go-cart-actor/pkg/order/email.go

package order

import (
	"bytes"
	"context"
	"crypto/tls"
	"embed"
	"encoding/json"
	"fmt"
	htmltmpl "html/template"
	"io/fs"
	"mime"
	"mime/quotedprintable"
	"net"
	"net/mail"
	"net/smtp"
	"os"
	"path/filepath"
	"strings"
	texttmpl "text/template"
	"time"

	"git.k6n.net/mats/go-cart-actor/pkg/flow"
)

// EmailMessage is the rendered mail payload a sender delivers.
type EmailMessage struct {
	From     mail.Address
	To       []mail.Address
	Subject  string
	TextBody string
	HTMLBody string
}

// EmailSender delivers an already-rendered mail and exposes its default sender.
type EmailSender interface {
	Send(ctx context.Context, msg EmailMessage) error
	DefaultFrom() mail.Address
}

// SMTPEmailSenderConfig configures the SMTP mail transport.
type SMTPEmailSenderConfig struct {
	Host        string
	Port        int
	Username    string
	Password    string
	DefaultFrom mail.Address
	Timeout     time.Duration
}

type smtpEmailSender struct {
	host        string
	addr        string
	auth        smtp.Auth
	defaultFrom mail.Address
	timeout     time.Duration
}

// NewSMTPEmailSender returns an SMTP-backed sender. It supports plain SMTP with
// opportunistic STARTTLS, which is the only configured transport for now.
func NewSMTPEmailSender(cfg SMTPEmailSenderConfig) (EmailSender, error) {
	if strings.TrimSpace(cfg.Host) == "" {
		return nil, fmt.Errorf("smtp sender: missing host")
	}
	if cfg.Port <= 0 {
		return nil, fmt.Errorf("smtp sender: invalid port %d", cfg.Port)
	}
	if cfg.Timeout <= 0 {
		cfg.Timeout = 10 * time.Second
	}
	if strings.TrimSpace(cfg.DefaultFrom.Address) == "" {
		return nil, fmt.Errorf("smtp sender: missing default from address")
	}
	s := &smtpEmailSender{
		host:        cfg.Host,
		addr:        net.JoinHostPort(cfg.Host, fmt.Sprintf("%d", cfg.Port)),
		defaultFrom: cfg.DefaultFrom,
		timeout:     cfg.Timeout,
	}
	if cfg.Username != "" {
		s.auth = smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
	}
	return s, nil
}

func (s *smtpEmailSender) DefaultFrom() mail.Address { return s.defaultFrom }

func (s *smtpEmailSender) Send(ctx context.Context, msg EmailMessage) error {
	if strings.TrimSpace(msg.From.Address) == "" {
		return fmt.Errorf("smtp sender: missing from address")
	}
	if len(msg.To) == 0 {
		return fmt.Errorf("smtp sender: missing recipients")
	}
	if strings.TrimSpace(msg.Subject) == "" {
		return fmt.Errorf("smtp sender: missing subject")
	}
	body, err := buildSMTPMessage(msg)
	if err != nil {
		return err
	}

	conn, err := (&net.Dialer{Timeout: s.timeout}).DialContext(ctx, "tcp", s.addr)
	if err != nil {
		return fmt.Errorf("smtp sender: dial %s: %w", s.addr, err)
	}
	defer conn.Close()
	_ = conn.SetDeadline(time.Now().Add(s.timeout))

	client, err := smtp.NewClient(conn, s.host)
	if err != nil {
		return fmt.Errorf("smtp sender: create client: %w", err)
	}
	defer client.Close()

	if ok, _ := client.Extension("STARTTLS"); ok {
		if err := client.StartTLS(&tls.Config{ServerName: s.host, MinVersion: tls.VersionTLS12}); err != nil {
			return fmt.Errorf("smtp sender: starttls: %w", err)
		}
	}
	if s.auth != nil {
		if ok, _ := client.Extension("AUTH"); !ok {
			return fmt.Errorf("smtp sender: server does not support auth")
		}
		if err := client.Auth(s.auth); err != nil {
			return fmt.Errorf("smtp sender: auth: %w", err)
		}
	}
	if err := client.Mail(msg.From.Address); err != nil {
		return fmt.Errorf("smtp sender: mail from %s: %w", msg.From.Address, err)
	}
	for _, rcpt := range msg.To {
		if err := client.Rcpt(rcpt.Address); err != nil {
			return fmt.Errorf("smtp sender: rcpt to %s: %w", rcpt.Address, err)
		}
	}
	w, err := client.Data()
	if err != nil {
		return fmt.Errorf("smtp sender: data: %w", err)
	}
	if _, err := w.Write(body); err != nil {
		_ = w.Close()
		return fmt.Errorf("smtp sender: write body: %w", err)
	}
	if err := w.Close(); err != nil {
		return fmt.Errorf("smtp sender: close body: %w", err)
	}
	if err := client.Quit(); err != nil {
		return fmt.Errorf("smtp sender: quit: %w", err)
	}
	return nil
}

func buildSMTPMessage(msg EmailMessage) ([]byte, error) {
	if strings.TrimSpace(msg.TextBody) == "" && strings.TrimSpace(msg.HTMLBody) == "" {
		return nil, fmt.Errorf("email: missing body")
	}

	var buf bytes.Buffer
	writeHeader := func(name, value string) {
		buf.WriteString(name)
		buf.WriteString(": ")
		buf.WriteString(value)
		buf.WriteString("\r\n")
	}
	writeHeader("From", msg.From.String())
	toList := make([]string, 0, len(msg.To))
	for _, rcpt := range msg.To {
		toList = append(toList, rcpt.String())
	}
	writeHeader("To", strings.Join(toList, ", "))
	writeHeader("Subject", mime.QEncoding.Encode("utf-8", msg.Subject))
	writeHeader("Date", time.Now().Format(time.RFC1123Z))
	writeHeader("MIME-Version", "1.0")

	switch {
	case msg.TextBody != "" && msg.HTMLBody != "":
		boundary := fmt.Sprintf("alt-%d", time.Now().UnixNano())
		writeHeader("Content-Type", fmt.Sprintf(`multipart/alternative; boundary="%s"`, boundary))
		buf.WriteString("\r\n")
		writeMIMEPart(&buf, boundary, "text/plain; charset=utf-8", msg.TextBody)
		writeMIMEPart(&buf, boundary, "text/html; charset=utf-8", msg.HTMLBody)
		buf.WriteString("--")
		buf.WriteString(boundary)
		buf.WriteString("--\r\n")
	case msg.HTMLBody != "":
		writeHeader("Content-Type", `text/html; charset=utf-8`)
		writeHeader("Content-Transfer-Encoding", "quoted-printable")
		buf.WriteString("\r\n")
		if err := writeQuotedPrintable(&buf, msg.HTMLBody); err != nil {
			return nil, fmt.Errorf("email: encode html body: %w", err)
		}
	default:
		writeHeader("Content-Type", `text/plain; charset=utf-8`)
		writeHeader("Content-Transfer-Encoding", "quoted-printable")
		buf.WriteString("\r\n")
		if err := writeQuotedPrintable(&buf, msg.TextBody); err != nil {
			return nil, fmt.Errorf("email: encode text body: %w", err)
		}
	}
	return buf.Bytes(), nil
}

func writeMIMEPart(buf *bytes.Buffer, boundary, contentType, body string) {
	buf.WriteString("--")
	buf.WriteString(boundary)
	buf.WriteString("\r\n")
	buf.WriteString("Content-Type: ")
	buf.WriteString(contentType)
	buf.WriteString("\r\n")
	buf.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
	_ = writeQuotedPrintable(buf, body)
	buf.WriteString("\r\n")
}

func writeQuotedPrintable(buf *bytes.Buffer, body string) error {
	w := quotedprintable.NewWriter(buf)
	if _, err := w.Write([]byte(strings.ReplaceAll(body, "\n", "\r\n"))); err != nil {
		return err
	}
	return w.Close()
}

// EmailTemplate is a named mail template, typically selected by a flow hook.
type EmailTemplate struct {
	Subject string `json:"subject"`
	Text    string `json:"text,omitempty"`
	HTML    string `json:"html,omitempty"`
}

func (t EmailTemplate) validate(name string) error {
	if strings.TrimSpace(t.Subject) == "" {
		return fmt.Errorf("email template %q: missing subject", name)
	}
	if strings.TrimSpace(t.Text) == "" && strings.TrimSpace(t.HTML) == "" {
		return fmt.Errorf("email template %q: missing text/html body", name)
	}
	return nil
}

// EmailTemplateStore resolves a template by name.
type EmailTemplateStore interface {
	Get(name string) (EmailTemplate, error)
}

type emailTemplateCatalog struct {
	templates map[string]EmailTemplate
}

func newEmailTemplateCatalog(seed map[string]EmailTemplate) *emailTemplateCatalog {
	out := &emailTemplateCatalog{templates: make(map[string]EmailTemplate, len(seed))}
	for name, tmpl := range seed {
		out.templates[name] = tmpl
	}
	return out
}

func (c *emailTemplateCatalog) Get(name string) (EmailTemplate, error) {
	tmpl, ok := c.templates[name]
	if !ok {
		return EmailTemplate{}, fmt.Errorf("unknown template %q", name)
	}
	return tmpl, nil
}

//go:embed email_templates/*.json
var embeddedEmailTemplateFS embed.FS

// LoadEmailTemplates returns the embedded templates overlaid by any JSON files in
// dir (same precedence model as flow definitions: on-disk wins).
func LoadEmailTemplates(dir string) (EmailTemplateStore, error) {
	templates := map[string]EmailTemplate{}

	matches, err := fs.Glob(embeddedEmailTemplateFS, "email_templates/*.json")
	if err != nil {
		return nil, fmt.Errorf("list embedded email templates: %w", err)
	}
	for _, match := range matches {
		data, err := embeddedEmailTemplateFS.ReadFile(match)
		if err != nil {
			return nil, fmt.Errorf("read embedded email template %s: %w", match, err)
		}
		name := strings.TrimSuffix(filepath.Base(match), ".json")
		tmpl, err := parseEmailTemplate(name, data)
		if err != nil {
			return nil, err
		}
		templates[name] = tmpl
	}

	if dir != "" {
		if _, err := os.Stat(dir); err == nil {
			files, err := filepath.Glob(filepath.Join(dir, "*.json"))
			if err != nil {
				return nil, fmt.Errorf("list email templates in %s: %w", dir, err)
			}
			for _, file := range files {
				data, err := os.ReadFile(file)
				if err != nil {
					return nil, fmt.Errorf("read email template %s: %w", file, err)
				}
				name := strings.TrimSuffix(filepath.Base(file), ".json")
				tmpl, err := parseEmailTemplate(name, data)
				if err != nil {
					return nil, err
				}
				templates[name] = tmpl
			}
		} else if !os.IsNotExist(err) {
			return nil, fmt.Errorf("stat email template dir %s: %w", dir, err)
		}
	}

	return newEmailTemplateCatalog(templates), nil
}

func parseEmailTemplate(name string, data []byte) (EmailTemplate, error) {
	var tmpl EmailTemplate
	if err := json.Unmarshal(data, &tmpl); err != nil {
		return EmailTemplate{}, fmt.Errorf("parse email template %q: %w", name, err)
	}
	if err := tmpl.validate(name); err != nil {
		return EmailTemplate{}, err
	}
	return tmpl, nil
}

type emailHookParams struct {
	Template string `json:"template"`
	To       string `json:"to,omitempty"`
	From     string `json:"from,omitempty"`
	Subject  string `json:"subject,omitempty"`
}

type flowTemplateData struct {
	Order           *OrderGrain
	OrderID         string
	Step            string
	Phase           flow.Phase
	Error           string
	Vars            map[string]any
	Fulfillment     *Fulfillment
	ShippingAddress any
	BillingAddress  any
}

// RegisterEmailHook registers the "send_email" flow hook. It reads the current
// order for template data, renders the named template, and delivers it through
// the configured sender. Hook params:
//
//	{
//	  "template": "fulfillment-shipped",
//	  "to": "{{ .Order.CustomerEmail }}",
//	  "from": "Warehouse <warehouse@example.com>"
//	}
func RegisterEmailHook(reg *flow.Registry, app Applier, sender EmailSender, templates EmailTemplateStore) {
	reg.HookWithMeta("send_email", func(ctx context.Context, st *flow.State, info flow.HookInfo, params json.RawMessage) error {
		if sender == nil {
			return fmt.Errorf("send_email: no sender configured")
		}
		if templates == nil {
			return fmt.Errorf("send_email: no template store configured")
		}
		var p emailHookParams
		if len(params) > 0 {
			if err := json.Unmarshal(params, &p); err != nil {
				return fmt.Errorf("send_email: bad params: %w", err)
			}
		}
		if p.Template == "" {
			return fmt.Errorf("send_email: missing template")
		}
		o, err := app.Get(ctx, st.ID)
		if err != nil {
			return err
		}
		tmpl, err := templates.Get(p.Template)
		if err != nil {
			return fmt.Errorf("send_email: %w", err)
		}
		data := buildFlowTemplateData(o, st, info)

		subjectSource := tmpl.Subject
		if p.Subject != "" {
			subjectSource = p.Subject
		}
		subject, err := renderTextTemplate("email-subject", subjectSource, data)
		if err != nil {
			return fmt.Errorf("send_email: render subject: %w", err)
		}
		textBody, err := renderOptionalTextTemplate("email-text", tmpl.Text, data)
		if err != nil {
			return fmt.Errorf("send_email: render text body: %w", err)
		}
		htmlBody, err := renderOptionalHTMLTemplate("email-html", tmpl.HTML, data)
		if err != nil {
			return fmt.Errorf("send_email: render html body: %w", err)
		}

		toSource := p.To
		if strings.TrimSpace(toSource) == "" {
			toSource = o.CustomerEmail
		}
		toRendered, err := renderTextTemplate("email-to", toSource, data)
		if err != nil {
			return fmt.Errorf("send_email: render recipient: %w", err)
		}
		recipients, err := mail.ParseAddressList(toRendered)
		if err != nil {
			return fmt.Errorf("send_email: parse recipient %q: %w", toRendered, err)
		}
		to := make([]mail.Address, 0, len(recipients))
		for _, rcpt := range recipients {
			to = append(to, *rcpt)
		}

		from := sender.DefaultFrom()
		if strings.TrimSpace(p.From) != "" {
			fromRendered, err := renderTextTemplate("email-from", p.From, data)
			if err != nil {
				return fmt.Errorf("send_email: render sender: %w", err)
			}
			parsed, err := mail.ParseAddress(strings.TrimSpace(fromRendered))
			if err != nil {
				return fmt.Errorf("send_email: parse sender %q: %w", fromRendered, err)
			}
			from = *parsed
		}

		return sender.Send(ctx, EmailMessage{
			From:     from,
			To:       to,
			Subject:  subject,
			TextBody: textBody,
			HTMLBody: htmlBody,
		})
	}, flow.CapabilityMeta{
		Description:   "Render a named email template and send it through the configured sender.",
		ExampleParams: json.RawMessage(`{"template":"fulfillment-shipped","to":"{{ .Order.CustomerEmail }}","from":"Store <no-reply@example.com>"}`),
	})
}

func buildFlowTemplateData(o *OrderGrain, st *flow.State, info flow.HookInfo) flowTemplateData {
	errStr := ""
	if info.Err != nil {
		errStr = info.Err.Error()
	}
	var lastFulfillment *Fulfillment
	if n := len(o.Fulfillments); n > 0 {
		lastFulfillment = &o.Fulfillments[n-1]
	}
	return flowTemplateData{
		Order:           o,
		OrderID:         OrderId(st.ID).String(),
		Step:            info.Step,
		Phase:           info.Phase,
		Error:           errStr,
		Vars:            st.Vars,
		Fulfillment:     lastFulfillment,
		ShippingAddress: decodeEmailTemplateJSON(o.ShippingAddress),
		BillingAddress:  decodeEmailTemplateJSON(o.BillingAddress),
	}
}

func decodeEmailTemplateJSON(raw json.RawMessage) any {
	if len(raw) == 0 {
		return nil
	}
	var v any
	if err := json.Unmarshal(raw, &v); err != nil {
		return string(raw)
	}
	return v
}

func renderTextTemplate(name, src string, data any) (string, error) {
	tmpl, err := texttmpl.New(name).Option("missingkey=error").Parse(src)
	if err != nil {
		return "", err
	}
	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, data); err != nil {
		return "", err
	}
	return strings.TrimSpace(buf.String()), nil
}

func renderOptionalTextTemplate(name, src string, data any) (string, error) {
	if strings.TrimSpace(src) == "" {
		return "", nil
	}
	return renderTextTemplate(name, src, data)
}

func renderOptionalHTMLTemplate(name, src string, data any) (string, error) {
	if strings.TrimSpace(src) == "" {
		return "", nil
	}
	tmpl, err := htmltmpl.New(name).Option("missingkey=error").Parse(src)
	if err != nil {
		return "", err
	}
	var buf bytes.Buffer
	if err := tmpl.Execute(&buf, data); err != nil {
		return "", err
	}
	return strings.TrimSpace(buf.String()), nil
}