add check downloaded plugin zip has same or lesser version

Author: jjw24

Plugins/Flow.Launcher.Plugin.PluginsManager/Languages/en.xaml

@@ -14,6 +14,7 @@
     <system:String x:Key="plugin_pluginsmanager_install_in_progress">Plugin installation in progress. Please wait...</system:String>
     <system:String x:Key="plugin_pluginsmanager_install_success_restart">Plugin successfully installed. Restarting Flow, please wait...</system:String>
     <system:String x:Key="plugin_pluginsmanager_install_errormetadatafile">Unable to find the plugin.json metadata file from the extracted zip file.</system:String>
+    <system:String x:Key="plugin_pluginsmanager_install_error_duplicate">Error: A plugin which has the same or greater version with {0} already exists.</system:String>
     <system:String x:Key="plugin_pluginsmanager_install_error_title">Error installing plugin</system:String>
     <system:String x:Key="plugin_pluginsmanager_install_error_subtitle">Error occured while trying to install {0}</system:String>
     <system:String x:Key="plugin_pluginsmanager_update_noresult_title">No update available</system:String>

Plugins/Flow.Launcher.Plugin.PluginsManager/PluginsManager.cs

@@ -10,6 +10,7 @@
 using System.IO;
 using System.Linq;
 using System.Net.Http;
+using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Windows;
@@ -438,6 +439,17 @@ private void Install(UserPlugin plugin, string downloadedFilePath)
                     string.Format("Unable to find plugin.json from the extracted zip file, or this path {0} does not exist", pluginFolderPath));
             }
 
+            if (SameOrLesserPluginVersionExists(metadataJsonFilePath))
+            {
+                MessageBox.Show(string.Format(Context.API.GetTranslation("plugin_pluginsmanager_install_error_duplicate"), plugin.Name),
+                                Context.API.GetTranslation("plugin_pluginsmanager_install_error_title"));
+
+                throw new InvalidOperationException(
+                    string.Format("A plugin with the same ID and version already exists, " +
+                                    "or the version is greater than this downloaded plugin {0}",
+                                    plugin.Name));
+            }
+
             var directory = string.IsNullOrEmpty(plugin.Version) ? $"{plugin.Name}-{Guid.NewGuid()}" : $"{plugin.Name}-{plugin.Version}";
             var newPluginPath = Path.Combine(DataLocation.PluginsDirectory, directory);
 
@@ -532,5 +544,14 @@ private List<Result> AutoCompleteReturnAllResults(string search, string hotkey,
 
             return new List<Result>();
         }
+
+        private bool SameOrLesserPluginVersionExists(string metadataPath)
+        {
+            var newMetadata = JsonSerializer.Deserialize<PluginMetadata>(File.ReadAllText(metadataPath));
+            return Context.API.GetAllPlugins()
+                                .Any(x => x.Metadata.ID == newMetadata.ID 
+                                    && (x.Metadata.Version == newMetadata.Version) 
+                                        || newMetadata.Version.CompareTo(x.Metadata.Version) < 0);
+        }
     }
 }