3 files changed, 193 insertions, 0 deletions
diff --git a/src/lib/routes/helpers.ts b/src/lib/routes/helpers.ts
new file mode 100644
index 000000000..be76b9669
--- /dev/null
+++ b/src/lib/routes/helpers.ts
@@ -0,0 +1,77 @@
+import {State, RouteParams} from './types'
+
+export function getCurrentRoute(state: State) {
+  let node = state.routes[state.index || 0]
+  while (node.state?.routes && typeof node.state?.index === 'number') {
+    node = node.state?.routes[node.state?.index]
+  }
+  return node
+}
+
+export function isStateAtTabRoot(state: State | undefined) {
+  if (!state) {
+    // NOTE
+    // if state is not defined it's because init is occuring
+    // and therefore we can safely assume we're at root
+    // -prf
+    return true
+  }
+  const currentRoute = getCurrentRoute(state)
+  return (
+    isTab(currentRoute.name, 'Home') ||
+    isTab(currentRoute.name, 'Search') ||
+    isTab(currentRoute.name, 'Notifications')
+  )
+}
+
+export function isTab(current: string, route: string) {
+  // NOTE
+  // our tab routes can be variously referenced by 3 different names
+  // this helper deals with that weirdness
+  // -prf
+  return (
+    current === route ||
+    current === `${route}Tab` ||
+    current === `${route}Inner`
+  )
+}
+
+export enum TabState {
+  InsideAtRoot,
+  Inside,
+  Outside,
+}
+export function getTabState(state: State | undefined, tab: string): TabState {
+  if (!state) {
+    return TabState.Outside
+  }
+  const currentRoute = getCurrentRoute(state)
+  if (isTab(currentRoute.name, tab)) {
+    return TabState.InsideAtRoot
+  } else if (isTab(state.routes[state.index || 0].name, tab)) {
+    return TabState.Inside
+  }
+  return TabState.Outside
+}
+
+export function buildStateObject(
+  stack: string,
+  route: string,
+  params: RouteParams,
+) {
+  if (stack === 'Flat') {
+    return {
+      routes: [{name: route, params}],
+    }
+  }
+  return {
+    routes: [
+      {
+        name: stack,
+        state: {
+          routes: [{name: route, params}],
+        },
+      },
+    ],
+  }
+}
diff --git a/src/lib/routes/router.ts b/src/lib/routes/router.ts
new file mode 100644
index 000000000..05e0a63de
--- /dev/null
+++ b/src/lib/routes/router.ts
@@ -0,0 +1,55 @@
+import {RouteParams, Route} from './types'
+
+export class Router {
+  routes: [string, Route][] = []
+  constructor(description: Record<string, string>) {
+    for (const [screen, pattern] of Object.entries(description)) {
+      this.routes.push([screen, createRoute(pattern)])
+    }
+  }
+
+  matchName(name: string): Route | undefined {
+    for (const [screenName, route] of this.routes) {
+      if (screenName === name) {
+        return route
+      }
+    }
+  }
+
+  matchPath(path: string): [string, RouteParams] {
+    let name = 'NotFound'
+    let params: RouteParams = {}
+    for (const [screenName, route] of this.routes) {
+      const res = route.match(path)
+      if (res) {
+        name = screenName
+        params = res.params
+        break
+      }
+    }
+    return [name, params]
+  }
+}
+
+function createRoute(pattern: string): Route {
+  let matcherReInternal = pattern.replace(
+    /:([\w]+)/g,
+    (_m, name) => `(?<${name}>[^/]+)`,
+  )
+  const matcherRe = new RegExp(`^${matcherReInternal}([?]|$)`, 'i')
+  return {
+    match(path: string) {
+      const res = matcherRe.exec(path)
+      if (res) {
+        return {params: res.groups || {}}
+      }
+      return undefined
+    },
+    build(params: Record<string, string>) {
+      return pattern.replace(
+        /:([\w]+)/g,
+        (_m, name) => params[name] || 'undefined',
+      )
+    },
+  }
+}
diff --git a/src/lib/routes/types.ts b/src/lib/routes/types.ts
new file mode 100644
index 000000000..e339a46bf
--- /dev/null
+++ b/src/lib/routes/types.ts
@@ -0,0 +1,61 @@
+import {NavigationState, PartialState} from '@react-navigation/native'
+import type {NativeStackNavigationProp} from '@react-navigation/native-stack'
+
+export type {NativeStackScreenProps} from '@react-navigation/native-stack'
+
+export type CommonNavigatorParams = {
+  NotFound: undefined
+  Settings: undefined
+  Profile: {name: string}
+  ProfileFollowers: {name: string}
+  ProfileFollows: {name: string}
+  PostThread: {name: string; rkey: string}
+  PostUpvotedBy: {name: string; rkey: string}
+  PostRepostedBy: {name: string; rkey: string}
+  Debug: undefined
+  Log: undefined
+}
+
+export type HomeTabNavigatorParams = CommonNavigatorParams & {
+  Home: undefined
+}
+
+export type SearchTabNavigatorParams = CommonNavigatorParams & {
+  Search: undefined
+}
+
+export type NotificationsTabNavigatorParams = CommonNavigatorParams & {
+  Notifications: undefined
+}
+
+export type FlatNavigatorParams = CommonNavigatorParams & {
+  Home: undefined
+  Search: undefined
+  Notifications: undefined
+}
+
+export type AllNavigatorParams = CommonNavigatorParams & {
+  HomeTab: undefined
+  Home: undefined
+  SearchTab: undefined
+  Search: undefined
+  NotificationsTab: undefined
+  Notifications: undefined
+}
+
+// NOTE
+// this isn't strictly correct but it should be close enough
+// a TS wizard might be able to get this 100%
+// -prf
+export type NavigationProp = NativeStackNavigationProp<AllNavigatorParams>
+
+export type State =
+  | NavigationState
+  | Omit<PartialState<NavigationState>, 'stale'>
+
+export type RouteParams = Record<string, string>
+export type MatchResult = {params: RouteParams}
+export type Route = {
+  match: (path: string) => MatchResult | undefined
+  build: (params: RouteParams) => string
+}