export type BoardRowOrderByDay = Record<string, string[]>;

const STORAGE_PREFIX = "shoc:wo-board-row-order:v1:";

export function boardRowOrderStorageKey(weekMonday: string, ownerId = ""): string {
  const owner = ownerId.trim() || "local";
  return `${STORAGE_PREFIX}${owner}:${weekMonday}`;
}

export function legacyBoardRowOrderStorageKey(weekMonday: string): string {
  return `${STORAGE_PREFIX}${weekMonday}`;
}

function isStringArray(value: unknown): value is string[] {
  return Array.isArray(value) && value.every((item) => typeof item === "string");
}

function isBoardRowOrderByDay(value: unknown): value is BoardRowOrderByDay {
  if (value === null || typeof value !== "object" || Array.isArray(value)) {
    return false;
  }
  return Object.values(value).every(isStringArray);
}

function readStoredOrder(key: string): BoardRowOrderByDay {
  try {
    const raw = localStorage.getItem(key);
    if (!raw) {
      return {};
    }
    const parsed: unknown = JSON.parse(raw);
    return isBoardRowOrderByDay(parsed) ? parsed : {};
  } catch {
    return {};
  }
}

export function loadBoardRowOrder(weekMonday: string, ownerId = ""): BoardRowOrderByDay {
  if (typeof window === "undefined" || !weekMonday) {
    return {};
  }

  const scoped = readStoredOrder(boardRowOrderStorageKey(weekMonday, ownerId));
  if (Object.keys(scoped).length) {
    return scoped;
  }
  return readStoredOrder(legacyBoardRowOrderStorageKey(weekMonday));
}

export function saveBoardRowOrder(
  weekMonday: string,
  orderByDay: BoardRowOrderByDay,
  ownerId = "",
): void {
  if (typeof window === "undefined" || !weekMonday) {
    return;
  }

  try {
    localStorage.setItem(boardRowOrderStorageKey(weekMonday, ownerId), JSON.stringify(orderByDay));
  } catch {
    // Quota exceeded or storage blocked — keep in-memory order only.
  }
}

/** Reorder `items` so known ids follow `orderedIds`; unknown ids stay at the end (stable). */
export function applyDayRowOrder<T extends { id: string | number }>(
  items: T[],
  orderedIds: string[] | undefined,
): T[] {
  if (!orderedIds?.length || items.length <= 1) {
    return items;
  }

  const orderMap = new Map(orderedIds.map((id, idx) => [id, idx]));
  return [...items].sort((a, b) => {
    const ai = orderMap.get(String(a.id));
    const bi = orderMap.get(String(b.id));
    if (ai === undefined && bi === undefined) {
      return 0;
    }
    if (ai === undefined) {
      return 1;
    }
    if (bi === undefined) {
      return -1;
    }
    return ai - bi;
  });
}

/** Apply saved per-day orders across a flat row list (preserves relative order across days). */
export function applyRowOrderByDay<T extends { id: string | number; dayGroup: string }>(
  items: T[],
  orderByDay: BoardRowOrderByDay,
): T[] {
  if (!items.length || !Object.keys(orderByDay).length) {
    return items;
  }

  const byDay = new Map<string, T[]>();
  for (const item of items) {
    const group = byDay.get(item.dayGroup);
    if (group) {
      group.push(item);
    } else {
      byDay.set(item.dayGroup, [item]);
    }
  }

  const orderedByDay = new Map<string, T[]>();
  for (const [dayGroup, dayItems] of byDay) {
    orderedByDay.set(dayGroup, applyDayRowOrder(dayItems, orderByDay[dayGroup]));
  }

  const nextIndex = new Map<string, number>();
  return items.map((item) => {
    const dayItems = orderedByDay.get(item.dayGroup)!;
    const idx = nextIndex.get(item.dayGroup) ?? 0;
    nextIndex.set(item.dayGroup, idx + 1);
    return dayItems[idx]!;
  });
}

/** Same-day neighbor for keyboard reorder; null at list ends or if the row is missing. */
export function neighborIdForReorder<T extends { id: string | number; dayGroup: string }>(
  rows: T[],
  row: T,
  delta: -1 | 1,
  isReorderTarget: (item: T) => boolean = () => true,
): string | number | null {
  const dayRows = rows.filter((item) => item.dayGroup === row.dayGroup);
  const index = dayRows.findIndex((item) => String(item.id) === String(row.id));
  if (index < 0) {
    return null;
  }
  for (let cursor = index + delta; cursor >= 0 && cursor < dayRows.length; cursor += delta) {
    const candidate = dayRows[cursor];
    if (candidate && isReorderTarget(candidate)) {
      return candidate.id;
    }
  }
  return null;
}

export function reorderIdsInList(ids: string[], dragId: string, overId: string): string[] | null {
  const dragIdx = ids.indexOf(dragId);
  const overIdx = ids.indexOf(overId);
  if (dragIdx < 0 || overIdx < 0 || dragIdx === overIdx) {
    return null;
  }
  const next = [...ids];
  next.splice(dragIdx, 1);
  next.splice(overIdx, 0, dragId);
  return next;
}

/** Remove an id from every day bucket (used when a row changes dayGroup). */
export function removeIdFromRowOrder(
  orderByDay: BoardRowOrderByDay,
  id: string,
): BoardRowOrderByDay {
  let changed = false;
  const next: BoardRowOrderByDay = {};
  for (const [dayGroup, ids] of Object.entries(orderByDay)) {
    if (!ids.includes(id)) {
      next[dayGroup] = ids;
      continue;
    }
    changed = true;
    const filtered = ids.filter((item) => item !== id);
    if (filtered.length) {
      next[dayGroup] = filtered;
    }
  }
  return changed ? next : orderByDay;
}

/** Drop the id from every day, then append it to the destination day. */
export type TransferIdToDestinationWeekOrderInput = {
  sourceWeekMonday: string;
  destinationWeekMonday: string;
  ownerId: string;
  id: string;
  nextDayGroup: string;
};

/** Persist a moved row under the destination week when schedule crosses week boundaries. */
export function transferIdToDestinationWeekOrder({
  sourceWeekMonday,
  destinationWeekMonday,
  ownerId,
  id,
  nextDayGroup,
}: TransferIdToDestinationWeekOrderInput): void {
  if (!sourceWeekMonday || !destinationWeekMonday || !nextDayGroup) {
    return;
  }
  if (sourceWeekMonday === destinationWeekMonday) {
    return;
  }

  const sourceOrder = loadBoardRowOrder(sourceWeekMonday, ownerId);
  const sourceWithoutId = removeIdFromRowOrder(sourceOrder, id);
  if (sourceWithoutId !== sourceOrder) {
    saveBoardRowOrder(sourceWeekMonday, sourceWithoutId, ownerId);
  }

  const destinationOrder = loadBoardRowOrder(destinationWeekMonday, ownerId);
  saveBoardRowOrder(
    destinationWeekMonday,
    moveIdToDayOrder(destinationOrder, id, nextDayGroup),
    ownerId,
  );
}

export function moveIdToDayOrder(
  orderByDay: BoardRowOrderByDay,
  id: string,
  nextDayGroup: string,
): BoardRowOrderByDay {
  if (!nextDayGroup) {
    return removeIdFromRowOrder(orderByDay, id);
  }
  const without = removeIdFromRowOrder(orderByDay, id);
  const dest = without[nextDayGroup] ?? [];
  if (dest.includes(id)) {
    return without;
  }
  return { ...without, [nextDayGroup]: [...dest, id] };
}

/**
 * Merge a visible day's new order into stored order: visible ids take the new sequence,
 * ids that were stored but not currently visible stay after the visible block (preserving
 * their prior relative order).
 */
export function mergeDayOrder(
  previousDayIds: string[] | undefined,
  visibleOrderedIds: string[],
): string[] {
  if (!previousDayIds?.length) {
    return visibleOrderedIds;
  }
  const visibleSet = new Set(visibleOrderedIds);
  const hidden = previousDayIds.filter((id) => !visibleSet.has(id));
  return [...visibleOrderedIds, ...hidden];
}