// Copyright 2018 Brian Smith.

// SPDX-License-Identifier: ISC

// Modifications copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.

// SPDX-License-Identifier: Apache-2.0 OR ISC

#![allow(dead_code)]

//! Initialization Vector (IV) cryptographic primitives

use crate::error::Unspecified;

use crate::rand;

use zeroize::Zeroize;

/// Length of a 128-bit IV in bytes.

pub const IV_LEN_128_BIT: usize = 16;

/// An initialization vector that must be unique for the lifetime of the associated key

/// it is used with.

pub struct FixedLength<const L: usize>([u8; L]);

impl<const L: usize> FixedLength<L> {

    /// Returns the size of the iv in bytes.

    #[allow(clippy::must_use_candidate)]

    pub fn size(&self) -> usize {

        L

    }

    /// Constructs a new [`FixedLength`] from pseudo-random bytes.

    ///

    /// # Errors

    ///

    /// * [`Unspecified`]: Returned if there is a failure generating `L` bytes.

    pub fn new() -> Result<Self, Unspecified> {

        let mut iv_bytes = [0u8; L];

        rand::fill(&mut iv_bytes)?;

        Ok(Self(iv_bytes))

    }

}

impl<const L: usize> Drop for FixedLength<L> {

    fn drop(&mut self) {

        self.0.zeroize();

    }

}

impl<const L: usize> AsRef<[u8; L]> for FixedLength<L> {

    #[inline]

    fn as_ref(&self) -> &[u8; L] {

        &self.0

    }

}

impl<const L: usize> From<&[u8; L]> for FixedLength<L> {

    #[inline]

    fn from(bytes: &[u8; L]) -> Self {

        FixedLength(bytes.to_owned())

    }

}

impl<const L: usize> From<[u8; L]> for FixedLength<L> {

    #[inline]

    fn from(bytes: [u8; L]) -> Self {

        FixedLength(bytes)

    }

}

impl<const L: usize> TryFrom<&[u8]> for FixedLength<L> {

    type Error = Unspecified;

    fn try_from(value: &[u8]) -> Result<Self, Self::Error> {

        let value: &[u8; L] = value.try_into()?;

        Ok(Self::from(*value))

    }

}

impl<const L: usize> TryFrom<FixedLength<L>> for [u8; L] {

    type Error = Unspecified;

    fn try_from(value: FixedLength<L>) -> Result<Self, Self::Error> {

        Ok(value.0)

    }

}

#[cfg(test)]

mod tests {

    use crate::iv::FixedLength;

    #[test]

    fn test_size() {

        let fixed = FixedLength::from([0u8; 16]);

        assert_eq!(16, fixed.size());

        let array = [0u8; 12];

        let fixed = FixedLength::<12>::try_from(array.as_slice()).unwrap();

        assert_eq!(12, fixed.size());

        assert!(FixedLength::<16>::try_from(array.as_slice()).is_err());

        assert!(TryInto::<[u8; 12]>::try_into(fixed).is_ok());

    }

}