use Value::*;

#[derive(Debug)]
enum Value {
    I(i64),
}

#[derive(Debug)]
enum Error {
    NotEnoughData,
    InvalidInteger,
}

fn read_int(mut buf: &[u8], size_in_bytes: usize) -> Result<Value, Error> {
    let mut acc = 0;

    for _ in 0..size_in_bytes {
        if buf.is_empty() { return Err(Error::NotEnoughData) }
        acc <<= 8;
        acc |= buf[0] as i64;
        buf = &buf[1..];
    }

    Ok(I(acc))
}

fn cbor_decode(buf: &[u8]) -> Result<Value, Error> {
    match buf[0] {
        0x00 ... 0x17 => Ok(I(buf[0] as i64)),
        0x18 ... 0x1b => read_int(&buf[1..], (buf[0] - 0x17) as usize),
        _             => Err(Error::InvalidInteger),
    }
}

fn main() {
    let x = [0x1a, 1, 0, 0];
    let y = cbor_decode(&x);
    println!("{:?}", y);
}

extern crate byteorder;

use byteorder::{ByteOrder, BigEndian};

fn read_int(buf: &[u8], size_in_bytes: usize) -> Result<Value, Error> {
    if buf.len() < size_in_bytes {
        Err(Error::NotEnoughData)
    } else {
        Ok(I(BigEndian::read_int(buf, size_in_bytes)))
    }
}