import { PromiseOrValue } from "@implab/core-amd/interfaces";
import { isPromise } from "@implab/core-amd/safe";
import { observe, Observable } from "./observable";

export interface OrderedUpdate<T> {
    /** The item is being updated */
    readonly item: T;

    /** The previous index of the item, -1 in case it is inserted */
    readonly prevIndex: number;

    /** The new index of the item, -1 in case it is deleted */
    readonly newIndex: number;

}

export type QueryResults<T> = Observable<OrderedUpdate<T>>;

interface DjObservableResults<T> {
    /**
     * Allows observation of results
     */
    observe(listener: (object: T, previousIndex: number, newIndex: number) => void, includeUpdates?: boolean): {
        remove(): void;
    };
}

interface Queryable<T, Q, O> {
    query(query?: Q, options?: O): PromiseOrValue<T[]>;
}

export const isDjObservableResults = <T>(v: object): v is DjObservableResults<T> =>
    v && (typeof (v as { observe?: unknown; }).observe === "function");

export const query = <T, Q, O>(store: Queryable<T, Q, O>, includeUpdates = true) =>
    (query?: Q, options?: O & { observe?: boolean }) => {
        return observe<OrderedUpdate<T>>(({ next, complete, error, isClosed }) => {

            const processResults = (items: T[]) =>
                items.forEach((item, newIndex) => next({ item, newIndex, prevIndex: -1 }));

            try {
                const results = store.query(query, options);
                if (isPromise(results)) {
                    results.then(processResults).then(undefined, error);
                } else {
                    processResults(results);
                }

                if (!isClosed() && (options?.observe !== false) && isDjObservableResults<T>(results)) {
                    const h = results.observe((item, prevIndex, newIndex) => next({ item, prevIndex, newIndex }), includeUpdates);
                    return () => h.remove();
                } else {
                    complete();
                }
            } catch (err) {
                error(err);
            }
        });

    };