TweetDuck/Browser/Handling/General/FileDialogHandler.cs

using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Windows.Forms;
using CefSharp;

namespace TweetDuck.Browser.Handling.General{
    sealed class FileDialogHandler : IDialogHandler{
        public bool OnFileDialog(IWebBrowser browserControl, IBrowser browser, CefFileDialogMode mode, CefFileDialogFlags flags, string title, string defaultFilePath, List<string> acceptFilters, int selectedAcceptFilter, IFileDialogCallback callback){
            if (mode == CefFileDialogMode.Open || mode == CefFileDialogMode.OpenMultiple){
                string allFilters = string.Join(";", acceptFilters.SelectMany(ParseFileType).Where(filter => !string.IsNullOrEmpty(filter)).Select(filter => "*" + filter));

                using(OpenFileDialog dialog = new OpenFileDialog{
                    AutoUpgradeEnabled = true,
                    DereferenceLinks = true,
                    Multiselect = mode == CefFileDialogMode.OpenMultiple,
                    Title = "Open Files",
                    Filter = $"All Supported Formats ({allFilters})|{allFilters}|All Files (*.*)|*.*"
                }){
                    if (dialog.ShowDialog() == DialogResult.OK){
                        string ext = Path.GetExtension(dialog.FileName)?.ToLower();
                        callback.Continue(acceptFilters.FindIndex(filter => ParseFileType(filter).Contains(ext)), dialog.FileNames.ToList());
                    }
                    else{
                        callback.Cancel();
                    }

                    callback.Dispose();
                }

                return true;
            }
            else{
                callback.Dispose();
                return false;
            }
        }

        private static IEnumerable<string> ParseFileType(string type){
            if (string.IsNullOrEmpty(type)){
                return new string[0];
            }
            
            if (type[0] == '.'){
                return new string[]{ type };
            }

            switch(type){
                case "image/jpeg": return new string[]{ ".jpg", ".jpeg" };
                case "image/png": return new string[]{ ".png" };
                case "image/gif": return new string[]{ ".gif" };
                case "image/webp": return new string[]{ ".webp" };
                case "video/mp4": return new string[]{ ".mp4" };
                case "video/quicktime": return new string[]{ ".mov", ".qt" };
            }

            System.Diagnostics.Debugger.Break();
            return new string[0];
        }
    }
}