Basic implementation of structured emails

app/src/main/java/eu/faircode/email/StructuredEmail.java

@@ -19,25 +19,77 @@ package eu.faircode.email;
     Copyright 2018-2023 by Marcel Bokhorst (M66B)
 */
 
+import org.json.JSONArray;
 import org.json.JSONException;
 import org.json.JSONObject;
 import org.jsoup.nodes.Document;
 
+import java.util.Iterator;
+
 // https://structured.email/content/introduction/getting_started.html
 // https://schema.org/FlightReservation
 
 public class StructuredEmail {
-    private JSONObject jroot;
+    private final JSONObject jroot;
 
     public StructuredEmail(String json) throws JSONException {
         jroot = new JSONObject(json);
     }
 
     public String getHtml() throws JSONException {
+        StringBuilder sb = new StringBuilder();
+        getHtml(jroot, 0, sb);
         Document d = Document.createShell("");
         d.appendElement("pre")
                 .attr("style", "font-size: smaller !important;")
-                .text(jroot.toString(2));
+                .text(sb.toString());
         return d.html();
     }
+
+    private void getHtml(Object obj, int indent, StringBuilder sb) throws JSONException {
+        if (obj instanceof JSONObject) {
+            JSONObject jobject = (JSONObject) obj;
+            Iterator<String> keys = jobject.keys();
+            while (keys.hasNext()) {
+                String key = keys.next();
+                if (key == null || key.startsWith("@"))
+                    continue;
+                Object v = (jobject.isNull(key) ? "" : jobject.get(key));
+                if (v instanceof JSONObject || v instanceof JSONArray) {
+                    sb.append(split(key))
+                            .append(':')
+                            .append('\n');
+                    getHtml(v, indent + 1, sb);
+                } else
+                    sb.append(indent(indent))
+                            .append(split(key))
+                            .append(": ")
+                            .append(v)
+                            .append('\n');
+            }
+        } else if (obj instanceof JSONArray) {
+            JSONArray jarray = (JSONArray) obj;
+            for (int i = 0; i < jarray.length(); i++)
+                getHtml(jarray.get(i), indent + 1, sb);
+        }
+    }
+
+    private String split(String key) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < key.length(); i++) {
+            char kar = key.charAt(i);
+            if (Character.isUpperCase(kar))
+                sb.append(' ').append(Character.toLowerCase(kar));
+            else
+                sb.append(kar);
+        }
+        return sb.toString();
+    }
+
+    private String indent(int count) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < count; i++)
+            sb.append("  ");
+        return sb.toString();
+    }
 }