// SPDX-License-Identifier: AGPL-3.0-or-later
//! Code for converting [Writecap]s to and from the X.509 certificate format.
//! TODO: Improve the efficiency and quality of this code by moving to a different library for
//! handling X.509 certificates.

use crate::{
    bterr,
    crypto::{AsymKeyPub, BitLen, HashKind, RsaSsaPss, Sha2_256, Sha2_512, Sign, Signature},
    BlockPath, Epoch, Principal, Principaled, Result, Writecap, WritecapBody,
};
use bcder::{
    decode::{BytesSource, Constructed, DecodeError, SliceSource},
    encode::{PrimitiveContent, Values},
    BitString, Captured, Integer, Mode, OctetString, Oid, Tag, Utf8String,
};
use bytes::{BufMut, Bytes, BytesMut};
use chrono::{offset::Utc, TimeZone};
use std::ops::Deref;
use x509_certificate::{
    asn1time::{Time, UtcTime},
    certificate::X509Certificate,
    rfc3280::{AttributeValue, Name},
    rfc5280::{
        AlgorithmIdentifier, AlgorithmParameter, Certificate, CertificateSerialNumber, Extension,
        Extensions, SubjectPublicKeyInfo, TbsCertificate, Validity, Version,
    },
};

mod private {
    use super::*;

    fn oid(slice: &'static [u8]) -> Oid {
        Oid(Bytes::from(slice))
    }

    macro_rules! bit_string {
        ($bytes:expr) => {
            BitString::new(0, Bytes::from($bytes))
        };
    }

    impl Sha2_256 {
        // The DER encoding of the OID 2.16.840.1.101.3.4.2.1
        const OID: &[u8] = &[0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01];
    }

    impl Sha2_512 {
        // The DER encoding of the OID 2.16.840.1.101.3.4.2.3
        const OID: &[u8] = &[0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03];
    }

    impl HashKind {
        const fn oid(&self) -> &'static [u8] {
            match self {
                HashKind::Sha2_256 => Sha2_256::OID,
                HashKind::Sha2_512 => Sha2_512::OID,
            }
        }

        fn from_oid(slice: &[u8]) -> Result<Self> {
            if slice == Sha2_256::OID {
                Ok(Self::Sha2_256)
            } else if slice == Sha2_512::OID {
                Ok(Self::Sha2_512)
            } else {
                Err(bterr!("unrecognized OID"))
            }
        }
    }

    /// The DER encoding of 1.2.840.113549.1.1.8 (id-mgf1 in RFC 4055)
    const MGF1_OID: &[u8] = &[0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x08];

    struct SingleParamAlgoId {
        algorithm: Oid,
        parameters: Oid,
    }

    impl SingleParamAlgoId {
        fn new(hash_kind: HashKind) -> Self {
            let algorithm = Oid(Bytes::from(MGF1_OID));
            let parameters = Oid(Bytes::from(hash_kind.oid()));
            Self {
                algorithm,
                parameters,
            }
        }

        fn encode_ref(&self) -> impl Values + '_ {
            self.encode_ref_as(Tag::SEQUENCE)
        }

        fn encode_ref_as(&self, tag: Tag) -> impl Values + '_ {
            bcder::encode::sequence_as(
                tag,
                (self.algorithm.encode_ref(), self.parameters.encode_ref()),
            )
        }

        fn take_from<S: bcder::decode::Source>(
            cons: &mut Constructed<'_, S>,
        ) -> std::result::Result<Self, DecodeError<S::Error>> {
            cons.take_sequence(|cons| {
                Ok(Self {
                    algorithm: Oid::take_from(cons)?,
                    parameters: Oid::take_from(cons)?,
                })
            })
        }
    }

    struct RsaSsaPssParams {
        hash_algorithm: Oid,
        mask_gen_algorithm: SingleParamAlgoId,
        salt_length: Integer,
        trailer_field: Option<Integer>,
    }

    impl RsaSsaPssParams {
        fn new(hash_kind: HashKind) -> Self {
            let hash_algorithm = Oid(Bytes::from(hash_kind.oid()));
            let mask_gen_algorithm = SingleParamAlgoId::new(hash_kind);
            let salt_length = Integer::from(hash_kind.len() as u64);
            Self {
                hash_algorithm,
                mask_gen_algorithm,
                salt_length,
                trailer_field: None,
            }
        }

        fn encode_ref(&self) -> impl bcder::encode::Values + '_ {
            self.encode_ref_as(bcder::Tag::SEQUENCE)
        }

        fn encode_ref_as(&self, tag: Tag) -> impl bcder::encode::Values + '_ {
            use bcder::encode::Constructed;
            bcder::encode::sequence_as(
                tag,
                (
                    Constructed::new(Tag::CTX_0, self.hash_algorithm.encode_ref()),
                    Constructed::new(Tag::CTX_1, self.mask_gen_algorithm.encode_ref()),
                    Constructed::new(Tag::CTX_2, self.salt_length.encode()),
                    self.trailer_field
                        .as_ref()
                        .map(|e| Constructed::new(Tag::CTX_3, e.encode())),
                ),
            )
        }

        fn take_from<S: bcder::decode::Source>(
            cons: &mut Constructed<'_, S>,
        ) -> std::result::Result<Option<Self>, DecodeError<S::Error>> {
            let option = cons.take_opt_value_if(Tag::SEQUENCE, |content| {
                let cons = content.as_constructed()?;
                Ok(RsaSsaPssParams {
                    hash_algorithm: cons.take_constructed_if(Tag::CTX_0, Oid::take_from)?,
                    mask_gen_algorithm: cons
                        .take_constructed_if(Tag::CTX_1, SingleParamAlgoId::take_from)?,
                    salt_length: cons.take_constructed_if(Tag::CTX_2, Integer::take_from)?,
                    trailer_field: cons.take_opt_constructed_if(Tag::CTX_3, Integer::take_from)?,
                })
            })?;
            if option.is_none() {
                cons.take_null()?;
            }
            Ok(option)
        }
    }

    impl RsaSsaPss {
        const USE_PSS_OID: bool = false;

        /// The OID 1.2.840.113549.1.1.10 (RSASSA-PSS)
        const RSA_PSS_OID: &[u8] = &[0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0A];

        /// The OID 1.2.840.113549.1.1.1 (RSA-ES)
        const RSA_ES_OID: &[u8] = &[0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01];

        const fn oid() -> &'static [u8] {
            if Self::USE_PSS_OID {
                Self::RSA_PSS_OID
            } else {
                Self::RSA_ES_OID
            }
        }

        fn params(&self) -> Result<Option<AlgorithmParameter>> {
            if Self::USE_PSS_OID {
                let params = RsaSsaPssParams::new(self.hash_kind);
                let values = params.encode_ref();
                let captured = Captured::from_values(bcder::Mode::Der, values);
                Ok(Some(AlgorithmParameter::from_captured(captured)))
            } else {
                Ok(None)
            }
        }

        fn from_params(sig_octet_len: u32, params: Option<&[u8]>) -> Result<Self> {
            let key_bits = BitLen::try_from(sig_octet_len)?;
            let hash_kind = match params {
                Some(params) => {
                    let source = SliceSource::new(params);
                    let params =
                        Constructed::decode(source, Mode::Der, RsaSsaPssParams::take_from)?;
                    if let Some(params) = params {
                        HashKind::from_oid(params.hash_algorithm.as_ref())?
                    } else {
                        HashKind::default()
                    }
                }
                None => HashKind::default(),
            };
            Ok(Self {
                key_bits,
                hash_kind,
            })
        }
    }

    impl Sign {
        const fn oid(&self) -> &'static [u8] {
            match self {
                Sign::RsaSsaPss(..) => RsaSsaPss::oid(),
            }
        }

        fn params(&self) -> Result<Option<AlgorithmParameter>> {
            match self {
                Sign::RsaSsaPss(inner) => inner.params(),
            }
        }

        fn from_der(sig_octet_len: u32, oid: &[u8], params: Option<&[u8]>) -> Result<Sign> {
            if oid == RsaSsaPss::oid() {
                Ok(Sign::RsaSsaPss(RsaSsaPss::from_params(
                    sig_octet_len,
                    params,
                )?))
            } else {
                Err(bterr!("OID does not match a Sign variant"))
            }
        }

        fn to_algo_id(self) -> Result<AlgorithmIdentifier> {
            Ok(AlgorithmIdentifier {
                algorithm: oid(self.oid()),
                parameters: self.params()?,
            })
        }

        fn from_algo_id(sig_octet_len: u32, algo_id: &AlgorithmIdentifier) -> Result<Sign> {
            let params = algo_id.parameters.as_ref().map(|e| e.as_ref());
            Sign::from_der(sig_octet_len, algo_id.algorithm.as_ref(), params)
        }
    }

    struct SubjectAltName {
        block_path: Utf8String,
    }

    impl SubjectAltName {
        /// OID 2.5.29.17 (Subject Alternative Name)
        const OID: &[u8] = &[0x55, 0x1D, 0x11];

        fn new(block_path: &BlockPath) -> Result<Self> {
            let block_path = Utf8String::from_string(block_path.to_string())
                .map_err(|err| bterr!("{:?}", err))?;
            Ok(Self { block_path })
        }

        fn encode(&self) -> impl Values + '_ {
            self.encode_as(Tag::SEQUENCE)
        }

        fn encode_as(&self, tag: Tag) -> impl Values + '_ {
            bcder::encode::sequence_as(tag, self.block_path.encode_ref())
        }

        fn take_from<S: bcder::decode::Source>(
            cons: &mut Constructed<'_, S>,
        ) -> std::result::Result<Self, DecodeError<S::Error>> {
            cons.take_sequence(|cons| {
                Ok(Self {
                    block_path: Utf8String::take_from(cons)?,
                })
            })
        }

        fn encode_der(&self) -> Result<Bytes> {
            let mut writer = BytesMut::new().writer();
            self.encode().write_encoded(Mode::Der, &mut writer)?;
            Ok(writer.into_inner().into())
        }

        fn decode_der<B: AsRef<[u8]>>(bytes: B) -> Result<Self> {
            let source = SliceSource::new(bytes.as_ref());
            Constructed::decode(source, Mode::Der, Self::take_from).map_err(|err| err.into())
        }
    }

    impl AsymKeyPub<Sign> {
        fn subject_public_key_info(&self) -> Result<SubjectPublicKeyInfo> {
            Ok(SubjectPublicKeyInfo {
                algorithm: self.scheme.to_algo_id()?,
                subject_public_key: self.to_bit_string()?,
            })
        }

        fn to_bit_string(&self) -> Result<BitString> {
            let der = self.pkey.public_key_to_der()?;
            let source = BytesSource::new(Bytes::from(der));
            let spki = Constructed::decode(source, Mode::Der, SubjectPublicKeyInfo::take_from)?;
            Ok(spki.subject_public_key)
        }

        fn from_subject_public_key_info(
            sig_octet_len: u32,
            spki: &SubjectPublicKeyInfo,
        ) -> Result<Self> {
            let scheme = Sign::from_algo_id(sig_octet_len, &spki.algorithm)?;
            let mut der = Vec::new();
            spki.encode_ref().write_encoded(Mode::Der, &mut der)?;
            AsymKeyPub::new(scheme, der.as_slice())
        }

        pub fn to_der(&self) -> Result<Vec<u8>> {
            let spki = self.subject_public_key_info()?;
            let mut vec = Vec::new();
            spki.encode_ref().write_encoded(Mode::Der, &mut vec)?;
            Ok(vec)
        }
    }

    trait NameExt {
        fn try_get_common_name(&self) -> Result<&AttributeValue>;
    }

    impl NameExt for Name {
        fn try_get_common_name(&self) -> Result<&AttributeValue> {
            Ok(&self
                .iter_common_name()
                .next()
                .ok_or_else(|| bterr!("no CommonName component in Name"))?
                .value)
        }
    }

    trait TryAsStr {
        fn try_as_str(&self) -> Result<&str>;
    }

    impl<T: ?Sized + AsRef<[u8]>> TryAsStr for T {
        fn try_as_str(&self) -> Result<&str> {
            std::str::from_utf8(self.as_ref()).map_err(|err| err.into())
        }
    }

    trait TimeExt {
        fn try_to_epoch(&self) -> Result<Epoch>;
    }

    impl TimeExt for Time {
        fn try_to_epoch(&self) -> Result<Epoch> {
            match self {
                Self::UtcTime(time) => Ok(Epoch::from_value(time.timestamp() as u64)),
                Self::GeneralTime(..) => Err(bterr!("unsupported Time variant encountered")),
            }
        }
    }

    trait ExtensionsExt {
        fn find_subject_alt_name(&self) -> Result<SubjectAltName>;
    }

    impl ExtensionsExt for Extensions {
        fn find_subject_alt_name(&self) -> Result<SubjectAltName> {
            let extensions: &[Extension] = self.deref();
            for extension in extensions {
                if extension.id.as_ref() == SubjectAltName::OID {
                    return SubjectAltName::decode_der(extension.value.to_bytes());
                }
            }
            Err(bterr!("SubjectAltName not found"))
        }
    }

    impl Principal {
        fn to_name(&self) -> Result<Name> {
            let mut name = Name::default();
            let string = self.to_string();
            name.append_common_name_utf8_string(&string)
                .map_err(|_| bterr!("failed to create Name for Principal"))?;
            Ok(name)
        }

        fn from_name(name: &Name) -> Result<Self> {
            let principal = name
                .try_get_common_name()?
                .to_string()?
                .as_str()
                .try_into()?;
            Ok(principal)
        }

        pub fn to_name_der(&self) -> Result<Vec<u8>> {
            let name = self.to_name()?;
            let mut vec = Vec::new();
            name.encode_ref().write_encoded(Mode::Der, &mut vec)?;
            Ok(vec)
        }
    }

    impl Writecap {
        fn to_cert(&self, subject_key: &AsymKeyPub<Sign>) -> Result<Vec<u8>> {
            let version = Some(Version::V3);
            let serial_number = CertificateSerialNumber::from(1);
            let signature_algorithm = self.body.signing_key.scheme.to_algo_id()?;
            let issuer = self.body.signing_key.principal().to_name()?;
            let expires = Utc
                .timestamp_millis_opt(1000 * self.body.expires.to_unix())
                .single()
                .ok_or_else(|| {
                    bterr!("failed to convert writecap expiration to chrono DataTime")
                })?;
            let validity = Validity {
                not_before: Time::UtcTime(UtcTime::now()),
                not_after: Time::from(expires),
            };
            let subject = self.body.issued_to.to_name()?;
            let subject_public_key_info = subject_key.subject_public_key_info()?;
            let mut extensions = Extensions::default();
            let san = SubjectAltName::new(&self.body.path)?;
            extensions.push(Extension {
                id: oid(SubjectAltName::OID),
                critical: Some(false),
                value: OctetString::new(san.encode_der()?),
            });
            let tbs_certificate = TbsCertificate {
                version,
                serial_number,
                signature: signature_algorithm.clone(),
                issuer,
                validity,
                subject,
                subject_public_key_info,
                issuer_unique_id: None,
                subject_unique_id: None,
                extensions: Some(extensions),
                raw_data: None,
            };
            let cert = Certificate {
                tbs_certificate,
                signature_algorithm,
                signature: bit_string!(self.signature.data.clone()),
            };
            let cert: X509Certificate = cert.into();
            cert.encode_der().map_err(|err| err.into())
        }

        fn to_cert_chain_impl(&self, subject_key: &AsymKeyPub<Sign>) -> Result<Vec<Vec<u8>>> {
            let mut chain = match self.next.as_ref() {
                Some(next) => next.as_ref().to_cert_chain_impl(&self.body.signing_key)?,
                None => {
                    // An extra cert is added to the end of the chain to contain the root
                    // principal's signing key.
                    let mut vec = Vec::with_capacity(2);
                    let root_principal = self.body.signing_key.principal();
                    let path = BlockPath::new(root_principal.clone(), vec![]);
                    let writecap = Writecap {
                        body: WritecapBody {
                            issued_to: root_principal,
                            expires: Epoch::now(),
                            path,
                            signing_key: self.body.signing_key.clone(),
                        },
                        signature: self.signature.clone(),
                        next: None,
                    };
                    vec.push(writecap.to_cert(&self.body.signing_key)?);
                    vec
                }
            };

            chain.push(self.to_cert(subject_key)?);
            Ok(chain)
        }

        pub fn to_cert_chain(&self, subject_key: &AsymKeyPub<Sign>) -> Result<Vec<Vec<u8>>> {
            let mut chain = self.to_cert_chain_impl(subject_key)?;
            chain.reverse();
            Ok(chain)
        }

        pub fn from_cert_chain<B: AsRef<[u8]>>(
            first: &B,
            rest: &[B],
        ) -> Result<(Writecap, AsymKeyPub<Sign>)> {
            let (next, signing_key) = if !rest.is_empty() {
                let (writecap, signing_key) = Self::from_cert_chain(&rest[0], &rest[1..])?;
                // Remove the extra writecap at the end.
                let writecap = if rest.len() == 1 {
                    None
                } else {
                    Some(writecap)
                };
                (writecap, Some(signing_key))
            } else {
                (None, None)
            };

            let x509_cert = X509Certificate::from_der(first)?;
            let cert: &Certificate = x509_cert.as_ref();
            if cert.signature.unused() > 0 {
                return Err(bterr!("signature length is not divisible by 8"));
            }
            let extensions = cert
                .tbs_certificate
                .extensions
                .as_ref()
                .ok_or_else(|| bterr!("no extensions present"))?;
            let san = extensions.find_subject_alt_name()?;
            let path = BlockPath::try_from(san.block_path.into_bytes().try_as_str()?)
                .map_err(|err| bterr!(err))?;
            let sig_octet_len: u32 = cert.signature.octet_len().try_into()?;
            let scheme = Sign::from_algo_id(
                sig_octet_len,
                &cert.tbs_certificate.subject_public_key_info.algorithm,
            )?;
            let signature = Signature::new(scheme, cert.signature.octet_bytes().into());
            let cert = &cert.tbs_certificate;
            let subject_key = AsymKeyPub::from_subject_public_key_info(
                sig_octet_len,
                &cert.subject_public_key_info,
            )?;
            let issued_to = Principal::from_name(&cert.subject)?;
            let expires = cert.validity.not_after.try_to_epoch()?;
            // If signing_key is None, then we're at the last certificate in the chain, which is
            // self-signed. So the subject_key is the same as the issuer's signing key.
            let signing_key = signing_key.unwrap_or_else(|| subject_key.clone());
            let writecap = Writecap {
                body: WritecapBody {
                    issued_to,
                    signing_key,
                    path,
                    expires,
                },
                signature,
                next: next.map(Box::new),
            };
            Ok((writecap, subject_key))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use std::time::Duration;
    use webpki::EndEntityCert;

    use crate::{
        crypto::{ConcreteCreds, Creds, CredsPriv, CredsPub},
        test_helpers::node_creds,
    };

    #[allow(dead_code)]
    fn save_first_writecap_der_to_file() {
        let node_creds = node_creds();
        let chain = node_creds
            .writecap
            .as_ref()
            .unwrap()
            .to_cert_chain(&node_creds.sign.public)
            .unwrap();
        let first = chain.first().unwrap();
        std::fs::write("/tmp/cert.der", first).unwrap();
    }

    #[test]
    fn node_writecap_to_cert_chain() {
        let node_creds = node_creds();

        let result = node_creds
            .writecap
            .as_ref()
            .unwrap()
            .to_cert_chain(&node_creds.sign.public);

        assert!(result.is_ok())
    }

    #[test]
    fn node_writecap_to_cert_chain_end_cert_can_be_parsed() {
        let node_creds = node_creds();
        let chain = node_creds
            .writecap
            .as_ref()
            .unwrap()
            .to_cert_chain(&node_creds.sign.public)
            .unwrap();
        let der = chain.first().unwrap();

        let result = EndEntityCert::try_from(der.as_slice());

        result.unwrap();
    }

    #[test]
    fn round_trip_writecap() {
        let node_creds = node_creds();
        let expected_key = node_creds.public_sign();
        let expected_wc = node_creds.writecap().unwrap();

        let certs = expected_wc.to_cert_chain(expected_key).unwrap();
        let (actual_wc, actual_key) =
            Writecap::from_cert_chain(certs.first().unwrap(), &certs[1..]).unwrap();

        assert_eq!(expected_key, &actual_key);
        assert_eq!(expected_wc, &actual_wc);
        actual_wc.assert_valid_for(&expected_wc.body.path).unwrap();
    }

    #[test]
    fn round_trip_chain_of_length_two() {
        let node_creds = node_creds();
        let mut process_creds = ConcreteCreds::generate().unwrap();
        let writecap = node_creds
            .issue_writecap(
                process_creds.principal(),
                vec!["console".to_string()],
                Epoch::now() + Duration::from_secs(3600),
            )
            .unwrap();
        process_creds.set_writecap(writecap);
        let expected_key = process_creds.public_sign();
        let expected_wc = process_creds.writecap().unwrap();

        let certs = expected_wc.to_cert_chain(expected_key).unwrap();
        let (actual_wc, actual_key) =
            Writecap::from_cert_chain(certs.first().unwrap(), &certs[1..]).unwrap();

        assert_eq!(expected_key, &actual_key);
        assert_eq!(expected_wc, &actual_wc);
        actual_wc.assert_valid_for(&expected_wc.body.path).unwrap();
    }
}