// docs/SIDEBAR.md: the session card's meta line — activity colour mapping and
// the shared duration format. Both clients compute it identically; the TUI
// mirrors this in crates/maestro-tui.

import type { ActivityState, IsoTimestamp, Session } from "./types.js";
import { sessionBlockers } from "./types.js";

/** A state held shorter than this keeps the card to one line (contract rule 1). */
const META_LINE_MIN_HOLD_MS = 30_000;

// Payloads predating #102 default `activity_since` to the Unix epoch; anything
// implausibly old is treated as "never observed" rather than a huge duration.
const PLAUSIBLE_EPOCH_MS = Date.UTC(2010, 0, 1);

export function activityHeldMs(since: IsoTimestamp | undefined, now: number): number | null {
  if (!since) return null;
  const t = Date.parse(since);
  if (Number.isNaN(t) || t < PLAUSIBLE_EPOCH_MS) return null;
  return Math.max(0, now - t);
}

/** `<60s` → whole seconds, `<60m` → whole minutes, else whole hours. Floored
 *  everywhere so the counter never shows a duration the state hasn't reached. */
export function activityDurationLabel(heldMs: number): string {
  const s = Math.floor(heldMs / 1000);
  if (s < 60) return `${s}s`;
  const m = Math.floor(s / 60);
  if (m < 60) return `${m}m`;
  return `${Math.floor(m / 60)}h`;
}

/** CSS hook for the state's colour (`styles.css` maps slugs to tokens). An
 *  unknown variant degrades to idle so rendering never fails (Precedence). */
export function activityColorSlug(state: ActivityState | string): string {
  switch (state) {
    case "Active":
      return "active";
    case "AwaitingInput":
      return "awaiting-input";
    case "Error":
      return "error";
    default:
      return "idle";
  }
}

/** Line 2 renders only when at least one contract trigger holds. */
export function showsMetaLine(s: Session, now: number = Date.now()): boolean {
  const held = activityHeldMs(s.activity_since, now);
  return (
    (held !== null && held >= META_LINE_MIN_HOLD_MS) ||
    sessionBlockers(s) !== null ||
    s.status === "Dead" ||
    s.activity === "Error"
  );
}