Implemented basic external transform function

* "InputXSLT:transform" expects two input arguments and executes the given transformation into the given target file
** this function respresents a important step in the direction of making it possible to write an actual static site generator on top of InputXSLT using XSLT
* added basic "transform" test case
* updated README.md to include this new function

9 files changed, 256 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5173ef4..da44f2b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,6 +27,7 @@ set(
 	src/function/read_file.cc
 	src/function/read_xml_file.cc
 	src/function/read_directory.cc
+	src/function/transform.cc
 	src/support/filesystem_context.cc
 	src/support/stylesheet_parameter_guard.cc
 	src/support/dom/document_cache.cc
diff --git a/README.md b/README.md
index 5ae65e5..867de8f 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,7 @@ Contrary to popular opinion I actually like XSLT as a content transformation lan
 - external `read-file` function for read-only access to text files
 - external `read-xml-file` function for read-only access to XML files
 - external `read-directory` function for read-only directory traversal
+- external `transform` function for executing transformations inside transformations
 
 ## Requirements:
 
diff --git a/src/function/transform.cc b/src/function/transform.cc
new file mode 100644
index 0000000..9b600d9
--- /dev/null
+++ b/src/function/transform.cc
@@ -0,0 +1,113 @@
+#include "transform.h"
+
+#include <xercesc/dom/DOMDocument.hpp>
+#include <xercesc/dom/DOMImplementation.hpp>
+#include <xercesc/dom/DOMElement.hpp>
+
+#include "transformation_facade.h"
+#include "support/xerces_string_guard.h"
+
+namespace {
+
+using InputXSLT::XercesStringGuard;
+
+xercesc::DOMDocument* constructDocument(
+	const InputXSLT::FilesystemContext&,
+	const boost::filesystem::path& transformationPath,
+	const boost::filesystem::path& targetPath
+) {
+	xercesc::DOMDocument* const domDocument(
+		xercesc::DOMImplementation::getImplementation()->createDocument(
+			nullptr,
+			*XercesStringGuard<XMLCh>("content"),
+			nullptr
+		)
+	);
+
+	xercesc::DOMNode* const rootNode(
+		domDocument->getDocumentElement()
+	);
+
+	InputXSLT::TransformationFacade transformation(
+		transformationPath.string()
+	);
+
+	const int result = transformation.generate(
+		targetPath.string()
+	);
+
+	if ( result == 0 ) {
+		xercesc::DOMElement* const resultNode(
+			domDocument->createElement(*XercesStringGuard<XMLCh>("result"))
+		);
+
+		resultNode->setAttribute(
+			*XercesStringGuard<XMLCh>("name"),
+			*XercesStringGuard<XMLCh>(targetPath.string())
+		);
+
+		rootNode->appendChild(resultNode);
+	} else {
+		xercesc::DOMElement* const resultNode(
+			domDocument->createElement(*XercesStringGuard<XMLCh>("error"))
+		);
+
+		rootNode->appendChild(resultNode);
+	}
+
+	return domDocument;
+}
+
+}
+
+namespace InputXSLT {
+
+FunctionTransform::FunctionTransform():
+	document_cache_(std::make_shared<DomDocumentCache>()) { }
+
+xalan::XObjectPtr FunctionTransform::execute(
+	xalan::XPathExecutionContext& executionContext,
+	xalan::XalanNode*,
+	const xalan::XObjectPtr argument1,
+	const xalan::XObjectPtr argument2,
+	const xalan::Locator* locator
+) const {
+	const FilesystemContext fsContext(locator);
+
+	xalan::XalanDocument* const domDocument(
+		this->document_cache_->create(
+			constructDocument(
+				fsContext,
+				fsContext.resolve(argument1->str()),
+				fsContext.resolve(argument2->str())
+			)
+		)
+	);
+
+	xalan::XPathExecutionContext::BorrowReturnMutableNodeRefList nodeList(
+		executionContext
+	);
+
+	nodeList->addNodes(
+		*domDocument->getDocumentElement()->getChildNodes()
+	);
+
+	return executionContext.getXObjectFactory().createNodeSet(nodeList);
+}
+
+FunctionTransform* FunctionTransform::clone(
+	xalan::MemoryManager& manager) const {
+	return xalan::XalanCopyConstruct(
+		manager,
+		*this
+	);
+}
+
+const xalan::XalanDOMString& FunctionTransform::getError(
+	xalan::XalanDOMString& result) const {
+	result.assign("The function expects two arguments of type string.");
+
+	return result;
+}
+
+}
diff --git a/src/function/transform.h b/src/function/transform.h
new file mode 100644
index 0000000..41bba05
--- /dev/null
+++ b/src/function/transform.h
@@ -0,0 +1,43 @@
+#ifndef INPUTXSLT_SRC_FUNCTION_TRANSFORM_H_
+#define INPUTXSLT_SRC_FUNCTION_TRANSFORM_H_
+
+#include <xalanc/XalanTransformer/XalanTransformer.hpp>
+#include <xalanc/XPath/XObjectFactory.hpp>
+#include <xalanc/XPath/Function.hpp>
+#include <xalanc/XPath/XObject.hpp>
+
+#include <memory>
+
+#include "common.h"
+#include "support/dom/document_cache.h"
+#include "support/filesystem_context.h"
+
+namespace InputXSLT {
+
+class FunctionTransform : public xalan::Function {
+	public:
+		FunctionTransform();
+
+		virtual xalan::XObjectPtr execute(
+			xalan::XPathExecutionContext&,
+			xalan::XalanNode*,
+			const xalan::XObjectPtr,
+			const xalan::XObjectPtr,
+			const xalan::Locator*
+		) const;
+
+		virtual FunctionTransform* clone(xalan::MemoryManager&) const;
+
+		FunctionTransform& operator=(const FunctionTransform&) = delete;
+		bool operator==(const FunctionTransform&) const        = delete;
+
+	private:
+		std::shared_ptr<DomDocumentCache> document_cache_;
+
+		const xalan::XalanDOMString& getError(xalan::XalanDOMString&) const;
+
+};
+
+}
+
+#endif  // INPUTXSLT_SRC_FUNCTION_TRANSFORM_H_
diff --git a/src/plattform_guard.cc b/src/plattform_guard.cc
index 2c3cee4..da3b6d7 100644
--- a/src/plattform_guard.cc
+++ b/src/plattform_guard.cc
@@ -9,6 +9,7 @@
 #include "function/read_file.h"
 #include "function/read_xml_file.h"
 #include "function/read_directory.h"
+#include "function/transform.h"
 
 namespace InputXSLT {
 
@@ -37,6 +38,12 @@ PlattformGuard::PlattformGuard() {
 		xalan::XalanDOMString("read-directory"),
 		InputXSLT::FunctionReadDirectory()
 	);
+
+	xalan::XalanTransformer::installExternalFunctionGlobal(
+		customNamespace,
+		xalan::XalanDOMString("transform"),
+		InputXSLT::FunctionTransform()
+	);
 }
 
 PlattformGuard::~PlattformGuard() {
diff --git a/test/read_directory/reference.xml b/test/read_directory/reference.xml
index 76fb84f..fedd903 100644
--- a/test/read_directory/reference.xml
+++ b/test/read_directory/reference.xml
@@ -5,6 +5,7 @@
 <item>read_xml_file</item>
 <item>common</item>
 <item>read_file</item>
+<item>transform</item>
 <item>default_params</item>
 </function_read_directory>
 </test_case>
diff --git a/test/transform/reference.xml b/test/transform/reference.xml
new file mode 100644
index 0000000..37c060e
--- /dev/null
+++ b/test/transform/reference.xml
@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<test_case>
+<transform>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
+&lt;xsl:stylesheet
+	version="1.0"
+	xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+	xmlns:InputXSLT="function.inputxslt.application"
+	exclude-result-prefixes="InputXSLT"
+&gt;
+
+&lt;xsl:output
+	method="xml"
+	omit-xml-declaration="no"
+	encoding="UTF-8"
+	indent="yes"
+/&gt;
+
+&lt;xsl:template match="/"&gt;
+&lt;test_case&gt;
+	&lt;transform&gt;
+		&lt;xsl:variable
+			name   = "result"
+			select = "InputXSLT:transform('test.xsl', 'test_actual.xml')"
+		/&gt;
+
+		&lt;xsl:value-of select="
+			InputXSLT:read-xml-file('test_actual.xml')/test_case/transform_test
+		"/&gt;
+	&lt;/transform&gt;
+&lt;/test_case&gt;
+&lt;/xsl:template&gt;
+
+&lt;/xsl:stylesheet&gt;
+</transform>
+</test_case>
diff --git a/test/transform/test.xsl b/test/transform/test.xsl
new file mode 100644
index 0000000..40134c4
--- /dev/null
+++ b/test/transform/test.xsl
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet
+	version="1.0"
+	xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+	xmlns:InputXSLT="function.inputxslt.application"
+	exclude-result-prefixes="InputXSLT"
+>
+
+<xsl:output
+	method="xml"
+	omit-xml-declaration="no"
+	encoding="UTF-8"
+	indent="yes"
+/>
+
+<xsl:template match="/">
+<test_case>
+	<transform_test>
+		<xsl:value-of select="InputXSLT:read-file('transformation.xsl')"/>
+	</transform_test>
+</test_case>
+</xsl:template>
+
+</xsl:stylesheet>
diff --git a/test/transform/transformation.xsl b/test/transform/transformation.xsl
new file mode 100644
index 0000000..9039642
--- /dev/null
+++ b/test/transform/transformation.xsl
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet
+	version="1.0"
+	xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+	xmlns:InputXSLT="function.inputxslt.application"
+	exclude-result-prefixes="InputXSLT"
+>
+
+<xsl:output
+	method="xml"
+	omit-xml-declaration="no"
+	encoding="UTF-8"
+	indent="yes"
+/>
+
+<xsl:template match="/">
+<test_case>
+	<transform>
+		<xsl:variable
+			name   = "result"
+			select = "InputXSLT:transform('test.xsl', 'test_actual.xml')"
+		/>
+
+		<xsl:value-of select="
+			InputXSLT:read-xml-file('test_actual.xml')/test_case/transform_test
+		"/>
+	</transform>
+</test_case>
+</xsl:template>
+
+</xsl:stylesheet>