/* This is the line count program I coded up in Lecture 08.
 * It shows how a simple C program is laid out, including taking command-line
 * arguments, printing to stdout and stderr, and reading from a file.
 * This program is incomplete, and even generates a compiler warning.
 * A complete version will be posted with Lecture 09.
 */

#include <stdio.h> // standard library stuff for printing and file I/O

// during compilation MAX_LINE_LENGTH will get replaced with 500
#define MAX_LINE_LENGTH 500 

int main(int argc, char **argv) {
    // we expect exactly two arguments
    //    argv[0] is the command (i.e., "./line_count")
    //    argv[1] FILE
    if (argc != 2) {
        // use fprintf to print to stderr
        fprintf(stderr, "usage: ./line_count FILE\n");
        return 1; // exit status of 1 indicates error
    }

    FILE *file = fopen(argv[1], "r"); // try to open the file in "read" mode
    // check if we were able to open the file (fopen returns NULL if it fails)
    if (file != NULL) { 
        int lines = count_lines(file); // compiler warning on this line since we haven't declared count_lines beforehand
        // could use fprintf(stdout, ...) to print to stdout, but printf is easier
        printf("%i\n", lines); // %i is the format string for an int
        return 0; // exit status of 0 for success
    } else {
        // %s is the format string for a string
        fprintf(stderr, "line_count: error opening %s\n", argv[1]);
        return 2;
    }
}

int count_lines(FILE *file) {
    int count = 0;
    char line[MAX_LINE_LENGTH]; // will get turned into char line[500] at compilation
    /* fgets reads up to MAX_LINE_LENGTH characters from file and stores them in line, stopping at newlines
     * file keeps track of what has been read, so the next call to fgets will pick up where it left off
     * if successful, fgets returns line, which gets treated as true
     * if it fails (e.g., there are no more characters to read), fgets returns NULL, which gets treated as false
     */
    while(fgets(line, MAX_LINE_LENGTH, file)) {
        count++;
    }
    return count;
}