use num_bigint_dig::{traits::ModInverse, BigUint};
use num_traits::identities::One;
use rsa::{PublicKey, RSAPrivateKey};

use super::*;

impl KeyExt for RSAPrivateKey {
    fn to_pem_pkcs8(&self) -> Result<String, KeyError> {
        let bytes = write_pkcs1(self).ok_or(KeyError::Serialize)?;
        let oid = yasna::models::ObjectIdentifier::from_slice(&RSA_OID);

        let contents = yasna::construct_der(|writer| {
            writer.write_sequence(|writer| {
                writer.next().write_i64(0); // version is 0
                writer.next().write_sequence(|writer| {
                    writer.next().write_oid(&oid);
                });
                writer.next().write_bytes(&bytes);
            });
        });

        let p = pem::Pem {
            tag: "PRIVATE KEY".to_owned(),
            contents,
        };

        Ok(pem::encode(&p))
    }

    fn from_pem_pkcs8(pem: &str) -> Result<Self, KeyError> {
        let data = pem::parse(pem).map_err(|_| KeyError::Pem)?;

        if data.tag != "PRIVATE KEY" {
            return Err(KeyError::Kind.into());
        }

        let expected_oid = yasna::models::ObjectIdentifier::from_slice(&RSA_OID);

        let pkey = yasna::parse_der(&data.contents, |reader| {
            // Read the outer DER-encoded value
            reader.read_sequence(|reader| {
                let version = reader.next().read_i64()?;

                // PKCS#8 defines version == 0
                if version != 0 {
                    return Err(yasna::ASN1Error::new(yasna::ASN1ErrorKind::Invalid));
                }

                let oid = reader
                    .next()
                    .read_sequence(|reader| reader.next().read_oid())?;

                // RSA defines OID == 1.2.840.113549.1.1.1
                if oid != expected_oid {
                    return Err(yasna::ASN1Error::new(yasna::ASN1ErrorKind::Invalid));
                }

                let bytes = reader.next().read_bytes()?;

                parse_pkcs1(&bytes)
            })
        })?;

        pkey.validate().map_err(|_| KeyError::Validate)?;

        Ok(pkey)
    }

    fn to_pem_pkcs1(&self) -> Result<String, KeyError> {
        let contents = write_pkcs1(self).ok_or(KeyError::Serialize)?;

        let p = pem::Pem {
            tag: "RSA PRIVATE KEY".to_owned(),
            contents,
        };

        Ok(pem::encode(&p))
    }

    fn from_pem_pkcs1(pem: &str) -> Result<Self, KeyError> {
        let data = pem::parse(pem).map_err(|_| KeyError::Pem)?;

        if data.tag != "RSA PRIVATE KEY" {
            return Err(KeyError::Kind.into());
        }

        let pkey = parse_pkcs1(&data.contents)?;

        pkey.validate().map_err(|_| KeyError::Validate)?;

        Ok(pkey)
    }
}

fn write_pkcs1(rsa: &RSAPrivateKey) -> Option<Vec<u8>> {
    let exp1 = rsa.d() % (rsa.primes()[0].clone() - BigUint::one());
    let exp2 = rsa.d() % (rsa.primes()[1].clone() - BigUint::one());
    let coeff = rsa.primes()[0]
        .clone()
        .mod_inverse(rsa.primes()[1].clone())?;

    Some(yasna::construct_der(|writer| {
        writer.write_sequence(|writer| {
            writer.next().write_i64(0);
            writer.next().write_biguint(&from_dig(rsa.n()));
            writer.next().write_biguint(&from_dig(rsa.e()));
            writer.next().write_biguint(&from_dig(rsa.d()));
            writer.next().write_biguint(&from_dig(&rsa.primes()[0]));
            writer.next().write_biguint(&from_dig(&rsa.primes()[1]));
            writer.next().write_biguint(&from_dig(&exp1));
            writer.next().write_biguint(&from_dig(&exp2));
            writer.next().write_bigint(&int_from_dig(&coeff));
        })
    }))
}

fn parse_pkcs1(bytes: &[u8]) -> Result<RSAPrivateKey, yasna::ASN1Error> {
    yasna::parse_der(bytes, |reader| {
        reader.read_sequence(|reader| {
            let version = reader.next().read_i64()?;
            // version 0 (two primes) is the only supported RSAPrivateKey version, 1 (multi-prime) is unsupported
            if version != 0 {
                return Err(yasna::ASN1Error::new(yasna::ASN1ErrorKind::Invalid));
            }

            let modulus = reader.next().read_biguint()?;
            let pubexp = reader.next().read_biguint()?;
            let privexp = reader.next().read_biguint()?;
            let prime1 = reader.next().read_biguint()?;
            let prime2 = reader.next().read_biguint()?;
            // These need to be read or else the parser will error
            let _exp1 = reader.next().read_biguint()?;
            let _exp2 = reader.next().read_biguint()?;
            let _coeff = reader.next().read_biguint()?;

            let pkey = RSAPrivateKey::from_components(
                to_dig(&modulus),
                to_dig(&pubexp),
                to_dig(&privexp),
                vec![to_dig(&prime1), to_dig(&prime2)],
            );

            Ok(pkey)
        })
    })
}