tsk-29: Place restrictions on adding scheduled message event (#30)

Closes #29

Reviewed-on: phoenix/textsender-api#30
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

internal/store/scheduled_message_store.go

@@ -2,13 +2,17 @@ package store
 
 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 ScheduledMessageStore interface {
+	Get(ctx context.Context, id uuid.UUID) (*scheduling.ScheduledMessage, error)
 	CreateScheduledMessage(ctx context.Context, schedMsg *scheduling.ScheduledMessage) error
 }
 
@@ -20,6 +24,25 @@ func NewScheduledMessageStore(db *pgxpool.Pool) *PGScheduledMessageStore {
 	return &PGScheduledMessageStore{db: db}
 }
 
+func (s *PGScheduledMessageStore) Get(ctx context.Context, id uuid.UUID) (*scheduling.ScheduledMessage, error) {
+	query := `
+		SELECT id, scheduled, created, status, user_id FROM scheduled_messages WHERE id = $1
+	`
+
+	var schMsg scheduling.ScheduledMessage
+	err := s.db.QueryRow(ctx, query, id).Scan(
+		&schMsg.Id, &schMsg.Scheduled, &schMsg.Created, &schMsg.Status, &schMsg.UserId,
+	)
+
+	if err == pgx.ErrNoRows {
+		return nil, fmt.Errorf("No rows")
+	} else if err != nil {
+		return nil, fmt.Errorf("Getting scheduled message: %w", err)
+	}
+
+	return &schMsg, nil
+}
+
 func (s *PGScheduledMessageStore) CreateScheduledMessage(ctx context.Context, schedMsg *scheduling.ScheduledMessage) error {
 	query := `
 		INSERT INTO scheduled_messages (scheduled, status, user_id)