"use strict";

const net = require("net");
const os = require("os");
const execa = require("execa");

const args = {
  v4: ["-4", "r"],
  v6: ["-6", "r"],
};

const get = family => {
  return execa.stdout("ip", args[family]).then(stdout => {
    let result;

    (stdout || "").trim().split("\n").some(line => {
      const results = /default( via .+?)?( dev .+?)( |$)/.exec(line) || [];
      const gateway = (results[1] || "").substring(5);
      const iface = (results[2] || "").substring(5);
      if (gateway && net.isIP(gateway)) { // default via 1.2.3.4 dev en0
        result = {gateway: gateway, interface: (iface ? iface : null)};
        return true;
      } else if (iface && !gateway) { // default via dev en0
        const interfaces = os.networkInterfaces();
        const addresses = interfaces[iface];
        if (!addresses || !addresses.length) return;

        addresses.some(function(addr) {
          if (addr.family.substring(2) === family && net.isIP(addr.address)) {
            result = {gateway: addr.address, interface: (iface ? iface : null)};
            return true;
          }
        });
      }
    });

    if (!result) {
      throw new Error("Unable to determine default gateway");
    }

    return result;
  });
};

module.exports.v4 = () => get("v4");
module.exports.v6 = () => get("v6");
