"""Persistent-boundary-compatible budget guard; provider invocation happens after this check."""

from dataclasses import dataclass
from datetime import datetime, timezone
from threading import Lock


@dataclass(frozen=True)
class BudgetLimits:
    max_run_cost_usd: float = 0.54
    max_daily_cost_usd: float = 1.00
    max_monthly_cost_usd: float = 10.00
    max_requests_per_day: int = 100
    max_new_products_per_run: int = 750


@dataclass(frozen=True)
class BudgetDecision:
    allowed: bool
    reason: str
    reserved_cost_usd: float


@dataclass(frozen=True)
class UsageEntry:
    run_id: str
    tenant: str
    cost_usd: float
    requests: int
    new_products: int
    timestamp: str


class BudgetLedger:
    """Atomic in-process ledger with an explicit persistence boundary for Hub storage."""

    def __init__(self, limits: BudgetLimits):
        self.limits = limits
        self.entries: list[UsageEntry] = []
        self._lock = Lock()

    def check_and_reserve(self, run_id: str, tenant: str, cost_usd: float, requests: int, new_products: int) -> BudgetDecision:
        with self._lock:
            run_cost = sum(e.cost_usd for e in self.entries if e.run_id == run_id)
            day = datetime.now(timezone.utc).date()
            day_entries = [e for e in self.entries if e.timestamp[:10] == day.isoformat()]
            month_entries = [e for e in self.entries if e.timestamp[:7] == day.strftime("%Y-%m")]
            if run_cost + cost_usd > self.limits.max_run_cost_usd:
                return BudgetDecision(False, "AI_BUDGET_EXHAUSTED", 0.0)
            if sum(e.cost_usd for e in day_entries) + cost_usd > self.limits.max_daily_cost_usd:
                return BudgetDecision(False, "AI_BUDGET_EXHAUSTED", 0.0)
            if sum(e.cost_usd for e in month_entries) + cost_usd > self.limits.max_monthly_cost_usd:
                return BudgetDecision(False, "AI_BUDGET_EXHAUSTED", 0.0)
            if sum(e.requests for e in day_entries) + requests > self.limits.max_requests_per_day:
                return BudgetDecision(False, "AI_BUDGET_EXHAUSTED", 0.0)
            if sum(e.new_products for e in self.entries if e.run_id == run_id) + new_products > self.limits.max_new_products_per_run:
                return BudgetDecision(False, "AI_BUDGET_EXHAUSTED", 0.0)
            self.entries.append(UsageEntry(run_id, tenant, cost_usd, requests, new_products, datetime.now(timezone.utc).isoformat()))
            return BudgetDecision(True, "RESERVED", cost_usd)