1 files changed, 273 insertions, 0 deletions
diff --git a/src/mailinglist/mailinglist.go b/src/mailinglist/mailinglist.go
new file mode 100644
index 0000000..d9bdcc0
--- /dev/null
+++ b/src/mailinglist/mailinglist.go
@@ -0,0 +1,273 @@
+// Package mailinglist manages the list of subscribed emails and allows emailing
+// out to them.
+package mailinglist
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"html/template"
+	"io"
+	"net/url"
+	"strings"
+
+	"github.com/google/uuid"
+	"github.com/mediocregopher/blog.mediocregopher.com/srv/cfg"
+	"github.com/mediocregopher/mediocre-go-lib/v2/mctx"
+	"github.com/tilinna/clock"
+)
+
+var (
+	// ErrAlreadyVerified is used when the email is already fully subscribed.
+	ErrAlreadyVerified = errors.New("email is already subscribed")
+)
+
+// MailingList is able to subscribe, unsubscribe, and iterate through emails.
+type MailingList interface {
+
+	// May return ErrAlreadyVerified.
+	BeginSubscription(email string) error
+
+	// May return ErrNotFound or ErrAlreadyVerified.
+	FinalizeSubscription(subToken string) error
+
+	// May return ErrNotFound.
+	Unsubscribe(unsubToken string) error
+
+	// Publish blasts the mailing list with an update about a new blog post.
+	Publish(postTitle, postURL string) error
+}
+
+// Params are parameters used to initialize a new MailingList. All fields are
+// required unless otherwise noted.
+type Params struct {
+	Store  Store
+	Mailer Mailer
+	Clock  clock.Clock
+
+	// PublicURL is the base URL which site visitors can navigate to.
+	// MailingList will generate links based on this value.
+	PublicURL *url.URL
+}
+
+// SetupCfg implement the cfg.Cfger interface.
+func (p *Params) SetupCfg(cfg *cfg.Cfg) {
+	publicURLStr := cfg.String("ml-public-url", "http://localhost:4000", "URL this service is accessible at")
+
+	cfg.OnInit(func(ctx context.Context) error {
+		var err error
+		*publicURLStr = strings.TrimSuffix(*publicURLStr, "/")
+		if p.PublicURL, err = url.Parse(*publicURLStr); err != nil {
+			return fmt.Errorf("parsing -ml-public-url: %w", err)
+		}
+
+		return nil
+	})
+}
+
+// Annotate implements mctx.Annotator interface.
+func (p *Params) Annotate(a mctx.Annotations) {
+	a["mlPublicURL"] = p.PublicURL
+}
+
+// New initializes and returns a MailingList instance using the given Params.
+func New(params Params) MailingList {
+	return &mailingList{params: params}
+}
+
+type mailingList struct {
+	params Params
+}
+
+var beginSubTpl = template.Must(template.New("beginSub").Parse(`
+Welcome to the Mediocre Blog mailing list! By subscribing to this mailing list
+you are signing up to receive an email everytime a new blog post is published.
+
+In order to complete your subscription please navigate to the following link:
+
+{{ .SubLink }}
+
+This mailing list is built and run using my own hardware and software, and I
+solemnly swear that you'll never receive an email from it unless there's a new
+blog post.
+
+If you did not initiate this email, and/or do not wish to subscribe to the
+mailing list, then simply delete this email and pretend that nothing ever
+happened.
+
+- Brian
+`))
+
+func (m *mailingList) BeginSubscription(email string) error {
+
+	emailRecord, err := m.params.Store.Get(email)
+
+	if errors.Is(err, ErrNotFound) {
+		emailRecord = Email{
+			Email:     email,
+			SubToken:  uuid.New().String(),
+			CreatedAt: m.params.Clock.Now(),
+		}
+
+		if err := m.params.Store.Set(emailRecord); err != nil {
+			return fmt.Errorf("storing pending email: %w", err)
+		}
+
+	} else if err != nil {
+		return fmt.Errorf("finding existing email record: %w", err)
+
+	} else if !emailRecord.VerifiedAt.IsZero() {
+		return ErrAlreadyVerified
+	}
+
+	body := new(bytes.Buffer)
+	err = beginSubTpl.Execute(body, struct {
+		SubLink string
+	}{
+		SubLink: fmt.Sprintf(
+			"%s/mailinglist/finalize?subToken=%s",
+			m.params.PublicURL.String(),
+			emailRecord.SubToken,
+		),
+	})
+
+	if err != nil {
+		return fmt.Errorf("executing beginSubTpl: %w", err)
+	}
+
+	err = m.params.Mailer.Send(
+		email,
+		"Mediocre Blog - Please verify your email address",
+		body.String(),
+	)
+
+	if err != nil {
+		return fmt.Errorf("sending email: %w", err)
+	}
+
+	return nil
+}
+
+func (m *mailingList) FinalizeSubscription(subToken string) error {
+	emailRecord, err := m.params.Store.GetBySubToken(subToken)
+
+	if err != nil {
+		return fmt.Errorf("retrieving email record: %w", err)
+
+	} else if !emailRecord.VerifiedAt.IsZero() {
+		return ErrAlreadyVerified
+	}
+
+	emailRecord.VerifiedAt = m.params.Clock.Now()
+	emailRecord.UnsubToken = uuid.New().String()
+
+	if err := m.params.Store.Set(emailRecord); err != nil {
+		return fmt.Errorf("storing verified email: %w", err)
+	}
+
+	return nil
+}
+
+func (m *mailingList) Unsubscribe(unsubToken string) error {
+	emailRecord, err := m.params.Store.GetByUnsubToken(unsubToken)
+
+	if err != nil {
+		return fmt.Errorf("retrieving email record: %w", err)
+	}
+
+	if err := m.params.Store.Delete(emailRecord.Email); err != nil {
+		return fmt.Errorf("deleting email record: %w", err)
+	}
+
+	return nil
+}
+
+var publishTpl = template.Must(template.New("publish").Parse(`
+A new post has been published to the Mediocre Blog!
+
+{{ .PostTitle }}
+{{ .PostURL }}
+
+If you're interested then please check it out!
+
+If you'd like to unsubscribe from this mailing list then visit the following
+link instead:
+
+{{ .UnsubURL }}
+
+- Brian
+`))
+
+type multiErr []error
+
+func (m multiErr) Error() string {
+	if len(m) == 0 {
+		panic("multiErr with no members")
+	}
+
+	b := new(strings.Builder)
+	fmt.Fprintln(b, "The following errors were encountered:")
+	for _, err := range m {
+		fmt.Fprintf(b, "\t- %s\n", err.Error())
+	}
+
+	return b.String()
+}
+
+func (m *mailingList) Publish(postTitle, postURL string) error {
+
+	var mErr multiErr
+
+	iter := m.params.Store.GetAll()
+	for {
+		emailRecord, err := iter()
+		if errors.Is(err, io.EOF) {
+			break
+
+		} else if err != nil {
+			mErr = append(mErr, fmt.Errorf("iterating through email records: %w", err))
+			break
+
+		} else if emailRecord.VerifiedAt.IsZero() {
+			continue
+		}
+
+		body := new(bytes.Buffer)
+		err = publishTpl.Execute(body, struct {
+			PostTitle string
+			PostURL   string
+			UnsubURL  string
+		}{
+			PostTitle: postTitle,
+			PostURL:   postURL,
+			UnsubURL: fmt.Sprintf(
+				"%s/mailinglist/unsubscribe?unsubToken=%s",
+				m.params.PublicURL.String(),
+				emailRecord.UnsubToken,
+			),
+		})
+
+		if err != nil {
+			mErr = append(mErr, fmt.Errorf("rendering publish email template for %q: %w", emailRecord.Email, err))
+			continue
+		}
+
+		err = m.params.Mailer.Send(
+			emailRecord.Email,
+			fmt.Sprintf("Mediocre Blog - New Post! - %s", postTitle),
+			body.String(),
+		)
+
+		if err != nil {
+			mErr = append(mErr, fmt.Errorf("sending email to %q: %w", emailRecord.Email, err))
+			continue
+		}
+	}
+
+	if len(mErr) > 0 {
+		return mErr
+	}
+
+	return nil
+}