<?php
/**
 * Lightweight service container.
 *
 * @package BlockSieve
 */

namespace BlockSieve\Container;

use BlockSieve\Exception\ServiceNotFoundException;

/**
 * A minimal dependency-injection container with singleton resolution.
 *
 * Services are registered as factory closures. The first call to get() resolves
 * the closure (passing the container itself) and caches the result, so each
 * registered service is a shared singleton.
 */
final class Container {

	/**
	 * Registered factory closures, keyed by service id.
	 *
	 * @var array<string, callable>
	 */
	private array $factories = array();

	/**
	 * Resolved service instances, keyed by service id.
	 *
	 * @var array<string, mixed>
	 */
	private array $resolved = array();

	/**
	 * Registers a service factory, resolved once and cached as a singleton.
	 *
	 * @param string   $id      Service identifier (usually a FQCN).
	 * @param callable $factory Factory receiving the container and returning the service.
	 * @return void
	 */
	public function set( string $id, callable $factory ): void {
		$this->factories[ $id ] = $factory;
		unset( $this->resolved[ $id ] );
	}

	/**
	 * Registers an already-constructed value as a singleton.
	 *
	 * @param string $id    Service identifier.
	 * @param mixed  $value Concrete value.
	 * @return void
	 */
	public function value( string $id, $value ): void {
		$this->resolved[ $id ] = $value;
		unset( $this->factories[ $id ] );
	}

	/**
	 * Resolves and returns a service.
	 *
	 * @param string $id Service identifier.
	 * @return mixed
	 *
	 * @throws ServiceNotFoundException When the id is not registered.
	 */
	public function get( string $id ) {
		if ( array_key_exists( $id, $this->resolved ) ) {
			return $this->resolved[ $id ];
		}

		if ( ! isset( $this->factories[ $id ] ) ) {
			throw new ServiceNotFoundException( esc_html( "Service [$id] is not registered." ) );
		}

		$service               = ( $this->factories[ $id ] )( $this );
		$this->resolved[ $id ] = $service;

		return $service;
	}

	/**
	 * Reports whether a service is registered.
	 *
	 * @param string $id Service identifier.
	 * @return bool
	 */
	public function has( string $id ): bool {
		return isset( $this->factories[ $id ] ) || array_key_exists( $id, $this->resolved );
	}
}