import {Canonical} from "./Canonical";
import {Singleton} from "../di";

/**
 * Error throw when a duplicate canonical key is registered.
 * @extends Error
 */
export class DuplicateResolverKeyError extends Error {
    constructor(key: string) {
        super(`There is already a canonical unit with the scope ${key} registered.`)
    }
}

/**
 * Error throw when a key that isn't registered with the service.
 * @extends Error
 */
export class NoSuchCanonicalResolverKeyError extends Error {
    constructor(key: string) {
        super(`There is no such canonical unit with the scope ${key} registered.`)
    }

}

/**
 * Service used to access various canonical resources.
 */
@Singleton()
export class Canon {
    /**
     * The resources registered with this service. Map of canonical service name
     * to canonical service instance.
     * @type object
     */
    protected resources: { [key: string]: Canonical<any> } = {}

    /**
     * Get a canonical resource by its name key.
     * @param {string} key
     * @return Canonical
     */
    resource<T>(key: string): Canonical<T> {
        if ( !this.resources[key] ) throw new NoSuchCanonicalResolverKeyError(key)
        return this.resources[key] as Canonical<T>
    }

    /**
     * Register a canonical resource.
     * @param {Canonical} unit
     */
    registerCanonical(unit: Canonical<any>) {
        const key = unit.canonicalItems
        if ( this.resources[key] ) throw new DuplicateResolverKeyError(key)
        this.resources[key] = unit
    }
}