<?php

namespace App\Services;

use App\Enums\PredictionSource;
use App\Enums\TrendDirection;
use App\Models\BrentPrice;
use App\Models\PricePrediction;
use App\Services\LlmPrediction\OilPredictionProvider;
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\Http;
use Illuminate\Support\Facades\Log;
use Throwable;

class OilPriceService
{
    /**
     * Decay factor for EWMA. Higher = more weight on recent prices.
     */
    private const float EWMA_ALPHA = 0.3;

    /**
     * Minimum % change in EWMA to be considered rising/falling.
     */
    private const float EWMA_THRESHOLD_PCT = 1.5;

    /**
     * EWMA confidence is capped lower than LLM — it's a simpler model.
     */
    private const int EWMA_MAX_CONFIDENCE = 65;

    /**
     * Minimum price rows needed before EWMA is meaningful.
     */
    private const int EWMA_MIN_ROWS = 14;

    public function __construct(
        private readonly ApiLogger $apiLogger,
        private readonly OilPredictionProvider $provider,
    ) {}

    /**
     * Fetch the last 30 days of Brent crude prices from FRED and store them.
     */
    public function fetchBrentPrices(): void
    {
        $url = 'https://api.stlouisfed.org/fred/series/observations';

        try {
            $response = $this->apiLogger->send('fred', 'GET', $url, fn () => Http::timeout(10)
                ->get($url, [
                    'series_id' => 'DCOILBRENTEU',
                    'api_key' => config('services.fred.api_key'),
                    'sort_order' => 'desc',
                    'limit' => 30,
                    'file_type' => 'json',
                ]));

            if (! $response->successful()) {
                Log::error('OilPriceService: FRED request failed', ['status' => $response->status()]);

                return;
            }

            $rows = collect($response->json('observations') ?? [])
                ->filter(fn (array $obs) => $obs['value'] !== '.') // FRED uses '.' for missing data
                ->map(fn (array $obs) => [
                    'date' => $obs['date'],
                    'price_usd' => (float) $obs['value'],
                ])
                ->all();

            if (empty($rows)) {
                Log::warning('OilPriceService: no valid FRED observations returned');

                return;
            }

            BrentPrice::upsert($rows, ['date'], ['price_usd']);
        } catch (Throwable $e) {
            Log::error('OilPriceService: fetchBrentPrices failed', ['error' => $e->getMessage()]);
        }
    }

    /**
     * Generate predictions from all available sources and store each one.
     * EWMA always runs. LLM provider runs and returns null if not configured.
     * Returns the highest-confidence prediction (LLM preferred over EWMA).
     */
    public function generatePrediction(): ?PricePrediction
    {
        $prices = BrentPrice::orderBy('date', 'desc')->limit(30)->get();

        if ($prices->count() < self::EWMA_MIN_ROWS) {
            Log::warning('OilPriceService: not enough price data to generate prediction', [
                'rows' => $prices->count(),
            ]);

            return null;
        }

        $ewma = $this->generateEwmaPrediction($prices);

        if ($ewma !== null) {
            PricePrediction::create($ewma->toArray());
        }

        $llm = $this->provider->predict($prices);

        if ($llm !== null) {
            PricePrediction::create($llm->toArray());
        }

        return $llm ?? $ewma;
    }

    /**
     * Option A — EWMA-based trend extrapolation. Used as fallback when LLM is unavailable.
     * Compares the 3-day EWMA against the 7-day EWMA to detect direction.
     */
    public function generateEwmaPrediction(Collection $prices): ?PricePrediction
    {
        $chronological = $prices->sortBy('date')->pluck('price_usd')->values()->all();

        if (count($chronological) < self::EWMA_MIN_ROWS) {
            return null;
        }

        $ewma3 = $this->computeEwma(array_slice($chronological, -3));
        $ewma7 = $this->computeEwma(array_slice($chronological, -7));

        $changePct = (($ewma3 - $ewma7) / $ewma7) * 100;

        [$direction, $confidence] = match (true) {
            $changePct >= self::EWMA_THRESHOLD_PCT => [
                TrendDirection::Rising,
                $this->ewmaConfidence($changePct),
            ],
            $changePct <= -self::EWMA_THRESHOLD_PCT => [
                TrendDirection::Falling,
                $this->ewmaConfidence(abs($changePct)),
            ],
            default => [TrendDirection::Flat, 50],
        };

        $reasoning = sprintf(
            '3-day EWMA ($%.2f) vs 7-day EWMA ($%.2f): %.2f%% %s.',
            $ewma3,
            $ewma7,
            abs($changePct),
            $direction === TrendDirection::Flat ? 'difference (flat)' : $direction->value,
        );

        return new PricePrediction([
            'predicted_for' => now()->toDateString(),
            'source' => PredictionSource::Ewma,
            'direction' => $direction,
            'confidence' => $confidence,
            'reasoning' => $reasoning,
            'generated_at' => now(),
        ]);
    }

    /**
     * Compute Exponential Weighted Moving Average for a series of prices.
     *
     * @param  float[]  $prices  Chronological order (oldest first)
     */
    private function computeEwma(array $prices): float
    {
        $ema = $prices[0];

        foreach (array_slice($prices, 1) as $price) {
            $ema = self::EWMA_ALPHA * $price + (1 - self::EWMA_ALPHA) * $ema;
        }

        return round($ema, 4);
    }

    /**
     * Map a % change magnitude to a 0–EWMA_MAX_CONFIDENCE confidence score.
     * 1.5% → ~30, 3% → ~50, 5%+ → 65.
     */
    private function ewmaConfidence(float $changePct): int
    {
        $scaled = min($changePct / 5.0, 1.0) * self::EWMA_MAX_CONFIDENCE;

        return (int) round(max(30, $scaled));
    }
}
