fix: account for onlyFavorites filter in candidateIds (#37)

src/App.tsx

@@ -13,7 +13,7 @@ import { GetNextFiltered, GetPrevFiltered } from "./controllers/pokemonControlle
 
 export default function App() {
   const [currentId, setCurrentId] = useState(1);
-  const { favoritePokemons, isFavorite, toggleFavorite, isLoadingFavorites } =
+  const { favoriteIds, favoritePokemons, isFavorite, toggleFavorite, isLoadingFavorites } =
     useFavorites();
   const { filters, setFilter, resetFilters } = useFilters();
 
@@ -23,14 +23,14 @@ export default function App() {
   });
 
   const handlePrevious = async () => {
-    const prevPokemon = await GetPrevFiltered(currentId, filters);
+    const prevPokemon = await GetPrevFiltered(currentId, filters, favoriteIds);
     if (prevPokemon) {
       setCurrentId(prevPokemon.id);
     }
   };
 
   const handleNext = async () => {
-    const nextPokemon = await GetNextFiltered(currentId, filters);
+    const nextPokemon = await GetNextFiltered(currentId, filters, favoriteIds);
     if (nextPokemon) {
       setCurrentId(nextPokemon.id);
     }

src/components/PokemonList/PokemonList.tsx

@@ -37,8 +37,13 @@ export function PokemonList({
 
   const loading = !onlyFavorites && isPending;
 
+  // Extract IDs from favoritePokemons so matchesFilter can accurately check favorite status
+  const favoriteIds = favoritePokemons.map((pokemon) => pokemon.id);
+
   const pokemonList = onlyFavorites
-    ? favoritePokemons.filter((pokemon) => matchesFilter(pokemon, filters))
+    ? favoritePokemons.filter((pokemon) =>
+        matchesFilter(pokemon, filters, favoriteIds),
+      )
     : fetchedList;
 
   const ordered = [...pokemonList].sort((a, b) =>
@@ -139,4 +144,4 @@ async function buildPokemonList(
   }
 
   return pokemonList;
-}
+}

src/controllers/pokemonController.ts

@@ -29,7 +29,10 @@ function isInRange(val: number, rangeStr?: string): boolean {
 export function matchesFilter(
   pokemon: PokemonData,
   rules: FilterRules,
+  favoriteIds: number[] = [],
 ): boolean {
+
+  if (rules.onlyFavorites && !favoriteIds.includes(pokemon.id)) return false;
   if (rules.type && rules.type.length > 0) {
     const hasType = pokemon.types.some((t) =>
       rules.type?.includes(t.type.name),
@@ -92,15 +95,16 @@ export async function GetMany(ids: number[]): Promise<PokemonData[]> {
 export async function GetPrevFiltered(
   currentId: number,
   rules: FilterRules,
+  favoriteIds: number[] = [],
 ): Promise<PokemonData | null> {
-  const candidates = await candidateIds(rules);
+  const candidates = await candidateIds(rules, favoriteIds);
 
   if (candidates) {
     for (let i = candidates.length - 1; i >= 0; i--) {
       const id = candidates[i];
       if (id >= currentId) continue;
       const pokemon = await fetchSafe(id);
-      if (pokemon && matchesFilter(pokemon, rules)) return pokemon;
+      if (pokemon && matchesFilter(pokemon, rules, favoriteIds)) return pokemon;
     }
     return null;
   }
@@ -109,7 +113,7 @@ export async function GetPrevFiltered(
 
   while (prevId >= 1) {
     const pokemon = await fetchSafe(prevId);
-    if (pokemon && matchesFilter(pokemon, rules)) {
+    if (pokemon && matchesFilter(pokemon, rules, favoriteIds)) {
       return pokemon;
     }
     prevId--;
@@ -120,14 +124,15 @@ export async function GetPrevFiltered(
 export async function GetNextFiltered(
   currentId: number,
   rules: FilterRules,
+  favoriteIds: number[] = [],
 ): Promise<PokemonData | null> {
-  const candidates = await candidateIds(rules);
+  const candidates = await candidateIds(rules, favoriteIds);
 
   if (candidates) {
     for (const id of candidates) {
       if (id <= currentId) continue;
       const pokemon = await fetchSafe(id);
-      if (pokemon && matchesFilter(pokemon, rules)) return pokemon;
+      if (pokemon && matchesFilter(pokemon, rules, favoriteIds)) return pokemon;
     }
     return null;
   }
@@ -136,29 +141,44 @@ export async function GetNextFiltered(
 
   while (nextId <= MAX_POKEMON_ID) {
     const pokemon = await fetchSafe(nextId);
-    if (pokemon && matchesFilter(pokemon, rules)) {
+    if (pokemon && matchesFilter(pokemon, rules, favoriteIds)) {
       return pokemon;
     }
     nextId++;
   }
   return null;
 }
 
-// The ids worth looking at for these rules, or null when every id qualifies.
-// A type rule narrows it to the members of those types, which turns a walk
-// through the whole pokedex into a walk through a short list
+// Returns a sorted, deduplicated list of candidate IDs filtered by type and/or favorites, or null if no candidate filters are active.
 export async function candidateIds(
   rules: FilterRules,
+  favoriteIds: number[] = [],
 ): Promise<number[] | null> {
-  if (!rules.type || rules.type.length === 0) {
+  const hasTypeFilter = Array.isArray(rules.type) && rules.type.length > 0;
+
+  if (!rules.onlyFavorites && !hasTypeFilter) {
     return null;
   }
 
-  const lists = await Promise.all(rules.type.map(idsForType));
+  let typeIdsSet: Set<number> | null = null;
+  if (hasTypeFilter) {
+    const lists = await Promise.all(rules.type!.map(idsForType));
+    // matchesFilter keeps a pokemon that has any of the chosen types, so the
+    // lists are merged rather than intersected
+    typeIdsSet = new Set(lists.flat());
+  }
+
+  if (rules.onlyFavorites) {
+    const uniqueFavorites = Array.from(new Set(favoriteIds));
 
-  // matchesFilter keeps a pokemon that has any of the chosen types, so the
-  // lists are merged rather than intersected
-  return [...new Set(lists.flat())].sort((a, b) => a - b);
+    const result = typeIdsSet
+      ? uniqueFavorites.filter((id) => typeIdsSet!.has(id))
+      : uniqueFavorites;
+
+    return result.sort((a, b) => a - b);
+  }
+
+  return Array.from(typeIdsSet!).sort((a, b) => a - b);
 }
 
 // The members of a type never change during a session, so the id list is
@@ -181,4 +201,4 @@ async function idsForType(type: string): Promise<number[]> {
   } catch {
     return [];
   }
-}
+}

src/controllers/useFavorites.ts

@@ -34,6 +34,7 @@ export function useFavorites() {
   );
 
   return {
+    favoriteIds,
     favoritePokemons,
     isLoadingFavorites: favoriteIds.length > 0 && isPending,
     isFavorite,