#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

// Define a structure to hold the characters
typedef struct List_type
{
  struct List_type *next;
  int value;
} List;

int toLower = 0;

// Add new element to the list
List* add_entry(int value, List *lastElement)
{
  List *pTemp;

  pTemp = malloc(sizeof(List));		// Allocate adequate memory

  pTemp->value = value;		        	// Insert the character
  pTemp->next    = NULL;		      	// Terminate the extended list
  lastElement->next     = pTemp;		// Link on the new item

  return pTemp;		               		// Return the new end value
}

// Change characters
int changeCharacter (int character)
{
  if (isupper(character))
  {
    toLower++;
    return tolower(character);
  }
  else
    return toupper(character);
}

// Method to print changed characters to standard output
void printChangedText (List *fromEntry, int count)
{
  putchar('\n');
  while (fromEntry != NULL)
  {
    putchar(changeCharacter(fromEntry->value));
    fromEntry = fromEntry->next;
  }
  putchar('\n');
  printf("Read %d characters in total,", count);
  printf(" %d converted to upper-case,", count-toLower);
  printf(" %d to lower-case\n", toLower);
}

// Free the allocated
void freeMemory (List *dummy)
{
  while (dummy->next != NULL)
  {
    List *temp;
    temp = dummy->next;
    dummy->next = temp->next;
    free(temp);
  }
}

int main(int argc, char **argv)
{
  int noOfChar = 0;
  int current;

// ====================================================
// Ask the user for input and output if there is any
// ====================================================
  printf("Would you like to use an input file? (y/n)\n");
  int answer = getchar();
  // ====================================================
  // If the input is from a file
  // ====================================================
  if (answer == 'y')
  {
    char fileName[20];
    FILE *fileIn, *fileOut;

    printf("What is the file name?\n");
    scanf("%s", fileName);
    if ((fileIn = fopen(fileName, "r")))
    {
      printf("Would you like to use an output file? (y/n)\n");
      fflush(stdin);
      int answer2 = getchar();
      // ====================================================
      // If there is an output file too
      // ====================================================
      if (answer2 == 'y')
      {
        printf("What is the file name?\n");
        scanf("%s", fileName);

        fileOut = fopen(fileName, "w+");

        current = fgetc(fileIn);
        while (current != EOF)
        {
          noOfChar++;
          fputc(changeCharacter(current), fileOut);
          current = fgetc(fileIn);
        }
        fputc('\n', fileOut);
        fprintf(fileOut, "Read %d characters in total,", noOfChar);
        fprintf(fileOut, " %d converted to upper-case,", noOfChar-toLower);
        fprintf(fileOut, " %d to lower-case\n", toLower);
        fclose(fileIn);
        fclose(fileOut);
      }
      else if (answer2 == 'n')
      {
        current = fgetc(fileIn);
        while (current != EOF)
        {
          noOfChar++;
          putchar(changeCharacter(current));
          current = fgetc(fileIn);
        }
        putchar('\n');
        printf("Read %d characters in total,", noOfChar);
        printf(" %d converted to upper-case,", noOfChar-toLower);
        printf(" %d to lower-case\n", toLower);
        fclose(fileIn);
      }
      else
      {
        printf("Answer does not exist. Please try again. %d\n", answer2);
        exit(1);
      }
    }
    else
      printf("Sorry, the file does not exist\n");
      exit(1);
  }
  else if (answer == 'n')
  {
    printf("Please type your text\n");
    // Last element
    List *lastElement;
    // Add a dummy entry as a start of the list
    List dummy;
    dummy.value = -1;
    dummy.next = NULL;
    lastElement = &dummy;                       // Set dummy as last element of the list

    current = getchar();                 // Read the first character

    while (current != EOF)               // Investigate the character != EOF
    {
      lastElement = add_entry(current, lastElement);
      noOfChar++;
      current = getchar();
    }

    printChangedText(dummy.next, noOfChar);
    freeMemory (&dummy);
  }
  else
  {
    printf("Answer does not exist. Please try again.\n");
    exit(1);
  }
}