import: add support to import any xml tab element to XmlComponent (#8)

- make method to import/convert to XmlComponent
 - expose method to add childElement to Header/Footer
 - add tests

src/file/xml-components/imported-xml-component.ts

@@ -1,4 +1,53 @@
 import { XmlComponent, IXmlableObject } from ".";
+import * as fastXmlParser from "fast-xml-parser";
+import { flatMap } from "lodash";
+
+export const parseOptions = {
+    ignoreAttributes: false,
+    attributeNamePrefix: "",
+    attrNodeName: "_attr",
+};
+
+/**
+ * Converts the given xml element (in json format) into XmlComponent.
+ * Note: If element is array, them it will return ImportedXmlComponent[]. Example for given:
+ * element = [
+ *  { w:t: "val 1"},
+ *  { w:t: "val 2"}
+ * ]
+ * will return
+ * [
+ *   ImportedXmlComponent { rootKey: "w:t", root: [ "val 1" ]},
+ *   ImportedXmlComponent { rootKey: "w:t", root: [ "val 2" ]}
+ * ]
+ *
+ * @param elementName name (rootKey) of the XmlComponent
+ * @param element the xml element in json presentation
+ */
+export function convertToXmlComponent(elementName: string, element: any): ImportedXmlComponent | ImportedXmlComponent[] {
+    const xmlElement = new ImportedXmlComponent(elementName, element._attr);
+    if (Array.isArray(element)) {
+        const out: any[] = [];
+        element.forEach((itemInArray) => {
+            out.push(convertToXmlComponent(elementName, itemInArray));
+        });
+        return flatMap(out);
+    } else if (typeof element === "object") {
+        Object.keys(element)
+            .filter((key) => key !== "_attr")
+            .map((item) => convertToXmlComponent(item, element[item]))
+            .forEach((converted) => {
+                if (Array.isArray(converted)) {
+                    converted.forEach(xmlElement.push.bind(xmlElement));
+                } else {
+                    xmlElement.push(converted);
+                }
+            });
+    } else if (element !== "") {
+        xmlElement.push(element);
+    }
+    return xmlElement;
+}
 
 /**
  * Represents imported xml component from xml file.
@@ -53,6 +102,23 @@ export class ImportedXmlComponent extends XmlComponent {
     push(xmlComponent: XmlComponent) {
         this.root.push(xmlComponent);
     }
+
+    /**
+     * Converts the xml string to a XmlComponent tree.
+     *
+     * @param importedContent xml content of the imported component
+     */
+    static fromXmlString(importedContent: string): ImportedXmlComponent {
+        const imported = fastXmlParser.parse(importedContent, parseOptions);
+        const elementName = Object.keys(imported)[0];
+        
+        const converted = convertToXmlComponent(elementName, imported[elementName]);
+
+        if (Array.isArray(converted) && converted.length > 1)  {
+            throw new Error("Invalid conversion, input must be one element.");
+        }
+        return Array.isArray(converted) ? converted[0] : converted;
+    }
 }
 
 /**