Parse multiple .ics feeds into one and create the file and serve it via http.

main.go

package main

import (
	"bufio"
	"crypto/md5"
	"encoding/hex"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/PuloV/ics-golang"
)

// EventParsed ... i just want this warning gone
type EventParsed struct {
	start         time.Time
	end           time.Time
	created       time.Time
	importedId    string
	description   string
	summary       string
	id            string
	wholeDayEvent bool
}

func GetMD5Hash(text string) string {
	hasher := md5.New()
	hasher.Write([]byte(text))
	return hex.EncodeToString(hasher.Sum(nil))
}

func main() {
	parser := ics.New()
	// We are just using this for the timestamp on the served static site
	var lastModified time.Time

	m := make(map[string]EventParsed)

	f, err := os.Create("tmp/output-calendar.ics")
	lastModified = time.Now()

	w := bufio.NewWriter(f)
	// Write the header of the calendar file
	_, err = w.WriteString("BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:icalendar-ruby\r\nCALSCALE:GREGORIAN\r\nBEGIN:VTIMEZONE\r\nTZID:Europe/Vienna\r\nEND:VTIMEZONE\r\n")
	if err != nil {
		log.Print("error while writing file")
	}

	// Parse all our RSS feeds we want to unify
	parserChan := parser.GetInputChan()
	parserChan <- "https://trakt.tv/calendars/premieres.ics?slurm=xxx&countries=au%2Cat%2Cbr%2Cde%2Cnz%2Cgb%2Cus&ratings=10-100"
	parserChan <- "https://trakt.tv/calendars/new-shows.ics?slurm=xxx&countries=au%2Cat%2Cbr%2Cde%2Cnz%2Cgb%2Cus&ratings=10-100"
	parserChan <- "https://trakt.tv/calendars/premieres.ics?slurm=xxx&networks=Netflix"

	outputChan := parser.GetOutputChan()

	// Add all our events to our map. Key is on summary because that way we can take advantage of the maps unique key constraint
	go func() {
		for event := range outputChan {
			m[fmt.Sprintf("%x", md5.Sum([]byte(event.GetSummary())))] = EventParsed{event.GetStart(), event.GetEnd(), event.GetCreated(), fmt.Sprintf("%x", md5.Sum([]byte(event.GetSummary()))), event.GetDescription(), event.GetSummary(), event.GetID(), event.GetWholeDayEvent()}
		}
	}()

	parser.Wait()
	t := time.Now()
	// iterate through all events in our map and add them to the file
	for _, value := range m {
		var datestringStart string
		var dateStringEnd string

		datestring := fmt.Sprintf("%d%02d%02dT%02d%02d%02d", value.start.Year(), value.start.Month(), value.start.Day(), t.Hour(), t.Minute(), t.Second())

		// If there's something close to the end of the month we just move it a few days earlier. This is needed because some calender clients need to have the
		// timestamp in a certain format for events to show up as all day events. Because I don't want to deal with timestamps overlapping month / years etc. it's done
		// this way.
		if value.start.Day() == 30 || value.start.Day() == 31 || value.start.Day() == 29 {
			datestringStart = fmt.Sprintf("%d%02d%02d", value.start.Year(), value.start.Month(), value.start.Day()-1)
			dateStringEnd = fmt.Sprintf("%d%02d%02d", value.start.Year(), value.start.Month(), value.start.Day())
		} else {
			datestringStart = fmt.Sprintf("%d%02d%02d", value.start.Year(), value.start.Month(), value.start.Day())
			dateStringEnd = fmt.Sprintf("%d%02d%02d", value.start.Year(), value.start.Month(), value.start.Day()+1)
		}

		stringEvent := fmt.Sprintf("BEGIN:VEVENT\r\nDTSTAMP:%sZ\r\nUID:%s\r\nDTSTART;TZID=Europe/Vienna:%s\r\nDTEND;TZID=Europe/Vienna:%s\r\nDESCRIPTION:%s\r\nSUMMARY:%s\r\nURL:%s\r\nEND:VEVENT\r\n", datestring, value.importedId, datestringStart, dateStringEnd, value.description, value.summary, "https://example.com")

		_, err = w.WriteString(stringEvent)

		if err != nil {
			log.Print("error")
		}
	}

	// Write the last line of the calender
	_, err = w.WriteString("END:VCALENDAR")
	if err != nil {
		log.Print("error while writing end calendar")
	}

	// Make sure all write operations are cleared
	w.Flush()

	// Serve file via http on localhost
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		handler(w, r, lastModified)
	})

	// Serve static file
	http.HandleFunc("/tmp/", func(w http.ResponseWriter, r *http.Request) {
		http.ServeFile(w, r, r.URL.Path[1:])
	})

	// Listen on localhost
	err = http.ListenAndServe(":9001", nil)
	if err != nil {
		log.Fatal(err)
	}
}

// Render the site
func handler(w http.ResponseWriter, r *http.Request, t time.Time) {
	fmt.Fprintf(w, fmt.Sprintf("<body><h1>Unified Trakt.TV calendar</h1><p>Download .ics file <a href=/tmp/output-calendar.ics>here</a><br>Last updated: %s</body>", t.Format("Mon Jan _2 15:04:05 2006")))
}