const head = arr => (arr && arr.length ? arr[0] : undefined);

head([1, 2, 3]); // 1
head([]); // undefined
head(null); // undefined
head(undefined); // undefined

const deepMerge = (a, b, fn) =>
  [...new Set([...Object.keys(a), ...Object.keys(b)])].reduce(
    (acc, key) => ({ ...acc, [key]: fn(key, a[key], b[key]) }),
    {}
  );
  
deepMerge(
  { a: true, b: { c: [1, 2, 3] } },
  { a: false, b: { d: [1, 2, 3] } },
  (key, a, b) => (key === 'a' ? a && b : Object.assign({}, a, b))
);
// { a: false, b: { c: [ 1, 2, 3 ], d: [ 1, 2, 3 ] } }

require("dotenv").config();
const mongoose = require("mongoose");

const db = process.env.MONGO_URI;

const connectDB = async () => {
	try {
	await mongoose.connect(db, {
	useNewUrlParser: true,
	useUnifiedTopology: true,
	useFindAndModify: false,
	useCreateIndex: true
	});

	console.log("MongoDB Connected");
	} catch (err) {
	console.error(err.message);
	}
};

module.exports = connectDB;

const kMeans = (data, k = 1) => {
  const centroids = data.slice(0, k);
  const distances = Array.from({ length: data.length }, () =>
    Array.from({ length: k }, () => 0)
  );
  const classes = Array.from({ length: data.length }, () => -1);
  let itr = true;

  while (itr) {
    itr = false;

    for (let d in data) {
      for (let c = 0; c < k; c++) {
        distances[d][c] = Math.hypot(
          ...Object.keys(data[0]).map(key => data[d][key] - centroids[c][key])
        );
      }
      const m = distances[d].indexOf(Math.min(...distances[d]));
      if (classes[d] !== m) itr = true;
      classes[d] = m;
    }

    for (let c = 0; c < k; c++) {
      centroids[c] = Array.from({ length: data[0].length }, () => 0);
      const size = data.reduce((acc, _, d) => {
        if (classes[d] === c) {
          acc++;
          for (let i in data[0]) centroids[c][i] += data[d][i];
        }
        return acc;
      }, 0);
      for (let i in data[0]) {
        centroids[c][i] = parseFloat(Number(centroids[c][i] / size).toFixed(2));
      }
    }
  }

  return classes;
};
kMeans([[0, 0], [0, 1], [1, 3], [2, 0]], 2); // [0, 1, 1, 0]

//Disclaimer: I do not condone mass web scraping of ESPN websites, and this is just theoretical code that hasn't been used.

//Scrape player stats off of https://www.espn.com/nfl/team/roster/_/name/phi/philadelphia-eagles

//Example player JS object
/*
{
	"shortName": "S. Opeta",
	"name": "Sua Opeta",
	"href": "http://www.espn.com/nfl/player/_/id/3121009/sua-opeta",
	"uid": "s:20~l:28~a:3121009",
	"guid": "dec19157-e984-f981-3724-498281328c97",
	"id": "3121009",
	"height": "6' 4\"",
	"weight": "305 lbs",
	"age": 27,
	"position": "G",
	"jersey": "78",
	"birthDate": "08/15/96",
	"headshot": "https://a.espncdn.com/i/headshots/nfl/players/full/3121009.png",
	"lastName": "Sua Opeta",
	"experience": 4,
	"college": "Weber State"
}
*/

//The page needs to be focused, so you have to put this code in a bookmarklet and click the page before clicking it. Allegedly.
navigator.clipboard.writeText(JSON.stringify(
    window["__espnfitt__"].page.content.roster.groups.flatMap((group)=>{
        return group.athletes.map((athlete)=>{
            //We can assume all football players are above 100 lbs and below 1000 lbs.
            athlete.weight = parseInt(athlete.weight.substring(0,3));
            
            if(athlete.experience == "R") athlete.experience = 0;
            else athlete.experience = parseInt(athlete.experience);

            //We can assume players are at least 1 foot, or under 10 feet tall.
            athlete.inches = 12 * parseInt(athlete.height.substring(0, 1)); //Add feet in inches
            athlete.inches += parseInt(athlete.height.substring(2).replaceAll("\"", "").trim()); //Add remaining inches

            const monthDayYear = athlete.birthDate.split("/");
            athlete.birthMonth = parseInt(monthDayYear[0]);
            athlete.birthDay = parseInt(monthDayYear[1]);
            athlete.birthYear = parseInt(monthDayYear[2]);
            
            //The only really useful stuff we get from this is Height, weight, left handedness, age, position, and birthday
            return athlete;
        });
    })
, null, "\t")).then(null, ()=>{alert("That failed.")});

//Changes all the team links on this page https://www.espn.com/nfl/stats/team to the team's roster for easier scraping
$$("table > tbody > tr > td > div > div > a").forEach((elm)=>{
	elm.setAttribute("href", elm.getAttribute("href").replace("team/", "team/roster/"));
});

const permutations = arr => {
  if (arr.length <= 2) return arr.length === 2 ? [arr, [arr[1], arr[0]]] : arr;
  return arr.reduce(
    (acc, item, i) =>
      acc.concat(
        permutations([...arr.slice(0, i), ...arr.slice(i + 1)]).map(val => [
          item,
          ...val,
        ])
      ),
    []
  );
};
permutations([1, 33, 5]);
// [ [1, 33, 5], [1, 5, 33], [33, 1, 5], [33, 5, 1], [5, 1, 33], [5, 33, 1] ]