import {Container, MaybeDependency, MaybeFactory} from './Container'
import {DependencyKey} from './types'

/**
 * A container that uses some parent container as a base, but
 * can have other factories distinct from that parent.
 *
 * If an instance is not found in this container, it will be resolved from
 * the parent container.
 *
 * However, if an instance IS found in this container, it will ALWAYS be
 * resolved from this container, rather than the parent.
 *
 * This can be used to create scope-specific containers that can still resolve
 * the global dependencies, while keeping scope-specific dependencies separate.
 *
 * @example
 * The Request class from @extollo/lib is a ScopedContainer. It can resolve
 * all dependencies that exist in the global Container, but it can also have
 * request-specific services (like the Session) injected into it.
 *
 * @extends Container
 */
export class ScopedContainer extends Container {
    /**
     * Create a new scoped container based on a parent container instance.
     * @param container
     */
    public static fromParent(container: Container): ScopedContainer {
        return new ScopedContainer(container)
    }

    constructor(
        private parentContainer: Container,
    ) {
        super()
        this.registerSingletonInstance<ScopedContainer>(ScopedContainer, this)
    }

    hasInstance(key: DependencyKey): boolean {
        return super.hasInstance(key) || this.parentContainer.hasInstance(key)
    }

    hasKey(key: DependencyKey): boolean {
        return super.hasKey(key) || this.parentContainer.hasKey(key)
    }

    getExistingInstance(key: DependencyKey): MaybeDependency {
        const inst = super.getExistingInstance(key)
        if ( inst ) {
            return inst
        }

        return this.parentContainer.getExistingInstance(key)
    }

    resolve(key: DependencyKey): MaybeFactory<any> {
        const factory = super.resolve(key)
        if ( factory ) {
            return factory
        }

        return this.parentContainer?.resolve(key)
    }
}