import RSS from "rss";
import axios from "axios";
import fs from 'fs';
import path from 'path';

const API_URL = "https://aviationweather.gov/api/data/";
const METAR_SERVICE = "metar";
const generatorURL = "https://git.entropic.pro/Aiden/metar-rss";

let defaultConfig = {
    "outputdir": "/var/www/weather",
    "icaos": ["KJFK"],
    "siteurl": "https://example.com",
    "rss-baseurl": "https://example.com/weather",
    "check-interval": 10,
    "loglevel": 4
};
/** Load config file */
const configFile = "./config.json";
let configData;
try {
    configData = JSON.parse(fs.readFileSync(configFile));
} catch (err) {
    console.error(err);
    console.warn("Unable to read config file, using defaults");
    configData = defaultConfig;
}

/** Verify config data **/
if (Number(configData["loglevel"]) == NaN) {
    console.warn("loglevel is not a number, using " + defaultConfig["loglevel"]);
    configData["loglevel"] = defaultConfig["loglevel"];
}
const loglevel = Number(configData["loglevel"]);

try {
    if (!fs.lstatSync(configData["outputdir"]).isDirectory()) {
        if (loglevel >= 4) console.warn("outputdir is not a directory, using " + defaultConfig["outputdir"]);
        configData["outputdir"] = defaultConfig["outputdir"];
    }
} catch (err) {
    if (loglevel >= 3) console.error(err);
    if (loglevel >= 4) console.warn("error finding outputdir, using " + defaultConfig["outputdir"]);
    configData["outputdir"] = defaultConfig["outputdir"];
}
const outputDir = configData["outputdir"];

if (!Array.isArray(configData["icaos"])) {
    if (loglevel >= 4) console.warn("icao config must be an array of ICAO codes, using default");
    configData["icaos"] = defaultConfig["icaos"];
}
const icaos = configData["icaos"];

try {
    new URL(configData["siteurl"]);
} catch (err) {
    if (loglevel >= 4) console.warn("siteurl is not a valid URL, using " + defaultConfig["siteurl"]);
    configData["siteurl"] = defaultConfig["siteurl"];
}
const siteURL = new URL(configData["siteurl"]);

try {
    new URL(configData["rss-baseurl"]);
} catch (err) {
    if (loglevel >= 4) console.warn("rss-baseurl is not a valid URL, using " + defaultConfig["rss-baseurl"]);
    configData["rss-baseurl"] = defaultConfig["rss-baseurl"];
}
const rssBaseURL = new URL(configData["rss-baseurl"]);

if (Number(configData["check-interval"]) == NaN) {
    if (loglevel >= 4) console.warn("check-interval is NaN, using " + defaultConfig["check-interval"] + " minutes.");
    configData["check-interval"] = defaultConfig["check-interval"];
}
const checkInterval = Number(configData["check-interval"]) * 1000 * 60;


/** Start Service **/
checkMetar(); //Inital check run
const metarCheckJob = setInterval(checkMetar, checkInterval); //Run the check every interval

/**
 * Pulls the current metar and adds it to the feed if it is new
 */
function checkMetar() {
    for (let i = 0; i < icaos.length; i++) {
        let icao = icaos[i];
        if (loglevel >= 7) console.log("Checking METAR for " + icao);
        getMetar(icao).then(res => {
            let metarFile = icao+"-metars.json";
            let metars = [];
            if (fs.existsSync(metarFile)) 
                metars = JSON.parse(fs.readFileSync(icao+"-metars.json"))["data"];

            if (res.data != metars[0]) {
                if (loglevel >= 6) console.log("New METAR: " + res.data);
                metars.unshift(res.data);
                if (metars.length > 20) metars.pop();
                fs.writeFileSync(metarFile, JSON.stringify({"data": metars}));

                let items = [];
                for (let i = 0; i < metars.length; i++) {
                    if (newMetar(metars[i]) != undefined)
                        items.push(newMetar(metars[i]));
                }
                
                let outputPath = path.join(METAR_SERVICE, icao);
                writeFeed(generateFeed(METAR_SERVICE, icao, items, outputPath), outputPath);
            }
        });
    }
}

/**
 * Adds a new METAR to the given RSS Feed
 * @param {RSS} rss - RSS Feed to add the entry to
 * @param {String} metar - metar data to add
 * @returns {Object} - Object of RSS Item Data
 */
function newMetar(metar)  {
    let metarSplit = metar.split(" ");
    let date = new Date(Date.now());
    let eventDate = new Date(Date.UTC(date.getFullYear(), date.getMonth(), Number(metarSplit[2].substring(0,2)), Number(metarSplit[2].substring(2,4)), Number(metarSplit[2].substring(4,6))));

    let item =  {
        title: metarSplit[0] + " " + metarSplit[1] + " " + metarSplit[2],
        description: metar,
        url: API_URL + METAR_SERVICE,
        guid: metarSplit[1] + metarSplit[2],
        date: eventDate
    };
    return item
}

/**
 * Pulls METAR data from the API
 * @param {String} icao ICAO Airport Code
 * @returns Axios generated GET Request Response
 */
function getMetar(icao) {
    let requestURL = API_URL + METAR_SERVICE + "?ids=" + icao;
    return axios.get(requestURL);
}

/**
 * Generates and populates a feed for the given details
 * @param {String} service eg. "metar"
 * @param {String} icao ICAO Airpot Code
 * @param {Array} items Array of Objects containing RSS item details
 * @param {String} outputPath path for this Service + ICAO
 * @returns {RSS} RSS Feed with populated items
 */
function generateFeed(service, icao, items, outputPath) {
    let feedURL = new URL(rssBaseURL);
    feedURL.pathname = path.join(feedURL.pathname, outputPath, "rss.xml");

    let feedOptions = {
        title: icao + " " + service,
        description: service + " feed for " + icao + " Airport",
        feed_url: feedURL,
        site_url: siteURL,
        generator: generatorURL
    }
    let feed = new RSS(feedOptions);

    for (let i = 0; i < items.length; i++) {
        feed.item(items[i]);
    }

    return feed;
}

/**
 * Writes the given RSS feed to the specified file
 * @param {RSS} rss - RSS Feed to Write
 * @param {String} outputPath path for this Service + ICAO
 */
function writeFeed(rss, outputPath) {
    let xmlFeed = rss.xml({indent: true})
    let fullPath = path.join(outputDir, outputPath);
    let fullPathFile = path.join(fullPath, "rss.xml");

    if (!fs.existsSync(fullPath)){
        fs.mkdirSync(fullPath, { recursive: true });
    }

    try {
        fs.writeFileSync(fullPathFile, xmlFeed);
    } catch(err) {
        console.error(err);
    }
}