// CSE 303, Spring 2009, Marty Stepp
// This program prints the lines of a file in reverse order.
// If you run it with a file passed as a command-line parameter, it reads
// from that file.  If you don't pass a file, it reads from standard input.

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

int main(int argc, char* argv[]) {
    // argv[1] is the file to read
    FILE* f;
    int i;
    int capacity = 10;
    int line_count = 0;
    char** lines;         // array of strings
    char buf[1024];       // buffer to read each line
    
    if (argc > 1) {
        f = fopen(argv[1], "r");
        if (!f) {
            perror("Unable to open file");
            return 1;
        }
    } else {
        // printf("Usage: %s FILENAME\n", argv[0]);
        f = stdin;
    }

    lines = (char**) malloc(capacity * sizeof(char*));
    while (!feof(f)) {
        // read a line from the file
        // useful string functions: strcpy, strdup
        char* str;
        fgets(buf, sizeof(buf) - 1, f);
        if (buf[0] == '\n') {
            break;
        }
        str = strdup(buf);         // copy the string onto the heap

        if (line_count == capacity) {
            capacity *= 2;
            lines = (char**) realloc(lines, capacity * sizeof(char*));
        }
        lines[line_count] = str;   // put this string into the array
        line_count++;
    }
    
    for (i = line_count - 1; i >= 0; i--) {
        printf("%s", lines[i]);
        free(lines[i]);
    }
    free(lines);
    
    fclose(f);
    return 0;
}