From 50cf86ee613f95d93bcb5fad63ffd495c5a3c3a2 Mon Sep 17 00:00:00 2001
From: zhengchun <zhengchunster@gmail.com>
Date: Thu, 3 Jun 2021 16:16:35 +0800
Subject: [PATCH] add `groupQuery`, supports grouping node query, (xpath
 expression). fix #https://github.com/antchfx/htmlquery/issues/42

---
 build.go |  6 ++++++
 parse.go | 18 ++++++++++++++++++
 query.go | 29 +++++++++++++++++++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/build.go b/build.go
index 2edafb8..58d8f31 100644
--- a/build.go
+++ b/build.go
@@ -515,6 +515,12 @@ func (b *builder) processNode(root node) (q query, err error) {
 		q, err = b.processFunctionNode(root.(*functionNode))
 	case nodeOperator:
 		q, err = b.processOperatorNode(root.(*operatorNode))
+	case nodeGroup:
+		q, err = b.processNode(root.(*groupNode).Input)
+		if err != nil {
+			return
+		}
+		q = &groupQuery{Input: q}
 	}
 	return
 }
diff --git a/parse.go b/parse.go
index fb9abe3..acb0db9 100644
--- a/parse.go
+++ b/parse.go
@@ -65,6 +65,7 @@ const (
 	nodeOperator
 	nodeVariable
 	nodeConstantOperand
+	nodeGroup
 )
 
 type parser struct {
@@ -104,6 +105,10 @@ func newFilterNode(n, m node) node {
 	return &filterNode{nodeType: nodeFilter, Input: n, Condition: m}
 }
 
+func newGroupNode(n node) node {
+	return &groupNode{nodeType: nodeGroup, Input: n}
+}
+
 // newRootNode returns a root node.
 func newRootNode(s string) node {
 	return &rootNode{nodeType: nodeRoot, slash: s}
@@ -492,6 +497,9 @@ func (p *parser) parsePrimaryExpr(n node) (opnd node) {
 	case itemLParens:
 		p.next()
 		opnd = p.parseExpression(n)
+		if opnd.Type() != nodeConstantOperand {
+			opnd = newGroupNode(opnd)
+		}
 		p.skipItem(itemRParens)
 	case itemName:
 		if p.r.canBeFunc && !isNodeType(p.r) {
@@ -587,6 +595,16 @@ func (o *operandNode) String() string {
 	return fmt.Sprintf("%v", o.Val)
 }
 
+// groupNode holds a set of node expression
+type groupNode struct {
+	nodeType
+	Input node
+}
+
+func (g *groupNode) String() string {
+	return fmt.Sprintf("%s", g.Input)
+}
+
 // filterNode holds a condition filter.
 type filterNode struct {
 	nodeType
diff --git a/query.go b/query.go
index 47f8076..6e99ce5 100644
--- a/query.go
+++ b/query.go
@@ -669,6 +669,35 @@ func (c *constantQuery) Clone() query {
 	return c
 }
 
+type groupQuery struct {
+	posit int
+
+	Input query
+}
+
+func (g *groupQuery) Select(t iterator) NodeNavigator {
+	for {
+		node := g.Input.Select(t)
+		if node == nil {
+			return nil
+		}
+		g.posit++
+		return node.Copy()
+	}
+}
+
+func (g *groupQuery) Evaluate(t iterator) interface{} {
+	return g.Input.Evaluate(t)
+}
+
+func (g *groupQuery) Clone() query {
+	return &groupQuery{Input: g.Input}
+}
+
+func (g *groupQuery) position() int {
+	return g.posit
+}
+
 // logicalQuery is an XPath logical expression.
 type logicalQuery struct {
 	Left, Right query