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extern crate libc;
use libc::{c_int, c_ulonglong};
use std::marker::PhantomData;

#[link(name="sodium")]
extern "C" {

    fn sodium_init() -> c_int;

    // Signatures
    fn crypto_sign_keypair(pk: *mut u8, sk: *mut u8) -> c_int;
    fn crypto_sign_detached(sig: *mut u8, siglen: *mut c_ulonglong, m: *const u8, mlen: c_ulonglong, sk: *const u8) -> c_int;
    fn crypto_sign_verify_detached(sig: *const u8, m: *const u8, mlen: c_ulonglong, pk: *const u8) -> c_int;

    // Diffie-Hellman
    fn crypto_scalarmult_curve25519_base(q: *mut u8, n: *const u8) -> c_int;
    fn crypto_scalarmult_curve25519(q: *mut u8, n: *const u8, p: *const u8) -> c_int;

    // Chacha20
    fn crypto_stream_chacha20_xor(c: *mut u8, m: *const u8, mlen: c_ulonglong, n: *const u8, k: *const u8) -> c_int;
    fn crypto_stream_chacha20_xor_ic(c: *mut u8, m: *const u8, mlen: c_ulonglong, n: *const u8, ic: u64, k: *const u8) -> c_int;

    // Poly1305
    fn crypto_onetimeauth(out: *mut u8, in_: *const u8, inlen: c_ulonglong, k: *const u8) -> c_int;
    fn crypto_onetimeauth_verify(h: *const u8, in_: *const u8, inlen: c_ulonglong, k: *const u8) -> c_int;
}

/// "Proof" of initialisation of the library
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct Sodium(PhantomData<()>);
unsafe impl Send for Sodium{}
unsafe impl Sync for Sodium{}

impl Sodium {
    pub fn new() -> Self {
        unsafe { sodium_init(); }
        Sodium(PhantomData)
    }
}

pub mod chacha20 {
    use super::*;
    pub const NONCE_BYTES: usize = 8;
    pub const KEY_BYTES: usize = 32;
    pub struct Nonce(pub [u8; NONCE_BYTES]);
    pub struct Key(pub [u8; KEY_BYTES]);

    impl Sodium {
        pub fn chacha20_xor(&self, c: &mut [u8], n: &Nonce, k: &Key) {
            unsafe {
                crypto_stream_chacha20_xor(c.as_mut_ptr(), c.as_ptr(), c.len() as c_ulonglong, n.0.as_ptr(), k.0.as_ptr());
            }
        }

        pub fn chacha20_xor_ic(&self, c: &mut [u8], n: &Nonce, ic: u64, k: &Key) {
            unsafe {
                crypto_stream_chacha20_xor_ic(c.as_mut_ptr(), c.as_ptr(), c.len() as c_ulonglong, n.0.as_ptr(), ic, k.0.as_ptr());
            }
        }
    }
}

pub mod poly1305 {
    use super::*;
    pub const KEY_BYTES: usize = 32;
    pub const TAG_BYTES: usize = 16;
    pub struct Key(pub [u8; KEY_BYTES]);
    pub struct Tag(pub [u8; TAG_BYTES]);
    impl Sodium {
        pub fn poly1305_auth(&self, m: &[u8], key: &Key) -> Tag {
            let mut tag = Tag([0; TAG_BYTES]);
            unsafe {
                crypto_onetimeauth(tag.0.as_mut_ptr(), m.as_ptr(), m.len() as c_ulonglong, key.0.as_ptr());
            }
            tag
        }
        pub fn poly1305_verify(&self, tag: &[u8], m: &[u8], key: &Key) -> bool {
            if tag.len() != TAG_BYTES {
                false
            } else {
                unsafe {
                    crypto_onetimeauth_verify(tag.as_ptr(), m.as_ptr(), m.len() as c_ulonglong, key.0.as_ptr()) == 0
                }
            }
        }
    }
}

pub mod ed25519 {
    use super::*;
    pub const PUBLICKEY_BYTES: usize = 32;
    pub const SECRETKEY_BYTES: usize = 64;
    pub const SIGNATURE_BYTES: usize = 64;

    /// Ed25519 public key.
    #[derive(Debug, PartialEq, Eq, Clone)]
    pub struct PublicKey {
        /// Actual key
        pub key: [u8; PUBLICKEY_BYTES],
        /// "Proof" of initialisation of the library
        pub sodium: Sodium,
    }
    /// Ed25519 secret key.
    pub struct SecretKey {
        /// Actual key
        pub key: [u8; SECRETKEY_BYTES],
        /// "Proof" of initialisation of the library
        pub sodium: Sodium,
    }
    pub struct Signature(pub [u8; SIGNATURE_BYTES]);

    /// Generate a key pair.
    pub fn keypair() -> (PublicKey, SecretKey) {
        unsafe {
            let sodium = Sodium::new();
            let mut pk = PublicKey { key: [0; PUBLICKEY_BYTES], sodium };
            let mut sk = SecretKey { key: [0; SECRETKEY_BYTES], sodium };
            crypto_sign_keypair(pk.key.as_mut_ptr(), sk.key.as_mut_ptr());
            (pk, sk)
        }
    }

    /// Verify a signature, `sig` could as well be a `Signature`.
    pub fn verify_detached(sig: &[u8], m: &[u8], pk: &PublicKey) -> bool {
        if sig.len() == SIGNATURE_BYTES {
            unsafe {
                crypto_sign_verify_detached(sig.as_ptr(), m.as_ptr(), m.len() as c_ulonglong, pk.key.as_ptr()) == 0
            }
        } else {
            false
        }
    }

    /// Sign a message with a secret key.
    pub fn sign_detached(m: &[u8], sk: &SecretKey) -> Signature {
        let mut sig = Signature([0; SIGNATURE_BYTES]);
        let mut sig_len = 0;
        unsafe {
            crypto_sign_detached(
                sig.0.as_mut_ptr(), &mut sig_len,
                m.as_ptr(), m.len() as c_ulonglong,
                sk.key.as_ptr()
        );
        }
        sig
    }
}

pub mod scalarmult {
    use super::*;
    pub const BYTES: usize = 32;

    #[derive(Debug)]
    pub struct Scalar(pub [u8; BYTES]);
    #[derive(Debug)]
    pub struct GroupElement(pub [u8; BYTES]);

    impl Sodium {

        pub fn scalarmult_base(&self, n: &Scalar) -> GroupElement{
            let mut q = GroupElement([0; BYTES]);
            unsafe {
                crypto_scalarmult_curve25519_base(q.0.as_mut_ptr(), n.0.as_ptr());
            }
            q
        }

        pub fn scalarmult(&self, n: &Scalar, p: &GroupElement) -> GroupElement {
            let mut q = GroupElement([0; BYTES]);
            unsafe {
                crypto_scalarmult_curve25519(q.0.as_mut_ptr(), n.0.as_ptr(), p.0.as_ptr());
            }
            q
        }
    }
}