/**
 * The one fact that goes stale inside a session: the time.
 *
 * The session-start reminder stamps the clock once, so a conversation picked up
 * the next morning still believes it is yesterday. This line rides along with
 * every prompt instead, in the principal's own timezone, because "is it morning"
 * is the question the agent keeps getting wrong.
 */

import { identity, isEnabled } from "./settings";

const FIELDS = {
  weekday: "short",
  year: "numeric",
  month: "2-digit",
  day: "2-digit",
  hour: "2-digit",
  minute: "2-digit",
  hourCycle: "h23",
} as const;

function fieldsIn(now: Date, timeZone: string): Record<string, string> {
  const parts = new Intl.DateTimeFormat("en-US", { ...FIELDS, timeZone }).formatToParts(
    now
  );
  return Object.fromEntries(parts.map((p) => [p.type, p.value]));
}

/** The IANA name Intl settles on, or null when it does not recognise the input. */
export function canonicalTimeZone(timeZone: string): string | null {
  try {
    return new Intl.DateTimeFormat("en-US", { timeZone }).resolvedOptions().timeZone;
  } catch {
    return null;
  }
}

export function isValidTimeZone(timeZone: string): boolean {
  return canonicalTimeZone(timeZone) !== null;
}

/** A configured timezone is user input, and Intl throws on a bad one. UTC is always true. */
function zoneOrUtc(timeZone: string): string {
  return timeZone && isValidTimeZone(timeZone) ? timeZone : "UTC";
}

/** @lintignore exercised directly by test/wall-clock.test.ts */
export function wallClockLine(now: Date, configuredZone: string): string {
  const zone = zoneOrUtc(configuredZone);
  const f = fieldsIn(now, zone);
  return `Now: ${f.weekday} ${f.year}-${f.month}-${f.day} ${f.hour}:${f.minute} ${zone}`;
}

export function getWallClockReminder(now: Date = new Date()): string | null {
  if (!isEnabled("wallClock")) return null;
  const line = wallClockLine(now, identity().principal.timezone);
  return `<system-reminder>${line}</system-reminder>`;
}