import { useState } from 'react';
import { MessageSquare, Send, ChevronDown, ChevronRight } from 'lucide-react';
import type { Chat } from '@/api/types';
import { Button } from '@/components/ui/button';
import { Textarea } from '@/components/ui/textarea';
import { formatTokens } from '@/lib/format';

interface Props {
  sessionId: string;
  projectId: string;
  chats: Chat[];
  onOpenChat: (chatId: string) => void;
  onSend: (content: string) => void;
  onReopenChat: (chatId: string) => Promise<void>;
}

function relTime(iso: string): string {
  const now = Date.now();
  const t = Date.parse(iso);
  if (Number.isNaN(t)) return '';
  const sec = Math.max(0, Math.floor((now - t) / 1000));
  if (sec < 60) return `${sec}s ago`;
  const min = Math.floor(sec / 60);
  if (min < 60) return `${min}m ago`;
  const hr = Math.floor(min / 60);
  if (hr < 24) return `${hr}h ago`;
  const day = Math.floor(hr / 24);
  return `${day}d ago`;
}

function ChatRow({
  chat,
  onClick,
  dimmed,
  trailing,
}: {
  chat: Chat;
  onClick: () => void;
  dimmed?: boolean;
  trailing?: string;
}) {
  const meta: string[] = [relTime(chat.updated_at)];
  if (chat.message_count !== undefined && chat.message_count > 0) {
    meta.push(`${chat.message_count} msg`);
  }
  const tokens = formatTokens(chat.effective_context_tokens);
  if (tokens) meta.push(tokens);
  const preview = chat.last_message_preview;
  return (
    <button
      type="button"
      onClick={onClick}
      className="w-full flex flex-col gap-0.5 px-3 py-2 hover:bg-muted/50 text-left"
    >
      <div className="flex items-center gap-2 min-w-0">
        <MessageSquare className={`size-3.5 shrink-0 ${dimmed ? 'opacity-40' : 'opacity-70'}`} />
        <span className={`truncate text-sm flex-1 ${dimmed ? 'text-muted-foreground' : ''}`}>
          {chat.name ?? 'New chat'}
        </span>
        {trailing && (
          <span className="text-xs text-muted-foreground shrink-0">{trailing}</span>
        )}
      </div>
      <div className="ml-5 text-xs text-muted-foreground tabular-nums">
        {meta.join(' · ')}
      </div>
      {preview && (
        <div className="ml-5 text-xs italic text-muted-foreground truncate">
          {preview}
        </div>
      )}
    </button>
  );
}

export function SessionLandingPage({
  chats,
  onOpenChat,
  onSend,
  onReopenChat,
}: Props) {
  const [composerValue, setComposerValue] = useState('');
  const [showClosed, setShowClosed] = useState(false);

  const openChats = chats
    .filter((c) => c.status === 'open')
    .sort((a, b) => new Date(b.updated_at).getTime() - new Date(a.updated_at).getTime());
  const closedChats = chats
    .filter((c) => c.status === 'closed')
    .sort((a, b) => new Date(b.updated_at).getTime() - new Date(a.updated_at).getTime());

  function handleSend() {
    const text = composerValue.trim();
    if (!text) return;
    onSend(text);
    setComposerValue('');
  }

  // TODO: Landing page chat counts are a snapshot at mount. New messages in
  // visible chats won't update the per-row stats until next mount/navigation.
  // Wiring WS reactivity through here is deferred (rare use case: user is in
  // a pane when messages stream, not on the landing page).
  return (
    <div className="flex flex-col h-full min-h-0">
      <div className="flex-1 overflow-y-auto px-6 py-4 space-y-6">
        {/* Open chats */}
        {openChats.length > 0 && (
          <div>
            <h3 className="text-xs font-medium text-muted-foreground mb-2">Open chats</h3>
            <ul className="divide-y rounded-md border">
              {openChats.map((chat) => (
                <li key={chat.id}>
                  <ChatRow chat={chat} onClick={() => onOpenChat(chat.id)} />
                </li>
              ))}
            </ul>
          </div>
        )}

        {/* Closed chats */}
        {closedChats.length > 0 && (
          <div>
            <button
              type="button"
              onClick={() => setShowClosed(!showClosed)}
              className="flex items-center gap-1 text-xs font-medium text-muted-foreground mb-2 hover:text-foreground"
            >
              {showClosed ? <ChevronDown size={12} /> : <ChevronRight size={12} />}
              Closed chats ({closedChats.length})
            </button>
            {showClosed && (
              <ul className="divide-y rounded-md border">
                {closedChats.map((chat) => (
                  <li key={chat.id}>
                    <ChatRow
                      chat={chat}
                      onClick={() => void onReopenChat(chat.id)}
                      dimmed
                      trailing="Reopen"
                    />
                  </li>
                ))}
              </ul>
            )}
          </div>
        )}

        {openChats.length === 0 && closedChats.length === 0 && (
          <div className="text-sm text-muted-foreground py-8 text-center">
            No chats yet. Type below to start a conversation.
          </div>
        )}
      </div>

      {/* Composer */}
      <div className="border-t px-4 py-3 flex items-end gap-2 shrink-0">
        <Textarea
          value={composerValue}
          onChange={(e) => setComposerValue(e.target.value)}
          onKeyDown={(e) => {
            if (e.key === 'Enter' && (e.metaKey || e.ctrlKey)) {
              e.preventDefault();
              handleSend();
              return;
            }
            if (e.key === 'Enter' && !e.shiftKey) {
              e.preventDefault();
              handleSend();
            }
          }}
          placeholder="Start a new chat..."
          rows={2}
          className="resize-none min-h-[52px] max-h-[160px]"
        />
        <Button
          onClick={handleSend}
          disabled={!composerValue.trim()}
          size="icon-lg"
          aria-label="Send"
        >
          <Send />
        </Button>
      </div>
    </div>
  );
}