import { Observable, of, throwError } from 'rxjs';

import { MwOutput } from './middleware';

export function verifyResponse(output: MwOutput): Observable<MwOutput> {
    const errors = getPreloadErrors((output || {}).response);
    return errors.length === 0 ? of(output) : throwError(new Error(`preload errors: ${errors.join(', ')}`));
}

const kindHelp = 'can be one of `success`, `error`, `redirect` or `not-found`';
export function getPreloadErrors(resp: any): string[] {
    if (!resp || !resp.kind) return [`missing 'response.kind' - ${kindHelp}`];
    if (resp.kind === 'success') return [];
    switch (resp.kind) {
        case 'success':
            return [];
        case 'error': {
            if (typeof resp.statusCode !== 'number' || typeof resp.message !== 'string') {
                return ['for an error, you must return a `statusCode` and a `message`'];
            }
            return [];
        }
        case 'redirect': {
            if (typeof resp.statusCode !== 'number' || typeof resp.location !== 'string') {
                return ['for a redirect, you must return a `statusCode` and a `location`'];
            }
            return [];
        }
        case 'not-found': {
            if (typeof resp.statusCode !== 'number') {
                return ['for a not-found response, you must return a `statusCode`'];
            }
            return [];
        }
        default: {
            return [`'${resp.kind}' is not a valid kind - ${kindHelp}`];
        }
    }
}