<?php

namespace App\Services;

use App\Enums\PacePreference;
use App\Enums\WeeklyReviewStatus;
use App\Enums\WeightGoal;
use App\Models\MealPosts;
use App\Models\User;
use App\Models\WeeklyReview;
use Carbon\CarbonImmutable;
use Carbon\CarbonInterface;
use Illuminate\Support\Collection;

class WeeklyReviewService
{
    /**
     * Generate or refresh a review for the last completed week.
     */
    public function generate(User $user, ?CarbonImmutable $periodStart = null): WeeklyReview
    {
        $periodStart ??= CarbonImmutable::now()->subWeek()->startOfWeek(CarbonInterface::MONDAY);
        $periodStart = $periodStart->startOfDay();
        $periodEnd = $periodStart->endOfWeek(CarbonInterface::SUNDAY);
        $existingReview = $user->weeklyReviews()->whereDate('period_start', $periodStart)->first();

        if ($existingReview?->accepted_at !== null) {
            return $existingReview;
        }

        $currentPlan = $user->nutritionPlans()->where('is_active', true)->latest('effective_from')->firstOrFail();
        $nutritionPlan = $user->nutritionPlans()
            ->where('effective_from', '<=', $periodEnd)
            ->latest('effective_from')
            ->first()
            ?? $currentPlan;
        $meals = MealPosts::query()
            ->where('user_id', $user->getKey())
            ->whereBetween('eaten_at', [$periodStart, $periodEnd])
            ->get(['calories', 'proteins', 'carbs', 'fats', 'eaten_at']);
        $loggedDaysCount = $meals->pluck('eaten_at')
            ->map(fn (CarbonInterface $date): string => $date->toDateString())
            ->unique()
            ->count();
        $averages = $this->nutritionAverages($meals, $loggedDaysCount);
        $weights = $user->weightEntries()
            ->whereBetween('measured_at', [$periodStart->subWeek(), $periodEnd])
            ->oldest('measured_at')
            ->get();
        $trend = $this->weightTrend($weights);
        $latestWeight = $weights->last()?->weight_kg ?? $user->latestWeightEntry()->value('weight_kg');
        $targetTrend = $latestWeight === null ? null : $this->targetWeightTrend(
            (float) $latestWeight,
            $user->weight_goal,
            $user->pace_preference,
        );
        [$status, $adjustment, $messageCode] = $this->recommendation(
            loggedDaysCount: $loggedDaysCount,
            weightCount: $weights->count(),
            trend: $trend,
            targetTrend: $targetTrend,
            averageCalories: $averages['calories'],
            planCalories: $nutritionPlan->calories,
            weightGoal: $user->weight_goal,
        );

        if ($nutritionPlan->getKey() !== $currentPlan->getKey()) {
            $status = WeeklyReviewStatus::INSUFFICIENT_DATA;
            $adjustment = 0;
            $messageCode = 'WEEKLY_REVIEW_PLAN_CHANGED';
        }

        return $user->weeklyReviews()->updateOrCreate(
            ['period_start' => $periodStart->toDateString()],
            [
                'nutrition_plan_id' => $nutritionPlan->getKey(),
                'period_end' => $periodEnd->toDateString(),
                'average_calories' => $averages['calories'],
                'average_proteins' => $averages['proteins'],
                'average_carbs' => $averages['carbs'],
                'average_fats' => $averages['fats'],
                'logged_days_count' => $loggedDaysCount,
                'weight_entries_count' => $weights->count(),
                'weight_trend_kg' => $trend,
                'target_weight_trend_kg' => $targetTrend,
                'status' => $status,
                'recommended_calorie_adjustment' => $adjustment,
                'message_code' => $messageCode,
                'metrics' => [
                    'analysisStart' => $periodStart->subWeek()->toDateString(),
                    'analysisEnd' => $periodEnd->toDateString(),
                    'firstWeightKg' => $weights->first()?->weight_kg,
                    'lastWeightKg' => $weights->last()?->weight_kg,
                    'nutritionPlanCalories' => $nutritionPlan->calories,
                ],
                'generated_at' => now(),
            ],
        );
    }

    /**
     * @param  Collection<int, MealPosts>  $meals
     * @return array{calories: float, proteins: float, carbs: float, fats: float}
     */
    private function nutritionAverages(Collection $meals, int $loggedDaysCount): array
    {
        $divisor = max(1, $loggedDaysCount);

        return [
            'calories' => round((float) $meals->sum('calories') / $divisor, 2),
            'proteins' => round((float) $meals->sum('proteins') / $divisor, 2),
            'carbs' => round((float) $meals->sum('carbs') / $divisor, 2),
            'fats' => round((float) $meals->sum('fats') / $divisor, 2),
        ];
    }

    private function weightTrend(Collection $weights): ?float
    {
        $first = $weights->first();
        $last = $weights->last();

        if ($weights->count() < 4 || $first === null || $last === null) {
            return null;
        }

        $days = max(1, $first->measured_at->diffInDays($last->measured_at));

        if ($days < 7) {
            return null;
        }

        return round((($last->weight_kg - $first->weight_kg) / $days) * 7, 2);
    }

    private function targetWeightTrend(
        float $weightKg,
        WeightGoal $weightGoal,
        PacePreference $pacePreference,
    ): float {
        $percentage = match ($weightGoal) {
            WeightGoal::LOSE_WEIGHT => match ($pacePreference) {
                PacePreference::SLOW => -0.0025,
                PacePreference::NORMAL => -0.005,
                PacePreference::FAST => -0.0075,
            },
            WeightGoal::GAIN_WEIGHT => match ($pacePreference) {
                PacePreference::SLOW => 0.00125,
                PacePreference::NORMAL => 0.0025,
                PacePreference::FAST => 0.00375,
            },
            WeightGoal::MAINTAIN_WEIGHT => 0,
        };

        return round($weightKg * $percentage, 2);
    }

    /**
     * @return array{WeeklyReviewStatus, int, string}
     */
    private function recommendation(
        int $loggedDaysCount,
        int $weightCount,
        ?float $trend,
        ?float $targetTrend,
        float $averageCalories,
        int $planCalories,
        WeightGoal $weightGoal,
    ): array {
        if ($loggedDaysCount < 5 || $weightCount < 4 || $trend === null || $targetTrend === null) {
            return [
                WeeklyReviewStatus::INSUFFICIENT_DATA,
                0,
                'WEEKLY_REVIEW_INSUFFICIENT_TRACKING',
            ];
        }

        $calorieDifferenceRatio = abs($averageCalories - $planCalories) / max(1, $planCalories);

        if ($calorieDifferenceRatio > 0.15) {
            return [
                WeeklyReviewStatus::INSUFFICIENT_DATA,
                0,
                'WEEKLY_REVIEW_INSUFFICIENT_ADHERENCE',
            ];
        }

        $tolerance = $weightGoal === WeightGoal::MAINTAIN_WEIGHT
            ? 0.2
            : max(0.1, abs($targetTrend) * 0.35);
        $difference = $trend - $targetTrend;

        if (abs($difference) <= $tolerance) {
            return [
                WeeklyReviewStatus::ON_TRACK,
                0,
                'WEEKLY_REVIEW_ON_TRACK',
            ];
        }

        $adjustment = match ($weightGoal) {
            WeightGoal::LOSE_WEIGHT => $difference > 0 ? -100 : 100,
            WeightGoal::GAIN_WEIGHT => $difference < 0 ? 100 : -100,
            WeightGoal::MAINTAIN_WEIGHT => $trend > 0 ? -100 : 100,
        };

        return [
            WeeklyReviewStatus::ADJUSTMENT_RECOMMENDED,
            $adjustment,
            $this->adjustmentMessage($weightGoal, $adjustment),
        ];
    }

    private function adjustmentMessage(WeightGoal $weightGoal, int $adjustment): string
    {
        return match ($weightGoal) {
            WeightGoal::LOSE_WEIGHT => $adjustment < 0
                ? 'WEEKLY_REVIEW_LOSS_SLOWER'
                : 'WEEKLY_REVIEW_LOSS_FASTER',
            WeightGoal::GAIN_WEIGHT => $adjustment > 0
                ? 'WEEKLY_REVIEW_GAIN_SLOWER'
                : 'WEEKLY_REVIEW_GAIN_FASTER',
            WeightGoal::MAINTAIN_WEIGHT => $adjustment > 0
                ? 'WEEKLY_REVIEW_MAINTENANCE_DOWN'
                : 'WEEKLY_REVIEW_MAINTENANCE_UP',
        };
    }
}