From 8c5f152de896f3d79c95fe3ede91331a9e94e383 Mon Sep 17 00:00:00 2001
From: Asaf Gartner <asaf@handmade.network>
Date: Wed, 13 Sep 2023 00:15:40 +0300
Subject: [PATCH] Newsblaster using the Postmark template batch API

---
 .gitignore |   2 +
 go.mod     |  10 ++
 go.sum     |  10 ++
 main.go    | 393 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 415 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 go.mod
 create mode 100644 go.sum
 create mode 100644 main.go

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..997ac9c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+config.json
+data/
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..8ac3355
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,10 @@
+module git.handmade.network/hmn/newsblaster2000
+
+go 1.18
+
+require github.com/spf13/cobra v1.7.0
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..f3366a9
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,10 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.7.0 h1:hyqWnYt1ZQShIddO5kBpj3vu05/++x6tJ6dg8EC572I=
+github.com/spf13/cobra v1.7.0/go.mod h1:uLxZILRyS/50WlhOIKD7W6V5bgeIt+4sICxh6uRMrb0=
+github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
+github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..66a16e7
--- /dev/null
+++ b/main.go
@@ -0,0 +1,393 @@
+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 the subject.
+		* The rest of the file will be used as the 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()
+}