    // Copyright (C) 2004  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_ENTROPY_ENCODER_MODEL_KERNEl_2_
    #define DLIB_ENTROPY_ENCODER_MODEL_KERNEl_2_

    #include "../algs.h"
    #include "entropy_encoder_model_kernel_abstract.h"
    #include "../assert.h"

    namespace dlib
    {

        template <
            unsigned long alphabet_size,
            typename entropy_encoder,
            typename cc,
            typename ccbig
            >
        class entropy_encoder_model_kernel_2
        {
            /*!
                REQUIREMENTS ON cc
                    cc is an implementation of conditioning_class/conditioning_class_kernel_abstract.h
                    cc::get_alphabet_size() == alphabet_size+1
                    this will be used for the order-0 context

                REQUIREMENTS ON ccbig
                    ccbig is an implementation of conditioning_class/conditioning_class_kernel_abstract.h
                    ccbig::get_alphabet_size() == alphabet_size+1
                    this will be used for the order-1 context

                INITIAL VALUE
                    Initially this object's finite context model is empty
                    previous_symbol == 0

                CONVENTION
                    &get_entropy_encoder() == coder
                    &order_0.get_global_state() == &gs
                    &order_1[i]->get_global_state() == &gsbig

                    This is an order-1-0 model. The last symbol in the order-0 and order-1
                    context is an escape into the lower context.

                    previous_symbol == the last symbol seen
            !*/

        public:

            typedef entropy_encoder entropy_encoder_type;

            entropy_encoder_model_kernel_2 (
                entropy_encoder& coder
            );

            virtual ~entropy_encoder_model_kernel_2 (
            );

            inline void clear(
            );

            inline void encode (
                unsigned long symbol
            );

            entropy_encoder& get_entropy_encoder (
            ) { return coder; }

            static unsigned long get_alphabet_size (
            ) { return alphabet_size; }

        private:

            entropy_encoder& coder;
            typename cc::global_state_type gs;
            typename ccbig::global_state_type gsbig;
            cc order_0;
            ccbig* order_1[alphabet_size];
            unsigned long previous_symbol;

            // restricted functions
            entropy_encoder_model_kernel_2(entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>&);        // copy constructor
            entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>& operator=(entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>&);    // assignment operator

        };

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_encoder,
            typename cc,
            typename ccbig
            >
        entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>::
        entropy_encoder_model_kernel_2 (
            entropy_encoder& coder_
        ) :
            coder(coder_),
            order_0(gs),
            previous_symbol(0)
        {
            COMPILE_TIME_ASSERT( 1 < alphabet_size && alphabet_size < 65535 );

            unsigned long i;
            try
            {
                for (i = 0; i < alphabet_size; ++i)
                {
                    order_1[i] = new ccbig(gsbig);
                }
            }
            catch (...)
            {
                for (unsigned long j = 0; j < i; ++j)
                {
                    delete order_1[j];
                }
                throw;
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_encoder,
            typename cc,
            typename ccbig
            >
        entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>::
        ~entropy_encoder_model_kernel_2 (
        )
        {
            for (unsigned long i = 0; i < alphabet_size; ++i)
            {
                delete order_1[i];
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_encoder,
            typename cc,
            typename ccbig
            >
        void entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>::
        clear(
        )
        {
            previous_symbol = 0;
            order_0.clear();
            for (unsigned long i = 0; i < alphabet_size; ++i)
            {
                order_1[i]->clear();
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_encoder,
            typename cc,
            typename ccbig
            >
        void entropy_encoder_model_kernel_2<alphabet_size,entropy_encoder,cc,ccbig>::
        encode (
            unsigned long symbol
        )
        {
            unsigned long low_count = 0, high_count = 0, total_count = 0;

            ccbig& context = *order_1[previous_symbol];

            // if we have seen this symbol in the order-1 context
            if (context.get_range(symbol,low_count,high_count,total_count))
            {
                // update the count for this symbol
                context.increment_count(symbol,2);
                // encode this symbol
                coder.encode(low_count,high_count,total_count);
                previous_symbol = symbol;
                return;
            }

            // we didn't find the symbol in the order-1 context so we must escape to a
            // lower context.

            // escape to the order-0 context
            context.get_range(alphabet_size,low_count,high_count,total_count);
            coder.encode(low_count,high_count,total_count);

            // increment counts for the escape symbol and the current symbol
            context.increment_count(alphabet_size);
            context.increment_count(symbol,2);

            previous_symbol = symbol;

            // if we have seen this symbol in the order-0 context
            if (order_0.get_range(symbol,low_count,high_count,total_count))
            {
                // update the count for this symbol
                order_0.increment_count(symbol,2);
                // encode this symbol
                coder.encode(low_count,high_count,total_count);
                return;
            }

            // if we are here then the symbol does not appear in the order-0 context

            // since we have never seen the current symbol in this context
            // escape from order-0 context
            order_0.get_range(alphabet_size,low_count,high_count,total_count);
            coder.encode(low_count,high_count,total_count);
            // increment the count for the escape symbol
            order_0.increment_count(alphabet_size);

            // update the count for this symbol
            order_0.increment_count(symbol,2);

            // use order minus one context
            coder.encode(symbol,symbol+1,alphabet_size);

        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_ENTROPY_ENCODER_MODEL_KERNEl_2_