import { isString } from 'lodash';
import * as npa from 'npm-package-arg';
import { Observable, of } from 'rxjs';
import { mergeMap } from 'rxjs/operators';
import { maxSatisfying } from 'semver';
import { resolve } from 'url';

import { OPTION_NAME } from '../constants';
import { assertParameter } from './assert';
import { rxGetJson } from './rx.download';

export function getMatchingVersion(aVersions: string[], aRange: string): string {
    // find all matches
    return maxSatisfying(aVersions, aRange);
}

export interface ParsedReference {
    name: string;
    spec: string;
    escapedName: string;
}

export function parseReference(aReference: string): ParsedReference {
    // parse
    const res = npa(aReference);
    // sanity check
    assertParameter(res.name, OPTION_NAME);
    assertParameter(res.escapedName, OPTION_NAME);
    // get the spec
    const spec = res.rawSpec ? (res.rawSpec === 'latest') ? '*' : res.rawSpec : '*';
    // default
    return {
        name: res.name!,
        spec,
        escapedName: res.escapedName!
    };
}

function _getPackageJsonFromResponse(aResp: any, aBaseUrl: string, aReference: ParsedReference): Observable<any> {
    // read the versions
    const versions: string[] = Object.keys(aResp.versions);
    // select the best one
    const matching = getMatchingVersion(versions, aReference.spec);
    // now return the package
    const version = aResp.versions[matching];
    if (isString(version)) {
        // make an extra request
        return rxGetJson(aBaseUrl + '/' + encodeURIComponent(matching));
    }
    // default
    return of(version);
}

export function getPackageJson(aBaseUrl: string, aReference: ParsedReference): Observable<any> {
    // the url
    const url = resolve(aBaseUrl, aReference.escapedName);
    // make the request
    return rxGetJson(url).pipe(mergeMap(resp => _getPackageJsonFromResponse(resp, url, aReference)));
}