/*  Copyright 2013 IST Austria
    Contributed by: Hubert Wagner

    This file is part of PHAT.

    PHAT is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    PHAT is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with PHAT.  If not, see <http://www.gnu.org/licenses/>. */

#pragma once

#include <phat/helpers/misc.h>
#include <phat/representations/abstract_pivot_column.h>

namespace phat {

    // This is a bitset indexed with a 64-ary tree. Each node in the index
    // has 64 bits; i-th bit says that the i-th subtree is non-empty.
    // Supports practically O(1), inplace, zero-allocation: insert, remove, max_element
    // and clear in O(number of ones in the bitset).
    // 'add_index' is still the real bottleneck in practice.
    class bit_tree_column
    {
        size_t offset; // data[i + offset] = ith block of the data-bitset
        typedef uint64_t block_type;
        std::vector< block_type > data;

        // this static is not a problem with OMP, it's initialized just after program starts
        static const size_t debrujin_magic_table[64];

        enum { block_size_in_bits = 64 };
        enum { block_shift = 6 };

        // Some magic: http://graphics.stanford.edu/~seander/bithacks.html
        // Gets the position of the rightmost bit of 'x'. 0 means the most significant bit. 
        // (-x)&x isolates the rightmost bit.
        // The whole method is much faster than calling log2i, and very comparable to using ScanBitForward/Reverse intrinsic,
        // which should be one CPU instruction, but is not portable.
        size_t rightmost_pos(const block_type value) const
        {                
            return 64 - 1 - debrujin_magic_table[((value & (-(int64_t)value))*0x07EDD5E59A4E28C2) >> 58];
        }

        public:        

        void init(index num_cols)
        {
            int64_t n = 1; // in case of overflow
            int64_t bottom_blocks_needed = (num_cols+block_size_in_bits-1)/block_size_in_bits;
            int64_t upper_blocks = 1;        

            // How many blocks/nodes of index needed to index the whole bitset?
            while(n * block_size_in_bits < bottom_blocks_needed)
            {
                n *= block_size_in_bits;
                upper_blocks += n;
            }

            offset = upper_blocks;
            data.resize(upper_blocks + bottom_blocks_needed, 0);
        }

        index max_index() const
        {
            if (!data[0])
                return -1;

            const size_t size = data.size();
            size_t n = 0;

            while(true)
            {
                const block_type val = data[n];
                const size_t index = rightmost_pos(val);
                const size_t newn = (n << block_shift) + index + 1;

                if (newn >= size)
                {
                    const size_t bottom_index = n - offset;
                    return (bottom_index << block_shift) + index;
                }

                n = newn;
            }

            return -1;
        }

        bool empty() const
        {
            return data[0] == 0;
        }

        void add_index(const size_t entry)
        {
            const block_type ONE = 1;
            const block_type block_modulo_mask = ((ONE << block_shift) - 1);
            size_t index_in_level = entry >> block_shift;
            size_t address = index_in_level + offset;
            size_t index_in_block = entry & block_modulo_mask;

            block_type mask = (ONE << (block_size_in_bits - index_in_block - 1));

            while(true)
            {
                data[address]^=mask;

                // First we check if we reached the root.
                // Also, if anyone else was in this block, we don't need to update the path up.
                if (!address || (data[address] & ~mask))
                    return;

                index_in_block = index_in_level & block_modulo_mask;
                index_in_level >>= block_shift;
                --address;
                address >>= block_shift;
                mask = (ONE << (block_size_in_bits - index_in_block - 1));
            }
        }

        void get_column_and_clear(column &out)
        {
            out.clear();
            while(true)
            {
                index mx = this->max_index();
                if (mx == -1)
                    break;
                out.push_back(mx);
                add_index(mx);
            }

            std::reverse(out.begin(), out.end());
        }

        void add_column(const column &col)
        {
            for (size_t i = 0; i < col.size(); ++i)
            {
                add_index(col[i]);
            }
        }

        bool empty() {
            return !data[0];
        }
    };

    const size_t bit_tree_column::debrujin_magic_table[64] =  {
                    63,  0, 58,  1, 59, 47, 53,  2,
                    60, 39, 48, 27, 54, 33, 42,  3,
                    61, 51, 37, 40, 49, 18, 28, 20,
                    55, 30, 34, 11, 43, 14, 22,  4,
                    62, 57, 46, 52, 38, 26, 32, 41,
                    50, 36, 17, 19, 29, 10, 13, 21,
                    56, 45, 25, 31, 35, 16,  9, 12,
                    44, 24, 15,  8, 23,  7,  6,  5};

    typedef abstract_pivot_column<bit_tree_column> bit_tree_pivot_column;
}