/** Durable transcript markers for significant gaps in session activity. */

import { formatVerbose } from "./format.ts";

/** Four hours: short pauses stay quiet, while a resumed work period is explicit. */
export const DEFAULT_GAP_THRESHOLD_MS = 4 * 60 * 60 * 1_000;

export interface TimeShift {
  readonly fromMs: number;
  readonly toMs: number;
  readonly durationMs: number;
}

/** Return a time shift when both endpoints are valid and the configured threshold is reached. */
export function timeShift(
  fromMs: number | undefined,
  toMs: number,
  thresholdMs: number = DEFAULT_GAP_THRESHOLD_MS,
): TimeShift | undefined {
  if (
    fromMs === undefined ||
    !Number.isFinite(fromMs) ||
    !Number.isFinite(toMs) ||
    !Number.isFinite(thresholdMs) ||
    fromMs <= 0 ||
    toMs < fromMs ||
    thresholdMs < 0
  ) {
    return;
  }
  const durationMs = toMs - fromMs;
  if (durationMs < thresholdMs) return;
  return { fromMs, toMs, durationMs };
}

/** Stable, model-readable text that also serves as the human session notice. */
export function renderTimeShift(shift: TimeShift): string {
  return `[time-shift from="${new Date(shift.fromMs).toISOString()}" to="${new Date(shift.toMs).toISOString()}" duration="${formatVerbose(shift.durationMs)}"]`;
}