// Purpose
// A program to demonstrate the application of a simple digital filter
// 
// Overview
// A sequence of data items and digital filter values need to be entered by the
// user. The application of the filter to the data involves a simple convolution 
// operation. The filtered data are stored separately. 
//
// Example
//  before filtering: 
//   data_in = [0 1 3 6 3 1 0]
//   filter = [-0.5 1 -0.5]
//  after filtering:
//   data_out = [-0.5 -0.5 3 -0.5 -0.5]
//  where
//   data_out[0]=data_in[0]*filter[0]+data_in[1]*filter[1]+data_in[2]*filter[2]
//   data_out[1]=data_in[1]*filter[0]+data_in[2]*filter[1]+data_in[3]*filter[2]
//   data_out[2]=data_in[2]*filter[0]+data_in[3]*filter[1]+data_in[4]*filter[2]
//   data_out[3]=data_in[3]*filter[0]+data_in[4]*filter[1]+data_in[5]*filter[2]
//   data_out[4]=data_in[4]*filter[0]+data_in[5]*filter[1]+data_in[6]*filter[2]
//
// The program checks the following
// 1. The data and filter values must have been entered before the filter is 
//    applied
// 2. The filter is not applied if the number of filter values is greater than
//    the number of input data values
// 3. The data and filter values must have been entered and the filter applied 
//    before the filtered data can be displayed
#include <iostream>
using namespace std;
 
// the data values and the filter
struct TheFilter {
  double* Values;   // the filter values
  unsigned long Length;  // number of filter values
  bool Valid;   // true if the filter values have been Valid by the user
};

struct TheData {
  double* Values;  // holds the data to be filtered
  unsigned long Length;  // number of data values
  bool Valid;   // true if the data values have been Valid by the user
};

// function return values
enum {OK,FILTER_TOO_LONG};

// function prototypes
void EnterData(TheData&);
void EnterFilter(TheFilter&);
int ApplyFilter(TheFilter, TheData, TheData&);
void DisplayData(TheFilter, TheData, TheData);
 
// Control the principal operations of the program
// Arguments: None
// Returns: 0 on completion
int main()
{
  // define the filter and its initial values
  TheFilter Filter = {0,0,false};

  // define the original data and its initial values
  TheData OriginalData = {0,0,false};

  // define the filtered data and its initial values
  TheData FilteredData = {0,0,false};

  char UserInput;

  // loop until the user wishes to exit
  while (1) {
    
    // show the menu of options
    cout << endl;
    cout << "Filter Menu" << endl;
    cout << "-----------" << endl;
    cout << "1. Enter data for filtering" << endl;
    cout << "2. Enter filter values" << endl;
    cout << "3. Apply filter" << endl;
    cout << "4. Display filtered data" << endl;
    cout << "5. Exit from the program" << endl << endl;
    
    // get the user's choice
    cout << "Enter your option: ";
    cin >> UserInput;
    cout << endl;
    
    // act on the user's input
    switch(UserInput) {
      case '1':
        EnterData(OriginalData);
        FilteredData.Valid = false;
        break;

      case '2':
        EnterFilter(Filter);
        FilteredData.Valid = false;
        break;      
 
      case '3':
        if (Filter.Valid == true && OriginalData.Valid == true &&
            FilteredData.Valid == false) {
          if (ApplyFilter(Filter,OriginalData,FilteredData) == FILTER_TOO_LONG) {
             cout << "The filter must not be longer than the data" << endl;
          }
          else {
            FilteredData.Valid = true;
            cout << "Filter applied" << endl;
          }
        }
        break;

      case '4':
        if (Filter.Valid == true && OriginalData.Valid == true &&
            FilteredData.Valid == true) {
          DisplayData(Filter,OriginalData,FilteredData);
        }
	 else {
	    cout << "Data have not yet been filtered" << endl;
	 }
        break;

      case '5':
        delete [] Filter.Values;
        delete [] OriginalData.Values;
        delete [] FilteredData.Values;
        return 0;
        break;

      default:
        cout << "Invalid entry" << endl << endl;
        break;
    }
  }
}

// Allow the user to enter the data to be filtered
// Arguments:
//   (1) the structure containing the input data
// Returns: nothing
// 
void EnterData(TheData& GetData)
{  
  // initialize the data structure that holds the data to be filtered, including getting
  // the number of data values from the user
  delete [] GetData.Values;
  cout << "How many data values do you wish to enter: ";
  cin >> GetData.Length;
  GetData.Valid = true;

  // allocate memory to the data
  GetData.Values = new double[GetData.Length];
  if (GetData.Values == 0) {
    cout << "Unable to allocate sufficient memory" << endl;
    exit(1);
  }

  // obtain all of the data values
  cout << endl;
  cout << "Enter the data values" << endl;
  cout << "---------------------" << endl;
  for (unsigned long CountData = 0; CountData < GetData.Length; CountData++) {
    cout << "Enter value " << CountData+1 << ": ";
    cin >> GetData.Values[CountData];
  }
}

// Allow the user to enter the filter values
// Arguments:
//   (1) the structure of the filter to be defined
// Returns: nothing
// 
void EnterFilter(TheFilter& GetFilter)
{  
  // initialize the data structure that holds the filter, including getting the number of
  // filter values from the user
  delete [] GetFilter.Values;
  cout << "How many data values do you wish to enter: ";
  cin >> GetFilter.Length;
  GetFilter.Valid = true;

  // allocate memory to the filter values
  GetFilter.Values = new double[GetFilter.Length];
  if (GetFilter.Values == 0) {
    cout << "Unable to allocate sufficient memory" << endl;
    exit(1);
  }

  // obtain all of the filter values
  cout << endl;
  cout << "Enter the filter values" << endl;
  cout << "-----------------------" << endl;
  for (unsigned long CountData = 0; CountData < GetFilter.Length; CountData++) {
    cout << "Enter value " << CountData+1 << ": ";
    cin >> GetFilter.Values[CountData];
  }
}

// Apply the filter to the input data and store in the filtered data structure
// Arguments:
//   (1) the structure of the filter to be applied
//   (2) the structure containing the data to be filtered
//   (3) the structure to hold the filtered data
// Returns: OK - if the filter is applied
//          FILTER_TOO_LONG - the filter is longer than the data 
//  
int ApplyFilter(TheFilter Filter, TheData DataIn, TheData& DataOut)
{  
  // return an error if the filter is longer than the data
  if (Filter.Length > DataIn.Length) return FILTER_TOO_LONG;

  // initialize the data structure that holds the filtered data
  delete [] DataOut.Values;
  DataOut.Length = DataIn.Length - Filter.Length + 1;

  // get memory for the filtered data
  DataOut.Values = new double[DataOut.Length];
  if (DataOut.Values == 0) {
    cout << "Unable to allocate sufficient memory" << endl;
    exit(1);
  }

  // apply the filter to the data
  for (unsigned long CountData = 0; CountData < DataOut.Length; CountData++) {
    DataOut.Values[CountData] = 0.0; 
    for (unsigned long CountFilter = 0; CountFilter<Filter.Length; CountFilter++) {
      DataOut.Values[CountData] += DataIn.Values[CountData+CountFilter] *
                                   Filter.Values[CountFilter]; 
    }
  }

  return OK;
}


// Display input data, filter values and output data
// Arguments:
//   (1) the structure of the filter to be applied
//   (2) the structure containing the data to be filtered
//   (3) the structure that holds the filtered data
// Returns: nothing
// 
void DisplayData(TheFilter Filter, TheData DataIn, TheData DataOut)
{  
  // display all of the input data values
  cout << endl;
  cout << "The input data values" << endl;
  cout << "---------------------" << endl;
  cout << "[ ";
  for (unsigned long CountData = 0; CountData < DataIn.Length; CountData++) {
    cout << DataIn.Values[CountData] << " ";
  }
  cout << "]" << endl;
    
  // display all of the filter values
  cout << endl;
  cout << "The filter values" << endl;
  cout << "-----------------" << endl;
  cout << "[ ";
  for (unsigned long CountData = 0; CountData < Filter.Length; CountData++) {
    cout << Filter.Values[CountData] << " ";
  }
  cout << "]" << endl;
    
  // display all of the data output values
  cout << endl;
  cout << "The data output values" << endl;
  cout << "----------------------" << endl;
  cout << "[ ";
  for (unsigned long CountData = 0; CountData < DataOut.Length; CountData++) {
    cout << DataOut.Values[CountData] << " ";
  }
  cout << "]" << endl;
}

class FilterBase
{
    public:
        virtual ~FilterBase();
        virtual void ReadFilters() = 0;
        virtual bool Apply(const std::vector<double>& DataIn, std::vector<double>& DataOut) const = 0;
};

class Filter: public FilterBase
{
    public:
        void ReadFilters();
        bool Apply(const std::vector<double>& DataIn, std::vector<double>& DataOut) const;
    private:
        std::vector<double> filters;
};

int main()
{
    FilterBase* filter = new Filter;
    //...
}