import type { trainDataType } from "@/lib/trainPositionTextArray";
import {
  officialPositionLookupKey,
  type OfficialPositionLookupInput,
} from "@/lib/domain/railway";

const toLookupInput = (
  train: trainDataType,
): OfficialPositionLookupInput | null => {
  if (
    typeof train.Pos !== "string" ||
    train.Pos.length === 0 ||
    typeof train.Line !== "string" ||
    train.Line.length === 0 ||
    train.PosNum === undefined ||
    (typeof train.PosNum === "string" && train.PosNum.length === 0) ||
    (typeof train.PosNum === "number" && !Number.isFinite(train.PosNum))
  ) {
    return null;
  }
  return {
    line: train.Line,
    pos: train.Pos,
    posNum: train.PosNum,
  };
};

/**
 * Keeps the currently displayed official metadata while the next current-train
 * snapshot is being enriched. Only an identical line/position/position-number
 * tuple may carry metadata forward.
 */
export const carryForwardOfficialPositionMetadata = (
  next: readonly trainDataType[],
  previous: readonly trainDataType[],
): trainDataType[] => {
  const metadataByKey = new Map<
    string,
    NonNullable<trainDataType["officialPosition"]>
  >();

  for (const train of previous) {
    if (!train.officialPosition) continue;
    const input = toLookupInput(train);
    if (!input) continue;
    metadataByKey.set(
      officialPositionLookupKey(input),
      train.officialPosition,
    );
  }

  return next.map((train) => {
    if (train.officialPosition) return train;
    const input = toLookupInput(train);
    if (!input) return train;
    const metadata = metadataByKey.get(officialPositionLookupKey(input));
    return metadata ? { ...train, officialPosition: metadata } : train;
  });
};