checking the Blocks with the solution using the XML strings

src/components/Tutorial/compareXml.js

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+export const checkXml = (originalXmlString, userXmlString) => {
+  var originalXml = parseXml(originalXmlString);
+  var userXml = parseXml(userXmlString);
+  return compareXml(originalXml, userXml);
+};
+
+const parseXml = (xmlString) => {
+  var parser = new DOMParser();
+  var xmlDoc = parser.parseFromString(xmlString, "text/xml");
+  return xmlDoc;
+};
+
+const compareNumberOfBlocks = (originalBlocks, userBlocks) => {
+  if(originalBlocks.length !== userBlocks.length){
+    if(originalBlocks.length > userBlocks.length){
+      return {text: 'Es wurden zu wenig Blöcke verwendet.', type: 'error'};
+    }
+    else {
+      return {text: 'Es wurden zu viele Blöcke verwendet.', type: 'error'};
+    }
+  }
+};
+
+const compareBlockType = (originalBlock, userBlock, index) => {
+  if(originalBlock.attributes['type'].value !== userBlock.attributes['type'].value){
+    return {text: `Es wurde ein falscher Blocktyp an Position ${index+1} verwendet`, type: 'error'};
+  }
+};
+
+const compareParentBlock = (originalBlock, userBlock, index) => {
+  // using parentNode instead of parenElement
+  // see https://stackoverflow.com/questions/8685739/difference-between-dom-parentnode-and-parentelement
+  if(originalBlock.parentNode.attributes['name']){
+    if(userBlock.parentNode.attributes['name']){
+      // do the blocks have the same name-properties?
+      if(originalBlock.parentNode.attributes['name'].value !== userBlock.parentNode.attributes['name'].value){
+        if(userBlock.parentNode.attributes['name'].value === 'LOOP_FUNC' || userBlock.parentNode.attributes['name'].value === 'SETUP_FUNC'){
+          return {text: `Der Block mit dem Typen '${userBlock.attributes['type'].value}' wurde irrtümlicherweise in die ${userBlock.parentNode.attributes['name'].value === 'SETUP_FUNC' ? 'Setup' : 'Endlosschleifen'}-Funktion geschrieben.
+                        Verschiebe den gesamten Block (und alle dazugehörigen Blöcke) in die ${userBlock.parentNode.attributes['name'].value !== 'SETUP_FUNC' ? 'Setup' : 'Endlosschleifen'}-Funktion.`, type: 'error'};
+        }
+        // TODO: has a block two name-properties?
+        return {text: `Der Block mit dem Typen '${userBlock.attributes['type'].value}' hat ein falsches 'name'-Attribut`, type: 'error'};
+      }
+    }
+    // user-block has not a name-attribute
+    else {
+      // do the user-block has a xmlns-attribute -> user-block is not connected
+      if(userBlock.parentNode.attributes['xmlns']){
+        return {text: `Der Block mit dem Typen '${userBlock.attributes['type'].value}' hat keine Verbindung zu einem anderen Block.`, type: 'error'};
+      }
+      // user-block has not a xmlns- AND name-attribute
+      else {
+          return {text: `Der Block an Position ${index+1} ist falsch eingeordnet. Tipp: Block an Position ${index+1} einem vorherigen Block unterordnen.`, type: 'error'};
+      }
+    }
+  }
+};
+
+const compareXml = (originalXml, userXml) => {
+  var originalItemList = originalXml.getElementsByTagName("block");
+  var userItemList = userXml.getElementsByTagName("block");
+
+  // compare number of blocks
+  var number = compareNumberOfBlocks(originalItemList, userItemList);
+  if(number){return number;}
+
+  for(var i=0; i < originalItemList.length; i++){
+    // compare type
+    var type = compareBlockType(originalItemList[i], userItemList[i], i);
+    if(type){return type;}
+
+    // compare name
+    var parent = compareParentBlock(originalItemList[i], userItemList[i], i);
+    if(parent){return parent;}
+  }
+
+  return {text: 'Super. Alles richtig!', type: 'success'};
+};