Feature/custom iterator (#173)

* Added CollectionIterator interface

* Added PAGINATION function

* Fixed LIMIT clause

* Fixed linting issues

pkg/runtime/collections/collection.go

@@ -1,12 +1,14 @@
 package collections
 
 import (
+	"context"
 	"github.com/MontFerret/ferret/pkg/runtime/core"
 	"github.com/MontFerret/ferret/pkg/runtime/values"
 )
 
 type (
 	Collection interface {
+		core.Value
 		Length() values.Int
 	}
 
@@ -22,4 +24,54 @@ type (
 		Get(key values.String) (core.Value, values.Boolean)
 		Set(key values.String, value core.Value)
 	}
+
+	IterableCollection interface {
+		core.Value
+		Iterate(ctx context.Context) (CollectionIterator, error)
+	}
+
+	CollectionIterator interface {
+		Next(ctx context.Context) (value core.Value, key core.Value, err error)
+	}
+
+	collectionIteratorWrapper struct {
+		valVar string
+		keyVar string
+		values CollectionIterator
+	}
 )
+
+func NewCollectionIterator(
+	valVar,
+	keyVar string,
+	values CollectionIterator,
+) (Iterator, error) {
+	return &collectionIteratorWrapper{valVar, keyVar, values}, nil
+}
+
+func (iterator *collectionIteratorWrapper) Next(ctx context.Context, scope *core.Scope) (*core.Scope, error) {
+	val, key, err := iterator.values.Next(ctx)
+
+	if err != nil {
+		return nil, err
+	}
+
+	// end of iteration
+	if val == values.None {
+		return nil, nil
+	}
+
+	nextScope := scope.Fork()
+
+	if err := nextScope.SetVariable(iterator.valVar, val); err != nil {
+		return nil, err
+	}
+
+	if iterator.keyVar != "" {
+		if err := nextScope.SetVariable(iterator.keyVar, key); err != nil {
+			return nil, err
+		}
+	}
+
+	return nextScope, nil
+}

pkg/runtime/core/value.go

@@ -21,6 +21,7 @@ const (
 	HTMLElementType  Type = 8
 	HTMLDocumentType Type = 9
 	BinaryType       Type = 10
+	CustomType       Type = 99
 )
 
 var typestr = map[Type]string{
@@ -35,6 +36,7 @@ var typestr = map[Type]string{
 	HTMLElementType:  "HTMLElement",
 	HTMLDocumentType: "HTMLDocument",
 	BinaryType:       "BinaryType",
+	CustomType:       "CustomType",
 }
 
 func (t Type) String() string {

pkg/runtime/expressions/clauses/limit.go

@@ -9,15 +9,15 @@ import (
 type LimitClause struct {
 	src        core.SourceMap
 	dataSource collections.Iterable
-	count      int
-	offset     int
+	count      core.Expression
+	offset     core.Expression
 }
 
 func NewLimitClause(
 	src core.SourceMap,
 	dataSource collections.Iterable,
-	count int,
-	offset int,
+	count core.Expression,
+	offset core.Expression,
 ) (collections.Iterable, error) {
 	if dataSource == nil {
 		return nil, core.Error(core.ErrMissedArgument, "dataSource source")
@@ -33,10 +33,34 @@ func (clause *LimitClause) Iterate(ctx context.Context, scope *core.Scope) (coll
 		return nil, core.SourceError(clause.src, err)
 	}
 
+	count, err := clause.count.Exec(ctx, scope)
+
+	if err != nil {
+		return nil, core.SourceError(clause.src, err)
+	}
+
+	offset, err := clause.offset.Exec(ctx, scope)
+
+	if err != nil {
+		return nil, core.SourceError(clause.src, err)
+	}
+
+	countInt, err := clause.parseValue(count)
+
+	if err != nil {
+		return nil, err
+	}
+
+	offsetInt, err := clause.parseValue(offset)
+
+	if err != nil {
+		return nil, err
+	}
+
 	iterator, err := collections.NewLimitIterator(
 		src,
-		clause.count,
-		clause.offset,
+		int(countInt),
+		int(offsetInt),
 	)
 
 	if err != nil {
@@ -45,3 +69,15 @@ func (clause *LimitClause) Iterate(ctx context.Context, scope *core.Scope) (coll
 
 	return iterator, nil
 }
+
+func (clause *LimitClause) parseValue(val core.Value) (int, error) {
+	if val.Type() == core.IntType {
+		return val.Unwrap().(int), nil
+	}
+
+	if val.Type() == core.FloatType {
+		return int(val.Unwrap().(float64)), nil
+	}
+
+	return -1, core.TypeError(val.Type(), core.IntType, core.FloatType)
+}

pkg/runtime/expressions/data_source.go

@@ -49,6 +49,15 @@ func (ds *DataSource) Iterate(ctx context.Context, scope *core.Scope) (collectio
 	default:
 		// fallback to user defined types
 		switch data.(type) {
+		case collections.IterableCollection:
+			collection := data.(collections.IterableCollection)
+			iterator, err := collection.Iterate(ctx)
+
+			if err != nil {
+				return nil, err
+			}
+
+			return collections.NewCollectionIterator(ds.valVariable, ds.keyVariable, iterator)
 		case collections.KeyedCollection:
 			return collections.NewIndexedIterator(ds.valVariable, ds.keyVariable, data.(collections.IndexedCollection))
 		case collections.IndexedCollection:

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()))
+		})
+	})
+}

pkg/runtime/expressions/for.go

@@ -40,7 +40,7 @@ func NewForExpression(
 	}, nil
 }
 
-func (e *ForExpression) AddLimit(src core.SourceMap, size, count int) error {
+func (e *ForExpression) AddLimit(src core.SourceMap, size, count core.Expression) error {
 	limit, err := clauses.NewLimitClause(src, e.dataSource, size, count)
 
 	if err != nil {