Show problems with dialog in debugger

src/Debugger.svelte

 <script lang="ts">
   import { gameFactsStore, addGameFactToFactArray, toggleFactInFactArray } from './gameFacts'
   import type { Dialog, DialogMap, DialogSet } from './types';
+  import {findDialogSetProblems} from "./utils"
   
   export let currentDialog: Dialog;
   export let dialogSet: DialogSet;
@@ -28,7 +29,16 @@
 				{dialogName}
 			</option>
 		{/each}
-	</select>
+    </select>
+    <br>
+    <ol>
+        {#each findDialogSetProblems(dialogSet) as {sourceDialog, text}}
+        <li>
+            {sourceDialog}: <code style="color: orange">{text}</code>
+        </li>
+    {/each}
+    </ol>
+    
     <hr>
 
     <h3>Quest-Debugger</h3>

src/utils.ts

-import type { DialogSet } from "./types";
+import type { DialogMap, DialogOption, DialogSet } from "./types";
 
 /**
  * Returns true, if input is a valid name of a dialogSet.
@@ -39,3 +39,58 @@ export async function fetchDialogSet(): Promise<DialogSet> {
     throw error;
   }
 }
+
+export function findDialogSetProblems(dialogSet: DialogSet) {
+  const dialogReferenceProblems = checkForInvalidDialogReferences(dialogSet);
+  return [...dialogReferenceProblems];
+}
+
+interface DialogReferenceProblem {
+  type: "DialogReferenceProblem";
+  sourceDialog: string;
+  text: string;
+}
+
+function checkForInvalidDialogReferences(
+  dialogSet: DialogSet
+): DialogReferenceProblem[] {
+  const dialogs = dialogSet.dialogs;
+  const problems: DialogReferenceProblem[] = [];
+  const allDialogKeys = Object.keys(dialogs);
+  const allLinkedToDialogKeys: Set<string> = new Set();
+  for (const dialogName of allDialogKeys) {
+    // TODO check all buttons for invalid references
+    for (const { text, linksToDialog } of dialogs[dialogName].options) {
+      allLinkedToDialogKeys.add(linksToDialog);
+      if (!allDialogKeys.includes(linksToDialog)) {
+        problems.push({
+          type: "DialogReferenceProblem",
+          sourceDialog: dialogName,
+          text: `Dialog ${dialogName}'s option "${text}" links to unknown dialog '${linksToDialog}'`,
+        });
+      }
+
+      if (linksToDialog === dialogName) {
+        problems.push({
+          type: "DialogReferenceProblem",
+          sourceDialog: dialogName,
+          text: `Dialog ${dialogName}'s option "${text}" links to itself!`,
+        });
+      }
+    }
+  }
+
+  for (const dialogName of allDialogKeys) {
+    if (
+      !allLinkedToDialogKeys.has(dialogName) &&
+      dialogSet.startDialogName !== dialogName
+    ) {
+      problems.push({
+        type: "DialogReferenceProblem",
+        sourceDialog: dialogName,
+        text: `Dialog ${dialogName} is unreachable: Neither linked to from any other dialog, nor startDialog`,
+      });
+    }
+  }
+  return problems;
+}