/*
  173.308.02 - Advanced Physics Lab
  Professor: Tobias Marriage

  Written by Jake Mokris, 2/12/2011

  This simple (not robust) macro prompts for the name of a data file  (which MUST be 
  formatted as two columns of doubles, and MUST be in the same directory as this program) 
  and outputs a graph of the data points in ROOT. This was my macro for the photoelectric 
  effect lab. To run it in ROOT, open ROOT and type

  .L bla.C++ (this compiles the code and creates a shared library)
  bla() (this calls the function)

  Again, this is merely the initial version. If you know a better way to write some
  or all of this program, please tell me!
*/


#include<fstream>
#include<iostream>
#include<TGraph.h>
#include<TAxis.h>

using namespace std;

// This function takes a string and returns a const *char - once I get it to work...

const char *convert(string s)
{
  const int length = s.length();
  char name[length+1];
  for (int i = 0; i<length; i++) 
  {
    name[i] = s[i];
  }
  name[length]='\0';
  const char *converted_string = name;
  return(converted_string);
}

// ROOT does not execute the content of main when running C++ code; the proper way
// to run C++ code in ROOT is to put it into a void function and call the
// function. 

void bla()
{

  // The ifstream constructor accepts only const char *, so this reads in a string,
  // converts it into a char array, then turns that into a const char *.
  string file_string; // name of the file
  cout << "Enter the name of the data file you wish to read: ";
  cin >> file_string;
  const int length = file_string.length(); 
  char name[length+1];
  for (int i = 0; i<length; i++) 
  {
    name[i] = file_string[i];
  }
  name[length]='\0';
  const char *file_name = name;
  cout << file_name << endl;
  cout << convert(file_string);
  // Create ifstream object to input data from file
  ifstream data_file(file_name);

  // Check that the file opened properly
  if (!data_file) 
  {
    cerr << "Failed to open the file.\n";
    exit(EXIT_FAILURE);
  }

  // Count the number of lines of data in the file. Right now this just ignores up
  // to 5000 characters until it hits the end-of-line character. Clearly it needs
  // to ignore an arbitrary number of characters until reaching the end of the line,
  // but I haven't worked on implementing that yet.
  int number_of_lines = 0;
  while(data_file.ignore(5000, '\n'))
  {
    if (!data_file.eof())
    {
    number_of_lines++;
    }
  }
  cout << "The data file " << file_name << " contains " << number_of_lines << " data points." << endl;

  // Return to beginning of file; input data
  data_file.clear();
  data_file.seekg(0);
  double x_coordinate, y_coordinate;
  double x[number_of_lines], y[number_of_lines];
  
  cout << "Reading data file " << file_name << "." << endl;

  for(int i=0; i<number_of_lines && !data_file.eof(); i++)
  {
    data_file >> x_coordinate;
    data_file >> y_coordinate;

    if (!data_file.eof())
    {
      x[i]=x_coordinate;
      y[i]=y_coordinate;
    }
  }

  cout << "Data input complete." << endl;

  // Close the file
  data_file.close();

  // Create the TGraph object
  TGraph *graph = new TGraph(number_of_lines, x, y);

  // To modify the graph settings (axis titles and such), the graph must be drawn first
  graph->Draw();

  // Make the graph fancy
  graph->SetMarkerStyle(20); // Sets the point marker to a filled black circle
  graph->GetXaxis()->SetTitle("Frequency of emitted light (10^14 Hz)"); // Set x-axis title
  graph->GetYaxis()->SetTitle("Photoelectron stopping voltage (V)"); // Set y-axis title
  graph->GetXaxis()->SetLimits(4.5,8.5); // Set x-axis range

  // The axis titles are initially off-center
  graph->GetXaxis()->CenterTitle();
  graph->GetYaxis()->CenterTitle();

  /*
  Draw options:
  A - Include axes
  P - Draw a point marker at each data point
  */
  graph->Draw("AP"); // Redraw the graph

  // This fits the graph to a line ("pol1" means polynomial of degree 1) and draws it on
  // the graph. "WW" means ignore error bars. 
  graph->Fit("pol1", "WW");
}