[#25] Add placement policy QL encoder

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/policy/encode_test.go

@@ -0,0 +1,36 @@
+package policy_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/nspcc-dev/neofs-node/pkg/policy"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEncode(t *testing.T) {
+	testCases := []string{
+		`REP 1 IN X
+CBF 1
+SELECT 2 IN SAME Location FROM * AS X`,
+
+		`REP 1
+SELECT 2 IN City FROM Good
+FILTER Country EQ RU AS FromRU
+FILTER @FromRU AND Rating GT 7 AS Good`,
+
+		`REP 7 IN SPB
+SELECT 1 IN City FROM SPBSSD AS SPB
+FILTER City EQ SPB AND SSD EQ true OR City EQ SPB AND Rating GE 5 AS SPBSSD`,
+	}
+
+	for _, testCase := range testCases {
+		q, err := policy.Parse(testCase)
+		require.NoError(t, err)
+
+		got := policy.Encode(q)
+		fmt.Println(strings.Join(got, "\n"))
+		require.Equal(t, testCase, strings.Join(got, "\n"))
+	}
+}