Add comprehensive documentation comments

message.go

@@ -6,7 +6,9 @@ import (
 	"os"
 )
 
-// Message repräsentiert eine E-Mail-Nachricht
+// Message represents an email message with all its components including recipients,
+// content, headers, and attachments. Messages are constructed using the fluent builder
+// pattern provided by the setter methods.
 type Message struct {
 	To          []string     `json:"to"`
 	CC          []string     `json:"cc,omitempty"`
@@ -19,20 +21,21 @@ type Message struct {
 	Attachments []Attachment `json:"attachments,omitempty"`
 }
 
-// Header repräsentiert einen benutzerdefinierten E-Mail-Header
+// Header represents a custom email header as a name-value pair.
 type Header struct {
 	Header string `json:"header"`
 	Value  string `json:"value"`
 }
 
-// Attachment repräsentiert einen E-Mail-Anhang
+// Attachment represents an email attachment with its filename, MIME type, and base64-encoded data.
 type Attachment struct {
 	Filename string `json:"filename"`
-	Data     string `json:"data"` // Base64-kodiert
+	Data     string `json:"data"` // Base64-encoded file content
 	MimeType string `json:"mimetype"`
 }
 
-// NewMessage erstellt eine neue Message
+// NewMessage creates and returns a new empty Message with initialized slices for recipients,
+// headers, and attachments. Use the setter methods to populate the message fields.
 func NewMessage() *Message {
 	return &Message{
 		To:          []string{},
@@ -43,49 +46,58 @@ func NewMessage() *Message {
 	}
 }
 
-// AddTo fügt einen Empfänger hinzu
+// AddTo adds a recipient email address to the To field.
+// Returns the message for method chaining.
 func (m *Message) AddTo(email string) *Message {
 	m.To = append(m.To, email)
 	return m
 }
 
-// AddCC fügt einen CC-Empfänger hinzu
+// AddCC adds a recipient email address to the CC (carbon copy) field.
+// Returns the message for method chaining.
 func (m *Message) AddCC(email string) *Message {
 	m.CC = append(m.CC, email)
 	return m
 }
 
-// AddBCC fügt einen BCC-Empfänger hinzu
+// AddBCC adds a recipient email address to the BCC (blind carbon copy) field.
+// Returns the message for method chaining.
 func (m *Message) AddBCC(email string) *Message {
 	m.BCC = append(m.BCC, email)
 	return m
 }
 
-// SetSender setzt den Absender
+// SetSender sets the sender email address for the message.
+// Returns the message for method chaining.
 func (m *Message) SetSender(email string) *Message {
 	m.Sender = email
 	return m
 }
 
-// SetSubject setzt den Betreff
+// SetSubject sets the email subject line.
+// Returns the message for method chaining.
 func (m *Message) SetSubject(subject string) *Message {
 	m.Subject = subject
 	return m
 }
 
-// SetTextBody setzt den Text-Körper
+// SetTextBody sets the plain text body of the email.
+// Returns the message for method chaining.
 func (m *Message) SetTextBody(body string) *Message {
 	m.TextBody = body
 	return m
 }
 
-// SetHTMLBody setzt den HTML-Körper
+// SetHTMLBody sets the HTML body of the email.
+// Returns the message for method chaining.
 func (m *Message) SetHTMLBody(body string) *Message {
 	m.HTMLBody = body
 	return m
 }
 
-// AddHeader fügt einen benutzerdefinierten Header hinzu
+// AddHeader adds a custom email header with the specified name and value.
+// Common examples include "Reply-To", "X-Priority", or custom application headers.
+// Returns the message for method chaining.
 func (m *Message) AddHeader(name, value string) *Message {
 	m.Headers = append(m.Headers, Header{
 		Header: name,
@@ -94,7 +106,9 @@ func (m *Message) AddHeader(name, value string) *Message {
 	return m
 }
 
-// AttachFile fügt eine Datei als Anhang hinzu
+// AttachFile adds a file attachment to the message from a byte slice.
+// The data is automatically base64-encoded for transmission.
+// Returns the message for method chaining.
 func (m *Message) AttachFile(filename, mimeType string, data []byte) *Message {
 	m.Attachments = append(m.Attachments, Attachment{
 		Filename: filename,
@@ -104,7 +118,9 @@ func (m *Message) AttachFile(filename, mimeType string, data []byte) *Message {
 	return m
 }
 
-// AttachFileFromPath lädt eine Datei vom Dateisystem und fügt sie als Anhang hinzu
+// AttachFileFromPath reads a file from the filesystem and adds it as an attachment.
+// The filename is extracted from the path. Returns an error if the file cannot be read.
+// The file data is automatically base64-encoded for transmission.
 func (m *Message) AttachFileFromPath(path, mimeType string) error {
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -126,7 +142,13 @@ func (m *Message) AttachFileFromPath(path, mimeType string) error {
 	return nil
 }
 
-// Validate prüft, ob die Message gültig ist
+// Validate checks whether the message meets all required criteria for sending.
+// It returns an error if any validation rules are violated:
+//   - At least one recipient is required
+//   - Maximum of 255 recipients allowed
+//   - Sender must be specified
+//   - Subject must be specified
+//   - Either TextBody or HTMLBody (or both) must be provided
 func (m *Message) Validate() error {
 	if len(m.To) == 0 {
 		return errors.New("at least one recipient required")