Pre Uninstall event handlers

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using System;
using System.Data.SqlClient;
using System.Runtime.InteropServices;

using kCura.EventHandler;
using kCura.EventHandler.CustomAttributes;
using Relativity.API;

namespace Examples.EventHandlers.Install
{

    /// <summary>
    /// This event handler runs when the application is uninstalled and deletes a queue table from the EDDS database.
    /// </summary>
    [Description("Example uninstall event handler")]
    [Guid("B25E0A6D-57B5-416B-9110-69DD86A07B5A")]
    public class ExamplePreUninstallEventHandler : PreUninstallEventHandler
    {
        private static Guid EXAMPLE_APPLICATION_GUID = new Guid("B4F52C6C-F55C-488F-BA71-E8EE8B5C74F4");

        public override Response Execute()
        {
            //Construct a response object with default values.
            Response retVal = new Response();

            try
            {
                //Get the EDDS database context.
                IDBContext eddsDBContext = this.Helper.GetDBContext(-1);
                //Get the current workspace artifactID.
                int currentWorkspaceID = this.Helper.GetActiveCaseID();
                //Get the current workspace database context.
                IDBContext workspaceDBContext = this.Helper.GetDBContext(currentWorkspaceID);
                //Determine how many workspaces have this application installed.
                if (!IsLastApplicationInEnvironment(eddsDBContext, currentWorkspaceID))
                {
                    //If this application is installed on other workspaces, leave the table and delete entries for this workspace only.
                    RemoveWorkspaceEntriesFromQueueTable(eddsDBContext, currentWorkspaceID);
                }
                else
                {
                    //If this application isn't installed on any other workspaces, drop the queue table.
                    DropEDDSWorkspaceTablesIfExists(eddsDBContext);
                }

                retVal.Message = string.Empty;
                retVal.Success = true;
            }
            catch (Exception ex)
            {
                //Catch an exception if it occurs and fail the uninstall.
                retVal.Success = false;
                retVal.Message = ex.ToString();
            }

            return retVal;
        }

        /// <summary>
        /// Check to see if the application is installed in any other cases, or if this the last one.
        /// </summary>
        /// <param name="eddsDBContext">A properly constructed EDDS database context</param>
        /// <param name="currentWorkspaceID">Current workspace ArtifactID</param>
        /// <returns>True if no other workspaces have this application installed. False if other workspaces have this application installed.</returns>
        private static bool IsLastApplicationInEnvironment(IDBContext eddsDBContext, int currentWorkspaceID)
        {
            string applicationCountSQL = @"
DECLARE @applicationID INT = (SELECT [ArtifactID] FROM [LibraryApplication] WHERE [GUID] = @applicationGUID)
SELECT
    COUNT([CaseApplicationID])
FROM
    [CaseApplication]
WHERE
    [ApplicationID] IN (SELECT [ArtifactID] FROM [LibraryApplication] WHERE [GUID] = @applicationGUID)
    AND
    [CaseID] <> @workspaceArtifactID
";
            SqlParameter applicationGUIDParam = new SqlParameter("@applicationGUID", System.Data.SqlDbType.UniqueIdentifier)
            {
                Value = EXAMPLE_APPLICATION_GUID
            };
            SqlParameter workspaceArtifactIDParam1 = new SqlParameter("@workspaceArtifactID", System.Data.SqlDbType.Int)
            {
                Value = currentWorkspaceID
            };

            int installCount = eddsDBContext.ExecuteSqlStatementAsScalar<int>(applicationCountSQL, applicationGUIDParam, workspaceArtifactIDParam1);

            return installCount == 0;
        }

        /// <summary>
        /// Remove all workspace entries from queue table in the EDDS database.
        /// </summary>
        /// <param name="eddsDBContext">A properly constructed EDDS database context</param>
        /// <param name="currentWorkspaceID">Current workspace ArtifactID</param>
        private static void RemoveWorkspaceEntriesFromQueueTable(IDBContext eddsDBContext, int currentWorkspaceID)
        {
            string deleteWaitingJobsSQL = "DELETE FROM [ExampleMessageQueue] WHERE [WorkspaceArtifactID] = @workspaceArtifactID";
            SqlParameter workspaceArtifactIDParam = new SqlParameter("@workspaceArtifactID", System.Data.SqlDbType.Int)
            {
                Value = currentWorkspaceID
            };
            eddsDBContext.ExecuteNonQuerySQLStatement(deleteWaitingJobsSQL, new[] { workspaceArtifactIDParam });
        }

        /// <summary>
        /// Drop the EDDS tables from the environment when they are no longer needed.
        /// </summary>
        /// <param name="eddsDBContext">A properly constructed EDDS database context</param>
        private static void DropEDDSWorkspaceTablesIfExists(IDBContext eddsDBContext)
        {
            string sql = FormatDropTableSQL("ExampleMessageQueue");
            eddsDBContext.ExecuteNonQuerySQLStatement(sql);
        }

        /// <summary>
        /// Create a SQL statement to check if a table exists and drop the table if it does.
        /// </summary>
        /// <param name="tableName">Name of the table to look for</param>
        /// <returns></returns>
        private static string FormatDropTableSQL(string tableName)
        {
            return $"DROP TABLE IF EXISTS [{tableName}]";
        }
    }
}