#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stddef.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>

#define STDIN  0
#define STDOUT 1

static void print(const char* s)
{
    write(STDOUT, s, strlen(s));
}

static void touch(const char* path)
{
    int fd = open(path, O_CREAT | O_WRONLY, 0644);
    if (fd < 0) {
        print("touch: cannot create file\n");
        return;
    }

    close(fd);
}

static void ls(const char* path)
{
    struct dirent* entry;

    DIR* dir = opendir(path ? path : ".");
    if (!dir) {
        print("ls: cannot open directory\n");
        return;
    }

    while ((entry = readdir(dir)) != NULL)
    {
        // skip . and ..
        if (entry->d_name[0] == '.' &&
            (entry->d_name[1] == '\0' ||
            (entry->d_name[1] == '.' && entry->d_name[2] == '\0')))
            continue;

        print(entry->d_name);
        print("\n");
    }

    closedir(dir);
}

static void readline(char* buf, size_t max)
{
    size_t i = 0;

    while (i < max - 1)
    {
        char c;
        ssize_t n = read(STDIN, &c, 1);

        if (n <= 0)
            continue;

        if (c == '\n')
            break;

        if (c == '\b') {
            if (i > 0) i--;
            continue;
        }

        buf[i++] = c;
    }

    buf[i] = '\0';
}

static void cat(const char* path)
{
    char buf[256];

    int fd = open(path, O_RDONLY);
    if (fd < 0) {
        print("cat: cannot open file\n");
        return;
    }

    ssize_t n = read(fd, buf, sizeof(buf));
    close(fd);

    if (n > 0)
        write(STDOUT, buf, (size_t)n);
}

int main(void)
{
    const char* path = "/qwerty.txt";
    const char* msg  = "Suki Suki Daisuki Kekkon Shiyo, my honey!";

    char buf[128];

    int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
    write(fd, msg, strlen(msg));
    close(fd);

    fd = open(path, O_RDONLY);
    ssize_t n = read(fd, buf, sizeof(buf));
    close(fd);

    if (n > 0)
        write(STDOUT, buf, (size_t)n);

    char line[128];

    while (1)
    {
        print("> ");
        readline(line, sizeof(line));

        if (strcmp(line, "exit") == 0)
            break;

        if (line[0] == 'c' && line[1] == 'a' && line[2] == 't' && line[3] == ' ')
        {
            cat(&line[4]);
            continue;
        }

        if (line[0] == 't' && line[1] == 'o' && line[2] == 'u' && line[3] == 'c' && line[4] == 'h' && line[5] == ' ')
        {
            touch(&line[6]);
            continue;
        }

        if (line[0] == 'l' && line[1] == 's')
        {
            if (line[2] == ' ')
                ls(&line[3]);
            else
                ls(NULL);

            continue;
        }

        if (line[0] != '\0')
            print("Unknown command\n");
    }

    return 0;
}