text: // Copyright 2015 The Shaderc Authors. All rights reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #include "libshaderc_util/file_finder.h"
  #include "libshaderc_util/string_piece.h"
  
  #include <cassert>
  #include <fstream>
  #include <ios>
  
  namespace {
  
  // Returns "" if path is empty or ends in '/'.  Otherwise, returns "/".
  std::string MaybeSlash(const shaderc_util::string_piece& path) {
    return (path.empty() || path.back() == '/') ? "" : "/";
  }
  
  }  // anonymous namespace
  
  namespace shaderc_util {
  
  std::string FileFinder::FindReadableFilepath(
      const std::string& filename) const {
    assert(!filename.empty());
    static const auto for_reading = std::ios_base::in;
    std::filebuf opener;
    for (const auto& prefix : search_path_) {
      const std::string prefixed_filename =
          prefix + MaybeSlash(prefix) + filename;
      if (opener.open(prefixed_filename, for_reading)) return prefixed_filename;
    }
    return "";
  }
  
  std::string FileFinder::FindRelativeReadableFilepath(
      const std::string& requesting_file, const std::string& filename) const {
    assert(!filename.empty());
  
    string_piece dir_name(requesting_file);
  
    size_t last_slash = requesting_file.find_last_of("/\\");
    if (last_slash != std::string::npos) {
      dir_name = string_piece(requesting_file.c_str(),
                              requesting_file.c_str() + last_slash);
    }
  
    if (dir_name.size() == requesting_file.size()) {
      dir_name.clear();
    }
  
    static const auto for_reading = std::ios_base::in;
    std::filebuf opener;
    const std::string relative_filename =
        dir_name.str() + MaybeSlash(dir_name) + filename;
    if (opener.open(relative_filename, for_reading)) return relative_filename;
  
    return FindReadableFilepath(filename);
  }
  
  }  // namespace shaderc_util
  