u2f 0.1.2

use chrono::prelude::*;
use time::Duration;
use ring::rand::{SecureRandom, SystemRandom};
use bytes::{Bytes};
use base64::{encode_config, Config, CharacterSet, LineWrap};
use u2ferror::U2fError;

/// The `Result` type used in this crate.
type Result<T> = ::std::result::Result<T, U2fError>;

pub const U2F_V2: &'static str = "U2F_V2";

// Generates a challenge from a secure, random source.
pub fn generate_challenge(size: usize) -> Result<Vec<u8>> {
    let mut bytes: Vec<u8> = vec![0; size];

    let rng = SystemRandom::new();
    rng.fill(&mut bytes).map_err(|_e| U2fError::RandomSecureBytesError)?;
    Ok(bytes)
}

pub fn expiration(timestamp: String) -> Duration {
    let now: DateTime<Utc> = Utc::now();

    let ts = timestamp.parse::<DateTime<Utc>>();

    now.signed_duration_since(ts.unwrap())
}

// Decode initial bytes of buffer as ASN and return the length of the encoded structure.
// http://en.wikipedia.org/wiki/X.690
pub fn asn_length(mem: Bytes) -> Result<usize> {
    let buffer : &[u8] = &mem[..];

    if mem.len() < 2 || buffer[0] != 0x30 {  // Type 
        return Err(U2fError::Asm1DecoderError);
    }

    let len = buffer[1]; // Len
    if len & 0x80 == 0 {
        return Ok((len & 0x7f) as usize);
    }

    let numbem_of_bytes = len & 0x7f;
    if numbem_of_bytes == 0 {
        return Err(U2fError::Asm1DecoderError);
    }

    let mut length: usize = 0;
    for num in 0..numbem_of_bytes {
        length = length*0x100 + (buffer[(2+num) as usize] as usize);
    }
 
    length = length + (numbem_of_bytes as usize);

    Ok(length + 2) // Add the 2 initial bytes: type and length.
}

pub fn get_encoded(data: &[u8]) -> String {
    let config = Config::new(CharacterSet::UrlSafe, true, false, LineWrap::NoWrap);

    let encoded: String = encode_config(data, config);

    encoded.trim_right_matches('=').to_string()
}