Feature/custom iterator (#173)

* Added CollectionIterator interface

* Added PAGINATION function

* Fixed LIMIT clause

* Fixed linting issues

pkg/runtime/expressions/data_source_test.go

@@ -0,0 +1,126 @@
+package expressions_test
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/runtime/expressions"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"testing"
+
+	"github.com/MontFerret/ferret/pkg/runtime/collections"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+type (
+	testIterableCollection struct {
+		values collections.IndexedCollection
+	}
+
+	testCollectionIterator struct {
+		values   collections.IndexedCollection
+		position values.Int
+	}
+
+	TestDataSourceExpression func(ctx context.Context, scope *core.Scope) (core.Value, error)
+)
+
+func (ds TestDataSourceExpression) Exec(ctx context.Context, scope *core.Scope) (core.Value, error) {
+	return ds(ctx, scope)
+}
+
+func (c *testIterableCollection) MarshalJSON() ([]byte, error) {
+	return nil, core.ErrInvalidOperation
+}
+func (c *testIterableCollection) Type() core.Type {
+	return core.Type(11)
+}
+func (c *testIterableCollection) String() string {
+	return ""
+}
+func (c *testIterableCollection) Compare(other core.Value) int {
+	return 1
+}
+func (c *testIterableCollection) Unwrap() interface{} {
+	return nil
+}
+func (c *testIterableCollection) Hash() uint64 {
+	return 0
+}
+func (c *testIterableCollection) Copy() core.Value {
+	return c
+}
+func (c *testIterableCollection) Iterate(ctx context.Context) (collections.CollectionIterator, error) {
+	return &testCollectionIterator{c.values, -1}, nil
+}
+
+func (i *testCollectionIterator) Next(ctx context.Context) (core.Value, core.Value, error) {
+	i.position++
+
+	if i.position > i.values.Length() {
+		return values.None, values.None, nil
+	}
+
+	return i.values.Get(i.position), i.position, nil
+}
+
+func TestDataSource(t *testing.T) {
+	Convey(".Iterate", t, func() {
+		Convey("Should return custom iterable collection", func() {
+			arr := values.NewArrayWith(
+				values.NewInt(1),
+				values.NewInt(2),
+				values.NewInt(3),
+				values.NewInt(4),
+				values.NewInt(5),
+				values.NewInt(6),
+				values.NewInt(7),
+				values.NewInt(8),
+				values.NewInt(9),
+				values.NewInt(10),
+			)
+
+			ds, err := expressions.NewDataSource(
+				core.SourceMap{},
+				collections.DefaultValueVar,
+				collections.DefaultKeyVar,
+				TestDataSourceExpression(func(ctx context.Context, scope *core.Scope) (core.Value, error) {
+					return &testIterableCollection{arr}, nil
+				}),
+			)
+
+			So(err, ShouldBeNil)
+
+			rootScope, _ := core.NewRootScope()
+			ctx := context.Background()
+			scope := rootScope.Fork()
+			out, err := ds.Iterate(ctx, scope)
+
+			So(err, ShouldBeNil)
+
+			pos := -1
+
+			nextScope := scope
+
+			for {
+				pos++
+				nextScope, err = out.Next(ctx, nextScope.Fork())
+
+				So(err, ShouldBeNil)
+
+				if nextScope == nil {
+					break
+				}
+
+				actualV, _ := nextScope.GetVariable(collections.DefaultValueVar)
+				actualK, _ := nextScope.GetVariable(collections.DefaultKeyVar)
+
+				expectedV := arr.Get(values.Int(pos))
+
+				So(actualV, ShouldEqual, expectedV)
+				So(actualK, ShouldEqual, values.Int(pos))
+			}
+
+			So(pos, ShouldEqual, int(arr.Length()))
+		})
+	})
+}