covid.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"sort"
	"strconv"
	"time"
)

func check(err error) {
	if err != nil {
		fmt.Printf("%+v", err)
		os.Exit(1)
	}
}

type payload struct {
	Features []struct {
		Attributes struct {
			AnzahlFall int64 `json:"AnzahlFall"`
			Meldedatum int64 `json:"Meldedatum"`
		} `json:"attributes"`
	} `json:"features"`
}

type im struct {
	ts     time.Time
	number int64
}

const (
	All    = "1=1"
	Bayern = "Bundesland='Bayern'"
	BaWü   = "Bundesland='Baden-Württemberg'"
	Hessen = "Bundesland='Hessen'"
	Berlin = "Bundesland='Berlin'"
)

func main() {
	var results = make(map[time.Time]int64)
	var offset int64

	var where = All

	p := fetch(offset, where)
	for len(p.Features) >= 2000 {
		offset = offset + 2000
		for _, f := range p.Features {
			ts := time.Unix(f.Attributes.Meldedatum/1000, 0).Round(time.Hour * 24)

			if _, found := results[ts]; found {
				results[ts] += f.Attributes.AnzahlFall
			} else {
				results[ts] = f.Attributes.AnzahlFall
			}
		}
		p = fetch(offset, where)
	}

	var interim []im
	for ts, count := range results {
		interim = append(interim, im{ts: ts, number: count})
	}

	sort.Slice(interim, func(i, j int) bool {
		return interim[i].ts.Before(interim[j].ts)
	})

	fmt.Printf("Date, New Cases, Total Cases, Change, Doubles Every\n")
	var total int64
	for _, item := range interim {
		change := (float64(total-total+item.number) / float64(total)) * 100.0
		total += item.number
		fmt.Printf("%s, %d, %d, %.4f%%, %.2f days\n", item.ts.Format("02/01/2006"), item.number, total, change, 100/change)
	}
}

func fetch(offset int64, where string) *payload {
	u, err := url.Parse("https://services7.arcgis.com/mOBPykOjAyBO2ZKk/arcgis/rest/services/RKI_COVID19/FeatureServer/0/query?f=json&where=1%%3D1&returnGeometry=false&spatialRel=esriSpatialRelIntersects&outFields=ObjectId%%2CAnzahlFall%%2CMeldedatum&orderByFields=Meldedatum%%20asc&cacheHint=true")
	check(err)

	q := u.Query()
	q.Set("resultOffset", strconv.FormatInt(offset, 10))
	q.Set("resultRecordCount", strconv.FormatInt(offset+2000, 10))
	q.Set("where", where)
	u.RawQuery = q.Encode()

	res, err := http.DefaultClient.Get(fmt.Sprintf("https://services7.arcgis.com/mOBPykOjAyBO2ZKk/arcgis/rest/services/RKI_COVID19/FeatureServer/0/query?f=json&where=1%%3D1&returnGeometry=false&spatialRel=esriSpatialRelIntersects&outFields=ObjectId%%2CAnzahlFall%%2CMeldedatum&orderByFields=Meldedatum%%20asc&resultOffset=%d&resultRecordCount=%d&cacheHint=true", offset, offset+2000))
	check(err)
	defer res.Body.Close()
	if res.StatusCode != 200 {
		check(errors.New("expected status code 200"))
	}
	var p payload
	check(json.NewDecoder(res.Body).Decode(&p))
	return &p
}