<?php

declare(strict_types=1);

namespace App\Models\Concerns;

use App\Models\Redirect;
use App\Support\SiteUrls;
use Illuminate\Database\Eloquent\Model;

/**
 * Leaves a redirect behind when a slug changes.
 *
 * Renaming a slug breaks every link anybody shared, every bookmark and every
 * search result — silently, because nothing notices and the frontend only
 * finds out when a visitor gets a 404. The moment the slug changes is the only
 * moment the old address is still known, so that is when the note is written.
 */
trait RecordsSlugChanges
{
    /**
     * The `site.paths` key this model publishes under.
     */
    abstract public function publicPathType(): string;

    public static function bootRecordsSlugChanges(): void
    {
        static::updated(function (Model $model): void {
            if (! $model->wasChanged('slug')) {
                return;
            }

            $model->recordSlugChange();
        });
    }

    protected function recordSlugChange(): void
    {
        $type = $this->publicPathType();
        $previous = (array) json_decode((string) json_encode($this->getOriginal('slug')), true);
        $current = (array) $this->getTranslations('slug');

        foreach (array_keys((array) config('locales.supported')) as $locale) {
            $was = (string) ($previous[$locale] ?? '');
            $now = (string) ($current[$locale] ?? '');

            // Nothing to redirect from when the record had no address in this
            // language, and nowhere to redirect to when it no longer has one.
            if (blank($was) || blank($now) || $was === $now) {
                continue;
            }

            $from = Redirect::normalise(SiteUrls::path($type, $locale, $was));
            $to = Redirect::normalise(SiteUrls::path($type, $locale, $now));

            if ($from === $to) {
                continue;
            }

            $this->writeRedirect($from, $to, $locale);
        }
    }

    protected function writeRedirect(string $from, string $to, string $locale): void
    {
        $scope = fn () => Redirect::query()->where('locale', $locale);

        // The new address resolves to this record again, so any rule pointing
        // away from it is now wrong — this is what renaming something back to
        // its original slug looks like.
        $scope()->where('from', $to)->delete();

        // Whoever pointed at the old address now points at the new one, so a
        // frontend never has to follow two hops.
        $scope()->where('to', $from)->update(['to' => $to]);

        $redirect = Redirect::query()->firstOrNew(['from' => $from, 'locale' => $locale]);

        // `source` is set here rather than through mass assignment: it records
        // what the application did, not anything somebody submitted.
        $redirect->forceFill([
            'to' => $to,
            'status' => 301,
            'is_enabled' => true,
            'source_type' => $this->getMorphClass(),
            'source_id' => $this->getKey(),
        ])->save();

        // Belt and braces: a rule pointing at its own address would send a
        // browser round for ever.
        Redirect::query()->whereColumn('from', 'to')->delete();
    }
}