newsblaster2000/main.go

package main

import (
	"bytes"
	"crypto/sha1"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/spf13/cobra"
)

type Config struct {
	PostmarkAPIToken      string
	PostmarkTemplateAlias string
	PostmarkMessageStream string
	TestEmailAddress      string
	FromAddress           string
	FromName              string
	BatchSize             int
}

func verifyConfig() (Config, bool) {
	defaultConfig := Config{BatchSize: 500} // NOTE(asaf): Max 500 messages per batch: https://postmarkapp.com/developer/api/templates-api#send-batch-with-templates
	defaultContents, err := json.MarshalIndent(&defaultConfig, "", "  ")
	contents, err := os.ReadFile("config.json")
	if err != nil {
		contents = defaultContents
		if errors.Is(err, fs.ErrNotExist) {
			os.WriteFile("config.json", contents, 0666)
			fmt.Printf("Created config.json file.\n")
		} else {
			fmt.Printf("Error while reading config.json: %v\n", err)
		}
	}

	var config Config
	err = json.Unmarshal(contents, &config)

	valid := true
	if config.PostmarkAPIToken == "" {
		fmt.Printf("Postmark API token missing in config.\n")
		valid = false
	}
	if config.PostmarkTemplateAlias == "" {
		fmt.Printf("Postmark template alias missing in config.\n")
		valid = false
	}
	if config.PostmarkMessageStream == "" {
		fmt.Printf("Postmark message stream missing in config.\n")
		valid = false
	}
	if config.TestEmailAddress == "" {
		fmt.Printf("Test email address is missing in config.\n")
		valid = false
	}
	if config.FromAddress == "" {
		fmt.Printf("FromAddress is missing in config. That's the return address that will appear on the email.\n")
		valid = false
	}
	if config.FromName == "" {
		fmt.Printf("FromName is missing in config. That's the name that will appear next to the 'from' field in the email.\n")
		valid = false
	}
	if !valid {
		fmt.Printf("Please edit config.json and rerun.\n")
	}

	return config, valid
}

func parseMailFile(contents string) (subject string, body string, valid bool) {
	valid = false
	parts := strings.SplitN(string(contents), "\n", 2)
	if len(parts) < 2 {
		fmt.Printf("File does not contain subject and body\n")
		return
	}
	subject = strings.TrimSpace(parts[0])
	rawBody := strings.Trim(parts[1], "\n")
	if subject == "" {
		fmt.Printf("Subject is empty\n")
		return
	}
	body = rawBody
	valid = true
	return
}

func sendTest(newsletterFile string) {
	cfg, valid := verifyConfig()
	if !valid {
		return
	}
	audience := []string{cfg.TestEmailAddress}
	contents, err := os.ReadFile(newsletterFile)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find file %s\n", newsletterFile)
		} else {
			fmt.Printf("Error reading file %s: %v\n", newsletterFile, err)
		}
		return
	}
	subject, body, valid := parseMailFile(string(contents))
	if !valid {
		return
	}

	trackingFile := newsletterFile + ".test.track"
	logFile := newsletterFile + "." + time.Now().Format("20060102T150405") + ".test.log"
	os.Truncate(trackingFile, 0)

	blastMail(cfg, logFile, trackingFile, audience, subject, body)

	sha1File := newsletterFile + ".sha1"
	sum := sha1.Sum(contents)
	sumString := fmt.Sprintf("%x", sum)
	os.WriteFile(sha1File, []byte(sumString), 0666)
}

func sendNews(audienceFile string, newsletterFile string) {
	cfg, valid := verifyConfig()
	if !valid {
		return
	}
	contents, err := os.ReadFile(newsletterFile)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find file %s\n", newsletterFile)
		} else {
			fmt.Printf("Error reading file %s: %v\n", newsletterFile, err)
		}
		return
	}
	subject, body, valid := parseMailFile(string(contents))
	if !valid {
		return
	}

	audienceContents, err := os.ReadFile(audienceFile)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find file %s\n", audienceFile)
		} else {
			fmt.Printf("Error reading file %s: %v\n", audienceFile, err)
		}
		return
	}

	audience := strings.Split(string(audienceContents), "\n")
	for i, a := range audience {
		audience[i] = strings.TrimSpace(a)
	}

	sha1File := newsletterFile + ".sha1"
	sum := sha1.Sum(contents)
	sumString := fmt.Sprintf("%x", sum)

	sha1, err := os.ReadFile(sha1File)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find hash file for this newsletter. Make sure you run the test command first!\n")
		} else {
			fmt.Printf("Error reading file %s: %v\n", audienceFile, err)
		}
		return
	}
	if string(sha1) != sumString {
		fmt.Printf("Hash doesn't match. Did you change the newsletter's contents? Rerun the test command please!\n")
		return
	}

	trackingFile := newsletterFile + ".track"
	logFile := newsletterFile + "." + time.Now().Format("20060102T150405") + ".log"

	blastMail(cfg, logFile, trackingFile, audience, subject, body)
}

func blastMail(cfg Config, logFile string, trackingFile string, audience []string, subject string, body string) {
	log, err := os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
	if err != nil {
		fmt.Printf("Can't open log file %s: %v\n", logFile, err)
		return
	}
	defer log.Close()
	contents, err := os.ReadFile(trackingFile)
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		fmt.Printf("Failed to read tracking file %s: %v\n", trackingFile, err)
		return
	}
	var sentToAddresses []string
	existingRecipients := strings.Split(string(contents), "\n")
	for _, e := range existingRecipients {
		if e != "" {
			sentToAddresses = append(sentToAddresses, e)
		}
	}

	var group []string
	for _, a := range audience {
		if a == "" {
			continue
		}
		found := false
		for _, s := range sentToAddresses {
			if a == s {
				found = true
				break
			}
		}
		if !found {
			group = append(group, a)
			if len(group) == cfg.BatchSize {
				results, err := sendMail(cfg, group, subject, body)
				if err != nil {
					fmt.Printf("Error while sending mail: %v\n", err)
					return
				}
				sentToAddresses = append(sentToAddresses, group...)
				os.WriteFile(trackingFile, []byte(strings.Join(sentToAddresses, "\n")), 0666)
				for i, res := range results {
					log.WriteString(fmt.Sprintf("%s: %s\n", group[i], res.Message))
				}
				group = group[0:0]
			}
		}
	}
	if len(group) > 0 {
		results, err := sendMail(cfg, group, subject, body)
		if err != nil {
			fmt.Printf("Error while sending mail: %v\n", err)
			return
		}
		sentToAddresses = append(sentToAddresses, group...)
		os.WriteFile(trackingFile, []byte(strings.Join(sentToAddresses, "\n")), 0666)
		for i, res := range results {
			log.WriteString(fmt.Sprintf("%s: %s\n", group[i], res.Message))
		}
	}
}

var postmarkClient = http.Client{}

type PostmarkTemplateModel struct {
	Subject string `json:"subject"`
	Body    string `json:"content_body"`
}

type PostmarkTemplateMessage struct {
	From          string                `json:"From"`
	To            string                `json:"To"`
	TemplateAlias string                `json:"TemplateAlias"`
	TemplateModel PostmarkTemplateModel `json:"TemplateModel"`
	TrackOpens    bool                  `json:"TrackOpens"`
	TrackLinks    string                `json:"TrackLinks"`
	MessageStream string                `json:"MessageStream"`
}

type PostmarkBatchWithTemplateBody struct {
	Messages []PostmarkTemplateMessage `json:"Messages"`
}

type PostmarkBatchResult struct {
	ErrorCode int    `json:"ErrorCode"`
	Message   string `json:"Message"`
}

func sendMail(cfg Config, recipients []string, subject, contentHtml string) ([]PostmarkBatchResult, error) {
	from := cfg.FromAddress
	if cfg.FromName != "" {
		from = fmt.Sprintf("%s <%s>", cfg.FromName, cfg.FromAddress)
	}
	body := PostmarkBatchWithTemplateBody{}
	for _, r := range recipients {
		body.Messages = append(body.Messages, PostmarkTemplateMessage{
			From:          from,
			To:            r,
			TemplateAlias: cfg.PostmarkTemplateAlias,
			TemplateModel: PostmarkTemplateModel{
				Subject: subject,
				Body:    contentHtml,
			},
			TrackOpens:    false,
			TrackLinks:    "None",
			MessageStream: cfg.PostmarkMessageStream,
		})
	}

	reqBody, err := json.Marshal(&body)
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequest(http.MethodPost, "https://api.postmarkapp.com/email/batchWithTemplates", bytes.NewReader(reqBody))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", "application/json")
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-Postmark-Server-Token", cfg.PostmarkAPIToken)
	res, err := postmarkClient.Do(req)
	if err != nil {
		return nil, err
	}
	var results []PostmarkBatchResult
	resBody, err := io.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		return nil, err
	}
	if res.StatusCode != 200 {
		return nil, fmt.Errorf("Bad response from postmark: %d", res.StatusCode)
	}
	err = json.Unmarshal(resBody, &results)
	if err != nil {
		fmt.Printf("Batch sent successfully, but failed to parse response from postmark.\n")
		return nil, nil
	}
	return results, nil
}

func main() {
	cmd := &cobra.Command{
		Use:   "newsblaster2000",
		Short: "NewsBlaster2000",
		Run: func(cmd *cobra.Command, args []string) {
			_, valid := verifyConfig()
			if valid {
				fmt.Printf(`Instructions:
	1. Create an audience file
		* Name it whatever you want.
		* The file should be a list of email addresses. One email per line.

	2. Create an email file
		* Name it whatever you want.
		* The first line of the file will be used as {{ subject }} in the postmark template.
		* The rest of the file will be used as {{{ content_body }}}.
		* Newlines between the subject and body will be removed.

	3. Do a test run
		* go run . test [email filename]
		* You must send the test email before blasting it to everyone.
		* If you modify the email file after testing, you must test again. Otherwise NewsBlaster2000 will complain.

	4. Start blasting
		* go run . blast [audience file] [email file]
		* Will batch send using the Postmark batch API.
		* Will produce a .track file that will list all email addresses that we attempted to send to.
		* In case of error, you can blast again. All emails listed in the .track file will be skipped.
		* Will produce a .log file with information received back from Postmark.
`)
			}
		},
	}

	testCmd := &cobra.Command{
		Use:   "test [email file]",
		Short: "Send a test mail to the test address specified in the config",
		Run: func(cmd *cobra.Command, args []string) {
			if len(args) < 1 {
				cmd.Usage()
				os.Exit(1)
			}
			newsletterFile := args[0]
			sendTest(newsletterFile)
		},
	}

	blastCmd := &cobra.Command{
		Use:   "blast [audience file] [email file]",
		Short: "Blast your newsletter to your followers",
		Run: func(cmd *cobra.Command, args []string) {
			if len(args) < 2 {
				cmd.Usage()
				os.Exit(1)
			}
			audienceFile := args[0]
			newsletterFile := args[1]
			sendNews(audienceFile, newsletterFile)
		},
	}

	cmd.AddCommand(testCmd)
	cmd.AddCommand(blastCmd)

	cmd.Execute()
}