main.go

package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/gocolly/colly/v2"
)

type Contest struct {
	Name      string `json:"name"`
	Duration  int    `json:"duration"`
	StartTime int64  `json:"startTime"`
	Link      string `json:"link"`
}

func home(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	contests := getUpcomingContests()
	encoder := json.NewEncoder(w)
	encoder.Encode(contests)
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", home)

	fmt.Println("Listening on port 8000...")
	http.ListenAndServe(":8000", mux)
}

func getUpcomingContests() []Contest {
	c := colly.NewCollector()
	contests := make([]Contest, 0)

	c.OnRequest(func(r *colly.Request) {
		fmt.Println("Visiting", r.URL)
	})

	c.OnHTML("div[id=contest-table-upcoming] > div.panel > div.table-responsive > table.table > tbody", func(h *colly.HTMLElement) {
		h.ForEach("tr", func(i int, h *colly.HTMLElement) {
			name := h.DOM.Find(":nth-child(2) > a").Text()

			baseURL := "https://atcoder.jp"
			contestPath, exists := h.DOM.Find(":nth-child(2) > a").Attr("href")
			if !exists {
				fmt.Println("href attribute does not exist")
			}
			link := baseURL + contestPath

			datetime := h.DOM.Find(":nth-child(1) > a > time.fixtime-full").Text()
			// reference time written in datetime's format for later parsing
			datetimeLayout := "2006-01-02 15:04:05-0700"
			t, err := time.Parse(datetimeLayout, datetime)
			if err != nil {
				fmt.Println(err)
			}
			startTime := t.Unix()

			durationString := h.DOM.ChildrenFiltered(":nth-child(3)").Text()
			duration := parseDuration(durationString)

			// initialize Contest struct var with parsed values
			contest := Contest{
				Name:      name,
				Duration:  duration,
				StartTime: startTime,
				Link:      link,
			}

			contests = append(contests, contest)
		})
	})

	c.Visit("https://atcoder.jp/contests/")

	return contests
}

// converts duration specified in HH:MM to seconds
func parseDuration(durationString string) int {
	parts := strings.Split(durationString, ":")
	hours, err := strconv.Atoi(parts[0])
	if err != nil {
		fmt.Println("Couldn't parse hours")
	}

	minutes, err := strconv.Atoi(parts[1])
	if err != nil {
		fmt.Println("Couldn't parse minutes")
	}

	duration := hours*60*60 + minutes*60
	return duration
}