// Module level: const with UPPER_SNAKE_CASE for primitives
const MAX_RETRIES = 3;
const userCache = new Map<string, User>();

// Inside functions: always let
function process(items: Item[]) {
  let total = 0;
  let result = [];
  for (let item of items) {
    total += item.price;
  }
  return { total, result };
}

// Good: function declaration
function calculateTotal(items: Item[]): number {
  let total = 0;
  for (let item of items) {
    total += item.price;
  }
  return total;
}

// Good: arrow for inline callbacks
let active = users.filter((u) => u.isActive);

// Good: arrow when type requires it
const handler: ActionFunction = async ({ request }) => {
  // ...
};

// Bad: default export
export default function formatCurrency(amount: number) { ... }

// Good: named export
export function formatCurrency(amount: number) { ... }

// Exception: Remix routes use default export named "Component"
export default function Component() { ... }

// Bad: type assertion
let user = response.data as User;

// Good: Zod validation
let user = UserSchema.parse(response.data);

// Good: type guard
if (isUser(response.data)) {
  let user = response.data;
}

// Bad: restates the code
// Set the user's name
let userName = user.name;

// Good: explains business rule
// Transactions under $250 don't require written acknowledgment per policy
if (transaction.amount < 250) {
  return { requiresAcknowledgment: false };
}

// Bad: O(n) per check
const allowedIds = ["a", "b", "c"];
items.filter((item) => allowedIds.includes(item.id));

// Good: O(1) per check
const allowedIds = new Set(["a", "b", "c"]);
items.filter((item) => allowedIds.has(item.id));

// Bad: O(n) per lookup = O(n*m) total
orders.map((order) => ({
  ...order,
  user: users.find((u) => u.id === order.userId),
}));

// Good: O(1) per lookup = O(n+m) total
const userById = new Map(users.map((u) => [u.id, u]));
orders.map((order) => ({
  ...order,
  user: userById.get(order.userId),
}));

// Bad: mutates original array
const sorted = users.sort((a, b) => a.name.localeCompare(b.name));

// Good: creates new sorted array
const sorted = users.toSorted((a, b) => a.name.localeCompare(b.name));

// Bad: 3 iterations
const admins = users.filter((u) => u.isAdmin);
const testers = users.filter((u) => u.isTester);
const inactive = users.filter((u) => !u.isActive);

// Good: 1 iteration
const admins: User[] = [],
  testers: User[] = [],
  inactive: User[] = [];
for (const user of users) {
  if (user.isAdmin) admins.push(user);
  if (user.isTester) testers.push(user);
  if (!user.isActive) inactive.push(user);
}

// Bad: repeated lookups
for (let i = 0; i < arr.length; i++) {
  process(obj.config.settings.value);
}

// Good: cached lookup
const value = obj.config.settings.value;
const len = arr.length;
for (let i = 0; i < len; i++) {
  process(value);
}

const slugifyCache = new Map<string, string>();

function cachedSlugify(text: string): string {
  if (!slugifyCache.has(text)) {
    slugifyCache.set(text, slugify(text));
  }
  return slugifyCache.get(text)!;
}

const storageCache = new Map<string, string | null>();

function getLocalStorage(key: string) {
  if (!storageCache.has(key)) {
    storageCache.set(key, localStorage.getItem(key));
  }
  return storageCache.get(key);
}

// Bad: continues after finding error
function validate(users: User[]) {
  let error = "";
  for (const user of users) {
    if (!user.email) error = "Email required";
  }
  return error ? { error } : { valid: true };
}

// Good: returns immediately
function validate(users: User[]) {
  for (const user of users) {
    if (!user.email) return { error: "Email required" };
  }
  return { valid: true };
}

// Bad: always sorts even when lengths differ
function hasChanges(a: string[], b: string[]) {
  return a.sort().join() !== b.sort().join();
}

// Good: early return if lengths differ
function hasChanges(a: string[], b: string[]) {
  if (a.length !== b.length) return true;
  let aSorted = a.toSorted();
  let bSorted = b.toSorted();
  return aSorted.some((v, i) => v !== bSorted[i]);
}

// Bad: O(n log n)
const latest = [...projects].sort((a, b) => b.updatedAt - a.updatedAt)[0];

// Good: O(n)
let latest = projects[0];
for (const p of projects) {
  if (p.updatedAt > latest.updatedAt) latest = p;
}

// Bad: creates regex every iteration
items.forEach(item => {
  if (/pattern/.test(item.text)) { ... }
})

// Good: create once
const PATTERN = /pattern/
items.forEach(item => {
  if (PATTERN.test(item.text)) { ... }
})

// Bad: interleaved reads/writes force reflows
element.style.width = "100px";
const width = element.offsetWidth; // forces reflow
element.style.height = "200px";

// Good: batch writes, then read
element.style.width = "100px";
element.style.height = "200px";
const { width, height } = element.getBoundingClientRect();

let result = success(data);
if (isFailure(result)) return handleError(result.error);