feat: bootstrap BoxBrain foundation

src/timing.ts

@@ -0,0 +1,78 @@
+import type { BoxBrainAvailability } from './types';
+
+export type RandomSource = () => number;
+
+export interface TypingDelayOptions {
+  rng?: RandomSource | undefined;
+  minSecondsPerCharacter?: number | undefined;
+  maxSecondsPerCharacter?: number | undefined;
+}
+
+export interface ReplyDelayOptions {
+  isFirstReplyInExchange: boolean;
+  rng?: RandomSource | undefined;
+  onlineMinSeconds?: number | undefined;
+  onlineMaxSeconds?: number | undefined;
+  dndReplyProbability?: number | undefined;
+  dndMinSeconds?: number | undefined;
+  dndMaxSeconds?: number | undefined;
+}
+
+export const ONLINE_AVAILABILITY: BoxBrainAvailability = { mode: 'online' };
+export const DND_AVAILABILITY: BoxBrainAvailability = { mode: 'do_not_disturb' };
+export const OFFLINE_AVAILABILITY: BoxBrainAvailability = { mode: 'offline' };
+
+export function createTypingDelay(message: string, options: TypingDelayOptions = {}): number {
+  if (message.length === 0) {
+    return 0;
+  }
+
+  const rng = options.rng ?? Math.random;
+  const min = options.minSecondsPerCharacter ?? 0.05;
+  const max = options.maxSecondsPerCharacter ?? 0.08;
+  const secondsPerCharacter = interpolate(min, max, clampUnit(rng()));
+
+  return roundSeconds(message.length * secondsPerCharacter);
+}
+
+export function createReplyDelay(
+  availability: BoxBrainAvailability,
+  options: ReplyDelayOptions,
+): number | null {
+  if (availability.mode === 'offline') {
+    return null;
+  }
+
+  if (!options.isFirstReplyInExchange) {
+    return 0;
+  }
+
+  const rng = options.rng ?? Math.random;
+
+  if (availability.mode === 'do_not_disturb') {
+    const probability = options.dndReplyProbability ?? 0.2;
+    if (clampUnit(rng()) > probability) {
+      return null;
+    }
+
+    return roundSeconds(interpolate(options.dndMinSeconds ?? 60, options.dndMaxSeconds ?? 600, clampUnit(rng())));
+  }
+
+  return roundSeconds(interpolate(options.onlineMinSeconds ?? 1, options.onlineMaxSeconds ?? 12, clampUnit(rng())));
+}
+
+function interpolate(min: number, max: number, ratio: number): number {
+  return min + (max - min) * ratio;
+}
+
+function clampUnit(value: number): number {
+  if (Number.isNaN(value)) {
+    return 0;
+  }
+
+  return Math.min(1, Math.max(0, value));
+}
+
+function roundSeconds(value: number): number {
+  return Math.round(value * 1_000_000) / 1_000_000;
+}