<?php

namespace App\Services\Budget;

use App\Models\User;
use App\Models\UserBudget;
use App\Exceptions\InsufficientBudgetException;
use Illuminate\Support\Facades\Cache;
use Illuminate\Support\Facades\Log;

class BudgetChecker
{
    /**
     * Check if user has sufficient budget for a request
     *
     * @param User $user
     * @param float $estimatedCost
     * @return bool
     * @throws InsufficientBudgetException
     */
    public function checkBudget(User $user, float $estimatedCost = 0.0): bool
    {
        $budget = $this->getOrCreateBudget($user);

        // If budget is already exceeded, deny immediately
        if ($budget->is_budget_exceeded) {
            throw new InsufficientBudgetException(
                "Budget limit exceeded. Current spending: $" . number_format($budget->current_month_spending, 2) . 
                " / Monthly limit: $" . number_format($budget->monthly_limit, 2)
            );
        }

        // Check daily limit if set
        if ($budget->daily_limit > 0) {
            $projectedDailySpending = $budget->current_day_spending + $estimatedCost;
            
            if ($projectedDailySpending > $budget->daily_limit) {
                throw new InsufficientBudgetException(
                    "Daily budget limit would be exceeded. Current: $" . number_format($budget->current_day_spending, 2) . 
                    " / Daily limit: $" . number_format($budget->daily_limit, 2)
                );
            }
        }

        // Check monthly limit
        if ($budget->monthly_limit > 0) {
            $projectedMonthlySpending = $budget->current_month_spending + $estimatedCost;
            
            if ($projectedMonthlySpending > $budget->monthly_limit) {
                throw new InsufficientBudgetException(
                    "Monthly budget limit would be exceeded. Current: $" . number_format($budget->current_month_spending, 2) . 
                    " / Monthly limit: $" . number_format($budget->monthly_limit, 2)
                );
            }

            // Check alert threshold
            $usagePercentage = ($projectedMonthlySpending / $budget->monthly_limit) * 100;
            
            if ($usagePercentage >= $budget->alert_threshold_percentage) {
                $this->sendBudgetAlert($user, $budget, $usagePercentage);
            }
        }

        return true;
    }

    /**
     * Update user budget after a request
     *
     * @param User $user
     * @param float $actualCost
     * @return void
     */
    public function updateBudget(User $user, float $actualCost): void
    {
        $budget = $this->getOrCreateBudget($user);

        // Reset periods if needed
        $this->checkAndResetPeriods($budget);

        // Update spending
        $budget->current_month_spending += $actualCost;
        $budget->current_day_spending += $actualCost;

        // Check if budget is now exceeded
        if ($budget->monthly_limit > 0 && $budget->current_month_spending >= $budget->monthly_limit) {
            $budget->is_budget_exceeded = true;
        }

        $budget->save();

        // Invalidate cache
        Cache::forget("user_budget:{$user->id}");

        Log::info('Budget updated', [
            'user_id' => $user->id,
            'cost' => $actualCost,
            'monthly_spending' => $budget->current_month_spending,
            'daily_spending' => $budget->current_day_spending
        ]);
    }

    /**
     * Get or create user budget
     *
     * @param User $user
     * @return UserBudget
     */
    private function getOrCreateBudget(User $user): UserBudget
    {
        $budget = $user->budget;

        if (!$budget) {
            $budget = UserBudget::create([
                'user_id' => $user->id,
                'monthly_limit' => config('llm.default_monthly_budget', 100.00),
                'daily_limit' => config('llm.default_daily_budget', 10.00),
                'month_started_at' => now()->startOfMonth(),
                'day_started_at' => now()->startOfDay(),
                'alert_threshold_percentage' => 80,
            ]);

            Log::info('Budget created for user', ['user_id' => $user->id]);
        }

        return $budget;
    }

    /**
     * Check and reset budget periods if needed
     *
     * @param UserBudget $budget
     * @return void
     */
    private function checkAndResetPeriods(UserBudget $budget): void
    {
        $now = now();

        // Reset monthly budget if new month
        if ($now->startOfMonth()->greaterThan($budget->month_started_at)) {
            $budget->current_month_spending = 0.0;
            $budget->month_started_at = $now->startOfMonth();
            $budget->is_budget_exceeded = false;
            $budget->last_alert_sent_at = null;
            
            Log::info('Monthly budget reset', ['user_id' => $budget->user_id]);
        }

        // Reset daily budget if new day
        if ($now->startOfDay()->greaterThan($budget->day_started_at)) {
            $budget->current_day_spending = 0.0;
            $budget->day_started_at = $now->startOfDay();
            
            Log::info('Daily budget reset', ['user_id' => $budget->user_id]);
        }
    }

    /**
     * Send budget alert to user
     *
     * @param User $user
     * @param UserBudget $budget
     * @param float $usagePercentage
     * @return void
     */
    private function sendBudgetAlert(User $user, UserBudget $budget, float $usagePercentage): void
    {
        // Only send alert once per day
        if ($budget->last_alert_sent_at && $budget->last_alert_sent_at->isToday()) {
            return;
        }

        Log::warning('Budget threshold reached', [
            'user_id' => $user->id,
            'user_email' => $user->email,
            'usage_percentage' => round($usagePercentage, 2),
            'current_spending' => $budget->current_month_spending,
            'monthly_limit' => $budget->monthly_limit
        ]);

        // TODO: Send email notification
        // Mail::to($user->email)->send(new BudgetAlertMail($budget, $usagePercentage));

        $budget->last_alert_sent_at = now();
        $budget->save();
    }

    /**
     * Get budget status for user
     *
     * @param User $user
     * @return array
     */
    public function getBudgetStatus(User $user): array
    {
        $budget = $this->getOrCreateBudget($user);

        return [
            'monthly_limit' => $budget->monthly_limit,
            'daily_limit' => $budget->daily_limit,
            'current_month_spending' => $budget->current_month_spending,
            'current_day_spending' => $budget->current_day_spending,
            'monthly_remaining' => max(0, $budget->monthly_limit - $budget->current_month_spending),
            'daily_remaining' => max(0, $budget->daily_limit - $budget->current_day_spending),
            'monthly_usage_percentage' => $budget->monthly_limit > 0 
                ? ($budget->current_month_spending / $budget->monthly_limit) * 100 
                : 0,
            'is_exceeded' => $budget->is_budget_exceeded,
            'month_started_at' => $budget->month_started_at,
            'day_started_at' => $budget->day_started_at,
        ];
    }
}