import { addDaysIso, mondayOf } from "@/domain/work-orders/utils/wizard-date-utils";

const ISO_DATE = /^\d{4}-\d{2}-\d{2}$/;

/**
 * Saturday of the week prior to the scheduledOn week (ISO date only).
 * Cutoff instant is end of that day (23:59:59 local).
 *
 * SH-184: backend recalculates `isAddOn` whenever scheduling moves across weeks
 * or is cleared, and owns audit. This helper is only a create-time FE hint.
 */
export function getAddonCutoffIso(scheduledOn: string): string | null {
  const trimmed = scheduledOn.trim();
  if (!ISO_DATE.test(trimmed)) {
    return null;
  }
  return addDaysIso(mondayOf(trimmed), -2);
}

/**
 * Preview whether Add-On would apply for a create-time schedule + createdAt.
 * Returns null when scheduledOn is missing — callers may use a manual override.
 *
 * Not a freeze: after create (and on every schedule patch/clear) the backend is
 * authoritative; FE must consume the returned `isAddOn` (SH-184).
 */
export function previewIsAddOnFromCutoff(input: {
  createdAt: Date | string | number;
  scheduledOn: string;
}): boolean | null {
  const cutoffIso = getAddonCutoffIso(input.scheduledOn);
  if (!cutoffIso) {
    return null;
  }

  const createdAt = input.createdAt instanceof Date ? input.createdAt : new Date(input.createdAt);
  if (Number.isNaN(createdAt.getTime())) {
    return null;
  }

  const cutoff = new Date(`${cutoffIso}T23:59:59`);
  return createdAt.getTime() > cutoff.getTime();
}

/** @deprecated Prefer `previewIsAddOnFromCutoff` — name implied a freeze (SH-126). */
export const computeIsAddOnAtCreation = previewIsAddOnFromCutoff;

/**
 * Resolve create-payload `isAddOn` hint: cutoff preview when scheduled, else
 * manual override. Backend may recalculate immediately and on later schedule
 * patches/clears; FE must not treat this value as frozen (SH-184).
 */
export function resolveIsAddOnForCreate(input: {
  createdAt?: Date | string | number;
  scheduledOn: string;
  manualOverride?: boolean;
}): boolean {
  const computed = previewIsAddOnFromCutoff({
    createdAt: input.createdAt ?? new Date(),
    scheduledOn: input.scheduledOn,
  });
  if (computed !== null) {
    return computed;
  }
  return Boolean(input.manualOverride);
}