<?php

namespace App\Services\Runware;

use App\Exceptions\BudgetExceededException;
use App\Models\Generation;
use Illuminate\Support\Facades\Cache;
use Illuminate\Support\Facades\DB;

/**
 * Enforces the hard monthly EUR spend cap on Runware usage. Every generation
 * must go through ensureCanSpend() before the API is called, and the actual
 * cost must be reconciled afterward via recordActualUsd() so the running
 * total reflects reality (Runware only bills successful generations).
 */
class BudgetGuard
{
    protected const LOCK_KEY = 'runware:budget-guard-lock';

    protected const LOCK_TIMEOUT_SECONDS = 10;

    public function __construct(protected CurrencyRateService $rates) {}

    public function capEur(): float
    {
        return (float) config('runware.monthly_cap_eur');
    }

    public function spentEurThisMonth(): float
    {
        return (float) Generation::query()
            ->where('created_at', '>=', now()->startOfMonth())
            ->whereNotNull('cost_eur')
            ->sum('cost_eur');
    }

    public function remainingEur(): float
    {
        return max(0.0, $this->capEur() - $this->spentEurThisMonth());
    }

    public function warnThresholdReached(): bool
    {
        $cap = $this->capEur();

        if ($cap <= 0) {
            return false;
        }

        return ($this->spentEurThisMonth() / $cap) >= (float) config('runware.warn_threshold');
    }

    /**
     * Throws BudgetExceededException if spending $estimatedUsd would push
     * this month's total (plus a safety margin) past the cap. Guards the
     * check with an atomic lock so concurrent requests can't both slip
     * through right at the boundary.
     */
    public function ensureCanSpend(float $estimatedUsd): void
    {
        Cache::lock(self::LOCK_KEY, self::LOCK_TIMEOUT_SECONDS)->block(5, function () use ($estimatedUsd) {
            $rate = $this->rates->usdToEur();
            $estimatedEur = $estimatedUsd * $rate;
            $spent = $this->spentEurThisMonth();
            $cap = $this->capEur();
            $margin = $cap * (float) config('runware.safety_margin');

            if ($spent + $estimatedEur + $margin > $cap) {
                throw new BudgetExceededException($spent, $cap, $estimatedEur);
            }
        });
    }
}