/*
    line_counter.c

    Written by Tanya Amert for Fall 2024

    Prints out the count of lines in a file (and optionally
    also the length of each line).

    Compile as usual:

        gcc -Wall -Werror -g -o line_counter line_counter.c

    Run with one command-line argument, specifying a valid filename:

        ./line_counter myfile.txt
*/

#include <stdio.h>

// Change to 0 to turn off debugging print statements
#define DEBUG 1

// Method declarations
void print_usage_statement(const char *program_name);
int get_line_count(const char *file_name);

// Counts the number of lines in a file specified
// as a command-line argument; prints the results to
// standard output
int main(int argc, char *argv[])
{
    // Check that we have enough command-line arguments
    if (argc != 2)
    {
        print_usage_statement(argv[0]);
        return 1; // anything other than 0 indicates failure
    }

    // Parse the command-line argument for the filename
    const char *input_file_name = argv[1];

    // Do the work
    int line_count = get_line_count(input_file_name);
    if (line_count < 0)
    {
        fprintf(stderr, "Trouble counting the lines in %s\n", input_file_name);
        return 1; // another failure case
    }

    printf("Number of lines: %d (0x%x)\n", line_count, line_count);

    return 0;
}

// Prints information for how to use this program.
void print_usage_statement(const char *program_name)
{
    fprintf(stderr, "Usage: %s inputfile\n", program_name);
    fprintf(stderr, "  prints to standard output the number of lines\n");
    fprintf(stderr, "  (as a decimal integer) in the specified file\n");
}

// Returns the number of lines in the specified file, or -1 if an error
// occurs.  Errors include failure to open or read from the file.
//
// If debugging print statements are enabled, also prints
// the length of each line and its first character (counts line
// numbers starting at 0).
//
// Assumes the last line does not end in '\n'.
int get_line_count(const char *file_name)
{
    // Open the file for reading
    FILE *input_file = fopen(file_name, "r");
    if (input_file == NULL)
    {
        return -1;
    }

    // Keep track of the current line number, how long it is, and what
    // the character before the previous one was (just use '\n' at the start)
    int current_line = 0;
    int current_length = 0;
    char prev = '\n';

    // Loop through the file one char/byte at a time, counting lines as we go
    char ch = fgetc(input_file);
    while (ch != EOF)
    {
        // Check if we found a newline character
        if (ch == '\n')
        {
            // If we're debugging, print out the length of this line
            if (DEBUG)
            {
                printf("Line %d has length: %d\n", current_line, current_length);
            }

            // Get ready for the next line
            current_line++;
            current_length = 0;
        }

        // If not, maybe this is the start of a new line
        else if (prev == '\n')
        {
            // Update the count
            current_length++;

            // If we're debugging, print out the first character of this line
            if (DEBUG)
            {
                printf("\nLine %d starts with: '%c'\n", current_line, ch);
            }
        }

        // Otherwise, just update the count
        else
        {
            current_length++;
        }

        // Store this character and read the next one
        prev = ch;
        ch = fgetc(input_file);
    }

    // If ferror returns true, we hit EOF because of some issue, so fail out
    if (ferror(input_file))
    {
        fclose(input_file);
        return -1;
    }

    // We assume the last line doesn't end in \n (not always true),
    // so by hitting EOF we finally saw its end
    if (DEBUG)
    {
        printf("Line %d has length: %d\n", current_line, current_length);
    }

    // Clean up after ourselves
    fclose(input_file);

    // Return the line count +1 as the number of lines we saw
    return current_line + 1;
}