///
//
// icey
// Copyright (c) 2005, icey <https://0state.com>
//
// SPDX-License-Identifier: LGPL-2.1+
//
/// @addtogroup net
/// @{


#pragma once


#include "icy/crypto/crypto.h"
#include "icy/crypto/rsa.h"
#include "icy/crypto/x509certificate.h"
#include "icy/net/net.h"
#include "icy/util.h"

#include <openssl/err.h>
#include <openssl/ssl.h>

#include <cstdlib>
#include <string>
#include <string_view>
#include <vector>


namespace icy {
namespace net {


/// OpenSSL SSL_CTX wrapper for client and server TLS configuration.
///
/// This class encapsulates context information for
/// an SSL server or client, such as the certificate
/// verification mode and the location of certificates
/// and private key files, as well as the list of
/// supported ciphers.
///
/// The Context class is also used to control
/// SSL session caching on the server and client side.
class Net_API SSLContext
{
public:
    using Ptr = std::shared_ptr<SSLContext>;

    enum Usage
    {
        CLIENT_USE,       ///<  Context is used by a client.
        SERVER_USE,       ///<  Context is used by a server.
        TLSV1_CLIENT_USE, ///<  Context is used by a client requiring TLSv1.
        TLSV1_SERVER_USE  ///<  Context is used by a server requiring TLSv2.
    };

    enum VerificationMode
    {
        /// Server: The server will not send a client certificate
        /// request to the client, so the client will not send a certificate.
        ///
        /// Client: If not using an anonymous cipher (by default disabled),
        /// the server will send a certificate which will be checked, but
        /// the result of the check will be ignored.
        VERIFY_NONE = SSL_VERIFY_NONE,

        /// Server: The server sends a client certificate request to the
        /// client. The certificate returned (if any) is checked.
        /// If the verification process fails, the TLS/SSL handshake is
        /// immediately terminated with an alert message containing the
        /// reason for the verification failure.
        ///
        /// Client: The server certificate is verified, if one is provided.
        /// If the verification process fails, the TLS/SSL handshake is
        /// immediately terminated with an alert message containing the
        /// reason for the verification failure.
        VERIFY_RELAXED = SSL_VERIFY_PEER,

        /// Server: If the client did not return a certificate, the TLS/SSL
        /// handshake is immediately terminated with a handshake failure
        /// alert.
        ///
        /// Client: Same as VERIFY_RELAXED.
        VERIFY_STRICT = SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT,

        /// Server: Only request a client certificate on the initial
        /// TLS/SSL handshake. Do not ask for a client certificate
        /// again in case of a renegotiation.
        ///
        /// Client: Same as VERIFY_RELAXED.
        VERIFY_ONCE = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE
    };

    /// Creates a Context.
    ///
    ///   * usage specifies whether the context is used by a client or server.
    ///   * privateKeyFile contains the path to the private key file used for
    ///   encryption.
    ///     Can be empty if no private key file is used.
    ///   * certificateFile contains the path to the certificate file (in PEM
    ///   format).
    ///     If the private key and the certificate are stored in the same file,
    ///     this
    ///     can be empty if privateKeyFile is given.
    ///   * caLocation contains the path to the file or directory containing the
    ///     CA/root certificates. Can be empty if the OpenSSL builtin CA
    ///     certificates
    ///     are used (see loadDefaultCAs).
    ///   * verificationMode specifies whether and how peer certificates are
    ///     validated.
    ///   * verificationDepth sets the upper limit for verification chain sizes.
    ///   Verification
    ///     will fail if a certificate chain larger than this is encountered.
    ///   * loadDefaultCAs specifies whether the builtin CA certificates from
    ///     OpenSSL are used.
    ///   * cipherList specifies the supported ciphers in OpenSSL notation.
    ///
    /// Note: If the private key is protected by a passphrase, a
    /// PrivateKeyPassphraseHandler
    /// must have been setup with the SSLManager, or the SSLManager's
    /// PrivateKeyPassphraseRequired
    /// event must be handled.
    SSLContext(
        Usage usage, const std::string& privateKeyFile,
        const std::string& certificateFile, const std::string& caLocation,
        VerificationMode verificationMode = VERIFY_RELAXED,
        int verificationDepth = 9, bool loadDefaultCAs = false,
        const std::string& cipherList = "ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH");

    /// Creates a Context.
    ///
    ///   * usage specifies whether the context is used by a client or server.
    ///   * caLocation contains the path to the file or directory containing the
    ///     CA/root certificates. Can be empty if the OpenSSL builtin CA
    ///     certificates
    ///     are used (see loadDefaultCAs).
    ///   * verificationMode specifies whether and how peer certificates are
    ///   validated.
    ///   * verificationDepth sets the upper limit for verification chain sizes.
    ///     Verification
    ///     will fail if a certificate chain larger than this is encountered.
    ///   * loadDefaultCAs specifies whether the builtin CA certificates from
    ///     OpenSSL are used.
    ///   * cipherList specifies the supported ciphers in OpenSSL notation.
    ///
    /// Note that a private key and/or certificate must be specified with
    /// usePrivateKey()/useCertificate() before the Context can be used.
    SSLContext(
        Usage usage, const std::string& caLocation,
        VerificationMode verificationMode = VERIFY_RELAXED,
        int verificationDepth = 9, bool loadDefaultCAs = false,
        const std::string& cipherList = "ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH");

    /// Destroys the Context.
    ~SSLContext() noexcept;

    /// Sets the certificate to be used by the Context.
    ///
    /// To set-up a complete certificate chain, it might be
    /// necessary to call addChainCertificate() to specify
    /// additional certificates.
    ///
    /// Note that useCertificate() must always be called before
    /// usePrivateKey().
    void useCertificate(crypto::X509Certificate& certificate);

    /// Adds a certificate for certificate chain validation.
    void addChainCertificate(crypto::X509Certificate& certificate);

    /// Sets the private key to be used by the Context.
    ///
    /// Note that useCertificate() must always be called before
    /// usePrivateKey().
    ///
    /// Note: If the private key is protected by a passphrase, a
    /// PrivateKeyPassphraseHandler
    /// must have been setup with the SSLManager, or the SSLManager's
    /// PrivateKeyPassphraseRequired
    /// event must be handled.
    // void usePrivateKey(const crypto::RSAKey& key);

    /// Adds the given certificate to the list of trusted certificates
    /// that will be used for verification.
    void addVerificationCertificate(crypto::X509Certificate& certificate);

    /// Returns the underlying OpenSSL SSL Context object.
    SSL_CTX* sslContext() const;

    /// Returns whether the context is for use by a client or by a server
    /// and whether TLSv1 is required.
    Usage usage() const;

    /// Returns true if the context is for use by a server.
    bool isForServerUse() const;

    /// Returns the verification mode.
    SSLContext::VerificationMode verificationMode() const;

    /// Enable or disable SSL/TLS session caching.
    /// For session caching to work, it must be enabled
    /// on the server, as well as on the client side.
    ///
    /// The default is disabled session caching.
    ///
    /// To enable session caching on the server side, use the
    /// two-argument version of this method to specify
    /// a session ID context.
    void enableSessionCache(bool flag = true);

    /// Enables or disables SSL/TLS session caching on the server.
    /// For session caching to work, it must be enabled
    /// on the server, as well as on the client side.
    ///
    /// SessionIdContext contains the application's unique
    /// session ID context, which becomes part of each
    /// session identifier generated by the server within this
    /// context. SessionIdContext can be an arbitrary sequence
    /// of bytes with a maximum length of SSL_MAX_SSL_SESSION_ID_LENGTH.
    ///
    /// A non-empty sessionIdContext should be specified even if
    /// session caching is disabled to avoid problems with clients
    /// requesting to reuse a session (e.g. Firefox 3.6).
    ///
    /// This method may only be called on SERVER_USE Context objects.
    void enableSessionCache(bool flag, std::string_view sessionIdContext);

    /// Returns true if the session cache is enabled.
    bool sessionCacheEnabled() const;

    /// Sets the maximum size of the server session cache, in number of
    /// sessions. The default size (according to OpenSSL documentation)
    /// is 1024*20, which may be too large for many applications,
    /// especially on embedded platforms with limited memory.
    ///
    /// Specifying a size of 0 will set an unlimited cache size.
    ///
    /// This method may only be called on SERVER_USE Context objects.
    void setSessionCacheSize(size_t size);

    /// Returns the current maximum size of the server session cache.
    ///
    /// This method may only be called on SERVER_USE Context objects.
    size_t getSessionCacheSize() const;

    /// Sets the timeout (in seconds) of cached sessions on the server.
    /// A cached session will be removed from the cache if it has
    /// not been used for the given number of seconds.
    ///
    /// This method may only be called on SERVER_USE Context objects.
    void setSessionTimeout(long seconds);

    /// Returns the timeout (in seconds) of cached sessions on the server.
    ///
    /// This method may only be called on SERVER_USE Context objects.
    long getSessionTimeout() const;

    /// Flushes the SSL session cache on the server.
    ///
    /// This method may only be called on SERVER_USE Context objects.
    void flushSessionCache();

    /// Newer versions of OpenSSL support RFC 4507 tickets for stateless
    /// session resumption.
    ///
    /// The feature can be disabled by calling this method.
    void disableStatelessSessionResumption();

    /// Set the ALPN protocols for negotiation.
    /// Protocols should be in preference order.
    /// Example: {"h2", "http/1.1"}
    void setALPNProtocols(const std::vector<std::string>& protocols);

    /// Enable SNI (Server Name Indication) for a specific SSL connection.
    /// The hostname is sent during the TLS handshake to allow the server
    /// to select the appropriate certificate.
    static void enableSNI(SSL* ssl, const std::string& hostname);

    SSLContext(const SSLContext&) = delete;
    SSLContext& operator=(const SSLContext&) = delete;
    SSLContext(SSLContext&&) = delete;
    SSLContext& operator=(SSLContext&&) = delete;

private:
    /// Create a SSL_CTX object according to Context configuration.
    void createSSLContext();

    Usage _usage;
    VerificationMode _mode;
    SSL_CTX* _sslContext;
    std::vector<unsigned char> _alpnWire; ///< Wire-format ALPN protocols for server selection.
};


inline SSLContext::Usage SSLContext::usage() const
{
    return _usage;
}


inline bool SSLContext::isForServerUse() const
{
    return _usage == SERVER_USE || _usage == TLSV1_SERVER_USE;
}


inline SSLContext::VerificationMode SSLContext::verificationMode() const
{
    return _mode;
}


inline SSL_CTX* SSLContext::sslContext() const
{
    return _sslContext;
}


//
// Utilities
//


/// Non-case sensitive conversion of a string to a VerificationMode enum.
/// If verMode is illegal an ArgumentException is thrown.
inline SSLContext::VerificationMode convertVerificationMode(const std::string& vMode)
{
    std::string mode = util::toLower(vMode);
    SSLContext::VerificationMode verMode = SSLContext::VERIFY_STRICT;

    if (mode == "none")
        verMode = SSLContext::VERIFY_NONE;
    else if (mode == "relaxed")
        verMode = SSLContext::VERIFY_RELAXED;
    else if (mode == "strict")
        verMode = SSLContext::VERIFY_STRICT;
    else if (mode == "once")
        verMode = SSLContext::VERIFY_ONCE;
    else
        throw std::invalid_argument("Invalid verification mode: " + vMode);

    return verMode;
}

/// Converts an SSL certificate handling error code into an error message.
inline std::string convertCertificateError(long errCode)
{
    std::string errMsg(X509_verify_cert_error_string(errCode));
    return errMsg;
}

/// Returns the last error from the error stack
inline std::string getLastError()
{
    unsigned long errCode = ERR_get_error();
    if (errCode != 0) {
        char buffer[256];
        ERR_error_string_n(errCode, buffer, sizeof(buffer));
        return std::string(buffer);
    } else
        return "No error";
}

/// Clears the error stack
inline void clearErrorStack()
{
    ERR_clear_error();
}


} // namespace net
} // namespace icy


/// @}
