docs: write godocs in Message

message.go

@@ -6,20 +6,30 @@ import (
 	"github.com/vvatanabe/dynamomq/internal/clock"
 )
 
+// Status represents the state of a message in a DynamoDB-based queue.
 type Status string
 
+// Constants defining various states of a message in the queue.
 const (
-	StatusReady      Status = "READY"
+	// StatusReady indicates that a message is ready to be processed.
+	StatusReady Status = "READY"
+	// StatusProcessing indicates that a message is currently being processed.
 	StatusProcessing Status = "PROCESSING"
 )
 
+// QueueType represents the type of queue in a DynamoDB-based messaging system.
 type QueueType string
 
+// Constants defining the types of queues available.
 const (
+	// QueueTypeStandard represents a standard queue.
 	QueueTypeStandard QueueType = "STANDARD"
-	QueueTypeDLQ      QueueType = "DLQ"
+	// QueueTypeDLQ represents a Dead Letter Queue, used for holding messages that failed to process.
+	QueueTypeDLQ QueueType = "DLQ"
 )
 
+// NewMessage creates a new instance of a Message with the provided data and initializes its timestamps.
+// This function is a constructor for Message, setting initial values and preparing the message for use in the queue.
 func NewMessage[T any](id string, data T, now time.Time) *Message[T] {
 	ts := clock.FormatRFC3339Nano(now)
 	return &Message[T]{
@@ -36,19 +46,40 @@ func NewMessage[T any](id string, data T, now time.Time) *Message[T] {
 	}
 }
 
+// Message represents a message structure in a DynamoDB-based queue system.
+// It uses the generic type T for the message content, allowing for flexibility in the data type of the message payload.
+// This struct includes tags for JSON serialization (`json:"..."`) and DynamoDB attribute value (`dynamodbav:"..."`) mappings.
 type Message[T any] struct {
-	ID               string    `json:"id" dynamodbav:"id"`
-	Data             T         `json:"data" dynamodbav:"data"`
-	ReceiveCount     int       `json:"receive_count" dynamodbav:"receive_count"`
-	QueueType        QueueType `json:"queue_type" dynamodbav:"queue_type,omitempty"`
-	Version          int       `json:"version" dynamodbav:"version"`
-	CreatedAt        string    `json:"created_at" dynamodbav:"created_at"`
-	UpdatedAt        string    `json:"updated_at" dynamodbav:"updated_at"`
-	SentAt           string    `json:"sent_at" dynamodbav:"sent_at"`
-	ReceivedAt       string    `json:"received_at" dynamodbav:"received_at"`
-	InvisibleUntilAt string    `json:"invisible_until_at" dynamodbav:"invisible_until_at"`
+	// ID is a unique identifier for the message.
+	ID string `json:"id" dynamodbav:"id"`
+	// Data is the content of the message. The type T defines the format of this data.
+	Data T `json:"data" dynamodbav:"data"`
+	// ReceiveCount is the number of times the message has been received from the queue.
+	ReceiveCount int `json:"receive_count" dynamodbav:"receive_count"`
+	// QueueType is the type of queue (standard or DLQ) to which the message belongs.
+	QueueType QueueType `json:"queue_type" dynamodbav:"queue_type,omitempty"`
+	// Version is the version number of the message, used for optimistic concurrency control.
+	Version int `json:"version" dynamodbav:"version"`
+	// CreatedAt is the timestamp when the message was created.
+	CreatedAt string `json:"created_at" dynamodbav:"created_at"`
+	// UpdatedAt is the timestamp when the message was last updated.
+	UpdatedAt string `json:"updated_at" dynamodbav:"updated_at"`
+	// SentAt is the timestamp when the message was sent to the queue.
+	SentAt string `json:"sent_at" dynamodbav:"sent_at"`
+	// ReceivedAt is the timestamp when the message was last received from the queue.
+	ReceivedAt string `json:"received_at" dynamodbav:"received_at"`
+	// InvisibleUntilAt: The deadline until which the message remains invisible in the queue.
+	// Until this timestamp, the message will not be visible to other consumers.
+	InvisibleUntilAt string `json:"invisible_until_at" dynamodbav:"invisible_until_at"`
 }
 
+// GetStatus determines the current status of the message based on the provided time.
+// It returns the status as either 'StatusReady' or 'StatusProcessing'.
+//
+// StatusReady if the message is ready to be processed (either 'InvisibleUntilAt' is empty
+// or the current time is after the 'InvisibleUntilAt' time).
+// StatusProcessing if the current time is before the 'InvisibleUntilAt' time, indicating
+// that the message is currently being processed and is not yet ready for further processing.
 func (m *Message[T]) GetStatus(now time.Time) Status {
 	if m.InvisibleUntilAt == "" {
 		return StatusReady