tsk-26: Retrieve scheduled message event endpoint (#28)

Closes #26

Reviewed-on: phoenix/textsender-api#28
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

internal/store/scheduled_message_event_store.go

@@ -4,12 +4,15 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.kundeng.us/phoenix/textsender-models/pkg/message/scheduling"
 )
 
 type ScheduledMessageEventStore interface {
+	Get(ctx context.Context, id uuid.UUID) (*scheduling.ScheduledMessageEvent, error)
 	CreateScheduledMessageEvent(ctx context.Context, event *scheduling.ScheduledMessageEvent) error
 	Exists(ctx context.Context, event *scheduling.ScheduledMessageEvent) (bool, error)
 }
@@ -22,6 +25,24 @@ func NewScheduledMessageEventStore(db *pgxpool.Pool) *PGScheduledMessageEventSto
 	return &PGScheduledMessageEventStore{db: db}
 }
 
+func (s *PGScheduledMessageEventStore) Get(ctx context.Context, id uuid.UUID) (*scheduling.ScheduledMessageEvent, error) {
+	query := `SELECT id, recipient_id, message_id, scheduled_message_id, created FROM scheduled_message_events WHERE id = $1`
+
+	var event scheduling.ScheduledMessageEvent
+	err := s.db.QueryRow(ctx, query, id).Scan(
+		&event.Id, &event.RecipientId, &event.MessageId, &event.ScheduledMessageId, &event.Created,
+	)
+
+	if err == pgx.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("getting scheduled message event by ID: %w", err)
+	}
+
+	return &event, nil
+}
+
 func (s *PGScheduledMessageEventStore) CreateScheduledMessageEvent(ctx context.Context, event *scheduling.ScheduledMessageEvent) error {
 	query := `
 		INSERT INTO scheduled_message_events (recipient_id, message_id, scheduled_message_id)