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

int is_string_numerical(char *str)
{
    int len = strlen(str);
    int i;
    for (i = 0; i < len; ++i) {
        if (!isdigit(str[i])) {
            return 0;
        }
    }
    return 1;
}

void backupfile(char *filename)
{
    FILE *file;
    FILE *backupfile;

    const int SIZE_backupfilename = strlen(filename) + 8; // TODO: we need less maybe
    char backupfilename[SIZE_backupfilename];
    strcpy(backupfilename, filename);
    strcat(backupfilename, "_backup");

    file = fopen(filename, "r");
    backupfile = fopen(backupfilename, "w");

    if (file == NULL) {
        printf("Error: could not open file %s\n", filename);
    }

    char c;
    while ((c = fgetc(file)) != EOF) {
        fputc(c, backupfile);
    }

    fclose(backupfile);
    fclose(file);
}

int main(int argc, char *argv[])
{
    int howmanyspaces; // how many spaces will be converted into a tab

    if (argc < 2) { // 1 program name, 1 argument
        printf("Error: too few arguments. \"spacestotabs -h\" for help.\n");
        return 1;
    }

    if (argc > 3) { // 1 program name, 1 number, 1 filename
        printf("Warning: too many arguments. Arguments after the second one will be ignored. \"spacestotabs -h\" for help.\n");
        return 1;
    }

    // Handle first argument
    if (argv[1][0] == '-') {
        switch (argv[1][1])
        {
        case 'h': // Help content
            printf("\nUsage: spacestotabs <number> <file name>\n");
            printf("\n<number> : Number of spaces that will be converted into a tab. Number has to be positive.\n\n");
            return 0;
        default: // Parameter not found, wrong parameter
            printf("Error: wrong arguments. \"spacestotabs -h\" for help.\n");
            return 1;
        }
    } else {
        if (!is_string_numerical(argv[1])) {
            printf("Error: wrong parameter. \"spacestotabs -h\" for help.\n");
            return 1;
        }

        howmanyspaces = atoi(argv[1]);

        if (howmanyspaces <= 0) {
            printf("Error: number is too small. \"spacestotabs -h\" for help.\n");
            return 1;
        }
    }

    const int SIZE_filename = strlen(argv[2]) + 10; // TODO: we need only + 7 or 8
    char filename[SIZE_filename];
    strcpy(filename, argv[2]);

    // Backup the file first
    do {
        printf("Would you like to backup your file before the operation? [Y / N] : ");

        char c = getchar();
        if (c == 'n' || c == 'N') {
            break;
        } else if (c == 'y' || c == 'Y') {
            backupfile(filename);
            printf("Backup is created in the same directory with the name %s_backup\n", filename);
            break;
        } else {
            printf("Error: unknown input. Use letters y or n to answer.\n");
        }
    } while (1);

    // TODO : Do the operation on the original file, don't create a new one.
    const int SIZE_outfilename = SIZE_filename + 5; // TODO: less will be enough
    char outfilename[SIZE_outfilename];
    strcpy(outfilename, filename);
    strcat(outfilename, "_out");

    FILE *file;
    FILE *out;
    file = fopen(filename, "r");
    out = fopen(outfilename, "w");

    if (file == NULL) {
        printf("Error: could not open file %s\n", filename);
    }

    int spacesinarow = 0;
    char c;
    while ((c = fgetc(file)) != EOF) {
        if (spacesinarow == howmanyspaces) {
            fputc('\t', out);
            spacesinarow = 0;
        }

        if (c == ' ') {
            ++spacesinarow;
        } else {
            if (spacesinarow) {
                int i;
                for (i = 0; i < spacesinarow; ++i) {
                    fputc(' ', out);
                }

                spacesinarow = 0;
            }

            fputc(c, out);
        }
    }

    fclose(file);
    fclose(out);

    printf("\nSpaces have been converted to tabs.\n");

    return 0;
}