<?php

namespace App\Http\Controllers\Api;

use App\Http\Controllers\Controller;
use App\Models\{Budget, LlmRequest};
use Illuminate\Http\JsonResponse;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Validator;
use Illuminate\Support\Facades\DB;

class BudgetController extends Controller
{
    /**
     * Get current budget status
     * 
     * Returns comprehensive budget information including total budget, used budget,
     * remaining budget, projections, and breakdowns by provider.
     * 
     * ## Example Response
     * 
     * ```json
     * {
     *   "data": {
     *     "total_budget": 100.00,
     *     "used_budget": 45.67,
     *     "remaining_budget": 54.33,
     *     "budget_percentage": 45.67,
     *     "currency": "USD",
     *     "period": "monthly",
     *     "period_start": "2025-11-01T00:00:00Z",
     *     "period_end": "2025-11-30T23:59:59Z",
     *     "days_remaining": 11,
     *     "projected_spend": 95.34,
     *     "projected_overspend": false,
     *     "limits": {
     *       "daily_limit": 10.00,
     *       "daily_used": 2.45,
     *       "daily_remaining": 7.55
     *     },
     *     "alerts": {
     *       "threshold_50_percent": false,
     *       "threshold_75_percent": false,
     *       "threshold_90_percent": false
     *     },
     *     "breakdown_by_provider": [
     *       {
     *         "provider": "openai",
     *         "provider_name": "OpenAI",
     *         "spent": 25.30,
     *         "percentage": 55.4,
     *         "requests": 850
     *       }
     *     ]
     *   }
     * }
     * ```
     * 
     * @tags Budget
     * 
     * @param Request $request
     * @return JsonResponse
     */
    public function index(Request $request): JsonResponse
    {
        $user = $request->user();
        
        // Get budget configuration
        $budget = Budget::where('gateway_user_id', $user->user_id)->first();
        
        if (!$budget) {
            return response()->json([
                'error' => [
                    'code' => 'not_found',
                    'message' => 'No budget configured for this user',
                    'status' => 404,
                ],
            ], 404);
        }
        
        // Calculate period dates
        $now = now();
        $periodStart = $now->copy()->startOfMonth();
        $periodEnd = $now->copy()->endOfMonth();
        $daysRemaining = $now->diffInDays($periodEnd, false);
        $daysInMonth = $periodStart->daysInMonth;
        $daysElapsed = $now->diffInDays($periodStart);
        
        // Get current month's spending
        $monthlySpending = LlmRequest::where('gateway_user_id', $user->user_id)
            ->whereYear('created_at', $now->year)
            ->whereMonth('created_at', $now->month)
            ->where('status', 'success')
            ->sum('total_cost') ?? 0;
        
        // Get today's spending
        $dailySpending = LlmRequest::where('gateway_user_id', $user->user_id)
            ->whereDate('created_at', $now->toDateString())
            ->where('status', 'success')
            ->sum('total_cost') ?? 0;
        
        // Calculate projections
        $dailyAverage = $daysElapsed > 0 ? ($monthlySpending / $daysElapsed) : 0;
        $projectedSpend = $dailyAverage * $daysInMonth;
        
        // Calculate remaining budget
        $remainingBudget = $budget->monthly_limit - $monthlySpending;
        $budgetPercentage = $budget->monthly_limit > 0 
            ? ($monthlySpending / $budget->monthly_limit) * 100 
            : 0;
        
        // Get breakdown by provider
        $providerBreakdown = LlmRequest::where('gateway_user_id', $user->user_id)
            ->whereYear('created_at', $now->year)
            ->whereMonth('created_at', $now->month)
            ->where('status', 'success')
            ->select('provider', DB::raw('SUM(total_cost) as spent'), DB::raw('COUNT(*) as requests'))
            ->groupBy('provider')
            ->orderByDesc('spent')
            ->get()
            ->map(function ($item) use ($monthlySpending) {
                $percentage = $monthlySpending > 0 ? ($item->spent / $monthlySpending) * 100 : 0;
                return [
                    'provider' => $item->provider,
                    'provider_name' => $this->getProviderName($item->provider),
                    'spent' => round($item->spent, 4),
                    'percentage' => round($percentage, 1),
                    'requests' => $item->requests,
                ];
            });
        
        // Calculate daily limit (monthly limit / days in month)
        $dailyLimit = $budget->monthly_limit / $daysInMonth;
        
        return response()->json([
            'data' => [
                'total_budget' => round($budget->monthly_limit, 2),
                'used_budget' => round($monthlySpending, 4),
                'remaining_budget' => round($remainingBudget, 4),
                'budget_percentage' => round($budgetPercentage, 2),
                'currency' => 'USD',
                'period' => 'monthly',
                'period_start' => $periodStart->toIso8601String(),
                'period_end' => $periodEnd->toIso8601String(),
                'days_remaining' => max(0, $daysRemaining),
                'projected_spend' => round($projectedSpend, 2),
                'projected_overspend' => $projectedSpend > $budget->monthly_limit,
                'limits' => [
                    'daily_limit' => round($dailyLimit, 2),
                    'daily_used' => round($dailySpending, 4),
                    'daily_remaining' => round($dailyLimit - $dailySpending, 4),
                ],
                'alerts' => [
                    'threshold_50_percent' => $budgetPercentage >= 50,
                    'threshold_75_percent' => $budgetPercentage >= 75,
                    'threshold_90_percent' => $budgetPercentage >= 90,
                    'approaching_daily_limit' => ($dailySpending / $dailyLimit) >= 0.8,
                ],
                'breakdown_by_provider' => $providerBreakdown,
                'updated_at' => now()->toIso8601String(),
            ],
        ]);
    }
    
    /**
     * Get budget history over time
     * 
     * Returns historical budget data with daily, weekly, or monthly aggregation.
     * 
     * ## Query Parameters
     * 
     * - `period` (optional) - Aggregation period: daily, weekly, monthly (default: daily)
     * - `days` (optional) - Number of days to look back (default: 30)
     * 
     * ## Example Response
     * 
     * ```json
     * {
     *   "data": [
     *     {
     *       "date": "2025-11-19",
     *       "total_cost": 2.45,
     *       "total_requests": 45,
     *       "total_tokens": 45000,
     *       "breakdown": [
     *         {
     *           "provider": "openai",
     *           "cost": 1.35,
     *           "requests": 25
     *         }
     *       ]
     *     }
     *   ],
     *   "meta": {
     *     "period": "daily",
     *     "days": 30,
     *     "total_cost": 45.67,
     *     "total_requests": 1250,
     *     "avg_daily_cost": 1.52,
     *     "avg_daily_requests": 41.7
     *   }
     * }
     * ```
     * 
     * @tags Budget
     * 
     * @param Request $request
     * @return JsonResponse
     */
    public function history(Request $request): JsonResponse
    {
        $validator = Validator::make($request->all(), [
            'period' => 'sometimes|string|in:daily,weekly,monthly',
            'days' => 'sometimes|integer|min:1|max:365',
        ]);
        
        if ($validator->fails()) {
            return response()->json([
                'error' => [
                    'code' => 'validation_error',
                    'message' => 'Invalid query parameters',
                    'status' => 422,
                    'details' => $validator->errors(),
                ],
            ], 422);
        }
        
        $user = $request->user();
        $period = $request->input('period', 'daily');
        $days = $request->input('days', 30);
        
        $startDate = now()->subDays($days)->startOfDay();
        
        // Get daily aggregated data
        $dailyData = LlmRequest::where('gateway_user_id', $user->user_id)
            ->where('created_at', '>=', $startDate)
            ->where('status', 'success')
            ->select(
                DB::raw('DATE(created_at) as date'),
                'provider',
                DB::raw('SUM(total_cost) as cost'),
                DB::raw('COUNT(*) as requests'),
                DB::raw('SUM(total_tokens) as tokens')
            )
            ->groupBy('date', 'provider')
            ->orderBy('date')
            ->get();
        
        // Group by date
        $groupedByDate = $dailyData->groupBy('date')->map(function ($items, $date) {
            return [
                'date' => $date,
                'total_cost' => round($items->sum('cost'), 4),
                'total_requests' => $items->sum('requests'),
                'total_tokens' => $items->sum('tokens'),
                'breakdown' => $items->map(function ($item) {
                    return [
                        'provider' => $item->provider,
                        'cost' => round($item->cost, 4),
                        'requests' => $item->requests,
                    ];
                })->values(),
            ];
        })->values();
        
        // Calculate meta statistics
        $totalCost = $groupedByDate->sum('total_cost');
        $totalRequests = $groupedByDate->sum('total_requests');
        $dataPoints = $groupedByDate->count();
        
        return response()->json([
            'data' => $groupedByDate,
            'meta' => [
                'period' => $period,
                'days' => $days,
                'total_cost' => round($totalCost, 4),
                'total_requests' => $totalRequests,
                'avg_daily_cost' => $dataPoints > 0 ? round($totalCost / $dataPoints, 4) : 0,
                'avg_daily_requests' => $dataPoints > 0 ? round($totalRequests / $dataPoints, 1) : 0,
            ],
        ]);
    }
    
    /**
     * Get human-readable provider name
     */
    private function getProviderName(string $provider): string
    {
        return match ($provider) {
            'openai' => 'OpenAI',
            'anthropic' => 'Anthropic',
            'gemini' => 'Google Gemini',
            'deepseek' => 'DeepSeek',
            'mistral' => 'Mistral AI',
            default => ucfirst($provider),
        };
    }
}