import type { ActiveChat } from '../../../../../packages/api-contracts/src/index.js';

/**
 * Inbox buckets. These are the operator's actual work queues, derived from
 * application read state rather than Matrix's unread count.
 *
 * `all` deliberately excludes resolved and snoozed conversations — the default
 * view is "what is still on my plate", and the two terminal buckets have their
 * own pills so nothing becomes unreachable.
 */
export type ConversationFilter =
  | 'all'
  | 'needs-reply'
  | 'unread'
  | 'awaiting-reply'
  | 'received-images'
  | 'snoozed'
  | 'done';

export type ConversationSort = 'recent' | 'oldest-unanswered';

export interface ConversationFilters {
  search: string;
  filter: ConversationFilter;
  showSellers: boolean;
  sort: ConversationSort;
  /** Reddit account id to narrow to, or `all`. */
  account: string;
}

export const DEFAULT_CONVERSATION_FILTERS: ConversationFilters = {
  search: '',
  filter: 'all',
  showSellers: false,
  sort: 'recent',
  account: 'all',
};

export const CONVERSATION_FILTERS: ReadonlyArray<{ value: ConversationFilter; label: string }> = [
  { value: 'all', label: 'All' },
  { value: 'needs-reply', label: 'Needs reply' },
  { value: 'unread', label: 'Unread' },
  { value: 'awaiting-reply', label: 'Waiting on them' },
  { value: 'received-images', label: 'Images' },
  { value: 'snoozed', label: 'Snoozed' },
  { value: 'done', label: 'Done' },
];

export const CONVERSATION_SORTS: ReadonlyArray<{ value: ConversationSort; label: string }> = [
  { value: 'recent', label: 'Newest activity' },
  { value: 'oldest-unanswered', label: 'Oldest unanswered' },
];

export function isConversationFilter(value: string | null): value is ConversationFilter {
  return CONVERSATION_FILTERS.some((option) => option.value === value);
}

export function isConversationSort(value: string | null): value is ConversationSort {
  return CONVERSATION_SORTS.some((option) => option.value === value);
}

export function triageStatus(conversation: ActiveChat): 'open' | 'snoozed' | 'done' {
  return conversation.triageStatus ?? 'open';
}

/**
 * True when the newest message is inbound and newer than the read watermark.
 *
 * Falls back to Matrix's `unread` only when the server has not supplied read
 * state at all, so an older backend keeps behaving as before rather than
 * showing an inbox with nothing unread.
 */
export function isUnread(conversation: ActiveChat): boolean {
  if (conversation.hasUnreadInbound !== undefined) return conversation.hasUnreadInbound;
  return conversation.unread;
}

export function needsReply(conversation: ActiveChat): boolean {
  if (conversation.needsReply !== undefined) return conversation.needsReply;
  return !conversation.isFromUs && triageStatus(conversation) === 'open';
}

/** We have replied and are waiting on them. */
export function isWaitingOnThem(conversation: ActiveChat): boolean {
  return conversation.isFromUs && triageStatus(conversation) === 'open';
}

export function matchesFilter(conversation: ActiveChat, filter: ConversationFilter): boolean {
  const status = triageStatus(conversation);
  switch (filter) {
    case 'needs-reply':
      return needsReply(conversation);
    case 'unread':
      return status === 'open' && isUnread(conversation);
    case 'awaiting-reply':
      return isWaitingOnThem(conversation);
    case 'received-images':
      return status === 'open' && conversation.hasReceivedImages === true;
    case 'snoozed':
      return status === 'snoozed';
    case 'done':
      return status === 'done';
    default:
      return status === 'open';
  }
}

export function matchesSearch(conversation: ActiveChat, search: string): boolean {
  const normalized = search.trim().toLowerCase();
  if (normalized.length === 0) return true;
  if (conversation.username.toLowerCase().includes(normalized)) return true;
  if (conversation.lastMessageSnippet.toLowerCase().includes(normalized)) return true;
  // Message text is only present for conversations whose history has been
  // loaded, so this is a bonus rather than a guarantee.
  return (conversation.messages ?? []).some((message) => message.text.toLowerCase().includes(normalized));
}

function matchesAccount(conversation: ActiveChat, account: string): boolean {
  return account === 'all' || conversation.owner?.accountId === account;
}

export interface ConversationListPartition {
  /** Conversations passing every active filter, in the requested order. */
  visible: ActiveChat[];
  /** How many were removed purely by the seller toggle, so the UI can say so. */
  hiddenSellerCount: number;
}

/**
 * `oldest-unanswered` puts the longest-waiting conversation that needs a reply
 * first — the order you actually want when draining a queue — and keeps
 * everything else in newest-first order behind it.
 */
function compareConversations(sort: ConversationSort) {
  return (left: ActiveChat, right: ActiveChat): number => {
    if (sort === 'oldest-unanswered') {
      const leftNeeds = needsReply(left);
      const rightNeeds = needsReply(right);
      if (leftNeeds !== rightNeeds) return leftNeeds ? -1 : 1;
      if (leftNeeds && rightNeeds) return left.lastMessageTime - right.lastMessageTime;
    }
    return right.lastMessageTime - left.lastMessageTime;
  };
}

export function partitionConversations(
  conversations: readonly ActiveChat[],
  filters: ConversationFilters,
): ConversationListPartition {
  let hiddenSellerCount = 0;
  const visible = conversations.filter((conversation) => {
    if (!matchesSearch(conversation, filters.search)) return false;
    if (!matchesFilter(conversation, filters.filter)) return false;
    if (!matchesAccount(conversation, filters.account)) return false;
    if (!filters.showSellers && conversation.sellerDetected === true) {
      hiddenSellerCount += 1;
      return false;
    }
    return true;
  });
  return { visible: visible.sort(compareConversations(filters.sort)), hiddenSellerCount };
}

/**
 * Per-bucket counts for the filter pills. Counts respect search, account and
 * the seller toggle so a pill never promises rows the list will not show.
 */
export function filterCounts(
  conversations: readonly ActiveChat[],
  filters: ConversationFilters,
): Record<ConversationFilter, number> {
  const candidates = conversations.filter((conversation) =>
    matchesSearch(conversation, filters.search)
    && matchesAccount(conversation, filters.account)
    && (filters.showSellers || conversation.sellerDetected !== true));
  const counts = {} as Record<ConversationFilter, number>;
  for (const { value } of CONVERSATION_FILTERS) {
    counts[value] = candidates.filter((conversation) => matchesFilter(conversation, value)).length;
  }
  return counts;
}

export interface ConversationAccountOption {
  accountId: string;
  redditUsername: string;
}

/** Distinct owning accounts present in the list, for the account switcher. */
export function accountOptions(conversations: readonly ActiveChat[]): ConversationAccountOption[] {
  const seen = new Map<string, string>();
  for (const conversation of conversations) {
    if (conversation.owner) seen.set(conversation.owner.accountId, conversation.owner.redditUsername);
  }
  return [...seen]
    .map(([accountId, redditUsername]) => ({ accountId, redditUsername }))
    .sort((left, right) => left.redditUsername.localeCompare(right.redditUsername));
}

export const SNOOZE_OPTIONS: ReadonlyArray<{ label: string; ms: number }> = [
  { label: '1 hour', ms: 60 * 60_000 },
  { label: 'Tomorrow', ms: 24 * 60 * 60_000 },
  { label: '3 days', ms: 3 * 24 * 60 * 60_000 },
  { label: '1 week', ms: 7 * 24 * 60 * 60_000 },
];