target-position/lib/index.js

Resolve target names to positions using the Sesame web service.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const cross_fetch_1 = require("cross-fetch");
const xml2js_1 = require("xml2js");
// Base URL for the Sesame query
let BASE_URL = "https://cdsweb.u-strasbg.fr/cgi-bin/nph-sesame/";
// The supported name resolver services, in lower case.
const SUPPORTED_RESOLVERS = ["ned", "simbad", "vizier"];
/**
 * Resolve a target name to a position by means of the Sesame web service.
 *
 * The position is returned as an object with a right ascension (in degrees), a
 * declination (in degrees) and an equinox (as a float).
 *
 * The function accepts an array of resolvers. The order of the array items
 * matters; the resolvers are tried in the order they appear in the array, and
 * the first target position found is returned.
 *
 * A promise is returned. If the target can be resolved, the promise is
 * resolved with the target position. Otherwise it is rejected with an Error.
 *
 * Params:
 * -------
 * targetName: Target name.
 * resolvers: Resolvers, in the order in which they should be tried,
 *
 * Returns:
 * --------
 * A promise which is resolved with the target position (if one is found) or
 * rejected with an Error.
 */
function targetPosition(targetName, resolvers = ["Simbad", "NED", "VizieR"]) {
    return new Promise((resolve, reject) => {
        // Make sure we have a target name without leading or trailing white space
        const trimmedTargetName = (targetName && targetName.trim()) || "";
        // Check that there is a target name
        if (!trimmedTargetName) {
            return reject(new Error("The target name is missing."));
        }
        // Check that all resolvers are supported
        const unsupportedResolvers = resolvers.filter(resolver => SUPPORTED_RESOLVERS.indexOf(resolver.toLowerCase()) === -1);
        if (unsupportedResolvers.length > 0) {
            return reject(new Error(`The following resolver${unsupportedResolvers.length !== 1 ? "s are" : " is"} not supported: ${unsupportedResolvers.join(", ")}. The available resolvers are Simbad, NED and VizieR.`));
        }
        // Use lower case throughout for consistency
        const lowerCaseResolvers = resolvers.map(resolver => resolver.toLowerCase());
        // Check that there is at least one resolver
        if (lowerCaseResolvers.length === 0) {
            return reject(new Error("At least one resolver must be given."));
        }
        // Check that every resolver is included only once
        if (new Set(lowerCaseResolvers).size !== lowerCaseResolvers.length) {
            return reject(new Error("A resolver may be used only once in the array of resolvers."));
        }
        // Encode the target name
        const encodedTargetName = encodeURIComponent(targetName);
        // Get the "code" (such "SNV" or "N") for the selected resolvers
        const resolverCode = lowerCaseResolvers
            .map(resolver => {
            switch (resolver) {
                case "simbad":
                    return "S";
                case "ned":
                    return "N";
                case "vizier":
                    return "V";
                default:
                    return "";
            }
        })
            .join("");
        // Construct the query URL
        const url = `${BASE_URL}/-ox/${resolverCode}?${encodedTargetName}`;
        // Parse the response text
        // (cf https://github.com/github/fetch/issues/203#issuecomment-266034180)
        const parseText = (res) => {
            return new Promise((innerResolve, innerReject) => {
                res
                    .text()
                    .then(text => {
                    innerResolve({
                        ok: res.ok,
                        text
                    });
                })
                    .catch(err => {
                    innerReject(err);
                });
            });
        };
        // Query Sesame
        cross_fetch_1.default(url)
            .then(parseText)
            .then(res => {
            // Handle errors
            if (!res.ok) {
                throw new Error(res.text);
            }
            /* tslint:disable:no-unsafe-any */
            // Extract the target
            xml2js_1.parseString(res.text, (err, root) => {
                const resolver = root.Sesame.Target[0].Resolver;
                if (!resolver || resolver.length === 0) {
                    // No target has been found for the name
                    return resolve(null);
                }
                // Parse the coordinates
                const ra = parseFloat(resolver[0].jradeg);
                const dec = parseFloat(resolver[0].jdedeg);
                if (!isNaN(ra) && !isNaN(dec)) {
                    return resolve({
                        declination: dec,
                        equinox: 2000,
                        rightAscension: ra
                    });
                }
                // We should never get here
                return resolve(null);
            });
        })
            .catch(reject);
    });
}
exports.default = targetPosition;
/**
 * Set the base URL for the Sesame web service.
 *
 * Params:
 * -------
 * url: The base URL for the Sesame web service.
 */
function setMirror(url) {
    BASE_URL = url;
}
exports.setMirror = setMirror;