Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/tools/js/CharacterBuilder/utils/navigationUtils.ts

@@ -0,0 +1,163 @@
+import { flatten } from "lodash";
+
+import {
+  featureFlagInfoSelectors,
+  rulesEngineSelectors,
+} from "@dndbeyond/character-rules-engine";
+
+import config from "~/config";
+import { NavigationType } from "~/subApps/builder/constants";
+
+import * as navConfig from "../config/navigation";
+import { builderSelectors } from "../selectors";
+
+const BASE_PATHNAME = config.basePathname;
+
+function checkIsRouteInNavConfig(targetRouteDef, navConfig) {
+  const routeDefs: Array<any> = flatten(
+    navConfig.map((section) => section.routes)
+  );
+  return routeDefs.filter((routeDef) => routeDef.key === targetRouteDef.key)
+    .length;
+}
+
+export function checkStdBuilderPageRequirements(routeDef, state) {
+  return (
+    builderSelectors.getBuilderMethod(state) !== null &&
+    checkIsRouteInNavConfig(
+      routeDef,
+      navConfig.getNavBuilderConfig(
+        builderSelectors.getBuilderMethod(state),
+        featureFlagInfoSelectors.getFeatureFlagInfo(state)
+      )
+    )
+  );
+}
+
+export function checkIsCurrentRouteInRoutePathing(state) {
+  const currentPath = state.routeControls.currentPath;
+  const characterId = rulesEngineSelectors.getId(state);
+  const routePathing = builderSelectors.getRoutePathing(state);
+  const currentRoutePathIdx = getRoutePathIdxByPath(
+    currentPath,
+    routePathing,
+    characterId
+  );
+  return currentRoutePathIdx > 0;
+}
+
+// TODO: This function seems to jsut return '/' so investigate it and remove it if it's not needed
+export const getAvailableRouteRedirect = (routeKey, state) => {
+  const routePath = navConfig.getRouteDefPath(routeKey);
+  const routePathing = builderSelectors.getRoutePathing(state);
+  const currentRoutePathIdx = getRoutePathIdxByPath(routePath, routePathing);
+
+  const currentRoutePathingNode = routePathing[currentRoutePathIdx];
+
+  if (currentRoutePathIdx === -1 || !currentRoutePathingNode.available) {
+    return "/";
+  }
+
+  return "/";
+};
+
+export const getRoutePathIdx = (routeKey, routePathDef) => {
+  const path = navConfig.getRouteDefPath(routeKey);
+  return routePathDef.findIndex((routeDef) => path === routeDef.path);
+};
+
+export function getRoutePathIdxByPath(path, routePathDef, characterId = 0) {
+  return routePathDef.findIndex(
+    (routeDef) => path === routeDef.path.replace(":characterId", characterId)
+  );
+}
+
+export function getCurrentSectionHelpRoutePath(state) {
+  const currentPath = builderSelectors.getCurrentPath(state);
+  const sections = navConfig.getNavigationSections(
+    builderSelectors.getBuilderMethod(state),
+    navConfig.getCurrentRouteDef(currentPath),
+    featureFlagInfoSelectors.getFeatureFlagInfo(state)
+  );
+  const currentSection = sections.find((section) => section.active);
+  const currentSectionHelpRoute = currentSection.routes.find(
+    (route) => route.type === NavigationType.HelpPage
+  );
+  //TODO change this to getRouteDefPath once it takes a routeDef instead of routeKey
+  if (currentSectionHelpRoute) {
+    return currentSectionHelpRoute.path;
+  } else {
+    return null;
+  }
+}
+
+export function getAvailablePathRedirect(state) {
+  const currentPath = builderSelectors.getCurrentPath(state);
+  const routePathing = builderSelectors.getRoutePathing(state);
+  const characterId = rulesEngineSelectors.getId(state);
+  const currentRoutePathIdx = getRoutePathIdxByPath(
+    currentPath,
+    routePathing,
+    characterId
+  );
+
+  const currentRoutePathingNode = routePathing[currentRoutePathIdx];
+  if (!currentRoutePathingNode.available) {
+    for (let i = currentRoutePathIdx; i < routePathing.length; i++) {
+      if (routePathing[i].available) {
+        return routePathing[i].path;
+      }
+    }
+  }
+
+  return null;
+}
+
+export const getAvailablePrevRoute = (routeDef, state) => {
+  const availableRoutePath = builderSelectors.getAvailableRoutePathing(state);
+  const currentRoutePathIdx = getRoutePathIdx(routeDef.key, availableRoutePath);
+
+  // -1 === can't find in route path
+  // 0 === first page in path and there isn't a previous
+  if (currentRoutePathIdx <= 0) {
+    return null;
+  }
+
+  return availableRoutePath[currentRoutePathIdx - 1];
+};
+
+export const getAvailableNextRoute = (routeDef, state) => {
+  const availableRoutePath = builderSelectors.getAvailableRoutePathing(state);
+  const currentRoutePathIdx = getRoutePathIdx(routeDef.key, availableRoutePath);
+  const lastAvailableRoutePathIdx = availableRoutePath.length - 1;
+
+  // -1 === can't find in route path
+  // current = last === can't go any next because at last
+  if (
+    currentRoutePathIdx < 0 ||
+    currentRoutePathIdx >= lastAvailableRoutePathIdx
+  ) {
+    return null;
+  }
+
+  return availableRoutePath[currentRoutePathIdx + 1];
+};
+
+export function getCharacterBuilderUrl(characterId): string {
+  return `${BASE_PATHNAME}/${characterId}/builder`;
+}
+
+export function getCharacterSheetUrl(characterId): string {
+  return `${BASE_PATHNAME}/${characterId}`;
+}
+
+export function getCharacterListingUrl(): string {
+  return `${BASE_PATHNAME}`;
+}
+
+export function getUrlWithParams(url?: string): string {
+  const baseUrl = url ?? BASE_PATHNAME;
+  return window.location.search
+    ? `${baseUrl}${window.location.search}`
+    : baseUrl;
+}