/** @file

  @section license License

  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you under the Apache License, Version 2.0 (the
  "License"); you may not use this file except in compliance
  with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 */

#pragma once

#include "iocore/eventsystem/IOBuffer.h"
#include "iocore/net/SSLTypes.h"
#include "ts/apidefs.h"
#include "tscore/List.h"
#include "tscore/Ptr.h"
#include "tsutil/TsSharedMutex.h"

#include <openssl/ssl.h>
#include <mutex>
#include <utility>

#define SSL_MAX_SESSION_SIZE      256
#define SSL_MAX_ORIG_SESSION_SIZE 4096

struct ssl_session_cache_exdata {
  ssl_curve_id curve = 0;
};

inline void
hash_combine(uint64_t &seed, uint64_t hash)
{
  // using boost's version of hash combine, substituting magic number with a 64bit version
  // https://www.boost.org/doc/libs/1_43_0/doc/html/hash/reference.html#boost.hash_combine
  seed ^= hash + 0x9E3779B97F4A7C15 + (seed << 6) + (seed >> 2);
}

struct SSLSessionID : public TSSslSessionID {
  SSLSessionID(const unsigned char *s, size_t l)
  {
    len = l;
    ink_release_assert(l <= sizeof(bytes));
    memcpy(bytes, s, l);
    hash();
  }

  SSLSessionID(const SSLSessionID &other)
  {
    if (other.len) {
      memcpy(bytes, other.bytes, other.len);
    }

    len = other.len;
    hash();
  }

  bool
  operator<(const SSLSessionID &other) const
  {
    if (len != other.len) {
      return len < other.len;
    }

    return (memcmp(bytes, other.bytes, len) < 0);
  }

  SSLSessionID &
  operator=(const SSLSessionID &other)
  {
    if (other.len) {
      memcpy(bytes, other.bytes, other.len);
    }

    len = other.len;
    return *this;
  }

  bool
  operator==(const SSLSessionID &other) const
  {
    if (len != other.len) {
      return false;
    }

    // memcmp returns 0 on equal
    return (memcmp(bytes, other.bytes, len) == 0);
  }

  const char *
  toString(char *buf, size_t buflen) const
  {
    char *cur_pos = buf;
    for (size_t i = 0; i < len && buflen > 0; ++i) {
      if (buflen > 2) { // we have enough space for 3 bytes, 2 hex and 1 null terminator
        snprintf(cur_pos, 3 /* including a null terminator */, "%02hhX", static_cast<unsigned char>(bytes[i]));
        cur_pos += 2;
        buflen  -= 2;
      } else { // not enough space for any more hex bytes, just null terminate
        *cur_pos = '\0';
        break;
      }
    }
    return buf;
  }

  uint64_t
  hash() const
  {
    // because the session ids should be uniformly random, we can treat the bits as a hash value
    // however we need to combine them if the length is longer than 64bits
    if (len >= sizeof(uint64_t)) {
      uint64_t seed = 0;
      for (uint64_t i = 0; i < len; i += sizeof(uint64_t)) {
        hash_combine(seed, static_cast<uint64_t>(bytes[i]));
      }
      return seed;
    } else if (len) {
      return static_cast<uint64_t>(bytes[0]);
    } else {
      return 0;
    }
  }
};

class SSLSession
{
public:
  SSLSessionID      session_id;
  Ptr<IOBufferData> asn1_data; /* this is the ASN1 representation of the SSL_CTX */
  size_t            len_asn1_data;
  Ptr<IOBufferData> extra_data;

  SSLSession(const SSLSessionID &id, const Ptr<IOBufferData> &ssl_asn1_data, size_t len_asn1, Ptr<IOBufferData> &exdata)
    : session_id(id), asn1_data(ssl_asn1_data), len_asn1_data(len_asn1), extra_data(exdata)
  {
  }

  LINK(SSLSession, link);
};

class SSLSessionBucket
{
public:
  SSLSessionBucket();
  ~SSLSessionBucket();
  void insertSession(const SSLSessionID &sid, SSL_SESSION *sess, SSL *ssl);
  bool getSession(const SSLSessionID &sid, SSL_SESSION **sess, ssl_session_cache_exdata **data);
  int  getSessionBuffer(const SSLSessionID &sid, char *buffer, int &len);
  void removeSession(const SSLSessionID &sid);

private:
  /* these method must be used while hold the lock */
  void print(const char *) const;
  void removeOldestSession(const std::unique_lock<ts::shared_mutex> &lock);

  mutable ts::shared_mutex             mutex;
  CountQueue<SSLSession>               bucket_que;
  std::map<SSLSessionID, SSLSession *> bucket_map;
};

class SSLSessionCache
{
public:
  bool getSession(const SSLSessionID &sid, SSL_SESSION **sess, ssl_session_cache_exdata **data) const;
  int  getSessionBuffer(const SSLSessionID &sid, char *buffer, int &len) const;
  void insertSession(const SSLSessionID &sid, SSL_SESSION *sess, SSL *ssl);
  void removeSession(const SSLSessionID &sid);
  SSLSessionCache();
  ~SSLSessionCache();

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

private:
  SSLSessionBucket *session_bucket = nullptr;
  size_t            nbuckets;
};

class SSLOriginSession
{
public:
  std::string                  key;
  ssl_curve_id                 curve_id;
  std::shared_ptr<SSL_SESSION> shared_sess = nullptr;

  SSLOriginSession(const std::string &lookup_key, ssl_curve_id curve, std::shared_ptr<SSL_SESSION> session)
    : key(lookup_key), curve_id(curve), shared_sess(std::move(session))
  {
  }

  LINK(SSLOriginSession, link);
};

class SSLOriginSessionCache
{
public:
  SSLOriginSessionCache();
  ~SSLOriginSessionCache();

  void                         insert_session(const std::string &lookup_key, SSL_SESSION *sess, SSL *ssl);
  std::shared_ptr<SSL_SESSION> get_session(const std::string &lookup_key, ssl_curve_id *curve);
  void                         remove_session(const std::string &lookup_key);

private:
  void remove_oldest_session(const std::unique_lock<ts::shared_mutex> &lock);

  mutable ts::shared_mutex                  mutex;
  CountQueue<SSLOriginSession>              orig_sess_que;
  std::map<std::string, SSLOriginSession *> orig_sess_map;
};
