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pub use crypto_api;
use crypto_api::rng::SecureRng;
use std::{
	error::Error,
	fmt::{ Display, Formatter, Result as FmtResult }
};


/// This error indicates that something went wrong while calling the OS' RNG
#[derive(Debug, Eq, PartialEq, Copy, Clone)]
pub struct OsRandomError;
impl Display for OsRandomError {
	fn fmt(&self, f: &mut Formatter) -> FmtResult {
		write!(f, "{:?}", self)
	}
}
impl Error for OsRandomError {}


/// An interface to the operating system's secure random number generator
pub struct OsRandom;
impl OsRandom {
	/// Creates a `SecureRng` instance with the OS' RNG as underlying implementation
	pub fn secure_rng() -> Box<dyn SecureRng> {
		Box::new(Self)
	}
}
impl SecureRng for OsRandom {
	fn random(&mut self, buf: &mut[u8]) -> Result<(), Box<dyn Error + 'static>> {
		// The API of the bridge library
		extern "C" {
			// uint8_t crypto_api_osrandom_secrandom(uint8_t* buf, size_t len);
			fn crypto_api_osrandom_secrandom(buf: *mut u8, len: usize) -> u8;
		}
		
		// Call the bridge library
		Ok(match unsafe{ crypto_api_osrandom_secrandom(buf.as_mut_ptr(), buf.len()) } {
			0 => (),
			_ => Err(OsRandomError)?
		})
	}
}