use std::cmp::Ordering;
use std::path::{Path, PathBuf};

use foreign_types_shared::ForeignType;
use foreign_types_shared::ForeignTypeRef;
use libc::c_long;
use openssl::asn1::Asn1Time;
use openssl::bn::{BigNum, MsbOption};
use openssl::ec::EcGroup;
use openssl::hash::MessageDigest;
use openssl::nid::Nid;
use openssl::pkey::{PKey, Private};
use openssl::x509::extension::{
    BasicConstraints, ExtendedKeyUsage, KeyUsage, SubjectAlternativeName, SubjectKeyIdentifier,
};
use openssl::x509::{X509Crl, X509Name, X509NameBuilder, X509Req, X509};
use openssl_sys::{
    X509_CRL_add0_revoked, X509_CRL_set1_lastUpdate, X509_CRL_set1_nextUpdate,
    X509_CRL_set_issuer_name, X509_CRL_set_version, X509_CRL_sign, X509_REVOKED_dup,
};

use crate::app_config::AppConfig;
use crate::crypto::crl_extension::CRLDistributionPointExt;

#[derive(thiserror::Error, Debug)]
pub enum PKIError {
    #[error("Certification Authority does not have a CRL")]
    MissingCRL,
    #[error("Certification Authority does not have a CRL next update time")]
    MissingCRLNextUpdate,
    #[error("Failed to initialize CRL! {0}")]
    GenCRLError(&'static str),
}

/// Certificate and private key
pub struct CertData {
    pub cert: X509,
    pub key: PKey<Private>,
    pub crl: Option<PathBuf>,
}

impl CertData {
    /// Load root CA
    fn load_root_ca() -> anyhow::Result<Self> {
        Ok(Self {
            cert: load_certificate_from_file(AppConfig::get().root_ca_cert_path())?,
            key: load_priv_key_from_file(AppConfig::get().root_ca_priv_key_path())?,
            crl: Some(AppConfig::get().root_ca_crl_path()),
        })
    }

    /// Load web CA
    pub fn load_web_ca() -> anyhow::Result<Self> {
        Ok(Self {
            cert: load_certificate_from_file(AppConfig::get().web_ca_cert_path())?,
            key: load_priv_key_from_file(AppConfig::get().web_ca_priv_key_path())?,
            crl: Some(AppConfig::get().web_ca_crl_path()),
        })
    }

    /// Load devices CA
    pub fn load_devices_ca() -> anyhow::Result<Self> {
        Ok(Self {
            cert: load_certificate_from_file(AppConfig::get().devices_ca_cert_path())?,
            key: load_priv_key_from_file(AppConfig::get().devices_ca_priv_key_path())?,
            crl: Some(AppConfig::get().devices_ca_crl_path()),
        })
    }

    /// Load server CA
    pub fn load_server() -> anyhow::Result<Self> {
        Ok(Self {
            cert: load_certificate_from_file(AppConfig::get().server_cert_path())?,
            key: load_priv_key_from_file(AppConfig::get().server_priv_key_path())?,
            crl: None,
        })
    }
}

/// Generate private key
fn gen_private_key() -> anyhow::Result<PKey<Private>> {
    let nid = Nid::X9_62_PRIME256V1; // NIST P-256 curve
    let group = EcGroup::from_curve_name(nid)?;
    let key = openssl::ec::EcKey::generate(&group)?;
    let key_pair = PKey::from_ec_key(key.clone())?;

    Ok(key_pair)
}

/// Load private key from PEM file
fn load_priv_key_from_file<P: AsRef<Path>>(path: P) -> anyhow::Result<PKey<Private>> {
    Ok(PKey::private_key_from_pem(&std::fs::read(path)?)?)
}

/// Load certificate from PEM file
fn load_certificate_from_file<P: AsRef<Path>>(path: P) -> anyhow::Result<X509> {
    Ok(X509::from_pem(&std::fs::read(path)?)?)
}

/// Load CRL from PEM file
fn load_crl_from_file<P: AsRef<Path>>(path: P) -> anyhow::Result<X509Crl> {
    Ok(X509Crl::from_pem(&std::fs::read(path)?)?)
}

#[allow(clippy::upper_case_acronyms)]
enum GenCertificatSubjectReq<'a> {
    Subject { cn: &'a str },
    CSR { csr: &'a X509Req },
}

impl<'a> Default for GenCertificatSubjectReq<'a> {
    fn default() -> Self {
        Self::Subject { cn: "" }
    }
}

#[derive(Default)]
struct GenCertificateReq<'a> {
    pub sub: GenCertificatSubjectReq<'a>,
    pub issuer: Option<&'a CertData>,
    pub ca: bool,
    pub web_server: bool,
    pub web_client: bool,
    pub subject_alternative_names: Vec<&'a str>,
}

/// Generate certificate
fn gen_certificate(req: GenCertificateReq) -> anyhow::Result<(Option<Vec<u8>>, Vec<u8>)> {
    let mut cert_builder = X509::builder()?;
    cert_builder.set_version(2)?;
    let serial_number = {
        let mut serial = BigNum::new()?;
        serial.rand(159, MsbOption::MAYBE_ZERO, false)?;
        serial.to_asn1_integer()?
    };
    cert_builder.set_serial_number(&serial_number)?;

    // Process subject
    let x509_name = match req.sub {
        GenCertificatSubjectReq::Subject { cn } => {
            let mut x509_name = X509NameBuilder::new()?;
            x509_name.append_entry_by_text("C", "FR")?;
            x509_name.append_entry_by_text("CN", cn)?;
            x509_name.build()
        }
        GenCertificatSubjectReq::CSR { csr } => X509Name::from_der(&csr.subject_name().to_der()?)?,
    };

    cert_builder.set_subject_name(&x509_name)?;

    match req.issuer {
        // Self-signed certificate
        None => cert_builder.set_issuer_name(&x509_name)?,
        // Certificate signed by another CA
        Some(i) => cert_builder.set_issuer_name(i.cert.subject_name())?,
    }

    let not_before = Asn1Time::days_from_now(0)?;
    cert_builder.set_not_before(&not_before)?;

    let not_after = Asn1Time::days_from_now(365 * 30)?;
    cert_builder.set_not_after(&not_after)?;

    // Specify CRL URL
    if let Some(issuer) = req.issuer {
        if let Some(crl) = &issuer.crl {
            let crl_url = format!(
                "{}/pki/{}",
                AppConfig::get().unsecure_origin(),
                crl.file_name().unwrap().to_string_lossy()
            );

            cert_builder
                .append_extension(CRLDistributionPointExt { url: crl_url }.as_extension()?)?;
        }
    }

    // If cert is a CA or not
    let mut basic = BasicConstraints::new();
    if req.ca {
        basic.ca();
    }
    cert_builder.append_extension(basic.critical().build()?)?;

    // Key usage
    let mut key_usage = KeyUsage::new();
    let mut eku = None;
    if req.ca {
        key_usage.key_cert_sign().crl_sign();
    }
    if req.web_server {
        key_usage.digital_signature().key_encipherment();
        eku = Some(
            ExtendedKeyUsage::new()
                .server_auth()
                .client_auth()
                .build()?,
        );
    }

    if req.web_client {
        key_usage.digital_signature().key_encipherment();
        eku = Some(ExtendedKeyUsage::new().client_auth().build()?);
    }
    cert_builder.append_extension(key_usage.critical().build()?)?;

    if let Some(eku) = eku {
        cert_builder.append_extension(eku)?;
    }

    // Subject alternative names
    if !req.subject_alternative_names.is_empty() {
        let mut ext = SubjectAlternativeName::new();
        for subj in req.subject_alternative_names {
            ext.dns(subj);
        }
        cert_builder.append_extension(ext.build(&cert_builder.x509v3_context(None, None))?)?;
    }

    // Subject key identifier
    let subject_key_identifier =
        SubjectKeyIdentifier::new().build(&cert_builder.x509v3_context(None, None))?;
    cert_builder.append_extension(subject_key_identifier)?;

    // Public key
    match req.sub {
        // Private key known
        GenCertificatSubjectReq::Subject { .. } => {
            let key_pair = gen_private_key()?;
            cert_builder.set_pubkey(&key_pair)?;

            // Sign certificate
            cert_builder.sign(
                match req.issuer {
                    None => &key_pair,
                    Some(i) => &i.key,
                },
                MessageDigest::sha256(),
            )?;
            let cert = cert_builder.build();

            Ok((Some(key_pair.private_key_to_pem_pkcs8()?), cert.to_pem()?))
        }

        // Private key unknown
        GenCertificatSubjectReq::CSR { csr } => {
            let pub_key = csr.public_key()?;
            cert_builder.set_pubkey(pub_key.as_ref())?;

            // Sign certificate
            cert_builder.sign(
                &req.issuer
                    .expect("Cannot issue certificate for CSR if issuer is not specified!")
                    .key,
                MessageDigest::sha256(),
            )?;
            let cert = cert_builder.build();
            Ok((None, cert.to_pem()?))
        }
    }
}

/// Initialize Root CA, if required
pub fn initialize_root_ca() -> anyhow::Result<()> {
    if AppConfig::get().root_ca_cert_path().exists()
        && AppConfig::get().root_ca_priv_key_path().exists()
    {
        return Ok(());
    }

    log::info!("Generating root ca...");

    let (key, cert) = gen_certificate(GenCertificateReq {
        sub: GenCertificatSubjectReq::Subject {
            cn: "SolarEnergy Root CA",
        },
        issuer: None,
        ca: true,
        ..Default::default()
    })?;

    // Serialize generated web CA
    std::fs::write(AppConfig::get().root_ca_priv_key_path(), key.unwrap())?;
    std::fs::write(AppConfig::get().root_ca_cert_path(), cert)?;

    Ok(())
}

/// Initialize web CA, if required
pub fn initialize_web_ca() -> anyhow::Result<()> {
    if AppConfig::get().web_ca_cert_path().exists()
        && AppConfig::get().web_ca_priv_key_path().exists()
    {
        return Ok(());
    }

    log::info!("Generating web ca...");

    let (key, cert) = gen_certificate(GenCertificateReq {
        sub: GenCertificatSubjectReq::Subject {
            cn: "SolarEnergy Web CA",
        },
        issuer: Some(&CertData::load_root_ca()?),
        ca: true,
        ..Default::default()
    })?;

    // Serialize generated web CA
    std::fs::write(AppConfig::get().web_ca_priv_key_path(), key.unwrap())?;
    std::fs::write(AppConfig::get().web_ca_cert_path(), cert)?;

    Ok(())
}

/// Initialize devices CA, if required
pub fn initialize_devices_ca() -> anyhow::Result<()> {
    if AppConfig::get().devices_ca_cert_path().exists()
        && AppConfig::get().devices_ca_priv_key_path().exists()
    {
        return Ok(());
    }

    log::info!("Generating devices ca...");

    let (key, cert) = gen_certificate(GenCertificateReq {
        sub: GenCertificatSubjectReq::Subject {
            cn: "SolarEnergy Devices CA",
        },
        issuer: Some(&CertData::load_root_ca()?),
        ca: true,
        ..Default::default()
    })?;

    // Serialize generated devices CA
    std::fs::write(AppConfig::get().devices_ca_priv_key_path(), key.unwrap())?;
    std::fs::write(AppConfig::get().devices_ca_cert_path(), cert)?;

    Ok(())
}

/// Initialize server certificate, if required
pub fn initialize_server_ca() -> anyhow::Result<()> {
    if AppConfig::get().server_cert_path().exists()
        && AppConfig::get().server_priv_key_path().exists()
    {
        return Ok(());
    }

    log::info!("Generating server certificate...");

    let (key, cert) = gen_certificate(GenCertificateReq {
        sub: GenCertificatSubjectReq::Subject {
            cn: AppConfig::get().hostname.as_str(),
        },
        issuer: Some(&CertData::load_web_ca()?),
        web_server: true,
        subject_alternative_names: vec![AppConfig::get().hostname.as_str()],
        ..Default::default()
    })?;

    std::fs::write(AppConfig::get().server_priv_key_path(), key.unwrap())?;
    std::fs::write(AppConfig::get().server_cert_path(), cert)?;

    Ok(())
}

/// Initialize or refresh a CRL
fn refresh_crl(d: &CertData) -> anyhow::Result<()> {
    let crl_path = d.crl.as_ref().ok_or(PKIError::MissingCRL)?;

    let old_crl = if crl_path.exists() {
        let crl = load_crl_from_file(crl_path)?;

        // Check if revocation is un-needed
        let next_update = crl.next_update().ok_or(PKIError::MissingCRLNextUpdate)?;
        if next_update.compare(Asn1Time::days_from_now(0)?.as_ref())? == Ordering::Greater {
            return Ok(());
        }

        Some(crl)
    } else {
        None
    };

    log::info!("Generating a new CRL...");

    // based on https://github.com/openssl/openssl/blob/master/crypto/x509/x509_vfy.c
    unsafe {
        let crl = openssl_sys::X509_CRL_new();
        if crl.is_null() {
            return Err(PKIError::GenCRLError("Could not construct CRL!").into());
        }

        const X509_CRL_VERSION_2: c_long = 1;
        if X509_CRL_set_version(crl, X509_CRL_VERSION_2) == 0 {
            return Err(PKIError::GenCRLError("X509_CRL_set_version").into());
        }
        if X509_CRL_set_issuer_name(crl, d.cert.subject_name().as_ptr()) == 0 {
            return Err(PKIError::GenCRLError("X509_CRL_set_issuer_name").into());
        }

        let last_update = Asn1Time::days_from_now(0)?;
        if X509_CRL_set1_lastUpdate(crl, last_update.as_ptr()) == 0 {
            return Err(PKIError::GenCRLError("X509_CRL_set1_lastUpdate").into());
        }

        let next_update = Asn1Time::days_from_now(10)?;
        if X509_CRL_set1_nextUpdate(crl, next_update.as_ptr()) == 0 {
            return Err(PKIError::GenCRLError("X509_CRL_set1_nextUpdate").into());
        }

        // Add old entries
        if let Some(old_crl) = old_crl {
            if let Some(entries) = old_crl.get_revoked() {
                for entry in entries {
                    if X509_CRL_add0_revoked(crl, X509_REVOKED_dup(entry.as_ptr())) == 0 {
                        return Err(PKIError::GenCRLError("X509_CRL_add0_revoked").into());
                    }
                }
            }
        }

        let md = MessageDigest::sha256();
        if X509_CRL_sign(crl, d.key.as_ptr(), md.as_ptr()) == 0 {
            return Err(PKIError::GenCRLError("X509_CRL_sign").into());
        }

        let crl = X509Crl::from_ptr(crl);
        std::fs::write(crl_path, crl.to_pem()?)?;
    }

    Ok(())
}

/// Refresh revocation lists
pub fn refresh_crls() -> anyhow::Result<()> {
    refresh_crl(&CertData::load_root_ca()?)?;
    refresh_crl(&CertData::load_web_ca()?)?;
    refresh_crl(&CertData::load_devices_ca()?)?;
    Ok(())
}

/// Generate a certificate for a device
pub fn gen_certificate_for_device(csr: &X509Req) -> anyhow::Result<String> {
    let (_, cert) = gen_certificate(GenCertificateReq {
        sub: GenCertificatSubjectReq::CSR { csr },
        issuer: Some(&CertData::load_devices_ca()?),
        web_client: true,
        ..Default::default()
    })?;

    Ok(String::from_utf8(cert)?)
}