// Copyright 2023 Daniel McCarney.

//

// Permission to use, copy, modify, and/or distribute this software for any

// purpose with or without fee is hereby granted, provided that the above

// copyright notice and this permission notice appear in all copies.

//

// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES

// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR

// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN

// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF

// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

use pki_types::{SignatureVerificationAlgorithm, UnixTime};

use crate::error::Error;

use crate::verify_cert::{Budget, PathNode, Role};

use crate::{der, public_values_eq};

use core::fmt::Debug;

mod types;

pub use types::{

    BorrowedCertRevocationList, BorrowedRevokedCert, CertRevocationList, RevocationReason,

};

#[cfg(feature = "alloc")]

pub use types::{OwnedCertRevocationList, OwnedRevokedCert};

/// Builds a RevocationOptions instance to control how revocation checking is performed.

#[derive(Debug, Copy, Clone)]

pub struct RevocationOptionsBuilder<'a> {

    crls: &'a [&'a CertRevocationList<'a>],

    depth: RevocationCheckDepth,

    status_policy: UnknownStatusPolicy,

    expiration_policy: ExpirationPolicy,

}

impl<'a> RevocationOptionsBuilder<'a> {

    /// Create a builder that will perform revocation checking using the provided certificate

    /// revocation lists (CRLs). At least one CRL must be provided.

    ///

    /// Use [RevocationOptionsBuilder::build] to create a [RevocationOptions] instance.

    ///

    /// By default revocation checking will be performed on both the end-entity (leaf) certificate

    /// and intermediate certificates. This can be customized using the

    /// [RevocationOptionsBuilder::with_depth] method.

    ///

    /// By default revocation checking will fail if the revocation status of a certificate cannot

    /// be determined. This can be customized using the

    /// [RevocationOptionsBuilder::with_status_policy] method.

    ///

    /// By default revocation checking will *not* fail if the verification time is beyond the time

    /// in the CRL nextUpdate field. This can be customized using the

    /// [RevocationOptionsBuilder::with_expiration_policy] method.

    pub fn new(crls: &'a [&'a CertRevocationList<'a>]) -> Result<Self, CrlsRequired> {

        if crls.is_empty() {

            return Err(CrlsRequired(()));

        }

        Ok(Self {

            crls,

            depth: RevocationCheckDepth::Chain,

            status_policy: UnknownStatusPolicy::Deny,

            expiration_policy: ExpirationPolicy::Ignore,

        })

    }

    /// Customize the depth at which revocation checking will be performed, controlling

    /// whether only the end-entity (leaf) certificate in the chain to a trust anchor will

    /// have its revocation status checked, or whether the intermediate certificates will as well.

    pub fn with_depth(mut self, depth: RevocationCheckDepth) -> Self {

        self.depth = depth;

        self

    }

    /// Customize whether unknown revocation status is an error, or permitted.

    pub fn with_status_policy(mut self, policy: UnknownStatusPolicy) -> Self {

        self.status_policy = policy;

        self

    }

    /// Customize whether the CRL nextUpdate field (i.e. expiration) is enforced.

    pub fn with_expiration_policy(mut self, policy: ExpirationPolicy) -> Self {

        self.expiration_policy = policy;

        self

    }

    /// Construct a [RevocationOptions] instance based on the builder's configuration.

    pub fn build(self) -> RevocationOptions<'a> {

        RevocationOptions {

            crls: self.crls,

            depth: self.depth,

            status_policy: self.status_policy,

            expiration_policy: self.expiration_policy,

        }

    }

}

/// Describes how revocation checking is performed, if at all. Can be constructed with a

/// [RevocationOptionsBuilder] instance.

#[derive(Debug, Copy, Clone)]

pub struct RevocationOptions<'a> {

    pub(crate) crls: &'a [&'a CertRevocationList<'a>],

    pub(crate) depth: RevocationCheckDepth,

    pub(crate) status_policy: UnknownStatusPolicy,

    pub(crate) expiration_policy: ExpirationPolicy,

}

impl<'a> RevocationOptions<'a> {

    #[allow(clippy::too_many_arguments)]

    pub(crate) fn check(

        &self,

        path: &PathNode<'_>,

        issuer_subject: untrusted::Input<'_>,

        issuer_spki: untrusted::Input<'_>,

        issuer_ku: Option<untrusted::Input<'_>>,

        supported_sig_algs: &[&dyn SignatureVerificationAlgorithm],

        budget: &mut Budget,

        time: UnixTime,

    ) -> Result<Option<CertNotRevoked>, Error> {

        assert!(public_values_eq(path.cert.issuer, issuer_subject));

        // If the policy only specifies checking EndEntity revocation state and we're looking at an

        // issuer certificate, return early without considering the certificate's revocation state.

        if let (RevocationCheckDepth::EndEntity, Role::Issuer) = (self.depth, path.role()) {

            return Ok(None);

        }

        let crl = self

            .crls

            .iter()

            .find(|candidate_crl| candidate_crl.authoritative(path));

        use UnknownStatusPolicy::*;

        let crl = match (crl, self.status_policy) {

            (Some(crl), _) => crl,

            // If the policy allows unknown, return Ok(None) to indicate that the certificate

            // was not confirmed as CertNotRevoked, but that this isn't an error condition.

            (None, Allow) => return Ok(None),

            // Otherwise, this is an error condition based on the provided policy.

            (None, _) => return Err(Error::UnknownRevocationStatus),

        };

        // Verify the CRL signature with the issuer SPKI.

        // TODO(XXX): consider whether we can refactor so this happens once up-front, instead

        //            of per-lookup.

        //            https://github.com/rustls/webpki/issues/81

        crl.verify_signature(supported_sig_algs, issuer_spki, budget)

            .map_err(crl_signature_err)?;

        if self.expiration_policy == ExpirationPolicy::Enforce {

            crl.check_expiration(time)?;

        }

        // Verify that if the issuer has a KeyUsage bitstring it asserts cRLSign.

        KeyUsageMode::CrlSign.check(issuer_ku)?;

        // Try to find the cert serial in the verified CRL contents.

        let cert_serial = path.cert.serial.as_slice_less_safe();

        match crl.find_serial(cert_serial)? {

            None => Ok(Some(CertNotRevoked::assertion())),

            Some(_) => Err(Error::CertRevoked),

        }

    }

}

// https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3

#[repr(u8)]

#[derive(Clone, Copy)]

enum KeyUsageMode {

    // DigitalSignature = 0,

    // ContentCommitment = 1,

    // KeyEncipherment = 2,

    // DataEncipherment = 3,

    // KeyAgreement = 4,

    // CertSign = 5,

    CrlSign = 6,

    // EncipherOnly = 7,

    // DecipherOnly = 8,

}

impl KeyUsageMode {

    // https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3

    fn check(self, input: Option<untrusted::Input<'_>>) -> Result<(), Error> {

        let bit_string = match input {

            Some(input) => {

                der::expect_tag(&mut untrusted::Reader::new(input), der::Tag::BitString)?

            }

            // While RFC 5280 requires KeyUsage be present, historically the absence of a KeyUsage

            // has been treated as "Any Usage". We follow that convention here and assume the absence

            // of KeyUsage implies the required_ku_bit_if_present we're checking for.

            None => return Ok(()),

        };

        let flags = der::bit_string_flags(bit_string)?;

        #[allow(clippy::as_conversions)] // u8 always fits in usize.

        match flags.bit_set(self as usize) {

            true => Ok(()),

            false => Err(Error::IssuerNotCrlSigner),

        }

    }

}

// When verifying CRL signed data we want to disambiguate the context of possible errors by mapping

// them to CRL specific variants that a consumer can use to tell the issue was with the CRL's

// signature, not a certificate.

fn crl_signature_err(err: Error) -> Error {

    match err {

        Error::UnsupportedSignatureAlgorithm => Error::UnsupportedCrlSignatureAlgorithm,

        Error::UnsupportedSignatureAlgorithmForPublicKey => {

            Error::UnsupportedCrlSignatureAlgorithmForPublicKey

        }

        Error::InvalidSignatureForPublicKey => Error::InvalidCrlSignatureForPublicKey,

        _ => err,

    }

}

/// Describes how much of a certificate chain is checked for revocation status.

#[derive(Debug, Copy, Clone, PartialEq, Eq)]

pub enum RevocationCheckDepth {

    /// Only check the end entity (leaf) certificate's revocation status.

    EndEntity,

    /// Check the revocation status of the end entity (leaf) and all intermediates.

    Chain,

}

/// Describes how to handle the case where a certificate's revocation status is unknown.

#[derive(Debug, Copy, Clone, PartialEq, Eq)]

pub enum UnknownStatusPolicy {

    /// Treat unknown revocation status permissively, acting as if the certificate were

    /// not revoked.

    Allow,

    /// Treat unknown revocation status as an error condition, yielding

    /// [Error::UnknownRevocationStatus].

    Deny,

}

/// Describes how to handle the nextUpdate field of the CRL (i.e. expiration).

#[derive(Debug, Copy, Clone, PartialEq, Eq)]

pub enum ExpirationPolicy {

    /// Enforce the verification time is before the time in the nextUpdate field.

    /// Treats an expired CRL as an error condition yielding [Error::CrlExpired].

    Enforce,

    /// Ignore the CRL nextUpdate field.

    Ignore,

}

// Zero-sized marker type representing positive assertion that revocation status was checked

// for a certificate and the result was that the certificate is not revoked.

pub(crate) struct CertNotRevoked(());

impl CertNotRevoked {

    // Construct a CertNotRevoked marker.

    fn assertion() -> Self {

        Self(())

    }

}

#[derive(Debug, Copy, Clone)]

/// An opaque error indicating the caller must provide at least one CRL when building a

/// [RevocationOptions] instance.

pub struct CrlsRequired(pub(crate) ());

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    // redundant clone, clone_on_copy allowed to verify derived traits.

    #[allow(clippy::redundant_clone, clippy::clone_on_copy)]

    fn test_revocation_opts_builder() {

        // Trying to build a RevocationOptionsBuilder w/o CRLs should err.

        let result = RevocationOptionsBuilder::new(&[]);

        assert!(matches!(result, Err(CrlsRequired(_))));

        // The CrlsRequired error should be debug and clone when alloc is enabled.

        #[cfg(feature = "alloc")]

        {

            let err = result.unwrap_err();

            std::println!("{:?}", err.clone());

        }

        // It should be possible to build a revocation options builder with defaults.

        let crl = include_bytes!("../../tests/crls/crl.valid.der");

        let crl = BorrowedCertRevocationList::from_der(&crl[..])

            .unwrap()

            .into();

        let crls = [&crl];

        let builder = RevocationOptionsBuilder::new(&crls).unwrap();

        #[cfg(feature = "alloc")]

        {

            // The builder should be debug, and clone when alloc is enabled

            std::println!("{:?}", builder);

            _ = builder.clone();

        }

        let opts = builder.build();

        assert_eq!(opts.depth, RevocationCheckDepth::Chain);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Deny);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Ignore);

        assert_eq!(opts.crls.len(), 1);

        // It should be possible to build a revocation options builder with custom depth.

        let opts = RevocationOptionsBuilder::new(&crls)

            .unwrap()

            .with_depth(RevocationCheckDepth::EndEntity)

            .build();

        assert_eq!(opts.depth, RevocationCheckDepth::EndEntity);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Deny);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Ignore);

        assert_eq!(opts.crls.len(), 1);

        // It should be possible to build a revocation options builder that allows unknown

        // revocation status.

        let opts = RevocationOptionsBuilder::new(&crls)

            .unwrap()

            .with_status_policy(UnknownStatusPolicy::Allow)

            .build();

        assert_eq!(opts.depth, RevocationCheckDepth::Chain);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Allow);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Ignore);

        assert_eq!(opts.crls.len(), 1);

        // It should be possible to specify both depth and unknown status policy together.

        let opts = RevocationOptionsBuilder::new(&crls)

            .unwrap()

            .with_status_policy(UnknownStatusPolicy::Allow)

            .with_depth(RevocationCheckDepth::EndEntity)

            .build();

        assert_eq!(opts.depth, RevocationCheckDepth::EndEntity);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Allow);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Ignore);

        assert_eq!(opts.crls.len(), 1);

        // The same should be true for explicitly forbidding unknown status.

        let opts = RevocationOptionsBuilder::new(&crls)

            .unwrap()

            .with_status_policy(UnknownStatusPolicy::Deny)

            .with_depth(RevocationCheckDepth::EndEntity)

            .build();

        assert_eq!(opts.depth, RevocationCheckDepth::EndEntity);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Deny);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Ignore);

        assert_eq!(opts.crls.len(), 1);

        // It should be possible to build a revocation options builder that allows unknown

        // revocation status.

        let opts = RevocationOptionsBuilder::new(&crls)

            .unwrap()

            .with_expiration_policy(ExpirationPolicy::Enforce)

            .build();

        assert_eq!(opts.depth, RevocationCheckDepth::Chain);

        assert_eq!(opts.status_policy, UnknownStatusPolicy::Deny);

        assert_eq!(opts.expiration_policy, ExpirationPolicy::Enforce);

        assert_eq!(opts.crls.len(), 1);

        // Built revocation options should be debug and clone when alloc is enabled.

        #[cfg(feature = "alloc")]

        {

            std::println!("{:?}", opts.clone());

        }

    }

}