#if 0
// simple example code
error
cd(Args args)
{
    switch (args.len) {
    case 0:
        errorf("reached cd with no arguments!");
        return 1;
    case 1:
    one:
        errorf("sh: expected argument to command 'cd'");
        return 1;
    case 2:
        if (args.a[1] == nil)
            goto one;
        break;
    default:
        errorf("sh: too many arguments to command 'cd'");
        return 1;
    }
    if (chdir(args.a[1]))
        errorf("cd fail: %s", strerror(errno));

    return 0;
}

error
quit(Args args)
{
    exit(0);
}

Builtin builtins[] = {
    { "cd",   cd },
    { "exit", quit },
};

void
clear(Header *arr)
{
    arr->len = 0;
}

int
readline(Code *code)
{
    int n, b;

    n = code->len;
getchar:
    if (code->len >= code->cap) {
        code->cap += 100;
        code->s = realloc(code->s, code->cap);
    }
    /* TODO: unicode? */
    switch ((b = getchar())) {
    case EOF:
        n = -1;
        goto null;
    case '\n':
        n = code->len - n;
    null:
        code->s[code->len] = '\0';
        break;
    default:
        code->s[code->len++] = b;
        goto getchar;
    }

    return n;
}

/* TODO: unicode */
int
readargs(Code code, Args *args)
{
    if (args->a)
        clear(&args->hdr);
    else {
        args->cap += 20;
        args->a    = realloc(args->a, args->cap);
    }

    args->a[args->len++] = code.s;
    while (*code.s) {
        if (!isspace(*code.s++))
            continue;

        code.s[-1] = '\0';
        /* consume all remaining space */
        while (isspace(*code.s))
            code.s++;

        if (args->len >= args->cap-1) {
            args->cap += 20;
            args->a = realloc(args->a, args->cap);
        }
        args->a[args->len++] = code.s;
    }
    /* nil acts as a sentinel value */
    args->a[args->len] = nil;

    return args->len;
}

error
execute(Args args)
{
    int i, status;
    pid_t cid, wid;

    for (i = 0; i < arrlen(builtins); i++) {
        if (strcmp(args.a[0], builtins[i].cmd) == 0)
            return builtins[i].func(args);
    }

    if ((cid = fork()) == 0) {
        if (execvp(args.a[0], args.a) == -1)
            errorf("exec failed: %s", strerror(errno));
        exit(1);
    } else if (cid > 0) 
        do
            wid = waitpid(cid, &status, WUNTRACED);
        while (!WIFEXITED(status) && !WIFSIGNALED(status));
    else
        errorf("fork failed: %s", strerror(errno));

    return status;
}

static
void
flush(void)
{
    io·flush(stdout);
}

static
void
prompt(void)
{
    printf(";");
    flush();
}

int
main(int argc, char *argv[])
{
    int  i, err, n;
    Code code = {0};
    Args args = {0};

    ARGBEGIN {
    } ARGEND;

    do {
        clear(&code.hdr);
        prompt();

        n = readline(&code);
        readargs(code, &args);
        err = execute(args);
    } while (!err && n > 0);
}
#endif