/**
 * @module algo.followUpScheduler
 *
 * Follow-Up Scheduling Algorithm
 * ===============================
 *
 * Determines the due date for follow-up activities created by the
 * opportunity workflow. The follow-up is always assigned to the user
 * who triggered its creation.
 *
 * ## TODO — Calendar-aware scheduling
 *
 * This module currently uses a **dummy algorithm** that schedules the
 * follow-up for the next business day at 10:00 AM local time.
 *
 * It needs to be replaced with an availability-aware algorithm that:
 *   1. Reads the assigned user's calendar (Microsoft Graph / CW schedule).
 *   2. Finds the earliest open slot of sufficient duration.
 *   3. Respects company-wide blackout dates (holidays, company events).
 *   4. Accounts for the user's working-hours preferences.
 *
 * Until that integration is complete, the simple "next business day"
 * heuristic is used as a placeholder.
 */

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

export interface FollowUpScheduleInput {
  /** The user who triggered the activity (follow-up is assigned to them). */
  triggeredByUserId: string;

  /** Optional override for "now" — useful for testing. */
  now?: Date;
}

export interface FollowUpScheduleResult {
  /** Suggested due date for the follow-up activity. */
  dueDate: Date;

  /** ISO string version for CW API payloads. */
  dueDateIso: string;
}

// ---------------------------------------------------------------------------
// Core
// ---------------------------------------------------------------------------

/**
 * Schedule a follow-up activity.
 *
 * Returns a suggested `dueDate` for the follow-up activity.
 * Currently uses dummy logic: next business day at 10:00 AM.
 *
 * @param input - Scheduling parameters
 * @returns The scheduled follow-up date
 */
export function scheduleFollowUp(
  input: FollowUpScheduleInput,
): FollowUpScheduleResult {
  const now = input.now ?? new Date();
  const dueDate = getNextBusinessDay(now);

  // Set to 10:00 AM
  dueDate.setHours(10, 0, 0, 0);

  return {
    dueDate,
    dueDateIso: dueDate.toISOString(),
  };
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

/**
 * Returns the next business day (Mon–Fri) from the given date.
 * If the given date is already a weekday before 10 AM, returns
 * the NEXT business day (not the same day).
 */
function getNextBusinessDay(from: Date): Date {
  const result = new Date(from);

  // Always advance at least one day
  result.setDate(result.getDate() + 1);

  const day = result.getDay();

  // Saturday → Monday (+2)
  if (day === 6) result.setDate(result.getDate() + 2);
  // Sunday → Monday (+1)
  if (day === 0) result.setDate(result.getDate() + 1);

  return result;
}