feat(api): derive stable placeholder names for hidden profiles (#3224)

fluxer_api/src/api/utils/UsernameGenerator.ts

@@ -8,19 +8,17 @@ import {UsernameType} from '@fluxer/schema/src/primitives/UserValidators';
 const scales = readFileSync(resolveAssetPath('words', 'scales.txt'), 'utf-8').trim().split('\n').filter(Boolean);
 const tails = readFileSync(resolveAssetPath('words', 'tails.txt'), 'utf-8').trim().split('\n').filter(Boolean);
 
+type IndexPicker = (size: number) => number;
+
 function capitalize(word: string): string {
 	return word.charAt(0).toUpperCase() + word.slice(1);
 }
 
-function pickRandom(words: Array<string>): string {
-	return words[randomInt(words.length)];
-}
-
-export function generateRandomUsername(): string {
+function generateUsername(pick: IndexPicker): string {
 	const MAX_LENGTH = 32;
 	const MAX_ATTEMPTS = 100;
 	for (let i = 0; i < MAX_ATTEMPTS; i++) {
-		const username = capitalize(pickRandom(scales)) + capitalize(pickRandom(tails));
+		const username = capitalize(scales[pick(scales.length)]) + capitalize(tails[pick(tails.length)]);
 		if (username.length <= MAX_LENGTH && UsernameType.safeParse(username).success) {
 			return username;
 		}
@@ -33,3 +31,25 @@ export function generateRandomUsername(): string {
 	}
 	return 'BotUser';
 }
+
+function seededPicker(seed: Uint8Array): IndexPicker {
+	const view = new DataView(seed.buffer, seed.byteOffset, seed.byteLength);
+	const words = Math.floor(seed.byteLength / 4);
+	let next = 0;
+	return (size) => {
+		const value = view.getUint32((next % words) * 4);
+		next++;
+		return value % size;
+	};
+}
+
+export function generateRandomUsername(): string {
+	return generateUsername((size) => randomInt(size));
+}
+
+export function generateSeededUsername(seed: Uint8Array): string {
+	if (seed.byteLength < 4) {
+		throw new Error('Username seed must hold at least four bytes');
+	}
+	return generateUsername(seededPicker(seed));
+}