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"

	"github.com/pelletier/go-toml/v2"
	"github.com/russross/blackfriday/v2"
)

// ------------- Api configs -------------
type ApiConfig struct {
	BatchSize int    `toml:"batch_size"`
	TestEmail string `toml:"test_email"`
	HMC       struct {
		ApiUrl       string `toml:"api_url"`
		SharedSecret string `toml:"shared_secret"`
		City         string `toml:"city"`
	} `toml:"hmc"`
	Postmark struct {
		ServerToken   string `toml:"server_token"`
		ApiUrl        string `toml:"api_url"`
		TemplateId    int    `toml:"template_id"`
		SenderName    string `toml:"sender_name"`
		SenderEmail   string `toml:"sender_email"`
		MessageStream string `toml:"message_stream"`
	} `toml:"postmark"`
}

// 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 {
	configFile := "app.toml"
	data, err := os.ReadFile(configFile)
	if err != nil {
		fmt.Println("Error reading TOML file:", err)
		os.Exit(1)
	}

	config := ApiConfig{}
	if err := toml.Unmarshal(data, &config); err != nil {
		fmt.Println("Error unmarshaling TOML:", err)
		os.Exit(1)
	}
	return config
}

func ParseArguments(rawArgs string) map[string]string {
	pairs := strings.Split(rawArgs, "&")
	result := make(map[string]string)
	for _, pair := range pairs {
		key_val := strings.Split(pair, "=")
		if len(key_val) != 2 {
			log.Fatalf("Cannot parse argument %v\n", pair)
		}
		result[key_val[0]] = key_val[1]
	}
	return result
}

/*
 * This is taken directly from the https://git.handmadecities.com/meetups/meetupinvite2000 repo
 * Although I have added the blackfriday processing to it rather than doing it separately.
 */
func parseMailFile(contents string) (subject string, body string, valid bool) {
	/* Remove leading and trailing newlines */
	/* *** */
	contents = strings.TrimSpace(contents)
	lines := strings.Split(contents, "\n")

	/* Check if there is at least one line */
	/* *** */
	if len(lines) == 0 {
		return "", "", false
	}

	/* Check if the first line is a title with the '#' Markdown symbol */
	/* *** */
	if strings.HasPrefix(lines[0], "#") { // Extract subject without the '#' symbol and leading/trailing spaces
		subject = strings.TrimSpace(strings.TrimPrefix(lines[0], "#"))
	} else {
		// If the first line is not a title, return an error
		return "", "", false
	}

	/* Concatenate the remaining lines to form the body */
	/* *** */
	body = strings.Join(lines[1:], "\n")

	/* Check if the body is not empty */
	/* *** */
	if body == "" {
		return "", "", false
	}

	html := blackfriday.Run([]byte(body))

	/* If all checks pass, set valid to true */
	/* *** */
	return subject, string(html), true
}

func GetMailingList(cfg ApiConfig) []string {
	type EmailsResonse struct {
		Emails []string `json:"emails"`
	}
	body := []byte(fmt.Sprintf("{\"city\": \"%s\"}", cfg.HMC.City))
	req, err := http.NewRequest("POST", cfg.HMC.ApiUrl, bytes.NewBuffer(body))
	if err != nil {
		panic(err)
	}

	req.Header.Add("Content-Type", "application/json")
	req.Header.Add("Authorization", cfg.HMC.SharedSecret)

	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)
	}
	return response.Emails
}

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

	// 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("%v %v", 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("%v %v", 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()
		arguments := ParseArguments(string(body))

		decoded_markdown, err := url.QueryUnescape(arguments["email_input"])
		if err != nil {
			panic(err)
		}

		subject, html_body, valid := parseMailFile(decoded_markdown)
		if !valid {
			log.Print("Failed to parse the provided markdown")
			return
		}

		// Return a response to HTMX
		model := PostmarkTemplateModel{
			Name:    apiConfig.Postmark.SenderName,
			Email:   apiConfig.Postmark.SenderEmail,
			Body:    html_body,
			Subject: subject, // TODO(jack): Get from user input on page
		}

		renderedEmail := renderPostmarkTemplate(apiConfig, postmarkTemplate, model)

		// Render the priview to a file so that we can include it as an Iframe as the rendered HTML is a full document.
		err = os.WriteFile("./static/preview.html", []byte(renderedEmail.Html), 0666)
		if err != nil {
			log.Panicf("Failed to write file %v", err)
		}
		templates.ExecuteTemplate(w, "mail_content", renderedEmail.Subject)
	})

	// 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) {
		log.Printf("%v %v", r.Method, r.URL)
		mailing_list := GetMailingList(apiConfig)
		templates.ExecuteTemplate(w, "mailing_list", mailing_list)
	})

	mux.HandleFunc("/send_email", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("%v %v", 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()

		body_string := string(body)
		arguments := ParseArguments(body_string)
		fmt.Printf("%v\n", arguments)

		var recipients []string
		if arguments["destination"] == "test" {
			recipients = []string{apiConfig.TestEmail}
		} else if arguments["destination"] == "mailing_list" {
			recipients = GetMailingList(apiConfig)
		} else {
			panic("unknown destination in arguments")
		}

		decoded_markdown, err := url.QueryUnescape(arguments["email_input"])
		if err != nil {
			panic(err)
		}

		subject, html_body, valid := parseMailFile(decoded_markdown)
		if !valid {
			log.Print("Failed to parse the provided markdown")
			return
		}
		sendBatchWithTemplate(apiConfig, html_body, subject, recipients)
	})

	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)
}