import React, { useEffect, useState } from 'react';
import clsx from 'clsx';
import {
  fetchSessions, createSession, deleteSession, updateSession,
  fetchFolders, createFolder, deleteFolder, updateFolder,
  type ChatSession, type ChatFolder,
} from '@/api/ai';

interface SessionListProps {
  activeSessionId: string | null;
  onSelectSession: (id: string) => void;
  isSidebar?: boolean;
  className?: string;
}

interface TreeNode {
  folder: ChatFolder | null;
  sessions: ChatSession[];
  children: TreeNode[];
}

function buildTree(folders: ChatFolder[], sessions: ChatSession[]): TreeNode[] {
  const rootSessions = sessions.filter((s) => !s.folder_id);
  const root: TreeNode = { folder: null, sessions: rootSessions, children: [] };

  const folderMap = new Map<string, TreeNode>();
  for (const f of folders) {
    folderMap.set(f.id, { folder: f, sessions: [], children: [] });
  }

  for (const f of folders) {
    const node = folderMap.get(f.id)!;
    if (f.parent_id && folderMap.has(f.parent_id)) {
      folderMap.get(f.parent_id)!.children.push(node);
    } else {
      root.children.push(node);
    }
  }

  for (const s of sessions) {
    if (s.folder_id && folderMap.has(s.folder_id)) {
      folderMap.get(s.folder_id)!.sessions.push(s);
    }
  }

  return [root];
}

function TreeItem({
  node, activeSessionId, onSelectSession, depth, onMoveSession, onDeleteFolder, onAddFolder,
}: {
  node: TreeNode;
  activeSessionId: string | null;
  onSelectSession: (id: string) => void;
  depth: number;
  onMoveSession: (sessionId: string, folderId: string | null) => void;
  onDeleteFolder: (folderId: string) => void;
  onAddFolder: (parentId: string | null) => void;
}) {
  const [expanded, setExpanded] = useState(true);
  const isRoot = node.folder === null;

  return (
    <div>
      {/* Folder header */}
      {!isRoot && (
        <div
          className="group flex items-center gap-1 px-2 py-1.5 text-sm font-medium text-secondary-700 hover:bg-secondary-100 rounded-md cursor-pointer"
          style={{ paddingLeft: depth * 12 + 8 }}
          onClick={() => setExpanded(!expanded)}
        >
          <svg className={clsx('w-4 h-4 transition-transform', expanded && 'rotate-90')} fill="none" viewBox="0 0 24 24" stroke="currentColor">
            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M9 5l7 7-7 7" />
          </svg>
          <svg className="w-4 h-4 text-secondary-400" fill="none" viewBox="0 0 24 24" stroke="currentColor">
            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M3 7v10a2 2 0 002 2h14a2 2 0 002-2V9a2 2 0 00-2-2h-6l-2-2H5a2 2 0 00-2 2z" />
          </svg>
          <span className="flex-1 truncate">{node.folder!.name}</span>
          <button
            onClick={(e) => { e.stopPropagation(); onAddFolder(node.folder!.id); }}
            className="opacity-0 group-hover:opacity-100 text-secondary-400 hover:text-primary-600"
            title="Unterordner"
          >+</button>
          <button
            onClick={(e) => { e.stopPropagation(); onDeleteFolder(node.folder!.id); }}
            className="opacity-0 group-hover:opacity-100 text-secondary-400 hover:text-red-600"
            title="Löschen"
          >✕</button>
        </div>
      )}

      {/* Sessions in this folder */}
      {(isRoot || expanded) && (
        <div>
          {node.sessions.map((session) => (
            <div
              key={session.id}
              onClick={() => onSelectSession(session.id)}
              className={clsx(
                'group flex items-center gap-2 px-3 py-1.5 text-sm cursor-pointer rounded-md',
                'hover:bg-secondary-100',
                activeSessionId === session.id && 'bg-primary-100 text-primary-700'
              )}
              style={{ paddingLeft: depth * 12 + 24 }}
            >
              <svg className="w-3.5 h-3.5 text-secondary-400 flex-shrink-0" fill="none" viewBox="0 0 24 24" stroke="currentColor">
                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M8 12h8M8 8h8m-8 4h8m-8 4h8" />
              </svg>
              <span className="flex-1 truncate">{session.title}</span>
              <button
                onClick={(e) => {
                  e.stopPropagation();
                  const folderId = node.folder?.id || null;
                  onMoveSession(session.id, folderId ? null : 'root');
                }}
                className="opacity-0 group-hover:opacity-100 text-secondary-400 hover:text-primary-600"
                title="Verschieben"
              >↦</button>
              <button
                onClick={(e) => { e.stopPropagation(); deleteSession(session.id).then(() => window.location.reload()); }}
                className="opacity-0 group-hover:opacity-100 text-secondary-400 hover:text-red-600"
                title="Löschen"
              >✕</button>
            </div>
          ))}
        </div>
      )}

      {/* Child folders */}
      {(isRoot || expanded) && node.children.map((child) => (
        <TreeItem
          key={child.folder!.id}
          node={child}
          activeSessionId={activeSessionId}
          onSelectSession={onSelectSession}
          depth={depth + 1}
          onMoveSession={onMoveSession}
          onDeleteFolder={onDeleteFolder}
          onAddFolder={onAddFolder}
        />
      ))}
    </div>
  );
}

export function SessionList({ activeSessionId, onSelectSession, isSidebar, className }: SessionListProps) {
  const [sessions, setSessions] = useState<ChatSession[]>([]);
  const [folders, setFolders] = useState<ChatFolder[]>([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  const loadData = async () => {
    try {
      setLoading(true);
      const [s, f] = await Promise.all([
        fetchSessions(isSidebar ? true : undefined),
        fetchFolders(),
      ]);
      setSessions(s);
      setFolders(f);
      setError(null);
    } catch (e) {
      setError(e instanceof Error ? e.message : 'Failed to load');
    } finally {
      setLoading(false);
    }
  };

  useEffect(() => { loadData(); }, [isSidebar]);

  const handleNewChat = async () => {
    try {
      const session = await createSession({ is_sidebar: isSidebar || false });
      setSessions((prev) => [session, ...prev]);
      onSelectSession(session.id);
    } catch (e) {
      setError(e instanceof Error ? e.message : 'Failed to create session');
    }
  };

  const handleAddFolder = (parentId: string | null) => {
    const name = prompt('Ordnername:');
    if (!name) return;
    createFolder({ name, parent_id: parentId || undefined })
      .then(() => loadData())
      .catch((e) => setError(e?.message));
  };

  const handleDeleteFolder = (folderId: string) => {
    if (!confirm('Ordner löschen? Chats bleiben erhalten.')) return;
    deleteFolder(folderId).then(() => loadData()).catch((e) => setError(e?.message));
  };

  const handleMoveSession = async (sessionId: string, target: string) => {
    const folderId = target === 'root' ? null : target;
    try {
      await updateSession(sessionId, { folder_id: folderId });
      loadData();
    } catch (e) {
      setError(e instanceof Error ? e.message : 'Failed to move');
    }
  };

  if (loading) return <div className="p-4 text-sm text-secondary-400">Laden...</div>;

  const tree = buildTree(folders, sessions);

  return (
    <div className={clsx('flex flex-col h-full', className)}>
      <div className="p-3 border-b border-secondary-200 flex gap-2">
        <button
          onClick={handleNewChat}
          className="flex-1 rounded-lg bg-primary-600 text-white px-3 py-2 text-sm font-medium hover:bg-primary-700"
        >
          + Neuer Chat
        </button>
        <button
          onClick={() => handleAddFolder(null)}
          className="rounded-lg border border-secondary-300 px-3 py-2 text-sm hover:bg-secondary-100"
          title="Neuer Ordner"
        >
          📁+
        </button>
      </div>
      {error && <div className="p-2 text-xs text-red-600">{error}</div>}
      <div className="flex-1 overflow-y-auto p-2">
        {tree.map((node) => (
          <TreeItem
            key={node.folder?.id || 'root'}
            node={node}
            activeSessionId={activeSessionId}
            onSelectSession={onSelectSession}
            depth={0}
            onMoveSession={handleMoveSession}
            onDeleteFolder={handleDeleteFolder}
            onAddFolder={handleAddFolder}
          />
        ))}
      </div>
    </div>
  );
}