Extending

// Core schema defines stable IDs so extensions can target them.
$page = ViewPage::make('catalog.products.view')
  ->blocks([
    DetailsBlock::make('details'),
    RelatedTableBlock::make('variants')->section('relations'),
  ]);

interface SchemaMutator
{
    public function appliesTo(string $pageId): bool;

    /** Lower runs earlier; allow ordering */
    public function priority(): int;

    public function mutate(PageSchema $schema, SchemaContext $ctx): void;
}

final class SchemaContext
{
    public function __construct(
        public Request $request,
        public User $user,
        public array $routeParams,
        public array $abilities,
    ) {}
}

final class SchemaMutatorRegistry
{
    /** @var list<SchemaMutator> */
    private array $mutators = [];

    public function register(SchemaMutator $m): void
    {
        $this->mutators[] = $m;
    }

    /** @return list<SchemaMutator> */
    public function forPage(string $pageId): array
    {
        $list = array_filter($this->mutators, fn($m) => $m->appliesTo($pageId));
        usort($list, fn($a, $b) => $a->priority() <=> $b->priority());
        return $list;
    }
}

final class SchemaPipeline
{
    public function __construct(private SchemaMutatorRegistry $registry) {}

    public function build(callable $baseFactory, string $pageId, SchemaContext $ctx): PageSchema
    {
        $schema = $baseFactory($ctx); // returns PageSchema (ViewPage/ListPage/FormPage)
        foreach ($this->registry->forPage($pageId) as $mutator) {
            $mutator->mutate($schema, $ctx);
        }
        return $schema;
    }
}

abstract class PageSchema
{
    public string $id;

    // ---- blocks
    public function addBlockAfter(string $existingBlockId, Block $block): void {}
    public function addBlockBefore(string $existingBlockId, Block $block): void {}
    public function addBlockToSection(string $sectionId, Block $block, ?int $position = null): void {}
    public function removeBlock(string $blockId): void {}

    // ---- forms
    public function addFields(string $sectionId, array $fields, ?string $afterFieldKey = null): void {}
    public function addSection(string $sectionId, string $title, ?string $afterSectionId = null): void {}

    // ---- tables
    public function addColumn(string $tableBlockId, Column $column, ?string $afterColumnKey = null): void {}
    public function addFilter(string $tableBlockId, Filter $filter): void {}
    public function addRowAction(string $tableBlockId, Action $action): void {}
}

final class StockMovementsBlockMutator implements SchemaMutator
{
    public function appliesTo(string $pageId): bool
    {
        return $pageId === 'catalog.products.view';
    }

    public function priority(): int { return 50; }

    public function mutate(PageSchema $schema, SchemaContext $ctx): void
    {
        if (!in_array('inventory.view', $ctx->abilities)) {
            return;
        }

        $productId = $ctx->routeParams['product']; // or record id

        $schema->addBlockAfter('variants', RelatedTableBlock::make('stock_movements')
            ->title('Stock movements')
            ->stateKey('stock')
            ->endpoint(route('inventory.products.stock.data', ['product' => $productId]))
            ->list(StockMovementsListSchema::make()) // reuse list schema
        );
    }
}

final class TaxFieldsMutator implements SchemaMutator
{
    public function appliesTo(string $pageId): bool
    {
        return $pageId === 'catalog.products.edit';
    }

    public function priority(): int { return 20; }

    public function mutate(PageSchema $schema, SchemaContext $ctx): void
    {
        $schema->addFields('pricing', [
            Field::select('tax_class_id')->label('Tax class')->optionsEndpoint(route('tax.classes.search')),
            Field::toggle('prices_include_tax')->label('Prices include tax'),
        ], afterFieldKey: 'price');
    }
}

final class VariantsEnhancementsMutator implements SchemaMutator
{
    public function appliesTo(string $pageId): bool
    {
        return $pageId === 'catalog.products.view';
    }

    public function priority(): int { return 60; }

    public function mutate(PageSchema $schema, SchemaContext $ctx): void
    {
        $schema->addColumn('variants', Column::badge('availability')->label('Availability'), afterColumnKey: 'sku');

        $schema->addRowAction('variants', Action::button('Edit')
            ->icon('pencil')
            ->opensModal('variants.edit') // framework knows this means “modal form payload + submit”
        );
    }
}

use App\Lunar\Http\Mutators\VariantsEnhancementsMutator;
use Lunar\Inventory\Http\Mutators\StockMovementsBlockMutator;

final class InventoryServiceProvider extends ServiceProvider
{
    public function boot(): void
    {
        app(SchemaMutatorRegistry::class)->register(new StockMovementsBlockMutator);
        app(SchemaMutatorRegistry::class)->register(new VariantsEnhancementsMutator);
    }
}

final class ProductViewController extends Controller
{
    public function __invoke(Request $request, SchemaPipeline $pipeline)
    {
        $ctx = new SchemaContext(
            request: $request,
            user: $request->user(),
            routeParams: $request->route()->parameters(),
            abilities: $this->abilitiesFor($request->user()),
        );

        $schema = $pipeline->build(
            baseFactory: fn($ctx) => ProductViewSchema::build($ctx->request),
            pageId: 'catalog.products.view',
            ctx: $ctx
        );

        return Inertia::render($schema->component(), [
            'page' => $schema->toArray(),
        ]);
    }
}