import {Model} from '../Model'
import {HasOneOrMany} from './HasOneOrMany'
import {RelationNotLoadedError} from './Relation'
import {Maybe} from '../../../util'

/**
 * One-to-one relation implementation.
 */
export class HasOne<T extends Model<T>, T2 extends Model<T2>> extends HasOneOrMany<T, T2, Maybe<T2>> {
    protected cachedValue?: T2

    protected cachedLoaded = false

    constructor(
        parent: T,
        related: T2,
        foreignKeyOverride?: keyof T & string,
        localKeyOverride?: keyof T2 & string,
    ) {
        super(parent, related, foreignKeyOverride, localKeyOverride)
    }

    /** Resolve the result of this relation. */
    async get(): Promise<Maybe<T2>> {
        return this.fetch().first()
    }

    /** Set the value of this relation. */
    public setValue(related: T2): void {
        this.cachedValue = related
        this.cachedLoaded = true
    }

    /** Get the value of this relation. */
    public getValue(): Maybe<T2> {
        if ( !this.cachedLoaded ) {
            throw new RelationNotLoadedError()
        }

        return this.cachedValue
    }

    /** Returns true if the relation has been loaded. */
    public isLoaded(): boolean {
        return this.cachedLoaded
    }
}