Consolidate DOM manipulation utilities to eliminate code duplication

- Move addClass and setAttribute from ContentEngine/Injector to utils.go
- Remove duplicate hasInsertrClass implementation
- Add RemoveClass and HasClass utilities for completeness
- Eliminates 74+ lines of exact duplication across files

internal/engine/engine.go

@@ -106,7 +106,7 @@ func (e *ContentEngine) ProcessContent(input ContentInput) (*ContentResult, erro
 		collectionID := e.idGenerator.Generate(collectionElem.Node, input.FilePath)
 
 		// Add data-collection-id attribute to the collection container
-		e.setAttribute(collectionElem.Node, "data-collection-id", collectionID)
+		SetAttribute(collectionElem.Node, "data-collection-id", collectionID)
 
 		// Process collection during enhancement or content injection
 		if input.Mode == Enhancement || input.Mode == ContentInjection {
@@ -161,7 +161,7 @@ func (e *ContentEngine) findEditableElements(doc *html.Node) ([]InsertrElement,
 	// First pass: find all .insertr and .insertr-add elements
 	e.walkNodes(doc, func(n *html.Node) {
 		if n.Type == html.ElementNode {
-			if e.hasInsertrClass(n) {
+			if hasInsertrClass(n) {
 				if isContainer(n) {
 					// Container element - mark for transformation
 					containersToTransform = append(containersToTransform, n)
@@ -189,7 +189,7 @@ func (e *ContentEngine) findEditableElements(doc *html.Node) ([]InsertrElement,
 		// Find viable children and add .insertr class to them
 		viableChildren := FindViableChildren(container)
 		for _, child := range viableChildren {
-			e.addClass(child, "insertr")
+			AddClass(child, "insertr")
 			insertrElements = append(insertrElements, InsertrElement{
 				Node: child,
 			})
@@ -207,12 +207,6 @@ func (e *ContentEngine) walkNodes(n *html.Node, fn func(*html.Node)) {
 	}
 }
 
-// hasInsertrClass checks if node has class="insertr"
-func (e *ContentEngine) hasInsertrClass(node *html.Node) bool {
-	classes := GetClasses(node)
-	return slices.Contains(classes, "insertr")
-}
-
 // hasInsertrAddClass checks if node has class="insertr-add" (collection)
 func (e *ContentEngine) hasInsertrAddClass(node *html.Node) bool {
 	classes := GetClasses(node)
@@ -222,63 +216,7 @@ func (e *ContentEngine) hasInsertrAddClass(node *html.Node) bool {
 // addContentAttributes adds data-content-id attribute only
 func (e *ContentEngine) addContentAttributes(node *html.Node, contentID string) {
 	// Add data-content-id attribute
-	e.setAttribute(node, "data-content-id", contentID)
-}
-
-// setAttribute sets an attribute on a HTML node
-func (e *ContentEngine) setAttribute(node *html.Node, key, value string) {
-	// Remove existing attribute if it exists
-	for i, attr := range node.Attr {
-		if attr.Key == key {
-			node.Attr[i].Val = value
-			return
-		}
-	}
-	// Add new attribute
-	node.Attr = append(node.Attr, html.Attribute{
-		Key: key,
-		Val: value,
-	})
-}
-
-// addClass safely adds a class to an HTML node
-func (e *ContentEngine) addClass(node *html.Node, className string) {
-	var classAttr *html.Attribute
-	var classIndex int = -1
-
-	// Find existing class attribute
-	for idx, attr := range node.Attr {
-		if attr.Key == "class" {
-			classAttr = &attr
-			classIndex = idx
-			break
-		}
-	}
-
-	var classes []string
-	if classAttr != nil {
-		classes = strings.Fields(classAttr.Val)
-	}
-
-	// Check if class already exists
-	if slices.Contains(classes, className) {
-		return
-	}
-
-	// Add new class
-	classes = append(classes, className)
-	newClassValue := strings.Join(classes, " ")
-
-	if classIndex >= 0 {
-		// Update existing class attribute
-		node.Attr[classIndex].Val = newClassValue
-	} else {
-		// Add new class attribute
-		node.Attr = append(node.Attr, html.Attribute{
-			Key: "class",
-			Val: newClassValue,
-		})
-	}
+	SetAttribute(node, "data-content-id", contentID)
 }
 
 // removeClass safely removes a class from an HTML node
@@ -367,7 +305,7 @@ func (e *ContentEngine) extractOriginalTemplate(node *html.Node) string {
 	return buf.String()
 }
 
-// extractCleanTemplate extracts a clean template without data-content-id attributes and with placeholder content
+// extractCleanTemplate extracts a clean template without data-content-id attributes and with placeholder content. Used for collection template variants.
 func (e *ContentEngine) extractCleanTemplate(node *html.Node) string {
 	// Clone the node to avoid modifying the original
 	clonedNode := e.cloneNode(node)
@@ -406,7 +344,7 @@ func (e *ContentEngine) extractCleanTemplate(node *html.Node) string {
 func (e *ContentEngine) removeAttribute(n *html.Node, key string) {
 	for i, attr := range n.Attr {
 		if attr.Key == key {
-			n.Attr = append(n.Attr[:i], n.Attr[i+1:]...)
+			n.Attr = slices.Delete(n.Attr, i, i+1)
 			break
 		}
 	}
@@ -605,7 +543,7 @@ func (e *ContentEngine) reconstructCollectionItems(collectionNode *html.Node, co
 
 				// Inject data-item-id attribute for collection item identification
 				if structuralChild.Type == html.ElementNode {
-					e.setAttribute(structuralChild, "data-item-id", item.ItemID)
+					SetAttribute(structuralChild, "data-item-id", item.ItemID)
 				}
 
 				collectionNode.AppendChild(structuralChild)
@@ -665,7 +603,7 @@ func (e *ContentEngine) generateStructuralTemplateFromChild(childElement *html.N
 		if n.Type == html.ElementNode && e.hasClass(n, "insertr") {
 			if entryIndex < len(contentEntries) {
 				// Set the data-content-id attribute
-				e.setAttribute(n, "data-content-id", contentEntries[entryIndex].ID)
+				SetAttribute(n, "data-content-id", contentEntries[entryIndex].ID)
 
 				// Clear content - this will be hydrated during reconstruction
 				for child := n.FirstChild; child != nil; {

internal/engine/injector.go

@@ -9,7 +9,6 @@ import (
 	"github.com/insertr/insertr/internal/config"
 	"github.com/insertr/insertr/internal/db"
 	"golang.org/x/net/html"
-	"slices"
 )
 
 // Injector handles content injection into HTML elements
@@ -168,8 +167,8 @@ func (i *Injector) findElementByTag(node *html.Node, tag string) *html.Node {
 
 // AddContentAttributes adds necessary data attributes and insertr class for editor functionality
 func (i *Injector) AddContentAttributes(node *html.Node, contentID string, contentType string) {
-	i.setAttribute(node, "data-content-id", contentID)
-	i.addClass(node, "insertr")
+	SetAttribute(node, "data-content-id", contentID)
+	AddClass(node, "insertr")
 }
 
 // InjectEditorAssets adds editor JavaScript to HTML document and injects demo gate if needed
@@ -200,63 +199,6 @@ func (i *Injector) findHeadElement(node *html.Node) *html.Node {
 	return nil
 }
 
-// setAttribute safely sets an attribute on an HTML node
-func (i *Injector) setAttribute(node *html.Node, key, value string) {
-	// Remove existing attribute if present
-	for idx, attr := range node.Attr {
-		if attr.Key == key {
-			node.Attr = slices.Delete(node.Attr, idx, idx+1)
-			break
-		}
-	}
-
-	// Add new attribute
-	node.Attr = append(node.Attr, html.Attribute{
-		Key: key,
-		Val: value,
-	})
-}
-
-// addClass safely adds a class to an HTML node
-func (i *Injector) addClass(node *html.Node, className string) {
-	var classAttr *html.Attribute
-	var classIndex int = -1
-
-	// Find existing class attribute
-	for idx, attr := range node.Attr {
-		if attr.Key == "class" {
-			classAttr = &attr
-			classIndex = idx
-			break
-		}
-	}
-
-	var classes []string
-	if classAttr != nil {
-		classes = strings.Fields(classAttr.Val)
-	}
-
-	// Check if class already exists
-	if slices.Contains(classes, className) {
-		return // Class already exists
-	}
-
-	// Add new class
-	classes = append(classes, className)
-	newClassValue := strings.Join(classes, " ")
-
-	if classIndex >= 0 {
-		// Update existing class attribute
-		node.Attr[classIndex].Val = newClassValue
-	} else {
-		// Add new class attribute
-		node.Attr = append(node.Attr, html.Attribute{
-			Key: "class",
-			Val: newClassValue,
-		})
-	}
-}
-
 // Element represents a parsed HTML element with metadata
 type Element struct {
 	Node    *html.Node

internal/engine/utils.go

@@ -32,6 +32,112 @@ func GetAttribute(node *html.Node, key string) string {
 	return ""
 }
 
+// SetAttribute sets an attribute on an HTML node
+func SetAttribute(node *html.Node, key, value string) {
+	// Check for existing attribute and update in place
+	for i, attr := range node.Attr {
+		if attr.Key == key {
+			node.Attr[i].Val = value
+			return
+		}
+	}
+	// Add new attribute if not found
+	node.Attr = append(node.Attr, html.Attribute{
+		Key: key,
+		Val: value,
+	})
+}
+
+// AddClass safely adds a class to an HTML node
+func AddClass(node *html.Node, className string) {
+	var classAttr *html.Attribute
+	var classIndex int = -1
+
+	// Find existing class attribute
+	for idx, attr := range node.Attr {
+		if attr.Key == "class" {
+			classAttr = &attr
+			classIndex = idx
+			break
+		}
+	}
+
+	var classes []string
+	if classAttr != nil {
+		classes = strings.Fields(classAttr.Val)
+	}
+
+	// Check if class already exists
+	if slices.Contains(classes, className) {
+		return
+	}
+
+	// Add new class
+	classes = append(classes, className)
+	newClassValue := strings.Join(classes, " ")
+
+	if classIndex >= 0 {
+		// Update existing class attribute
+		node.Attr[classIndex].Val = newClassValue
+	} else {
+		// Add new class attribute
+		node.Attr = append(node.Attr, html.Attribute{
+			Key: "class",
+			Val: newClassValue,
+		})
+	}
+}
+
+// RemoveClass safely removes a class from an HTML node
+func RemoveClass(node *html.Node, className string) {
+	var classIndex int = -1
+
+	// Find existing class attribute
+	for idx, attr := range node.Attr {
+		if attr.Key == "class" {
+			classIndex = idx
+			break
+		}
+	}
+
+	if classIndex == -1 {
+		return // No class attribute found
+	}
+
+	// Parse existing classes
+	classes := strings.Fields(node.Attr[classIndex].Val)
+
+	// Filter out the target class
+	var newClasses []string
+	for _, class := range classes {
+		if class != className {
+			newClasses = append(newClasses, class)
+		}
+	}
+
+	// Update or remove class attribute
+	if len(newClasses) == 0 {
+		// Remove class attribute entirely if no classes remain
+		node.Attr = slices.Delete(node.Attr, classIndex, classIndex+1)
+	} else {
+		// Update class attribute with remaining classes
+		node.Attr[classIndex].Val = strings.Join(newClasses, " ")
+	}
+}
+
+// HasClass checks if a node has a specific class
+func HasClass(node *html.Node, className string) bool {
+	for _, attr := range node.Attr {
+		if attr.Key == "class" {
+			classes := strings.Fields(attr.Val)
+			if slices.Contains(classes, className) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // Inline formatting elements that are safe for editing
 var inlineFormattingTags = map[string]bool{
 	"strong": true,