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

int crcount(char *fbuffer_p) {
        int count = 0;
        for (int i = 0; fbuffer_p[i]; ++i) {
                switch (fbuffer_p[i]) {
                        case '\n':
                                ++count;
                                break;
                        case '\r':
                                i += count += 1;
                }
        }

        return count;
}

void unixtodos(FILE *file_fp, const char *dest) {
        if (!file_fp) {
                fprintf(stderr, "Couldnt get a file descriptor for \"%s\"\n", dest);
                exit(1);
        }

        char chunkbuffer_p[8192];
        char outfilebuffer_p[8192];
        long int bytes_read;

        while ((bytes_read = fread(chunkbuffer_p, 1, 8192, file_fp))) {
                for (int i = 0, j = 0; chunkbuffer_p[i]; ++i) {
                        if (chunkbuffer_p[i] == '\n') {
                                outfilebuffer_p[j++] = '\r';
                                outfilebuffer_p[j++] = '\n';
                        } else
                                outfilebuffer_p[j++] = outfilebuffer_p[i];
                }

                file_fp = freopen(dest, "a", file_fp);
                fwrite(outfilebuffer_p, 1, bytes_read, file_fp);
                file_fp = freopen(dest, "r", file_fp);
        }

        if (fclose(file_fp) == EOF) {
                fprintf(stderr, "Failed to close file: \"%s\"\n", dest);
                exit(2);
        }
}

void dostounix(FILE *file_p, const char *dest) {
        if (!file_p) {
                fprintf(stderr, "Couldnt get a file descriptor for \"%s\"\n", dest);
                exit(1);
        }

        fseek(file_p, 0L, SEEK_END);
        int fsize = ftell(file_p);
        if ((fseek(file_p, 0L, SEEK_SET))) {
                fprintf(stderr, "Failed to reset file pointer for \"%s\"\n", dest);
                exit(1);
        }

        char *fbuffer_p = malloc(fsize);
        fread(fbuffer_p, 1, fsize, file_p);

        const int NEW_SIZE = fsize - (crcount(fbuffer_p) / 2);
        char *outfilebuffer_p = malloc(NEW_SIZE);

        int j = 0;
        for (int i = 0; fbuffer_p[i]; ++i) {
                if (fbuffer_p[i] != '\r')
                        outfilebuffer_p[j++] = fbuffer_p[i];
        }

        file_p = freopen(dest, "w", file_p);
        fwrite(outfilebuffer_p, 1, j, file_p);

        if (fclose(file_p) == EOF) {
                fprintf(stderr, "Failed to close file: \"%s\"\n", dest);
                exit(2);
        }
}

int main(int argc, const char **argv) {
        if (argc > 3) {
                fputs("Too many arguments", stderr);
                return 1;
        }


        if (strstr(*argv, "u2d"))
                unixtodos(fopen(argv[1], "r"), argv[1]);
        else
                dostounix(fopen(argv[1], "r"), argv[1]);

    return 0;
}