import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
import type { ActiveChat } from '../../../../../packages/api-contracts/src/index.js';
import { RedditUsernameLink, redditUsernameLabel } from '../../components/reddit-username-link.js';
import { ConversationDetail } from './conversation-detail.js';
import {
  useBulkMarkConversationsReadMutation,
  useConversationsQuery,
  useMarkConversationReadMutation,
  useMarkConversationUnreadMutation,
  useSetConversationStatusMutation,
} from './conversation-queries.js';
import { StartConversationForm } from './start-conversation-form.js';
import { ProcessedUserLookup } from './processed-user-lookup.js';
import { AccountOwnerBadge } from '../../components/account-owner-badge.js';
import './conversations.css';
import { ownedConversationId } from './conversation-identity.js';
import { conversationAge, formatExactTime, formatShortRelativeTime } from './relative-time.js';
import {
  CONVERSATION_FILTERS,
  CONVERSATION_SORTS,
  DEFAULT_CONVERSATION_FILTERS,
  accountOptions,
  filterCounts,
  isUnread,
  needsReply,
  partitionConversations,
  triageStatus,
  type ConversationFilter,
  type ConversationFilters,
  type ConversationSort,
} from './conversation-triage.js';

export type { ConversationFilter, ConversationFilters, ConversationSort } from './conversation-triage.js';

const SMALL_VIEWPORT_QUERY = '(max-width: 51.9999rem)';

export interface ConversationsPageProps {
  selectedConversationId?: string | null;
  onSelectedConversationChange?(conversationId: string | null): void;
  filters?: ConversationFilters;
  onFiltersChange?(filters: ConversationFilters): void;
}

interface ConversationRowProps {
  conversation: ActiveChat;
  isSelected: boolean;
  isChecked: boolean;
  /** Only worth the row space when more than one account is in play. */
  showOwner: boolean;
  now: number;
  onSelect(): void;
  onToggleChecked(): void;
  registerRef(element: HTMLButtonElement | null): void;
}

/** Independent state chips. A conversation can be several of these at once. */
function conversationChips(conversation: ActiveChat, now: number): string[] {
  const chips: string[] = [];
  if (isUnread(conversation)) chips.push('Unread');
  if (needsReply(conversation)) chips.push('Needs reply');
  else if (conversation.isFromUs && triageStatus(conversation) === 'open') chips.push('Waiting on them');
  const status = triageStatus(conversation);
  if (status === 'snoozed') chips.push('Snoozed');
  if (status === 'done') chips.push('Done');
  if (needsReply(conversation) && conversationAge(conversation.lastMessageTime, now) !== 'fresh') {
    chips.push('Overdue');
  }
  return chips;
}

function ConversationRow({
  conversation, isSelected, isChecked, showOwner, now, onSelect, onToggleChecked, registerRef,
}: ConversationRowProps) {
  const relativeTime = formatShortRelativeTime(conversation.lastMessageTime, now);
  const unread = isUnread(conversation);
  const overdue = needsReply(conversation) ? conversationAge(conversation.lastMessageTime, now) : 'fresh';
  const chips = conversationChips(conversation, now);
  const itemClasses = ['conversation-list-item'];
  if (isSelected) itemClasses.push('is-selected');
  if (unread) itemClasses.push('is-unread');
  if (isChecked) itemClasses.push('is-checked');

  const descriptors = [
    redditUsernameLabel(conversation.username),
    ...chips,
    relativeTime,
    ...(conversation.sellerDetected ? ['Seller'] : []),
    ...(conversation.hasReceivedImages ? ['Image received'] : []),
  ];

  return (
    <li className={itemClasses.join(' ')}>
      <label className="conversation-list-check">
        <input
          aria-label={`Select ${redditUsernameLabel(conversation.username)}`}
          checked={isChecked}
          onChange={onToggleChecked}
          type="checkbox"
        />
      </label>
      <button
        aria-current={isSelected || undefined}
        aria-label={descriptors.join(', ')}
        className="conversation-list-open"
        onClick={onSelect}
        ref={registerRef}
        type="button"
      >
        <span className="conversation-list-heading">
          <strong>{redditUsernameLabel(conversation.username)}</strong>
          <time
            className={overdue === 'fresh' ? undefined : `is-${overdue}`}
            dateTime={new Date(conversation.lastMessageTime).toISOString()}
            title={formatExactTime(conversation.lastMessageTime)}
          >
            {relativeTime}
          </time>
        </span>
        <span className="conversation-list-snippet">
          {conversation.lastMessageSnippet || 'No message preview'}
        </span>
      </button>
      <span className="conversation-list-chips">
        {chips.map((chip) => (
          <span className={`conversation-chip is-${chip.toLowerCase().replaceAll(' ', '-')}`} key={chip}>
            {chip}
          </span>
        ))}
        {showOwner ? <AccountOwnerBadge owner={conversation.owner} /> : null}
        {conversation.sellerDetected ? <span className="conversation-seller-marker">Seller</span> : null}
        {conversation.hasReceivedImages ? <span className="conversation-image-marker">Image received</span> : null}
        <span className="conversation-list-profile"><RedditUsernameLink username={conversation.username} /></span>
      </span>
    </li>
  );
}

export function ConversationsPage({
  selectedConversationId, onSelectedConversationChange, filters, onFiltersChange,
}: ConversationsPageProps) {
  const conversationsQuery = useConversationsQuery();
  const [internalSelectedId, setInternalSelectedId] = useState<string | null>(null);
  const [localFilters, setLocalFilters] = useState<ConversationFilters>(DEFAULT_CONVERSATION_FILTERS);
  const [isStartingConversation, setIsStartingConversation] = useState(false);
  const [now, setNow] = useState(() => Date.now());
  const [checkedIds, setCheckedIds] = useState<Set<string>>(() => new Set());
  const detailPanelRef = useRef<HTMLElement>(null);
  const searchRef = useRef<HTMLInputElement>(null);
  const rowRefs = useRef(new Map<string, HTMLButtonElement>());
  const activeConversationId = selectedConversationId !== undefined ? selectedConversationId : internalSelectedId;
  const activeFilters = filters ?? localFilters;
  const markRead = useMarkConversationReadMutation();
  const markUnread = useMarkConversationUnreadMutation();
  const setStatus = useSetConversationStatusMutation();
  const bulkMarkRead = useBulkMarkConversationsReadMutation();

  useEffect(() => {
    const interval = window.setInterval(() => setNow(Date.now()), 60_000);
    return () => window.clearInterval(interval);
  }, []);

  // On small viewports the detail panel sits below the list; bring it into
  // view when a conversation is picked so the selection isn't invisible.
  useEffect(() => {
    if (!activeConversationId) return;
    if (typeof window.matchMedia !== 'function') return;
    if (!window.matchMedia(SMALL_VIEWPORT_QUERY).matches) return;
    detailPanelRef.current?.scrollIntoView?.({ behavior: 'smooth', block: 'start' });
  }, [activeConversationId]);

  const updateFilters = useCallback((next: ConversationFilters) => {
    if (filters === undefined) setLocalFilters(next);
    onFiltersChange?.(next);
  }, [filters, onFiltersChange]);

  const allConversations = conversationsQuery.data ?? [];

  const { visible: liveConversations, hiddenSellerCount } = useMemo(
    () => partitionConversations(allConversations, activeFilters),
    [allConversations, activeFilters],
  );
  const counts = useMemo(() => filterCounts(allConversations, activeFilters), [allConversations, activeFilters]);
  const accounts = useMemo(() => accountOptions(allConversations), [allConversations]);

  // While a conversation is open the row order is frozen. A background poll
  // re-sorting the list would move rows out from under the operator mid-triage;
  // anything new is surfaced as an explicit refresh instead.
  const [frozenOrder, setFrozenOrder] = useState<string[] | null>(null);
  const liveIds = useMemo(
    () => liveConversations.map((conversation) => ownedConversationId(conversation)),
    [liveConversations],
  );

  useEffect(() => {
    if (!activeConversationId) {
      setFrozenOrder(null);
      return;
    }
    // Capture the order as it was when the conversation was opened. `liveIds` is
    // intentionally read once here rather than tracked, so later polls do not
    // re-freeze against a reordered list.
    setFrozenOrder((current) => current ?? liveIds);
  }, [activeConversationId, liveIds]);

  const visibleConversations = useMemo(() => {
    if (!frozenOrder) return liveConversations;
    const rank = new Map(frozenOrder.map((id, index) => [id, index]));
    return liveConversations
      .filter((conversation) => rank.has(ownedConversationId(conversation)))
      .sort((left, right) =>
        (rank.get(ownedConversationId(left)) ?? 0) - (rank.get(ownedConversationId(right)) ?? 0));
  }, [liveConversations, frozenOrder]);

  const pendingCount = liveConversations.length - visibleConversations.length;

  const visibleIds = useMemo(
    () => visibleConversations.map((conversation) => ownedConversationId(conversation)),
    [visibleConversations],
  );

  function selectConversation(id: string | null) {
    if (selectedConversationId === undefined) setInternalSelectedId(id);
    onSelectedConversationChange?.(id);
  }

  function releaseFrozenOrder() {
    setFrozenOrder(activeConversationId ? liveIds : null);
  }

  function toggleChecked(id: string) {
    setCheckedIds((current) => {
      const next = new Set(current);
      if (next.has(id)) next.delete(id);
      else next.add(id);
      return next;
    });
  }

  const checkedVisibleIds = visibleIds.filter((id) => checkedIds.has(id));
  const allVisibleChecked = visibleIds.length > 0 && checkedVisibleIds.length === visibleIds.length;

  function toggleAllVisible() {
    setCheckedIds(allVisibleChecked ? new Set() : new Set(visibleIds));
  }

  function moveFocus(offset: number) {
    if (visibleIds.length === 0) return;
    const focused = document.activeElement;
    let index = visibleIds.findIndex((id) => rowRefs.current.get(id) === focused);
    if (index < 0) index = visibleIds.findIndex((id) => id === activeConversationId);
    if (index < 0) {
      // Entering the list for the first time: land on the near end rather than
      // stepping past it.
      rowRefs.current.get(visibleIds[offset > 0 ? 0 : visibleIds.length - 1])?.focus();
      return;
    }
    const nextIndex = Math.min(visibleIds.length - 1, Math.max(0, index + offset));
    rowRefs.current.get(visibleIds[nextIndex])?.focus();
  }

  function focusedConversationId(): string | null {
    const focused = document.activeElement;
    const focusedId = visibleIds.find((id) => rowRefs.current.get(id) === focused);
    return focusedId ?? activeConversationId ?? null;
  }

  function isTypingTarget(target: EventTarget | null): boolean {
    if (!(target instanceof HTMLElement)) return false;
    return target.isContentEditable || ['INPUT', 'TEXTAREA', 'SELECT'].includes(target.tagName);
  }

  /**
   * Inbox keyboard shortcuts. Suppressed whenever focus is inside a text field
   * so typing a reply or a search term never triggers an action.
   */
  function handleShortcut(event: KeyboardEvent) {
    if (event.metaKey || event.ctrlKey || event.altKey) return;
    // A modal owns the keyboard while it is open — including Escape, which must
    // dismiss the dialog rather than the conversation behind it.
    if (event.defaultPrevented || document.querySelector('dialog[open]')) return;
    const typing = isTypingTarget(event.target);
    if (event.key === '/' && !typing) {
      event.preventDefault();
      searchRef.current?.focus();
      return;
    }
    if (event.key === 'Escape') {
      if (typing) (event.target as HTMLElement).blur();
      else if (activeConversationId) selectConversation(null);
      return;
    }
    if (typing) return;

    switch (event.key) {
      case 'j':
      case 'ArrowDown':
        event.preventDefault();
        moveFocus(1);
        break;
      case 'k':
      case 'ArrowUp':
        event.preventDefault();
        moveFocus(-1);
        break;
      case 'u': {
        const id = focusedConversationId();
        const conversation = allConversations.find((item) => ownedConversationId(item) === id);
        if (!id || !conversation) return;
        event.preventDefault();
        if (isUnread(conversation)) markRead.mutate({ id });
        else markUnread.mutate({ id });
        break;
      }
      case 'e': {
        const id = focusedConversationId();
        if (!id) return;
        event.preventDefault();
        setStatus.mutate({ id, status: 'done' });
        if (id === activeConversationId) selectConversation(null);
        break;
      }
      default:
        break;
    }
  }

  // The handler closes over per-render state, so it is kept in a ref and the
  // listener is registered once rather than re-bound on every render.
  const shortcutRef = useRef(handleShortcut);
  shortcutRef.current = handleShortcut;
  useEffect(() => {
    const listener = (event: KeyboardEvent) => shortcutRef.current(event);
    window.addEventListener('keydown', listener);
    return () => window.removeEventListener('keydown', listener);
  }, []);

  const lastSyncedLabel = conversationsQuery.dataUpdatedAt
    ? formatShortRelativeTime(conversationsQuery.dataUpdatedAt, now)
    : null;

  return (
    <div className="conversations-page">
      <header className="conversations-header">
        <div>
          <span className="conversation-eyebrow">Inbox</span>
          <h1>Conversations</h1>
          <p>Review replies, draft carefully, and send only after confirmation.</p>
        </div>
        <div className="conversations-header-actions">
          <div className="conversation-refresh">
            <button
              aria-busy={conversationsQuery.isFetching || undefined}
              disabled={conversationsQuery.isFetching}
              onClick={() => void conversationsQuery.refetch()}
              type="button"
            >
              {conversationsQuery.isFetching ? 'Refreshing…' : 'Refresh'}
            </button>
            <span className="conversation-refresh-note">
              {lastSyncedLabel ? `Updated ${lastSyncedLabel} · auto every 30s` : 'Auto-refreshes every 30s'}
            </span>
          </div>
          <button className="conversation-primary" onClick={() => setIsStartingConversation((current) => !current)} type="button">
            {isStartingConversation ? 'Close new conversation' : 'New conversation'}
          </button>
        </div>
      </header>

      {isStartingConversation ? (
        <section aria-labelledby="new-conversation-heading" className="new-conversation-panel">
          <h2 id="new-conversation-heading">Start a conversation</h2>
          <StartConversationForm onStarted={(id) => selectConversation(id)} />
        </section>
      ) : null}
      <ProcessedUserLookup />

      <div className="conversation-workspace">
        <section aria-label="Conversation inbox" className="conversation-master">
          <div className="conversation-toolbar">
            <label className="sr-only" htmlFor="conversation-search">Search conversations</label>
            <input
              id="conversation-search"
              onChange={(event) => updateFilters({ ...activeFilters, search: event.target.value })}
              placeholder="Search conversations (/)"
              ref={searchRef}
              type="search"
              value={activeFilters.search}
            />
            <div aria-label="Filter conversations" className="conversation-filter-pills" role="group">
              {CONVERSATION_FILTERS.map((option) => (
                <button
                  aria-label={`${option.label}, ${counts[option.value]}`}
                  aria-pressed={activeFilters.filter === option.value}
                  className="conversation-filter-pill"
                  key={option.value}
                  onClick={() => updateFilters({ ...activeFilters, filter: option.value })}
                  type="button"
                >
                  {option.label}
                  <span className="conversation-filter-count">{counts[option.value]}</span>
                </button>
              ))}
            </div>
            <div className="conversation-toolbar-row">
              <label className="conversation-sort">
                <span>Sort</span>
                <select
                  onChange={(event) => updateFilters({
                    ...activeFilters,
                    sort: event.target.value as ConversationSort,
                  })}
                  value={activeFilters.sort}
                >
                  {CONVERSATION_SORTS.map((option) => (
                    <option key={option.value} value={option.value}>{option.label}</option>
                  ))}
                </select>
              </label>
              {accounts.length > 1 ? (
                <label className="conversation-account-filter">
                  <span>Account</span>
                  <select
                    onChange={(event) => updateFilters({ ...activeFilters, account: event.target.value })}
                    value={activeFilters.account}
                  >
                    <option value="all">All accounts</option>
                    {accounts.map((account) => (
                      <option key={account.accountId} value={account.accountId}>
                        u/{account.redditUsername}
                      </option>
                    ))}
                  </select>
                </label>
              ) : null}
              <label className="conversation-seller-toggle">
                <input
                  checked={activeFilters.showSellers}
                  onChange={(event) => updateFilters({ ...activeFilters, showSellers: event.target.checked })}
                  type="checkbox"
                />
                Show sellers
              </label>
            </div>
            {visibleConversations.length > 0 ? (
              <div className="conversation-bulk-bar">
                <label className="conversation-bulk-select-all">
                  <input
                    aria-label="Select all visible conversations"
                    checked={allVisibleChecked}
                    onChange={toggleAllVisible}
                    type="checkbox"
                  />
                  {checkedVisibleIds.length > 0 ? `${checkedVisibleIds.length} selected` : 'Select all'}
                </label>
                {checkedVisibleIds.length > 0 ? (
                  <>
                    <button
                      disabled={bulkMarkRead.isPending}
                      onClick={() => bulkMarkRead.mutate(checkedVisibleIds, {
                        onSuccess: () => setCheckedIds(new Set()),
                      })}
                      type="button"
                    >
                      {bulkMarkRead.isPending ? 'Marking read…' : 'Mark read'}
                    </button>
                    <button
                      disabled={setStatus.isPending}
                      onClick={() => {
                        for (const id of checkedVisibleIds) setStatus.mutate({ id, status: 'done' });
                        setCheckedIds(new Set());
                      }}
                      type="button"
                    >
                      Mark done
                    </button>
                  </>
                ) : null}
              </div>
            ) : null}
            {pendingCount > 0 ? (
              <button className="conversation-pending-refresh" onClick={releaseFrozenOrder} type="button">
                {pendingCount} new {pendingCount === 1 ? 'conversation' : 'conversations'} — refresh list
              </button>
            ) : null}
          </div>
          {conversationsQuery.isPending ? (
            <div aria-label="Loading conversations" className="conversation-list-state" role="status">Loading conversations…</div>
          ) : conversationsQuery.isError ? (
            <div className="conversation-list-state conversation-inline-error" role="alert">
              <strong>Could not load conversations</strong>
              <span>{conversationsQuery.error.message}</span>
              <button onClick={() => void conversationsQuery.refetch()} type="button">Retry conversations</button>
            </div>
          ) : conversationsQuery.data.length === 0 ? (
            <div className="conversation-list-state"><strong>No conversations yet.</strong><span>Start one when you are ready.</span></div>
          ) : visibleConversations.length === 0 ? (
            <div className="conversation-list-state">
              <strong>No matching conversations.</strong>
              <span>Try a different search or filter.</span>
              {hiddenSellerCount > 0 ? (
                <span>{hiddenSellerCount} hidden by the seller filter.</span>
              ) : null}
            </div>
          ) : (
            <>
              <ul className="conversation-list">
                {visibleConversations.map((conversation) => {
                  const id = ownedConversationId(conversation);
                  return (
                    <ConversationRow
                      conversation={conversation}
                      isChecked={checkedIds.has(id)}
                      isSelected={id === activeConversationId}
                      key={id}
                      now={now}
                      onSelect={() => selectConversation(id)}
                      onToggleChecked={() => toggleChecked(id)}
                      showOwner={accounts.length > 1}
                      registerRef={(element) => {
                        if (element) rowRefs.current.set(id, element);
                        else rowRefs.current.delete(id);
                      }}
                    />
                  );
                })}
              </ul>
              <p className="conversation-list-footer">
                {hiddenSellerCount > 0
                  ? `${hiddenSellerCount} hidden by the seller filter.`
                  : null}
                <span className="conversation-shortcut-hint">
                  j/k move · Enter opens · u toggles unread · e marks done · / searches
                </span>
              </p>
            </>
          )}
        </section>

        <section aria-label="Selected conversation" className="conversation-detail-panel" ref={detailPanelRef}>
          {activeConversationId ? (
            <ConversationDetail conversationId={activeConversationId} key={activeConversationId} onClose={() => selectConversation(null)} />
          ) : (
            <div className="conversation-detail-state">
              <strong>Select a conversation</strong>
              <span>Message history and reply tools will appear here.</span>
            </div>
          )}
        </section>
      </div>
    </div>
  );
}