<?php

namespace App\Http\Controllers;

use App\Models\Customer;
use App\Models\Subscription;
use App\Services\Billing\PlanCatalogue;
use App\Services\Billing\SetupFee;
use App\Services\Provisioning\HostCapacity;
use App\Services\Stripe\StripeClient;
use Illuminate\Http\RedirectResponse;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Log;
use Throwable;

/**
 * Buying a package, without anyone having to write an email about it.
 *
 * The site used to end every path in "anfragen": a mailto: link and a promise
 * to answer the same working day. That is a person's afternoon per customer,
 * for a product whose entire point is that the machine does the work — and it
 * scales exactly as far as the operator's inbox does.
 *
 * So: a signed-in customer picks a package, pays, and provisioning starts by
 * itself. Where no host has room the order is parked rather than refused (see
 * ReserveResources) — that is the ONE case that still needs a human, and it
 * needs them to buy a server, not to answer a mail.
 *
 * This class does not take money and does not create a contract. It opens a
 * Stripe hosted checkout and gets out of the way; the purchase becomes real
 * when Stripe says so, on the webhook, which is the only place that may believe
 * a payment happened. A "thank you" page proves nothing — the customer can open
 * it by typing the URL.
 */
class CheckoutController extends Controller
{
    /**
     * Send the customer to Stripe for one package.
     *
     * Everything here is re-derived from the catalogue: the plan key arrives
     * from a form, and a form field is a string somebody can retype. The price
     * charged is the one the catalogue holds for the version on sale right now,
     * never a figure carried in the request.
     */
    public function start(Request $request, StripeClient $stripe, PlanCatalogue $catalogue): RedirectResponse
    {
        $data = $request->validate([
            'plan' => ['required', 'string', 'max:64'],
            'term' => ['nullable', 'in:'.Subscription::TERM_MONTHLY.','.Subscription::TERM_YEARLY],
            // The consumer's express request that we begin inside the
            // fourteen-day withdrawal window (FAGG §16, §356 BGB). Required,
            // because the cloud starts being built the moment the payment
            // lands: without this on record a withdrawal on day thirteen gets
            // the WHOLE amount back, however many days the machine actually
            // ran. A seller who cannot prove the consent was given cannot
            // charge for the days — and the proof is a timestamp taken here.
            'immediate_start' => ['accepted'],
        ], [
            'immediate_start.accepted' => __('checkout.immediate_start_required'),
        ]);

        $term = $data['term'] ?? Subscription::TERM_MONTHLY;
        $user = $request->user();

        // Somebody who already has a running contract is not buying a second
        // one by accident: changing package is a plan change, which prorates
        // and keeps their data where it is. A second checkout would build them
        // a second, empty cloud and bill for both.
        if ($this->hasLiveContract($user?->email)) {
            return redirect()->route('billing')->with('status', __('checkout.already_customer'));
        }

        if (! $stripe->isConfigured()) {
            // Nothing to send them to. Better a plain sentence than a redirect
            // into an error page on somebody else's domain.
            Log::error('Checkout attempted while Stripe is not configured.');

            return back()->withErrors(['plan' => __('checkout.unavailable')]);
        }

        try {
            $version = $catalogue->currentVersion($data['plan']);
            $price = $version->prices->firstWhere('term', $term);
        } catch (Throwable $e) {
            // An unknown, withdrawn or overlapping plan. The catalogue throws
            // by design; a shop must not guess which of two versions was meant.
            Log::warning('Checkout for an unavailable plan', ['plan' => $data['plan'], 'exception' => $e]);

            return back()->withErrors(['plan' => __('checkout.plan_gone')]);
        }

        // A price with no Stripe id was never synced. Sending the customer on
        // would open a checkout for nothing.
        if ($price === null || blank($price->stripe_price_id)) {
            Log::error('Checkout for a plan that is not on sale in Stripe', [
                'plan' => $data['plan'],
                'term' => $term,
            ]);

            return back()->withErrors(['plan' => __('checkout.plan_gone')]);
        }

        // The one-off setup fee, gross, or null where the operator has set none.
        // Advertised on the price sheet and on the booking page for months and
        // charged to nobody; it rides along as a second, non-recurring line on
        // this session, which Stripe puts on the initial invoice only.
        $setup = SetupFee::checkoutLine((string) $price->currency);

        try {
            $url = $stripe->createCheckoutSession(
                priceId: (string) $price->stripe_price_id,
                successUrl: route('checkout.done'),
                cancelUrl: route('order'),
                // Exactly the keys StripeWebhookController reads back. The
                // VERSION goes along, so the contract is opened on what the
                // customer was shown even if a new version is published while
                // they are typing their card number.
                metadata: [
                    'plan' => $version->family->key,
                    'plan_version_id' => (string) $version->id,
                    'datacenter' => app(HostCapacity::class)->preferredDatacenter(),
                    // Exactly '1', because StripeWebhookController compares
                    // against exactly that: a consent that can be produced by a
                    // typo is not a consent. It travels through Stripe rather
                    // than being stamped here — the contract only exists once
                    // the payment does, and a consent recorded for a checkout
                    // somebody abandoned would be a consent to nothing.
                    'immediate_start' => '1',
                    // What part of Stripe's amount_total is the setup fee, so the
                    // webhook can tell the two apart again: the package's charge
                    // is what the register holds against the contract price, and
                    // the fee is a line of its own on the first invoice.
                    'setup_fee_cents' => (string) ($setup['amount_cents'] ?? 0),
                ],
                customerEmail: $user?->email,
                oneOff: $setup,
            );
        } catch (Throwable $e) {
            Log::error('Stripe would not open a checkout session', ['exception' => $e]);

            return back()->withErrors(['plan' => __('checkout.unavailable')]);
        }

        return redirect()->away($url);
    }

    /**
     * Where Stripe sends them back to.
     *
     * Deliberately says "we are building it", not "you have paid": this page is
     * a redirect target, and a redirect target is a URL anybody can type. What
     * the customer actually sees underneath is the provisioning card on their
     * dashboard, which is driven by a run that only the webhook can start.
     */
    public function done(): RedirectResponse
    {
        return redirect()->route('dashboard')->with('status', __('checkout.thanks'));
    }

    /** Does this address already have a contract that is being billed? */
    private function hasLiveContract(?string $email): bool
    {
        if ($email === null) {
            return false;
        }

        $customer = Customer::query()->where('email', $email)->first();

        return $customer !== null && Subscription::query()
            ->where('customer_id', $customer->id)
            ->whereIn('status', ['active', 'past_due'])
            ->exists();
    }
}