/*  Copyright 2013 IST Austria
    Contributed by: Ulrich Bauer, Michael Kerber, Jan Reininghaus, 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 32-ary tree. Each node in the index
	// has 32 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; // present_data[i + offset] = ith block of the data-bitset
		typedef uint64_t block_type;
		std::vector<block_type> present_data;
		block_type *  present; // to prevent error checking in MS's vector...

		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'. First (-x)&x isolates the rightmost bit.
		// This is much faster than calling log2i, and faster than using ScanBitForward/Reverse intrinsic,
		// which should be one CPU instruction.
		inline size_t rightmost_pos(const block_type value) const
		{
				static const size_t tab64[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};
				return 64 - 1 - tab64[((value & (-value))*0x07EDD5E59A4E28C2) >> 58];
		}

		public:
		bit_tree_column() : present(0)
		{
			init(1);
		}

		bit_tree_column(const bit_tree_column &other) : present(0)
		{
			if (this == &other)
				return;
			this->offset = other.offset;
			this->present_data = other.present_data;
			*const_cast<block_type**>(&present) = &present_data[0];
		}

		void init(index num_cols)
		{
			size_t n = 1;
			size_t bottom_blocks_needed = (num_cols+block_size_in_bits-1)/block_size_in_bits;
			size_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;
			present_data.resize(upper_blocks + bottom_blocks_needed, 0);

			*const_cast<block_type**>(&present) = &present_data[0];
		}

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

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

			while(true)
			{
				const block_type val = present[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;
		}

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

		inline void add_index(const size_t entry)
		{
			static const block_type ONE = 1;
			static 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)
			{
				present[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 || (present[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]);
			}
		}

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

	typedef abstract_pivot_column<bit_tree_column> bit_tree_pivot_column;
}