//! Low level Elliptic Curve Digital Signature Algorithm (ECDSA) functions.
//!


use bn::{BigNum, BigNumRef};
use {cvt, cvt_n, cvt_p};
use ec::EcKey;
use error::ErrorStack;
use ffi;
use foreign_types::{ForeignType, ForeignTypeRef};
use pkey::{Private, Public};
use std::mem;


foreign_type_and_impl_send_sync! {
    type CType = ffi::ECDSA_SIG;
    fn drop = ffi::ECDSA_SIG_free;

    /// A low level interface to ECDSA
    ///
    /// OpenSSL documentation at [`ECDSA_sign`]
    ///
    /// [`ECDSA_sign`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_sign.html
    pub struct EcdsaSig;
    /// Reference to [`EcdsaSig`]
    ///
    /// [`EcdsaSig`]: struct.EcdsaSig.html
    pub struct EcdsaSigRef;
}

impl EcdsaSig {

    /// Computes a digital signature of the `dgstlen` bytes hash value `data` using the private EC key eckey.
    /// Some example values associated with `dgstlen` are: for SHA-1, it is 20; for SHA-256 it is 32 etc.
    ///
    /// OpenSSL documentation at [`ECDSA_do_sign`]
    ///
    /// [`ECDSA_do_sign`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_do_sign.html
    pub fn sign(data: &[u8], dgstlen: i32, eckey: &EcKey<Private>) -> Result<EcdsaSig, ErrorStack> {
        unsafe {
            let sig = cvt_p(ffi::ECDSA_do_sign(data.as_ptr(), dgstlen, eckey.as_ptr()))?;
            Ok(EcdsaSig::from_ptr(sig as *mut _))
        }
    }

    /// Returns a new `EcdsaSig` by setting the `r` and `s` values associated with a
    /// ECDSA signature.
    ///
    /// OpenSSL documentation at [`ECDSA_SIG_set0`]
    ///
    /// [`ECDSA_SIG_set0`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_SIG_set0.html
    pub fn from_private_components(r: BigNum, s: BigNum) -> Result<EcdsaSig, ErrorStack> {
        unsafe {
            let sig = cvt_p(ffi::ECDSA_SIG_new())?;
            cvt(compat::set_numbers(sig, r.as_ptr(), s.as_ptr()))?;
            mem::forget((r, s));
            Ok(EcdsaSig::from_ptr(sig as *mut _))
        }
    }

    /// Verifies if the signature is a valid ECDSA signature using the given public key
    ///
    /// OpenSSL documentation at [`ECDSA_do_verify`]
    ///
    /// [`ECDSA_do_verify`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_do_verify.html
    pub fn verify(&self, data: &[u8], dgstlen: i32, eckey: &EcKey<Public>) -> Result<bool, ErrorStack> {
        unsafe {
            let x = cvt_n(ffi::ECDSA_do_verify(data.as_ptr(), dgstlen, self.as_ptr(), eckey.as_ptr()))?;
            Ok(x == 1)
        }
    }

    /// Returns internal components: `r` and `s` of a `EcdsaSig`. (See X9.62 or FIPS 186-2)
    ///
    /// OpenSSL documentation at [`ECDSA_SIG_get0`]
    ///
    /// [`ECDSA_SIG_get0`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_SIG_get0.html
    pub fn private_components(&self) -> (Option<&BigNumRef>, Option<&BigNumRef>) {
        unsafe {
            let xs = compat::get_numbers(self.as_ptr());
            let r = if xs[0].is_null() { None } else { Some(BigNumRef::from_ptr(xs[0] as *mut _)) };
            let s = if xs[1].is_null() { None } else { Some(BigNumRef::from_ptr(xs[1] as *mut _)) };
            (r, s)
        }
    }

}

#[cfg(ossl110)]
mod compat {
    use std::ptr;

    use libc::c_int;
    use ffi::{self, BIGNUM, ECDSA_SIG};

    pub unsafe fn set_numbers(sig: *mut ECDSA_SIG, r: *mut BIGNUM, s: *mut BIGNUM) -> c_int {
        ffi::ECDSA_SIG_set0(sig, r, s)
    }

    pub unsafe fn get_numbers(sig: *mut ECDSA_SIG) -> [*const BIGNUM; 2] {
        let (mut r, mut s) = (ptr::null(), ptr::null());
        ffi::ECDSA_SIG_get0(sig, &mut r, &mut s);
        [r, s]
    }
}

#[cfg(ossl10x)]
mod compat {
    use libc::c_int;
    use ffi::{BIGNUM, ECDSA_SIG};

    pub unsafe fn set_numbers(sig: *mut ECDSA_SIG, r: *mut BIGNUM, s: *mut BIGNUM) -> c_int {
        (*sig).r = r;
        (*sig).s = s;
        1
    }

    pub unsafe fn get_numbers(sig: *mut ECDSA_SIG) -> [*const BIGNUM; 2] {
        [(*sig).r, (*sig).s]
    }

}

#[cfg(test)]
mod test {
    use nid::Nid;
    use ec::EcGroup;
    use super::*;

    static CURVE_IDENTIFER: Nid = Nid::X9_62_C2TNB191V1;
    static DGST_LEN: i32 = 20;

    fn get_public_key(group: &EcGroup, x: &EcKey<Private>) -> Result<EcKey<Public>, ErrorStack> {
        let public_key_point = x.public_key();
        Ok(EcKey::from_public_key(group, public_key_point)?)
    }

    #[test]
    fn sign_and_verify() {
        let group = EcGroup::from_curve_name(CURVE_IDENTIFER).unwrap();
        let private_key = EcKey::generate(&group).unwrap();
        let public_key = get_public_key(&group, &private_key).unwrap();

        let private_key2 = EcKey::generate(&group).unwrap();
        let public_key2 = get_public_key(&group, &private_key2).unwrap();

        let data = String::from("hello");
        let res = EcdsaSig::sign(data.as_bytes(), DGST_LEN, &private_key).unwrap();

        // Signature can be verified using the correct data & correct public key
        let verification = res.verify(data.as_bytes(), DGST_LEN, &public_key).unwrap();
        assert!(verification);

        // Signature will not be verified using the incorrect data but the correct public key
        let verification2 = res.verify(String::from("hello2").as_bytes(), DGST_LEN, &public_key).unwrap();
        assert!(verification2 == false);

        // Signature will not be verified using the correct data but the incorrect public key
        let verification3 = res.verify(data.as_bytes(), DGST_LEN, &public_key2).unwrap();
        assert!(verification3 == false);
    }

    #[test]
    fn check_private_components() {
        let group = EcGroup::from_curve_name(CURVE_IDENTIFER).unwrap();
        let private_key = EcKey::generate(&group).unwrap();
        let public_key = get_public_key(&group, &private_key).unwrap();
        let data = String::from("hello");
        let res = EcdsaSig::sign(data.as_bytes(), DGST_LEN, &private_key).unwrap();

        let verification = res.verify(data.as_bytes(), DGST_LEN, &public_key).unwrap();
        assert!(verification);

        let x = res.private_components();
        let r = x.0.unwrap().to_owned().unwrap();
        let s = x.1.unwrap().to_owned().unwrap();

        let res2 = EcdsaSig::from_private_components(r, s).unwrap();
        let verification2 = res2.verify(data.as_bytes(), DGST_LEN, &public_key).unwrap();
        assert!(verification2);
    }
}