import type { EmptyContainerSize } from "@/types/importOperations";

export interface EmptyLoadPick {
  id: string;
  containerSize: EmptyContainerSize;
}

export interface EmptyLoadAssignment extends EmptyLoadPick {
  wagonSequenceNo: number;
}

/**
 * Fill wagons with the picked empties: a wagon takes ONE 40ft or TWO 20ft,
 * never a mix. 40ft boxes are seated first so a half-filled 20ft wagon can
 * never block them, and the 20s pair up behind them.
 *
 * `freeWagons` is the caller's ordered list of wagon sequence numbers with no
 * cargo allocation. Returns the assignments that fit plus the picks that had
 * no wagon left — the caller surfaces the shortfall instead of silently
 * dropping boxes.
 */
export function packEmptiesOntoWagons(
  picks: EmptyLoadPick[],
  freeWagons: number[],
): { assignments: EmptyLoadAssignment[]; unplaced: EmptyLoadPick[] } {
  const forty = picks.filter((pick) => pick.containerSize === "40");
  const twenty = picks.filter((pick) => pick.containerSize === "20");

  const assignments: EmptyLoadAssignment[] = [];
  const unplaced: EmptyLoadPick[] = [];
  const wagons = [...freeWagons];

  for (const pick of forty) {
    const wagon = wagons.shift();
    if (wagon == null) unplaced.push(pick);
    else assignments.push({ ...pick, wagonSequenceNo: wagon });
  }

  for (let index = 0; index < twenty.length; index += 2) {
    const pair = twenty.slice(index, index + 2);
    const wagon = wagons.shift();
    if (wagon == null) unplaced.push(...pair);
    else assignments.push(...pair.map((pick) => ({ ...pick, wagonSequenceNo: wagon })));
  }

  return { assignments, unplaced };
}

/** Wagons the picks consume, whether or not enough are free. */
export function wagonsNeeded(picks: EmptyLoadPick[]): number {
  const forty = picks.filter((pick) => pick.containerSize === "40").length;
  const twenty = picks.length - forty;
  return forty + Math.ceil(twenty / 2);
}