<?php
declare(strict_types=1);

namespace Unsupervised\Schedular\Payment;

use Stripe\Event;
use Stripe\PaymentIntent;
use Stripe\StripeClient;
use Stripe\Webhook;

/**
 * Thin wrapper around the Stripe PHP SDK: creates PaymentIntents for card
 * payments and verifies inbound webhook signatures. All Stripe-specific knowledge
 * (amounts in cents, idempotency, signature checking) lives here so the rest of
 * the payment domain stays gateway-agnostic.
 */
class StripeGateway {

	private ?StripeClient $client;

	/**
	 * Build the gateway. The Stripe client is created lazily from the configured
	 * secret key, or injected directly in tests.
	 *
	 * @param StripeClient|null $client Injectable for tests; built lazily when null.
	 */
	public function __construct( private StudioSettings $settings, ?StripeClient $client = null ) {
		$this->client = $client;
	}

	public function isConfigured(): bool {
		return $this->settings->isStripeConfigured();
	}

	/**
	 * Create (or, when one already exists, return) a PaymentIntent for the billed
	 * total of a payment. The payment id is stored in metadata so the webhook can
	 * reconcile the charge back to our ledger row. Returns null on any Stripe error
	 * so callers can fail gracefully.
	 */
	public function createIntent( Payment $payment ): ?PaymentIntent {
		if ( ! $this->isConfigured() ) {
			return null;
		}

		try {
			return $this->paymentIntentsCreate(
				[
					'amount'      => $this->toMinorUnits( $payment->total() ),
					'currency'    => strtolower( $payment->currency ),
					'metadata'    => [
						'payment_id'        => (string) $payment->id,
						'registration_type' => $payment->registrationType,
						'registration_id'   => (string) $payment->registrationId,
						'student_id'        => (string) $payment->studentId,
					],
					'description' => sprintf( 'Lesson payment #%d', (int) $payment->id ),
				],
				[ 'idempotency_key' => 'usc-payment-' . $payment->id ]
			);
		} catch ( \Throwable $e ) {
			return null;
		}
	}

	/**
	 * Seam around the Stripe PaymentIntents create call so tests can stub the
	 * network request.
	 *
	 * @param array{amount: int, currency: string, metadata: array<string, string>, description: string} $params
	 * @param array{idempotency_key?: string} $options
	 */
	protected function paymentIntentsCreate( array $params, array $options ): PaymentIntent {
		return $this->client()->paymentIntents->create( $params, $options );
	}

	/**
	 * Verify a raw webhook payload against its signature header and return the
	 * decoded Stripe event, or null when verification fails or no signing secret is
	 * configured.
	 */
	public function verifyWebhook( string $payload, string $signatureHeader ): ?Event {
		$secret = $this->settings->webhookSecret();
		if ( '' === $secret || '' === $signatureHeader ) {
			return null;
		}

		try {
			return $this->constructEvent( $payload, $signatureHeader, $secret );
		} catch ( \Throwable $e ) {
			return null;
		}
	}

	/**
	 * Seam around the static Stripe verifier so tests can stub signature checking.
	 */
	protected function constructEvent( string $payload, string $signatureHeader, string $secret ): Event {
		return Webhook::constructEvent( $payload, $signatureHeader, $secret );
	}

	private function client(): StripeClient {
		if ( null === $this->client ) {
			$this->client = new StripeClient( $this->settings->secretKey() );
		}

		return $this->client;
	}

	/**
	 * Convert a dollar amount to the integer minor units (cents) Stripe expects.
	 */
	private function toMinorUnits( float $amount ): int {
		return (int) round( $amount * 100 );
	}
}