/*
  Name:    pmsort.c
  Purpose: "Poor man's" sort utility:  now with qsort()
  Author:  Bill Slough

  Usage:   pmsort filename
*/

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

int compare_strings(const void *p, const void *q);

int main(int argc, char *argv[ ]) {
    FILE *fp;             /* file pointer for an input stream */
    char **lines;         /* NULL-terminated array of strings */
    int i;

    /* Check for proper usage */
    if (argc != 2) {
        fprintf(stderr, "Usage: pmsort filename\n");
        exit(EXIT_FAILURE);
    }

    /* Try to open the input stream for reading */
    fp = fopen(argv[1], "r");
    if (fp == NULL) {
        fprintf(stderr, "Error: can't open \"%s\" for reading.\n", argv[1]);
        exit(EXIT_FAILURE);
    }

    /* Read and store the lines */
    lines = read_lines(fp);
    
    /* Process */
    qsort(lines, count_lines(lines), sizeof(char *), compare_strings);
    display_lines(lines);

    /* Free the space used for the lines */
    i = 0;
    while (lines[i] != NULL) {
        free(lines[i]);
        i++;
    }
    free(lines);

    /* Close the stream */
    fclose(fp);

    return 0;
}

/* compare two string values */
int compare_strings(const void *p, const void *q) {
    /* Cast the input parameters into the specific types */
    const char **p1 = (const char **) p;
    const char **q1 = (const char **) q;

    /* return negative, zero, or positive for <, ==, or > */
    return strcmp(*p1, *q1);
}