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

/*Input:  Integer array and its size
* Output: None
* Return: None
* Notes:  Function to sort the integers in the array
*/
void sort(int arr[], int * size)
{
    /*initializes local variables needed to run bubble sort*/
    int i;
    int j;
    int tmp;

    /*bubble sort implementation*/
    for(i=0; i<(*size-1); i++)
    {
        for(j=0; j<(*size-1); j++)
        {
            if (arr[j]>arr[j+1])
            {
                tmp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = tmp;
            }
        }
    }
}

/*Input:  Name of input and output files as command line argument
* Output: Writes sorted array to specified output file
* Return: Type = int, value = 0
* Notes:  main method which reads integers from given input file, calls sort
* function to sort the integers, then writes the sorted ints to given
* output file
*/
int main( int argc, char ** argv )
{
    /*declares all variables*/

    int i;
    int tmp;

    /*store the position in char array argv of input and output files
    * respectively
    */
    int input;
    int output;

    /*checki and checko facilitate verifying valid input and output file
    * flags were entered
    */
    int checki=0;
    int checko=0;

    /*tracks number of ints read from file*/
    int num_items=0;

    /*grow rate for array*/
    int grow=10;

    /*used to store return value for fread*/
    size_t size;

    /*array declaration and memory allocation*/
    int * arr = (int *)malloc( sizeof( int ) * grow);
    
    /*declares file pointer fptr*/
    FILE * fptr;

    /*for loop to check for flags declaring input and output files at
    * command line, when the appropriate flag is identified, the array
    * position of the input and output files is stored in the variables
    * input and output respectively. checki/checko incrememnt to signal
    * that a valid input/output file was entered when running program.
    */
    for ( i = 1 ; i < argc ; ++i )
    {
        if (strcmp(argv[i], "-i")==0)
        {
            input = i + 1;
            checki++;
        }

        if (strcmp(argv[i], "-o")==0)
        {
            output = i + 1;
            checko++;
        }
    }

    /*if either the input or the output files or flags were not entered,
    * error message prints to screen, program exits.
    */
    if (checki==0 || checko==0)
    {
        printf("enter valid input and output files!\n");
        exit( 1 );
    }
      
    /*open input file with read access*/ 
    fptr = fopen ( argv[input], "r" );

    /*resets i value to zero*/
    i = 0;

    /*this loop reads ints from file 1 at a time, stores value in array
    * buf, then grows array arr, and stores value in buf in arr[i] where
    * i is the current loop iteration. also tracks number of values
    * stored in the array. Loop runs as long as fread is successful in
    * reading one int
    */
    do
    {
        size = fread ( &tmp , sizeof( int ), 1, fptr);

        grow+=10;
        arr=(int *)realloc(arr, sizeof(int)*grow);

        arr[i]=tmp;

        /*if/block to ensure that num_items does not increment on final
        * iteration of do/while loop
        */
        if (size == 1)
        {
            num_items++;
        }

        ++i;
    } while( size == 1 );

    /*calls sort function to sort array arr*/
    sort(arr, &num_items);

    /*closes input file*/
    fclose( fptr );

    /*opens output file with write access*/
    fptr = fopen ( argv[output], "w" );

    /*writes integers stored array arr to output file*/
    fwrite ( arr, sizeof( int ), num_items, fptr );

    /*closes output file*/
    fclose( fptr );

    /*frees memory allocated to arr*/
    free( arr );

    return 0;
}