import { useMemo, useState } from 'react';

import type { Contact } from 'tinode-sdk';

import { Icon } from '@/app/Icon';
import { SelectionCheckbox } from '@/app/SelectionCheckbox';
import { avatarBgClass, avatarLetter } from '@/lib/avatar';
import { useEscapeKey } from '@/lib/hooks';
import { useChatList, useTinode } from '@/lib/tinode/hooks';

const MAX_COMMENT_LENGTH = 200;

interface ForwardPickerModalProps {
  onPick: (targetTopics: string[], comment: string) => void;
  onClose: () => void;
}

/**
 * README §3.6: multi-select targets + an optional comment, sent in one action. Used by the message
 * context menu's single-message "转发", the multi-select bulk bar's "转发", and favorites' bulk
 * forward -- all three previously shared this component when it only supported picking ONE target
 * and sending immediately with no comment, meaning forwarding to several people required repeating
 * the whole picker flow once per recipient. `forwardFavorites` (favorites.ts) already accepts
 * `target_topics: string[]`/`comment` server-side; chat-message forwarding has no such batch REST
 * endpoint (`forwardMessage` in lib/tinode/send.ts publishes one native {pub} per target instead),
 * so callers loop `targetTopics` themselves -- this component only collects the selection.
 */
export function ForwardPickerModal({ onPick, onClose }: ForwardPickerModalProps) {
  const contacts = useChatList();
  const tinode = useTinode();
  const [query, setQuery] = useState('');
  const [selected, setSelected] = useState<Set<string>>(new Set());
  const [comment, setComment] = useState('');
  // Both start expanded -- collapsing is for a long list getting in the way of the OTHER section,
  // not a default state anyone would want on first open.
  const [collapsed, setCollapsed] = useState<{ friends: boolean; groups: boolean }>({ friends: false, groups: false });
  useEscapeKey(onClose);
  const filtered = contacts.filter((c) => !query.trim() || (c.public?.fn || '').includes(query.trim()));

  // The list used to mix friends and groups in one flat run -- every other list in this app
  // (ChatListColumn's pinned/sorted rows, ContactsListColumn) already keeps the two visually
  // separate, so this was the odd one out and made a specific group hard to spot among dozens of
  // P2P contacts.
  const friends = useMemo(
    () => filtered.filter((c) => !!c.topic && !tinode.getTopic(c.topic).isGroupType()),
    [filtered, tinode],
  );
  const groups = useMemo(
    () => filtered.filter((c) => !!c.topic && tinode.getTopic(c.topic).isGroupType()),
    [filtered, tinode],
  );

  const toggle = (topic: string) => {
    setSelected((prev) => {
      const next = new Set(prev);
      if (next.has(topic)) next.delete(topic);
      else next.add(topic);
      return next;
    });
  };

  // 好友/群聊各自独立的全选 -- 一次转发常常只想覆盖其中一类（比如"发给所有群"但不想带上私聊
  // 好友），一个笼统的全选做不到这一点，所以拆成两个独立开关而不是列表整体一个。
  const friendTopics = useMemo(() => friends.map((c) => c.topic).filter((t): t is string => !!t), [friends]);
  const groupTopics = useMemo(() => groups.map((c) => c.topic).filter((t): t is string => !!t), [groups]);
  const allFriendsSelected = friendTopics.length > 0 && friendTopics.every((t) => selected.has(t));
  const allGroupsSelected = groupTopics.length > 0 && groupTopics.every((t) => selected.has(t));

  const toggleSectionSelectAll = (topics: string[], allSelected: boolean) => {
    setSelected((prev) => {
      if (allSelected) {
        // Only drop the ones the CURRENT search actually shows -- a selection made under an earlier,
        // now-cleared query shouldn't be wiped out by un-selecting "all" of a narrower view.
        const next = new Set(prev);
        for (const t of topics) next.delete(t);
        return next;
      }
      return new Set([...prev, ...topics]);
    });
  };

  const toggleCollapsed = (section: 'friends' | 'groups') => {
    setCollapsed((prev) => ({ ...prev, [section]: !prev[section] }));
  };

  const send = () => {
    if (selected.size === 0) return;
    onPick([...selected], comment.trim());
  };

  const renderRow = (c: Contact) => {
    const isSelected = !!c.topic && selected.has(c.topic);
    return (
      <button
        key={c.topic}
        type="button"
        onClick={() => c.topic && toggle(c.topic)}
        className="flex w-full items-center gap-3 rounded-lg px-3 py-2 text-left hover:bg-surface-rail"
      >
        <span
          className={`grid h-9 w-9 flex-none place-items-center rounded-lg text-sm font-medium text-white ${avatarBgClass(c.topic || '')}`}
        >
          {avatarLetter(c.public?.fn)}
        </span>
        <span className="min-w-0 flex-1 truncate text-sm text-text-body">{c.public?.fn || c.topic}</span>
        <SelectionCheckbox selected={isSelected} />
      </button>
    );
  };

  const renderSectionHeader = (label: string, section: 'friends' | 'groups', topics: string[], allSelected: boolean) => (
    <div className="flex items-center justify-between px-3 pb-1 pt-2">
      <button type="button" onClick={() => toggleCollapsed(section)} className="flex items-center gap-0.5 text-xs text-text-tertiary-2">
        <Icon name="chevron_right" className={`text-sm transition-transform ${collapsed[section] ? '' : 'rotate-90'}`} />
        {label}
      </button>
      <button type="button" onClick={() => toggleSectionSelectAll(topics, allSelected)} className="text-xs text-accent">
        {allSelected ? '取消全选' : '全选'}
      </button>
    </div>
  );

  return (
    <div className="fixed inset-0 z-50 flex items-center justify-center bg-[#22262d]/25" onClick={onClose}>
      <div className="flex h-[560px] w-[420px] flex-col rounded-xl bg-white shadow-modal" onClick={(e) => e.stopPropagation()}>
        <header className="flex h-14 flex-none items-center justify-between border-b border-border-list-item px-5">
          <strong className="text-[15px] font-semibold text-text-heading">
            转发到{selected.size ? `（已选 ${selected.size} 个接收方）` : ''}
          </strong>
          <button type="button" onClick={onClose} className="grid h-8 w-8 place-items-center text-text-tertiary-4">
            <Icon name="close" />
          </button>
        </header>
        <div className="flex-none px-4 pt-3">
          <div className="flex h-9 items-center rounded-lg bg-surface-search px-3">
            <Icon name="search" className="text-[18px] text-text-placeholder-2" />
            <input
              autoFocus
              value={query}
              onChange={(e) => setQuery(e.target.value)}
              placeholder="搜索会话或联系人"
              className="ml-2 w-full bg-transparent text-sm outline-none placeholder:text-text-placeholder-2"
            />
          </div>
        </div>
        <div className="flex-1 overflow-y-auto px-2 py-2">
          {friends.length ? (
            <>
              {renderSectionHeader('好友', 'friends', friendTopics, allFriendsSelected)}
              {collapsed.friends ? null : friends.map(renderRow)}
            </>
          ) : null}
          {groups.length ? (
            <>
              {renderSectionHeader('群聊', 'groups', groupTopics, allGroupsSelected)}
              {collapsed.groups ? null : groups.map(renderRow)}
            </>
          ) : null}
          {!friends.length && !groups.length ? (
            <div className="flex flex-col items-center justify-center gap-2 py-10 text-text-tertiary-4">
              <Icon name="search_off" className="!text-4xl" />
              <span className="text-sm">未找到相关联系人</span>
            </div>
          ) : null}
        </div>
        <div className="flex-none border-t border-border-list-item p-3">
          <textarea
            value={comment}
            onChange={(e) => setComment(e.target.value.slice(0, MAX_COMMENT_LENGTH))}
            rows={2}
            placeholder="附言（选填）"
            className="w-full resize-none rounded-lg bg-surface-input p-2.5 text-sm outline-none"
          />
          <button
            type="button"
            onClick={send}
            disabled={selected.size === 0}
            className="mt-2 h-9 w-full rounded-lg bg-btn text-sm font-medium text-white disabled:bg-btn-disabled"
          >
            发送{selected.size ? `（${selected.size}）` : ''}
          </button>
        </div>
      </div>
    </div>
  );
}