namespace bts.BlueOrb {
   using BCG;
   using System.IO;
   using System.Diagnostics;
   using System;

   [DataStreamUserRespresentation("PythonDataframeStream")]
   public class PythonDataframeStream : ViewStream {
      private ViewStream _parent_str;
      private readonly string _in_csv_file_name;
      private readonly string _out_csv_filename;
      private readonly string _transform_function;
      public PythonDataframeStream(ViewStream parent_str, string transform_function) {
         var guid = System.Guid.NewGuid();
         _in_csv_file_name = $"pdfs_in_{guid}.csv";
         _out_csv_filename = $"pdfs_out_{guid}.csv";
         _parent_str = new CSVSaverStream(parent_str, _in_csv_file_name);
         _transform_function = transform_function;
      }

      protected override void myOnFirstSubscriber() {
         _parent_str.onChange += _parent_str_onchange;
      }

      protected override void myOnLastSubscriber() {
         _parent_str.onChange -= _parent_str_onchange;
      }

      private void _parent_str_onchange(object dp_obj) {
         Log.assert(dp_obj != null);
         // the file _in_csv_file_name is now populated.
         // call py_func_wrapper_main and pass this file name as well
         // as the output file name
         // py_func_wrapper_main reads _in_csv_file_name into the df and calls 
         // transform function, which returns the tranformed df. py_func_wrapper_main then
         // writes it into the _out_csv_filename file.
         // now this function should read _out_csv_filename into a dp
         // and fire it
         _compute_and_write();
         //ViewStream rs = new SchemaGuesserStream(new CSVReaderStream(_out_csv_filename));
         ViewStream rs = new CSVReaderStream(_out_csv_filename);
         IBlueRowCollection nrows = null;
         rs.onChange += (dp_obj) => {
            nrows = (dp_obj as DataPacket).newRows;
         };
         var dp = BlueDataUtility.build_dp(nrows, myLastValue as DataPacket);
         myFireEvent(dp);
      }

      private void _compute_and_write() {
         File.WriteAllText("user_code.py", _transform_function);
         // wrapper function
         string py_func_wrapper_main = @"
import sys
from user_code import transform
import pandas as pd

if __name__ == '__main__':
   input_file_name = sys.argv[1]
   output_file_name = sys.argv[2]
# 1. load input_file_name into df
# 2. do some test calc
# 3. write the output of 2 into output_file_name
   df = pd.read_csv(input_file_name)   
   df_out = transform(df)
   df_out.to_csv(output_file_name, index=False)";


         File.WriteAllText("runner.py", py_func_wrapper_main);

         ProcessStartInfo psi = new ProcessStartInfo {
            FileName = "python",
            Arguments = $"runner.py {_in_csv_file_name} {_out_csv_filename}",
            RedirectStandardOutput = false,
            UseShellExecute = false
         };
         var proc = Process.Start(psi);
         proc.WaitForExit();

      }

      #region Unused test code
      private void _simple_test() {

         // actual function that needs to be called ////////////////////////
         string py_real_function = @"
def test(x, out_path):
   rv = x * 10
   with open(out_path, 'w') as f:
      f.write(str(rv))
   return rv";
         // the function is in a string object.
         File.WriteAllText("user_code.py", py_real_function);


         // runner app (top level main function) //////////////////////////////
         string py_func_wrapper_main = @"
import sys
from user_code import test

if __name__ == '__main__':
   arg = int(sys.argv[1])
   out_path = sys.argv[2]
   rv = test(arg, out_path)
   rv = rv + 12
   with open(out_path, 'w') as f:to \
      f.write(str(rv))";
   
         File.WriteAllText("runner.py", py_func_wrapper_main);

         string outputPath = "py_out.txt";
         ProcessStartInfo psi = new ProcessStartInfo {
            FileName = "python",
            Arguments = $"runner.py 4 {outputPath}",
            RedirectStandardOutput = false,
            UseShellExecute = false
         };
         var proc = Process.Start(psi);
         proc.WaitForExit();

         // Now read the output written by the function
         string result = File.ReadAllText(outputPath);
         Console.WriteLine(result); // Should print "6"

      }
      #endregion
   }
}