HMC_Host_Dashboard/main.go

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"strings"
	"time"

	"gopkg.in/ini.v1"
)

// ------------- Api configs -------------
type DefaultSectionConfig struct {
	Live       bool
	TestEmail  string
	SenderName string
}

type HMCConfig struct {
	ApiSecret string
	ApiUrl    string
	City      string
}

type PostmarkConfig struct {
	ServerToken   string
	ApiUrl        string
	TemplateId    int
	SenderEmail   string
	MessageStream string
}

type ApiConfig struct {
	Default  DefaultSectionConfig
	Hmc      HMCConfig
	Postmark PostmarkConfig
}

// ------------- HMC Api Responses -------------
type EmailsResonse struct {
	Emails []string `json:"emails"`
}

// Load the HMCsend-email app.ini and store the values in a structure, some of the keys in here
// we probably don't actualy care about for this usage.
func loadConfig() ApiConfig {
	// Read the config file and get the HMC api settings
	config, err := ini.Load("app.ini")
	if err != nil {
		panic(err)
	}

	defSection := config.Section("DEFAULT")
	def := DefaultSectionConfig{
		Live:       defSection.Key("LIVE").MustBool(),
		TestEmail:  defSection.Key("TEST_EMAIL").String(),
		SenderName: defSection.Key("SENDER_NAME").String(),
	}

	hmcSection := config.Section("hmc")
	hmc := HMCConfig{
		ApiSecret: hmcSection.Key("SHARED_SECRET").String(),
		ApiUrl:    hmcSection.Key("API_URL").String(),
		City:      hmcSection.Key("CITY").String(),
	}

	postmarkSection := config.Section("postmark")
	postmark := PostmarkConfig{
		ServerToken:   postmarkSection.Key("SERVER_TOKEN").String(),
		ApiUrl:        postmarkSection.Key("API_URL").String(),
		TemplateId:    postmarkSection.Key("TEMPLATE_ID").MustInt(),
		SenderEmail:   postmarkSection.Key("SENDER_EMAIL").String(),
		MessageStream: postmarkSection.Key("MESSAGE_STREAM").String(),
	}

	return ApiConfig{
		Default:  def,
		Hmc:      hmc,
		Postmark: postmark,
	}
}

func main() {
	apiConfig := loadConfig()
	postmarkTemplate := getPostmarkTemplate(apiConfig.Postmark)

	// Prepare the go html templates and static file server
	templates := template.Must(template.ParseGlob("templates/*.html"))
	static_files := http.FileServer(http.Dir("static/"))

	mux := http.NewServeMux()
	mux.Handle("/static/", http.StripPrefix("/static/", static_files))

	// The base endpoint for the web-app simply renders the index tempalte
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("Hello '%v %v' handler", r.Method, r.URL)
		templates.ExecuteTemplate(w, "index", nil)
	})

	// Endpoint called when editing the text area and posts to the postmark api to generate the email preview
	mux.HandleFunc("/mail-content", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("Hello '%v %v' handler", r.Method, r.URL)
		body, err := io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		defer r.Body.Close()
		textarea_content := string(body)
		decoded_textarea, err := url.QueryUnescape(textarea_content)
		if err != nil {
			panic(err)
		}
		email_content, _ := strings.CutPrefix(decoded_textarea, "email_input=")

		// Return a response to HTMX
		model := PostmarkTemplateModel{
			Name:    apiConfig.Default.SenderName,
			Email:   apiConfig.Postmark.SenderEmail,
			Body:    email_content,
			Subject: "This is a test subject", // TODO(jack): Get from user input on page
		}
		w.Write([]byte(renderPostmarkTemplate(apiConfig.Postmark, postmarkTemplate, model)))
	})

	// Endpoint called on load or button press by htmx to retrieve and populate the mailing list
	mux.HandleFunc("/mailing_list", func(w http.ResponseWriter, r *http.Request) {
		body := []byte(fmt.Sprintf("{\"city\": \"%s\"}", apiConfig.Hmc.City))

		req, err := http.NewRequest("POST", apiConfig.Hmc.ApiUrl, bytes.NewBuffer(body))
		if err != nil {
			panic(err)
		}

		req.Header.Add("Content-Type", "application/json")
		req.Header.Add("Authorization", apiConfig.Hmc.ApiSecret)

		client := &http.Client{}
		res, err := client.Do(req)
		if err != nil {
			panic(err)
		}
		defer res.Body.Close()

		response := &EmailsResonse{}
		decode_error := json.NewDecoder(res.Body).Decode(&response)
		if decode_error != nil {
			panic(decode_error)
		}

		templates.ExecuteTemplate(w, "mailing_list", response)
	})

	srv := &http.Server{
		Addr: "0.0.0.0:80",
		// Good practice to set timeouts to avoid Slowloris attacks.
		WriteTimeout: time.Second * 15,
		ReadTimeout:  time.Second * 15,
		IdleTimeout:  time.Second * 60,
		Handler:      mux,
	}

	go func() {
		if err := srv.ListenAndServe(); err != nil {
			log.Println(err)
		}
	}()

	////////////////////////////// Cleanup //////////////////////////////
	c := make(chan os.Signal, 1)
	// We'll accept graceful shutdowns when quit via SIGINT (Ctrl+C)
	// SIGKILL, SIGQUIT or SIGTERM (Ctrl+/) will not be caught.
	signal.Notify(c, os.Interrupt)

	log.Println("Waiting for interrupt")
	// Block until we receive our signal.
	<-c

	// Create a deadline to wait for.
	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	// Defer calling the canclefunction returned from context.WithTimeout
	defer cancel()

	// Doesn't block if no connections, but will otherwise wait
	// until the timeout deadline.
	srv.Shutdown(ctx)

	// Optionally, you could run srv.Shutdown in a goroutine and block on
	// <-ctx.Done() if your application should wait for other services
	// to finalize based on context cancellation.
	log.Println("shutting down")
	os.Exit(0)
}