program Fibonacci;

// Finds the fibonacci series for 12.
// Author: Jon Fast
// Last Modified: 10/31/2013

// compiler mode: Object Pascal used
{$mode objfpc}{$H+}

//libraries
uses
  SysUtils;

// write the depth of the recursive call to a string
// more tabs indicate greater call depth
  procedure writeDepth(depth: longint; var filevar: textfile);
  var
    i: longint;
  begin
    for i := 0 to depth do
      Write(filevar, '-    ');
  end;

  // calculate the current fibonacci number
  function calculate(number: longint; depth: longint; var filevar: textfile): longint;
  var
    fib1: longint;
    fib2: longint;
  begin
    // check for stopping conditions
    if number = 0 then
    begin
      writedepth(depth, filevar);
      writeln(filevar, 'Reached 0!');
      Result := number;
    end
    else
    if number = 1 then
    begin
      writedepth(depth, filevar);
      writeln(filevar, 'Reached 1!');
      Result := number;
    end
    // recurse
    else
    begin
      // calculate fib 1
      writedepth(depth, filevar);
      writeln(filevar, 'Calculating #1: f( ', number - 1, ' )');
      fib1 := calculate(number - 1, depth + 1, filevar);

      // calculate fib 2
      writedepth(depth, filevar);
      writeln(filevar, 'Calculating #2: f( ', number - 2, ' )');
      fib2 := calculate(number - 2, depth + 1, filevar);

      // result is addition of both
      writedepth(depth, filevar);
      writeln(filevar, 'Result is: ', fib1 + fib2);
      Result := fib1 + fib2;
    end;
  end;

  // fibonacci starter code
  procedure fibonacci(number: longint);
  var
    depth: longint;
    filevar: textfile;
    finalfib: integer;
  begin
    // starting depth is 0
    depth := 0;
    // if number is greater than 0, its fib can be found
    if number > 0 then
    begin
      try
        // initialize the file
        assignfile(filevar, 'fibonacci_trace.txt');
        rewrite(filevar);
        // what are we looking for?
        writeln(filevar, 'Fibonacci series of ', number, '...');
        writeln;
        // find it
        finalfib := calculate(number, depth, filevar);
        writeln('Fibonacci number ', number, ' is ', finalfib, '.');
        // no more
        closefile(filevar);
      except
        on e: EInOutError do
        begin
          // file not created
          writeln('File handling error occured.', e.message);
        end;
      end;
    end
    else
      // negative value error
      writeln('Error: Fibonacci number is not greater than 0.');
  end;

  // main program
begin
  // test: fibonacci 12
  fibonacci(12);
  // done
  writeln('Done: Press any key to continue...');
  readln;
end.