/*
  Name:    pmsort.c
  Purpose: "Poor man's" sort utility
  Author:  Bill Slough

  Usage:   pmsort filename
*/

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

void sort(char *v[ ], int n);
void swap(char **p, char **q);

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

    /* 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);
    nrLines = count_lines(lines);
    
    /* Process */
    sort(lines, nrLines);
    display_lines(lines);

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

    return 0;
}

/* sort an array of n strings into lexicographical order */
void sort(char *v[ ], int n) {
    int i;
    int j;
    int k;

    /* use selection sort to rearrange the strings in sorted order */
    i = 0;
    while (i < n - 1) {
        /* v[0], v[1], v[2], ..., v[i - 1] are in sorted order and they
           are the smallest among all the elements in v.

           To make progress, locate the smallest value in the tail end
           of v and place it at v[i]
        */
        j = i;    /* index of smallest known element among v[i] ... v[n - 1] */
        for (k = i + 1; k < n; k++) {
            /* is there a smaller value somewhere? */
            if (strcmp(v[k], v[j]) < 0)
                j = k;
        }
        swap(&v[i], &v[j]);
        i++;
    }
}

/* swap two strings in an array of strings */
void swap(char **p, char **q) {
    char *temp;
    temp = *p;
    *p = *q;
    *q = temp;
}