"""Durable LLM usage/cost accounting service.

Records per-organization, per-user LLM usage without storing any prompt content
or secrets. A simple default cost estimate (input/output per-token) is applied
and can be overridden by a rate table later.
"""

from __future__ import annotations

from typing import Optional

from sqlalchemy.orm import Session

from ..models.usage import UsageEvent

# Default per-1K token cost estimates (USD); a rate table can supersede later.
_DEFAULT_INPUT_RATE_PER_1K = 0.0025
_DEFAULT_OUTPUT_RATE_PER_1K = 0.0100


class UsageService:
    def __init__(self, session: Session):
        self.session = session

    def record_event(
        self,
        *,
        organization_id: str,
        user_id: Optional[str],
        operation: str,
        model: Optional[str] = None,
        input_tokens: int = 0,
        output_tokens: int = 0,
    ) -> str:
        if not isinstance(organization_id, str) or not organization_id:
            raise ValueError("organization_id_required")
        cost = (
            (input_tokens / 1000) * _DEFAULT_INPUT_RATE_PER_1K
            + (output_tokens / 1000) * _DEFAULT_OUTPUT_RATE_PER_1K
        )
        event = UsageEvent(
            organization_id=organization_id,
            user_id=user_id,
            operation=operation,
            model=model,
            input_tokens=int(input_tokens or 0),
            output_tokens=int(output_tokens or 0),
            estimated_cost=round(cost, 6),
        )
        self.session.add(event)
        self.session.flush()
        return event.id

    def list_events(self, *, organization_id: str, limit: int = 100) -> list[UsageEvent]:
        return (
            self.session.query(UsageEvent)
            .filter(UsageEvent.organization_id == organization_id)
            .order_by(UsageEvent.created_at.desc())
            .limit(min(max(int(limit), 1), 1000))
            .all()
        )

    def total_cost(self, *, organization_id: str) -> float:
        rows = (
            self.session.query(UsageEvent)
            .filter(UsageEvent.organization_id == organization_id)
            .all()
        )
        return round(sum(row.estimated_cost for row in rows), 6)