feat(migrate): add pending migrations function (#286)

Author: JustSamuel

Diff for: migrate/example/example_test.go

@@ -50,6 +50,12 @@ func TestExample(t *testing.T) {
 	reg.Add(migrate.CallComment, "3", log)
 	migrate.Callback = reg.Callback
 
+	pending, err := migrate.Pending(context.Background(), session, cql.Files)
+	if err != nil {
+		t.Fatal("Pending:", err)
+	}
+	t.Log("Pending migrations:", len(pending))
+
 	// First run prints data
 	if err := migrate.FromFS(context.Background(), session, cql.Files); err != nil {
 		t.Fatal("Migrate:", err)

Diff for: migrate/migrate.go

@@ -87,6 +87,48 @@ func List(ctx context.Context, session gocqlx.Session) ([]*Info, error) {
 	return v, nil
 }
 
+// Pending provides a listing of pending migrations.
+func Pending(ctx context.Context, session gocqlx.Session, f fs.FS) ([]*Info, error) {
+	applied, err := List(ctx, session)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create a set of applied migration names
+	appliedNames := make(map[string]struct{}, len(applied))
+	for _, migration := range applied {
+		appliedNames[migration.Name] = struct{}{}
+	}
+
+	fm, err := fs.Glob(f, "*.cql")
+	if err != nil {
+		return nil, fmt.Errorf("list migrations: %w", err)
+	}
+
+	pending := make([]*Info, 0)
+
+	for _, name := range fm {
+		baseName := filepath.Base(name)
+		// Check if the migration is not in the applied set
+		if _, exists := appliedNames[baseName]; !exists {
+			c, err := fileChecksum(f, name)
+			if err != nil {
+				return nil, fmt.Errorf("calculate checksum for %q: %w", name, err)
+			}
+
+			info := &Info{
+				Name:      baseName,
+				StartTime: time.Now(),
+				Checksum:  c,
+			}
+
+			pending = append(pending, info)
+		}
+	}
+
+	return pending, nil
+}
+
 func ensureInfoTable(ctx context.Context, session gocqlx.Session) error {
 	return session.ContextQuery(ctx, infoSchema, nil).ExecRelease()
 }

Diff for: migrate/migrate_test.go

@@ -45,6 +45,54 @@ func recreateTables(tb testing.TB, session gocqlx.Session) {
 	}
 }
 
+func TestPending(t *testing.T) {
+	session := gocqlxtest.CreateSession(t)
+	defer session.Close()
+	recreateTables(t, session)
+
+	ctx := context.Background()
+
+	t.Run("pending", func(t *testing.T) {
+		defer recreateTables(t, session)
+
+		f := memfs.New()
+		writeFile(f, 0, fmt.Sprintf(insertMigrate, 0)+";")
+
+		pending, err := migrate.Pending(ctx, session, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(pending) != 1 {
+			t.Fatal("expected 2 pending migrations got", len(pending))
+		}
+
+		err = migrate.FromFS(ctx, session, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		pending, err = migrate.Pending(ctx, session, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(pending) != 0 {
+			t.Fatal("expected no pending migrations got", len(pending))
+		}
+
+		for i := 1; i < 3; i++ {
+			writeFile(f, i, fmt.Sprintf(insertMigrate, i)+";")
+		}
+
+		pending, err = migrate.Pending(ctx, session, f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(pending) != 2 {
+			t.Fatal("expected 2 pending migrations got", len(pending))
+		}
+	})
+}
+
 func TestMigration(t *testing.T) {
 	session := gocqlxtest.CreateSession(t)
 	defer session.Close()