/*

    17 Jan 2020

    Usage: spacestotabs <number> <file name>

    number: how many spaces will be converted into a tab

*/

#include <stdio.h>
#include <string.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;
    char *backupfilename = strcat(filename, "_backup");

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

    char *c = file;
    while (*c != 'EOF') {
        fputc(*c, backupfile);
        ++c;
    }

    fclose(backupfile);
    fclose(file);
}

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

    if (argc < 2) {
        printf("Error: too few arguments. \"spacestotabs -h\" for help.\n");
    }

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

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

    // Backup the file first
    int iscorrectanswer = 0;
    do {
        printf("Would you like to backup your file before the operation? [Y / N] : ");

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

    // TODO : Do the operation on the original file, don't create a new one.
    char *outfilename = strcat(filename, "_out");

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

    int previousspacecount = 0; // how many spaces has been read in a row
    int writepointercooldown = 4; // TODO: Change this back to 'howmanyspaces' - 1

    char *read = file;
    char *write = read - 4; // TODO: Change this back to 'howmanyspaces' - 1
    while (*read != 'EOF') {
        if (*read == ' ') {
            ++previousspacecount;
        } else {
            previousspacecount = 0;
        }

        if (!writepointercooldown) {
            fputs(*read, out);
        }

        if (previousspacecount == howmanyspaces) {
            fputs('\t', write);
            writepointercooldown = howmanyspaces;
        }

        if (!writepointercooldown) {
            ++write;
        } else {
            --writepointercooldown;
        }

        ++read;
    }

    fclose(file);
    fclose(out);

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

    return 0;
}