/*

* (C) 2015,2017 Jack Lloyd

* (C) 2021 René Fischer

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/ffi.h>

#include <botan/auto_rng.h>

#include <botan/system_rng.h>

#include <botan/internal/ffi_rng.h>

#include <botan/internal/ffi_util.h>

#include <functional>

#include <memory>

#if defined(BOTAN_HAS_PROCESSOR_RNG)

   #include <botan/processor_rng.h>

#endif

extern "C" {

using namespace Botan_FFI;

int botan_rng_init(botan_rng_t* rng_out, const char* rng_type) {

   return ffi_guard_thunk(__func__, [=]() -> int {

      if(rng_out == nullptr) {

         return BOTAN_FFI_ERROR_NULL_POINTER;

      }

      const std::string rng_type_s(rng_type ? rng_type : "system");

      std::unique_ptr<Botan::RandomNumberGenerator> rng;

      if(rng_type_s == "system") {

         rng = std::make_unique<Botan::System_RNG>();

      } else if(rng_type_s == "user" || rng_type_s == "user-threadsafe") {

         rng = std::make_unique<Botan::AutoSeeded_RNG>();

      } else if(rng_type_s == "null") {

         rng = std::make_unique<Botan::Null_RNG>();

      }

#if defined(BOTAN_HAS_PROCESSOR_RNG)

      else if((rng_type_s == "rdrand" || rng_type_s == "hwrng") && Botan::Processor_RNG::available()) {

         rng = std::make_unique<Botan::Processor_RNG>();

      }

#endif

      if(!rng) {

         return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;

      }

      *rng_out = new botan_rng_struct(std::move(rng));

      return BOTAN_FFI_SUCCESS;

   });

}

int botan_rng_init_custom(botan_rng_t* rng_out,

                          const char* rng_name,

                          void* context,

                          int (*get_cb)(void* context, uint8_t* out, size_t out_len),

                          int (*add_entropy_cb)(void* context, const uint8_t input[], size_t length),

                          void (*destroy_cb)(void* context)) {

   return ffi_guard_thunk(__func__, [=]() -> int {

      if(rng_out == nullptr) {

         return BOTAN_FFI_ERROR_NULL_POINTER;

      }

      if(rng_name == nullptr) {

         return BOTAN_FFI_ERROR_NULL_POINTER;

      }

      if(get_cb == nullptr) {

         return BOTAN_FFI_ERROR_NULL_POINTER;

      }

      class Custom_RNG : public Botan::RandomNumberGenerator {

         public:

            Custom_RNG(std::string_view name,

                       void* context,

                       int (*get_cb)(void* context, uint8_t* out, size_t out_len),

                       int (*add_entropy_cb)(void* context, const uint8_t input[], size_t length),

                       void (*destroy_cb)(void* context)) :

                  m_name(name) {

               m_context = context;

               m_get_cb = get_cb;

               m_add_entropy_cb = add_entropy_cb;

               m_destroy_cb = destroy_cb;

            }

            ~Custom_RNG() override {

               if(m_destroy_cb) {

                  m_destroy_cb(m_context);

               }

            }

            Custom_RNG(const Custom_RNG& other) = delete;

            Custom_RNG(Custom_RNG&& other) = delete;

            Custom_RNG& operator=(const Custom_RNG& other) = delete;

            Custom_RNG& operator=(Custom_RNG&& other) = delete;

         protected:

            void fill_bytes_with_input(std::span<uint8_t> output, std::span<const uint8_t> input) override {

               if(accepts_input() && !input.empty()) {

                  int rc = m_add_entropy_cb(m_context, input.data(), input.size());

                  if(rc) {

                     throw Botan::Invalid_State("Failed to add entropy via C callback, rc=" + std::to_string(rc));

                  }

               }

               if(!output.empty()) {

                  int rc = m_get_cb(m_context, output.data(), output.size());

                  if(rc) {

                     throw Botan::Invalid_State("Failed to get random from C callback, rc=" + std::to_string(rc));

                  }

               }

            }

         public:

            bool accepts_input() const override { return m_add_entropy_cb != nullptr; }

            std::string name() const override { return m_name; }

            void clear() override {}

            bool is_seeded() const override { return true; }

         private:

            std::string m_name;

            void* m_context;

            std::function<int(void* context, uint8_t* out, size_t out_len)> m_get_cb;

            std::function<int(void* context, const uint8_t input[], size_t length)> m_add_entropy_cb;

            std::function<void(void* context)> m_destroy_cb;

      };

      auto rng = std::make_unique<Custom_RNG>(rng_name, context, get_cb, add_entropy_cb, destroy_cb);

      *rng_out = new botan_rng_struct(std::move(rng));

      return BOTAN_FFI_SUCCESS;

   });

}

int botan_rng_destroy(botan_rng_t rng) {

   return BOTAN_FFI_CHECKED_DELETE(rng);

}

int botan_rng_get(botan_rng_t rng, uint8_t* out, size_t out_len) {

   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.randomize(out, out_len); });

}

int botan_system_rng_get(uint8_t* out, size_t out_len) {

   return ffi_guard_thunk(__func__, [=]() -> int {

      Botan::system_rng().randomize(out, out_len);

      return BOTAN_FFI_SUCCESS;

   });

}

int botan_rng_reseed(botan_rng_t rng, size_t bits) {

   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.reseed_from_rng(Botan::system_rng(), bits); });

}

int botan_rng_add_entropy(botan_rng_t rng, const uint8_t* input, size_t len) {

   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.add_entropy(input, len); });

}

int botan_rng_reseed_from_rng(botan_rng_t rng, botan_rng_t source_rng, size_t bits) {

   return BOTAN_FFI_VISIT(rng, [=](auto& r) { r.reseed_from_rng(safe_get(source_rng), bits); });

}

}