stock-ticker/handlers.go

package main

import (
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"net/http"
)

func healthCheckHandleFunc(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Type", "text/plain")
	w.WriteHeader(http.StatusOK)

	fmt.Fprintln(w, "I'm all good!")
}

func stockPriceHandleFunc(apiKey, symbol string, nWeeks int) func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			w.Header().Set("Content-Type", "text/plain")
			w.WriteHeader(http.StatusMethodNotAllowed)

			fmt.Fprintf(w, "ERROR: The method '%s' is not allow at this endpoint.\n", r.Method)

			return
		}

		resp, err := http.Get(fmt.Sprintf(requestURLFormat, symbol, apiKey))
		if err != nil {
			w.Header().Set("Content-Type", "text/plain")
			w.WriteHeader(http.StatusBadGateway)

			fmt.Fprintf(w, "ERROR: Unable to get a response from Alpha Vantage; %v\n", err)

			return
		}
		defer resp.Body.Close()

		decoder := json.NewDecoder(resp.Body)

		var s Stock

		if err := decoder.Decode(&s); err != nil {
			w.Header().Set("Content-Type", "text/plain")
			w.WriteHeader(http.StatusBadGateway)

			fmt.Fprintf(w, "ERROR: Unable to decode the response from Alpha Vantage; %v\n", err)

			return
		}

		if nWeeks > len(s.TimeSeries) {
			nWeeks = len(s.TimeSeries)
		}

		var keys []string

		for k := range s.TimeSeries {
			keys = append(keys, k)
		}

		sort.Sort(sort.Reverse(sort.StringSlice(keys)))

		var b strings.Builder

		b.WriteString(fmt.Sprintf(tableFormat, s.MetaData.Symbol))

		for i := 0; i < nWeeks; i++ {
			b.WriteString(fmt.Sprintf("%s |   %s\n", keys[i], s.TimeSeries[keys[i]].Close))
		}

		w.Header().Set("Content-Type", "text/plain")
		w.WriteHeader(http.StatusOK)

		fmt.Fprintln(w, b.String())
	}
}