text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef CHROME_BROWSER_ICON_LOADER_H_
  #define CHROME_BROWSER_ICON_LOADER_H_
  
  #include <memory>
  #include <string>
  
  #include "base/callback.h"
  #include "base/files/file_path.h"
  #include "base/macros.h"
  #include "base/single_thread_task_runner.h"
  #include "base/task/task_traits.h"
  #include "build/build_config.h"
  #include "content/public/browser/browser_thread.h"
  #include "ui/gfx/image/image.h"
  
  ////////////////////////////////////////////////////////////////////////////////
  //
  // A facility to read a file containing an icon asynchronously in the IO
  // thread. Returns the icon in the form of an ImageSkia.
  //
  ////////////////////////////////////////////////////////////////////////////////
  class IconLoader {
   public:
    // An IconGroup is a class of files that all share the same icon. For all
    // platforms but Windows, and for most files on Windows, it is the file type
    // (e.g. all .mp3 files share an icon, all .html files share an icon). On
    // Windows, for certain file types (.exe, .dll, etc), each file of that type
    // is assumed to have a unique icon. In that case, each of those files is a
    // group to itself.
    using IconGroup = base::FilePath::StringType;
  
    enum IconSize {
      SMALL = 0,  // 16x16
      NORMAL,     // 32x32
      LARGE,      // Windows: 32x32, Linux: 48x48, Mac: Unsupported
      ALL,        // All sizes available
    };
  
    // The callback invoked when an icon has been read. The parameters are:
    // - The icon that was loaded (IsEmpty() will be true on failure to load).
    // - The determined group from the original requested path.
    using IconLoadedCallback =
        base::OnceCallback<void(gfx::Image, const IconGroup&)>;
  
    // Creates an IconLoader, which owns itself. If the IconLoader might outlive
    // the caller, be sure to use a weak pointer in the |callback|.
    static IconLoader* Create(const base::FilePath& file_path,
                              IconSize size,
                              IconLoadedCallback callback);
  
    // Starts the process of reading the icon. When the reading of the icon is
    // complete, the IconLoadedCallback callback will be fulfilled, and the
    // IconLoader will delete itself.
    void Start();
  
   private:
    IconLoader(const base::FilePath& file_path,
               IconSize size,
               IconLoadedCallback callback);
  
    ~IconLoader();
  
    // Given a file path, get the group for the given file.
    static IconGroup GroupForFilepath(const base::FilePath& file_path);
  
    // The TaskRunner that ReadIcon() must be called on.
    static scoped_refptr<base::TaskRunner> GetReadIconTaskRunner();
  
    void ReadGroup();
    void ReadIcon();
  
    // The traits of the tasks posted to base::ThreadPool by this class. These
    // operations may block, because they are fetching icons from the disk, yet
    // the result will be seen by the user so they should be prioritized
    // accordingly.
    static constexpr base::TaskTraits traits() {
      return {base::MayBlock(), base::TaskPriority::USER_VISIBLE};
    }
  
    // The task runner object of the thread in which we notify the delegate.
    scoped_refptr<base::SingleThreadTaskRunner> target_task_runner_;
  
    base::FilePath file_path_;
  
    IconGroup group_;
  
  #if !defined(OS_ANDROID)
    IconSize icon_size_;
  #endif  // !defined(OS_ANDROID)
  
    IconLoadedCallback callback_;
  
    DISALLOW_COPY_AND_ASSIGN(IconLoader);
  };
  
  #endif  // CHROME_BROWSER_ICON_LOADER_H_
  