar(stmt)
        if count and count > 0:
            raise ContactHasDealsError("Contact has related deals and cannot be deleted")

    async def _log_activities(
        self,
        *,
        deal_id: int,
        author_id: int,
        activities: Iterable[tuple[ActivityType, dict[str, str]]],
    ) -> None:
        entries = list(activities)
        if not entries:
            return
        for activity_type, payload in entries:
            activity = Activity(
                deal_id=deal_id, author_id=author_id, type=activity_type, payload=payload
            )
            self._repository.session.add(activity)
        await self._repository.session.flush()

    def _ensure_same_organization(self, organization_id: int, context: OrganizationContext) -> None:
        if organization_id != context.organization_id:
            raise DealOrganizationMismatchError("Operation targets a different organization")

    async def _ensure_contact_in_organization(
        self, contact_id: int, organization_id: int
    ) -> Contact:
        contact = await self._repository.session.get(Contact, contact_id)
        if contact is None or contact.organization_id != organization_id:
            raise DealOrganizationMismatchError("Contact belongs to another organization")
        return contact

    def _validate_stage_transition(
        self,
        current_stage: DealStage,
        new_stage: DealStage,
        role: OrganizationRole,
    ) -> None:
        if STAGE_ORDER[new_stage] < STAGE_ORDER[current_stage] and role not in {
            OrganizationRole.OWNER,
            OrganizationRole.ADMIN,
        }:
            raise DealStageTransitionError("Stage rollback requires owner or admin role")

    def _validate_status_transition(self, deal: Deal, updates: DealUpdateData) -> None:
        if updates.status != DealStatus.WON:
            return
        effective_amount = updates.amount if updates.amount is not None else deal.amount
        if effective_amount is None or Decimal(effective_amount) <= Decimal("0"):
            raise DealStatusValidationError(
                "Amount must be greater than zero to mark a deal as won"
            )