_findClassLongname(className) {
    // find in same file.
    for (const node of this._ast.program.body) {
      if (!['ExportDefaultDeclaration', 'ExportNamedDeclaration'].includes(node.type)) continue;
      if (node.declaration && node.declaration.type === 'ClassDeclaration' && node.declaration.id.name === className) {
        return `${this._pathResolver.filePath}~${className}`;
      }
    }

    // find in import.
    const importPath = ASTUtil.findPathInImportDeclaration(this._ast, className);
    if (importPath) return this._resolveLongname(className);

    // find in external
    return className;
  }
find class in same file, import or external.
@param {string} className - target class name.
@returns {string} found class long name.
@private