/*

Copyright (c) 2003, Arvid Norberg
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of the author nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#include "libtorrent/pch.hpp"

#include <vector>
#include <cmath>
#include <algorithm>
#include <numeric>

// non-standard header, is_sorted()
//#include <algo.h>

#include "libtorrent/piece_picker.hpp"
#include "libtorrent/aux_/session_impl.hpp"

#ifndef NDEBUG
#include "libtorrent/peer_connection.hpp"
#include "libtorrent/torrent.hpp"
#endif

//#define TORRENT_PIECE_PICKER_INVARIANT_CHECK INVARIANT_CHECK
#define TORRENT_PIECE_PICKER_INVARIANT_CHECK

namespace libtorrent
{

	piece_picker::piece_picker(int blocks_per_piece, int total_num_blocks)
		: m_piece_info(2)
		, m_piece_map((total_num_blocks + blocks_per_piece-1) / blocks_per_piece)
		, m_num_filtered(0)
		, m_num_have_filtered(0)
		, m_num_have(0)
		, m_sequenced_download_threshold(100)
	{
		TORRENT_ASSERT(blocks_per_piece > 0);
		TORRENT_ASSERT(total_num_blocks >= 0);
#ifndef NDEBUG
		m_files_checked_called = false;
#endif

		// the piece index is stored in 20 bits, which limits the allowed
		// number of pieces somewhat
		if (m_piece_map.size() >= piece_pos::we_have_index)
			throw std::runtime_error("too many pieces in torrent");
		
		m_blocks_per_piece = blocks_per_piece;
		m_blocks_in_last_piece = total_num_blocks % blocks_per_piece;
		if (m_blocks_in_last_piece == 0) m_blocks_in_last_piece = blocks_per_piece;

		TORRENT_ASSERT(m_blocks_in_last_piece <= m_blocks_per_piece);

		// allocate the piece_map to cover all pieces
		// and make them invalid (as if we don't have a single piece)
		std::fill(m_piece_map.begin(), m_piece_map.end()
			, piece_pos(0, 0));
		m_num_have = 0;
	}

	// pieces is a bitmask with the pieces we have
	void piece_picker::files_checked(
		std::vector<bool> const& pieces
		, std::vector<downloading_piece> const& unfinished
		, std::vector<int>& verify_pieces)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
#ifndef NDEBUG
		m_files_checked_called = true;
#endif
		for (std::vector<bool>::const_iterator i = pieces.begin();
			i != pieces.end(); ++i)
		{
			int index = static_cast<int>(i - pieces.begin());
			piece_pos& p = m_piece_map[index];
			if (*i)
			{
				++m_num_have;
				p.set_have();
				if (p.filtered())
				{
					++m_num_have_filtered;
					TORRENT_ASSERT(m_num_filtered > 0);
					--m_num_filtered;
				}
			}
			else
			{
				p.index = 0;
			}
		}

		// if we have fast resume info
		// use it
		if (!unfinished.empty())
		{
			for (std::vector<downloading_piece>::const_iterator i
				= unfinished.begin(); i != unfinished.end(); ++i)
			{
				for (int j = 0; j < m_blocks_per_piece; ++j)
				{
					if (i->info[j].state == block_info::state_finished)
						mark_as_finished(piece_block(i->index, j), 0);
				}
				if (is_piece_finished(i->index))
				{
					verify_pieces.push_back(i->index);
				}
			}
		}
	}

	void piece_picker::piece_info(int index, piece_picker::downloading_piece& st) const
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < int(m_piece_map.size()));

		if (m_piece_map[index].downloading)
		{
			std::vector<downloading_piece>::const_iterator piece = std::find_if(
				m_downloads.begin(), m_downloads.end()
				, bind(&downloading_piece::index, _1) == index);
			TORRENT_ASSERT(piece != m_downloads.end());
			st = *piece;
			st.info = 0;
			return;
		}
		st.info = 0;
		st.index = index;
		st.writing = 0;
		st.requested = 0;
		if (m_piece_map[index].have())
		{
			st.finished = blocks_in_piece(index);
			return;
		}
		st.finished = 0;
	}

	void piece_picker::set_sequenced_download_threshold(
		int sequenced_download_threshold)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		if (sequenced_download_threshold == m_sequenced_download_threshold)
			return;
			
		TORRENT_ASSERT(sequenced_download_threshold > 0);
		if (sequenced_download_threshold <= 0) return;
			
		int old_limit = m_sequenced_download_threshold;
		m_sequenced_download_threshold = sequenced_download_threshold;

		for (std::vector<piece_pos>::iterator i = m_piece_map.begin()
			, end(m_piece_map.end()); i != end; ++i)
		{
			if (i->priority(old_limit) != i->priority(m_sequenced_download_threshold))
			{
				piece_pos& p = *i;
				int prev_priority = p.priority(old_limit);
				if (prev_priority == 0) continue;
				move(prev_priority, p.index);
			}
		}
		
		typedef std::vector<int> info_t;

		if (old_limit < sequenced_download_threshold)
		{
			// the threshold was incremented, in case
			// the previous max availability was reached
			// we need to shuffle that bucket, if not, we
			// don't have to do anything
			if (int(m_piece_info.size()) > old_limit * 2)
			{
				info_t& in = m_piece_info[old_limit * 2];
				std::random_shuffle(in.begin(), in.end());
				int c = 0;
				for (info_t::iterator i = in.begin()
					, end(in.end()); i != end; ++i)
				{
					m_piece_map[*i].index = c++;
					TORRENT_ASSERT(m_piece_map[*i].priority(old_limit) == old_limit * 2);
				}
			}
		}
		else if (int(m_piece_info.size()) > sequenced_download_threshold * 2)
		{
			info_t& in = m_piece_info[sequenced_download_threshold * 2];
			std::sort(in.begin(), in.end());
			int c = 0;
			for (info_t::iterator i = in.begin()
				, end(in.end()); i != end; ++i)
			{
				m_piece_map[*i].index = c++;
				TORRENT_ASSERT(m_piece_map[*i].priority(
					sequenced_download_threshold) == sequenced_download_threshold * 2);
			}
		}
	}

	piece_picker::downloading_piece& piece_picker::add_download_piece()
	{
		int num_downloads = m_downloads.size();
		int block_index = num_downloads * m_blocks_per_piece;
		if (int(m_block_info.size()) < block_index + m_blocks_per_piece)
		{
			block_info* base = 0;
			if (!m_block_info.empty()) base = &m_block_info[0];
			m_block_info.resize(block_index + m_blocks_per_piece);
			if (!m_downloads.empty() && &m_block_info[0] != base)
			{
				// this means the memory was reallocated, update the pointers
				for (int i = 0; i < int(m_downloads.size()); ++i)
					m_downloads[i].info = &m_block_info[m_downloads[i].info - base];
			}
		}
		m_downloads.push_back(downloading_piece());
		downloading_piece& ret = m_downloads.back();
		ret.info = &m_block_info[block_index];
		for (int i = 0; i < m_blocks_per_piece; ++i)
		{
			ret.info[i].num_peers = 0;
			ret.info[i].state = block_info::state_none;
			ret.info[i].peer = 0;
		}
		return ret;
	}

	void piece_picker::erase_download_piece(std::vector<downloading_piece>::iterator i)
	{
		std::vector<downloading_piece>::iterator other = std::find_if(
			m_downloads.begin(), m_downloads.end()
			, bind(&downloading_piece::info, _1)
			== &m_block_info[(m_downloads.size() - 1) * m_blocks_per_piece]);
		TORRENT_ASSERT(other != m_downloads.end());

		if (i != other)
		{
			std::copy(other->info, other->info + m_blocks_per_piece, i->info);
			other->info = i->info;
		}
		m_downloads.erase(i);
	}

#ifndef NDEBUG

	void piece_picker::verify_pick(std::vector<piece_block> const& picked
		, std::vector<bool> const& bitfield) const
	{
		TORRENT_ASSERT(bitfield.size() == m_piece_map.size());
		for (std::vector<piece_block>::const_iterator i = picked.begin()
			, end(picked.end()); i != end; ++i)
		{
			TORRENT_ASSERT(i->piece_index >= 0);
			TORRENT_ASSERT(i->piece_index < int(bitfield.size()));
			TORRENT_ASSERT(bitfield[i->piece_index]);
			TORRENT_ASSERT(!m_piece_map[i->piece_index].have());
		}
	}
	
	void piece_picker::check_invariant(const torrent* t) const
	{
		TORRENT_ASSERT(sizeof(piece_pos) == 4);
		TORRENT_ASSERT(m_num_have >= 0);
		TORRENT_ASSERT(m_num_have_filtered >= 0);
		TORRENT_ASSERT(m_num_filtered >= 0);

		TORRENT_ASSERT(m_piece_info.empty() || m_piece_info[0].empty());

		if (!m_downloads.empty())
		{
			for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin();
				i != m_downloads.end() - 1; ++i)
			{
				downloading_piece const& dp = *i;
				downloading_piece const& next = *(i + 1);
				TORRENT_ASSERT(dp.finished + dp.writing >= next.finished + next.writing);
			}
		}

		if (t != 0)
			TORRENT_ASSERT((int)m_piece_map.size() == t->torrent_file().num_pieces());

		for (int i = m_sequenced_download_threshold * 2 + 1; i < int(m_piece_info.size()); ++i)
			TORRENT_ASSERT(m_piece_info[i].empty());

		for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin()
			, end(m_downloads.end()); i != end; ++i)
		{
			bool blocks_requested = false;
			int num_blocks = blocks_in_piece(i->index);
			int num_requested = 0;
			int num_finished = 0;
			int num_writing = 0;
			for (int k = 0; k < num_blocks; ++k)
			{
				if (i->info[k].state == block_info::state_finished)
				{
					++num_finished;
					continue;
				}
				if (i->info[k].state == block_info::state_requested)
				{
					++num_requested;
					blocks_requested = true;
					TORRENT_ASSERT(i->info[k].num_peers > 0);
				}
				if (i->info[k].state == block_info::state_writing)
				{
					++num_writing;
				}
			}
			TORRENT_ASSERT(blocks_requested == (i->state != none));
			TORRENT_ASSERT(num_requested == i->requested);
			TORRENT_ASSERT(num_writing == i->writing);
			TORRENT_ASSERT(num_finished == i->finished);
		}


		int num_filtered = 0;
		int num_have_filtered = 0;
		int num_have = 0;
		for (std::vector<piece_pos>::const_iterator i = m_piece_map.begin();
			i != m_piece_map.end(); ++i)
		{
			int index = static_cast<int>(i - m_piece_map.begin());
			if (i->filtered())
			{
				if (i->index != piece_pos::we_have_index)
					++num_filtered;
				else
					++num_have_filtered;
			}
			if (i->index == piece_pos::we_have_index)
				++num_have;

#if 0
			if (t != 0)
			{
				int actual_peer_count = 0;
				for (torrent::const_peer_iterator peer = t->begin();
					peer != t->end(); ++peer)
				{
					if (peer->second->has_piece(index)) actual_peer_count++;
				}

				TORRENT_ASSERT((int)i->peer_count == actual_peer_count);
/*
				int num_downloaders = 0;
				for (std::vector<peer_connection*>::const_iterator peer = t->begin();
					peer != t->end();
					++peer)
				{
					const std::vector<piece_block>& queue = (*peer)->download_queue();
					if (std::find_if(queue.begin(), queue.end(), has_index(index)) == queue.end()) continue;

					++num_downloaders;
				}

				if (i->downloading)
				{
					TORRENT_ASSERT(num_downloaders == 1);
				}
				else
				{
					TORRENT_ASSERT(num_downloaders == 0);
				}
*/
			}
#endif

			if (i->index == piece_pos::we_have_index)
			{
				TORRENT_ASSERT(t == 0 || t->have_piece(index));
				TORRENT_ASSERT(i->downloading == 0);
/*
				// make sure there's no entry
				// with this index. (there shouldn't
				// be since the piece_map is piece_pos::we_have_index)
				for (int i = 0; i < int(m_piece_info.size()); ++i)
				{
					for (int j = 0; j < int(m_piece_info[i].size()); ++j)
					{
						TORRENT_ASSERT(m_piece_info[i][j] != index);
					}
				}
*/
			}
			else
			{
				if (t != 0)
					TORRENT_ASSERT(!t->have_piece(index));

				int prio = i->priority(m_sequenced_download_threshold);
				TORRENT_ASSERT(prio < int(m_piece_info.size()));
				if (prio > 0)
				{
					const std::vector<int>& vec = m_piece_info[prio];
					assert (i->index < vec.size());
					TORRENT_ASSERT(vec[i->index] == index);
				}
/*
				for (int k = 0; k < int(m_piece_info.size()); ++k)
				{
					for (int j = 0; j < int(m_piece_info[k].size()); ++j)
					{
						TORRENT_ASSERT(int(m_piece_info[k][j]) != index
							|| (prio > 0 && prio == k && int(i->index) == j));
					}
				}
*/
			}

			int count = std::count_if(m_downloads.begin(), m_downloads.end()
				, has_index(index));
			if (i->downloading == 1)
			{
				TORRENT_ASSERT(count == 1);
			}
			else
			{
				TORRENT_ASSERT(count == 0);
			}
		}
		TORRENT_ASSERT(num_have == m_num_have);
		TORRENT_ASSERT(num_filtered == m_num_filtered);
		TORRENT_ASSERT(num_have_filtered == m_num_have_filtered);
	}
#endif

	float piece_picker::distributed_copies() const
	{
		const float num_pieces = static_cast<float>(m_piece_map.size());

		int min_availability = piece_pos::max_peer_count;
		// find the lowest availability count
		// count the number of pieces that have that availability
		// and also the number of pieces that have more than that.
		int integer_part = 0;
		int fraction_part = 0;
		for (std::vector<piece_pos>::const_iterator i = m_piece_map.begin()
			, end(m_piece_map.end()); i != end; ++i)
		{
			int peer_count = int(i->peer_count);
			// take ourself into account
			if (i->have()) ++peer_count;
			if (min_availability > peer_count)
			{
				min_availability = peer_count;
				fraction_part += integer_part;
				integer_part = 1;
			}
			else if (peer_count == min_availability)
			{
				++integer_part;
			}
			else
			{
				TORRENT_ASSERT(peer_count > min_availability);
				++fraction_part;
			}
		}
		TORRENT_ASSERT(integer_part + fraction_part == num_pieces);
		return float(min_availability) + (fraction_part / num_pieces);
	}

	void piece_picker::add(int index)
	{
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < int(m_piece_map.size()));
		piece_pos& p = m_piece_map[index];
		TORRENT_ASSERT(!p.filtered());
		TORRENT_ASSERT(!p.have());

		int priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(priority > 0);
		if (int(m_piece_info.size()) <= priority)
			m_piece_info.resize(priority + 1);

		TORRENT_ASSERT(int(m_piece_info.size()) > priority);

		if (is_ordered(priority))
		{
			// the piece should be inserted ordered, not randomly
			std::vector<int>& v = m_piece_info[priority];
//			TORRENT_ASSERT(is_sorted(v.begin(), v.end()/*, std::greater<int>()*/));
			std::vector<int>::iterator i = std::lower_bound(v.begin(), v.end()
				, index/*, std::greater<int>()*/);
			p.index = i - v.begin();
			v.insert(i, index);
			i = v.begin() + p.index + 1;
			for (;i != v.end(); ++i)
			{
				++m_piece_map[*i].index;
				TORRENT_ASSERT(v[m_piece_map[*i].index] == *i);
			}
//			TORRENT_ASSERT(is_sorted(v.begin(), v.end()/*, std::greater<int>()*/));
		}
		else if (m_piece_info[priority].size() < 2)
		{
			p.index = m_piece_info[priority].size();
			m_piece_info[priority].push_back(index);
		}
		else
		{
			// find a random position in the destination vector where we will place
			// this entry.
			int dst_index = rand() % m_piece_info[priority].size();
			
			// copy the entry at that position to the back
			m_piece_map[m_piece_info[priority][dst_index]].index
				= m_piece_info[priority].size();
			m_piece_info[priority].push_back(m_piece_info[priority][dst_index]);

			// and then replace the one at dst_index with the one we're moving.
			// this procedure is to make sure there's no ordering when pieces
			// are moved in sequenced order.
			p.index = dst_index;
			m_piece_info[priority][p.index] = index;
		}
	}

	// will update the piece with the given properties (priority, elem_index)
	// to place it at the correct position in the vectors.
	void piece_picker::move(int priority, int elem_index)
	{
		TORRENT_ASSERT(priority > 0);
		TORRENT_ASSERT(elem_index >= 0);
		TORRENT_ASSERT(m_files_checked_called);

		TORRENT_ASSERT(int(m_piece_info.size()) > priority);
		TORRENT_ASSERT(int(m_piece_info[priority].size()) > elem_index);

		int index = m_piece_info[priority][elem_index];
		// update the piece_map
		piece_pos& p = m_piece_map[index];
		TORRENT_ASSERT(int(p.index) == elem_index || p.have());		

		int new_priority = p.priority(m_sequenced_download_threshold);

		if (new_priority == priority) return;

		if (int(m_piece_info.size()) <= new_priority
			&& new_priority > 0)
		{
			m_piece_info.resize(new_priority + 1);
			TORRENT_ASSERT(int(m_piece_info.size()) > new_priority);
		}

		if (new_priority == 0)
		{
			// this means the piece should not have an entry
		}
		else if (is_ordered(new_priority))
		{
			// the piece should be inserted ordered, not randomly
			std::vector<int>& v = m_piece_info[new_priority];
//			TORRENT_ASSERT(is_sorted(v.begin(), v.end()/*, std::greater<int>()*/));
			std::vector<int>::iterator i = std::lower_bound(v.begin(), v.end()
				, index/*, std::greater<int>()*/);
			p.index = i - v.begin();
			v.insert(i, index);
			i = v.begin() + p.index + 1;
			for (;i != v.end(); ++i)
			{
				++m_piece_map[*i].index;
				TORRENT_ASSERT(v[m_piece_map[*i].index] == *i);
			}
//			TORRENT_ASSERT(is_sorted(v.begin(), v.end()/*, std::greater<int>()*/));
		}
		else if (m_piece_info[new_priority].size() < 2)
		{
			p.index = m_piece_info[new_priority].size();
			m_piece_info[new_priority].push_back(index);
		}
		else
		{
			// find a random position in the destination vector where we will place
			// this entry.
			int dst_index = rand() % m_piece_info[new_priority].size();
			
			// copy the entry at that position to the back
			m_piece_map[m_piece_info[new_priority][dst_index]].index
				= m_piece_info[new_priority].size();
			m_piece_info[new_priority].push_back(m_piece_info[new_priority][dst_index]);

			// and then replace the one at dst_index with the one we're moving.
			// this procedure is to make sure there's no ordering when pieces
			// are moved in sequenced order.
			p.index = dst_index;
			m_piece_info[new_priority][p.index] = index;
		}
		TORRENT_ASSERT(new_priority == 0 || p.index < m_piece_info[p.priority(m_sequenced_download_threshold)].size());
		TORRENT_ASSERT(new_priority == 0 || m_piece_info[p.priority(m_sequenced_download_threshold)][p.index] == index);

		if (is_ordered(priority))
		{
			// remove the element from the source vector and preserve the order
			std::vector<int>& v = m_piece_info[priority];
			v.erase(v.begin() + elem_index);
			for (std::vector<int>::iterator i = v.begin() + elem_index;
				i != v.end(); ++i)
			{
				--m_piece_map[*i].index;
				TORRENT_ASSERT(v[m_piece_map[*i].index] == *i);
			}
		}
		else
		{
			// this will remove elem from the source vector without
			// preserving order, but the order is random anyway
			int replace_index = m_piece_info[priority][elem_index] = m_piece_info[priority].back();
			if (index != replace_index)
			{
				// update the entry we moved from the back
				m_piece_map[replace_index].index = elem_index;

				TORRENT_ASSERT(int(m_piece_info[priority].size()) > elem_index);
				// this may not necessarily be the case. If we've just updated the threshold and are updating
				// the piece map
//				TORRENT_ASSERT((int)m_piece_map[replace_index].priority(m_sequenced_download_threshold) == priority);
				TORRENT_ASSERT(int(m_piece_map[replace_index].index) == elem_index);
				TORRENT_ASSERT(m_piece_info[priority][elem_index] == replace_index);
			}
			else
			{
				TORRENT_ASSERT(int(m_piece_info[priority].size()) == elem_index+1);
			}

			m_piece_info[priority].pop_back();
		}
	}

	void piece_picker::sort_piece(std::vector<downloading_piece>::iterator dp)
	{
		TORRENT_ASSERT(m_piece_map[dp->index].downloading);
		if (dp == m_downloads.begin()) return;
		int complete = dp->writing + dp->finished;
		for (std::vector<downloading_piece>::iterator i = dp, j(dp-1);
			i != m_downloads.begin(); --i, --j)
		{
			TORRENT_ASSERT(j >= m_downloads.begin());
			if (j->finished + j->writing >= complete) return;
			using std::swap;
			swap(*j, *i);
			if (j == m_downloads.begin()) break;
		}
	}

	void piece_picker::restore_piece(int index)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < (int)m_piece_map.size());
		TORRENT_ASSERT(m_files_checked_called);

		TORRENT_ASSERT(m_piece_map[index].downloading == 1);

		std::vector<downloading_piece>::iterator i
			= std::find_if(m_downloads.begin(),
			m_downloads.end(),
			has_index(index));
		TORRENT_ASSERT(i != m_downloads.end());
		erase_download_piece(i);

		piece_pos& p = m_piece_map[index];
		int prev_priority = p.priority(m_sequenced_download_threshold);
		p.downloading = 0;
		int new_priority = p.priority(m_sequenced_download_threshold);

		if (new_priority == prev_priority) return;

		if (prev_priority == 0)
		{
			add(index);
		}
		else
		{
			move(prev_priority, p.index);
		}
	}

	void piece_picker::inc_refcount_all()
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(m_files_checked_called);
		
		// in general priority = availability * 2
		// see piece_block::priority()
		
		// this will insert two empty vectors at the start of the
		// piece_info vector. It is done like this as an optimization,
		// to swap vectors instead of copying them
		while (m_piece_info.size() < 3
			|| (!m_piece_info.rbegin()->empty())
			|| (!(m_piece_info.rbegin()+1)->empty()))
		{
			m_piece_info.push_back(std::vector<int>());
		}
		TORRENT_ASSERT(m_piece_info.rbegin()->empty());
		TORRENT_ASSERT((m_piece_info.rbegin()+1)->empty());
		typedef std::vector<std::vector<int> > piece_info_t;
		for (piece_info_t::reverse_iterator i = m_piece_info.rbegin(), j(i+1)
			, k(j+1), end(m_piece_info.rend()); k != end; ++i, ++j, ++k)
		{
			k->swap(*i);
		}
		TORRENT_ASSERT(m_piece_info.begin()->empty());
		TORRENT_ASSERT((m_piece_info.begin()+1)->empty());

		// if we have some priorities that are clamped to the
		// sequenced download, move that vector back down
		int last_index = m_piece_info.size() - 1;
		int cap_index = m_sequenced_download_threshold * 2;
		if (last_index == cap_index)
		{
			// this is the case when the top bucket
			// was moved up into the sequenced download bucket.
			m_piece_info.push_back(std::vector<int>());
			m_piece_info[cap_index].swap(m_piece_info[cap_index+1]);
			++last_index;
		}
		else if (last_index > cap_index)
		{
			if (last_index - cap_index == 1)
			{
				m_piece_info.push_back(std::vector<int>());
				++last_index;
			}
			m_piece_info[cap_index+1].swap(m_piece_info[cap_index+2]);
			m_piece_info[cap_index].swap(m_piece_info[cap_index+1]);
		}
		
		// now, increase the peer count of all the pieces.
		// because of different priorities, some pieces may have
		// ended up in the wrong priority bucket. Adjust that.
		for (std::vector<piece_pos>::iterator i = m_piece_map.begin()
			, end(m_piece_map.end()); i != end; ++i)
		{
			int prev_prio = i->priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(prev_prio < int(m_piece_info.size()));
			++i->peer_count;
			// if the assumption that the priority would
			// increase by 2 when increasing the availability
			// by one isn't true for this particular piece, correct it.
			// that assumption is true for all pieces with priority 0 or 1
			int new_prio = i->priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(new_prio <= cap_index);
			if (prev_prio == 0 && new_prio > 0)
			{
				add(i - m_piece_map.begin());
				continue;
			}
			if (new_prio == 0)
			{
				TORRENT_ASSERT(prev_prio == 0);
				continue;
			}
			if (prev_prio == cap_index)
			{
				TORRENT_ASSERT(new_prio == cap_index);
				continue;
			}
			if (new_prio == prev_prio + 2 && new_prio != cap_index)
			{
				TORRENT_ASSERT(new_prio != cap_index);
				continue;
			}
			if (prev_prio + 2 >= cap_index)
			{
				// these two vectors will have moved one extra step
				// passed the sequenced download threshold
				++prev_prio;
			}
			TORRENT_ASSERT(prev_prio + 2 != cap_index);
			TORRENT_ASSERT(prev_prio + 2 != new_prio);
			move(prev_prio + 2, i->index);
		}
	}

	void piece_picker::dec_refcount_all()
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(m_files_checked_called);
		TORRENT_ASSERT(m_piece_info.size() >= 2);
		TORRENT_ASSERT(m_piece_info.front().empty());
		// swap all vectors two steps down
		if (m_piece_info.size() > 2)
		{
			typedef std::vector<std::vector<int> > piece_info_t;
			for (piece_info_t::iterator i = m_piece_info.begin(), j(i+1)
				, k(j+1), end(m_piece_info.end()); k != end; ++i, ++j, ++k)
			{
				k->swap(*i);
			}
		}
		else
		{
			m_piece_info.resize(3);
		}
		int last_index = m_piece_info.size() - 1;
		if ((m_piece_info.size() & 1) == 0)
		{
			// if there's an even number of vectors, swap
			// the last two to get the same layout in both cases
			m_piece_info[last_index].swap(m_piece_info[last_index-1]);
		}
		TORRENT_ASSERT(m_piece_info.back().empty());
		int pushed_out_index = m_piece_info.size() - 2;

		int cap_index = m_sequenced_download_threshold * 2;
		TORRENT_ASSERT(m_piece_info[last_index].empty());
		if (last_index >= cap_index)
		{
			TORRENT_ASSERT(pushed_out_index == cap_index - 1
				|| m_piece_info[cap_index - 1].empty());
			m_piece_info[cap_index].swap(m_piece_info[cap_index - 2]);
			if (cap_index == pushed_out_index)
				pushed_out_index = cap_index - 2;
		}
		
		// first is the vector that were
		// bumped down to 0. The should always be moved
		// since they have to be removed or reinserted
		std::vector<int>().swap(m_piece_info.front());

		for (std::vector<piece_pos>::iterator i = m_piece_map.begin()
			, end(m_piece_map.end()); i != end; ++i)
		{
			int prev_prio = i->priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(prev_prio < int(m_piece_info.size()));
			TORRENT_ASSERT(pushed_out_index < int(m_piece_info.size()));
			TORRENT_ASSERT(i->peer_count > 0);
			--i->peer_count;
			// if the assumption that the priority would
			// decrease by 2 when decreasing the availability
			// by one isn't true for this particular piece, correct it.
			// that assumption is true for all pieces with priority 0 or 1
			if (prev_prio == 0)
			{
				TORRENT_ASSERT(i->priority(m_sequenced_download_threshold) == 0);
				continue;
			}

			int new_prio = i->priority(m_sequenced_download_threshold);
			if (prev_prio == cap_index)
			{
				if (new_prio == cap_index) continue;
				prev_prio += 2;
			}
			else if (new_prio == prev_prio - 2)
			{
				continue;
			}
			else if (prev_prio == 2)
			{
				// if this piece was pushed down to priority 0, it was
				// removed
				TORRENT_ASSERT(new_prio > 0);
				add(i - m_piece_map.begin());
				continue;
			}
			else if (prev_prio == 1)
			{
				// if this piece was one of the vectors that was pushed to the
				// top, adjust the prev_prio to point to that vector, so that
				// the pieces are moved from there
				prev_prio = pushed_out_index + 2;
			}
			move(prev_prio - 2, i->index);
		}
	}

	void piece_picker::inc_refcount(int i)
	{
//		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(i >= 0);
		TORRENT_ASSERT(i < (int)m_piece_map.size());
		TORRENT_ASSERT(m_files_checked_called);

		piece_pos& p = m_piece_map[i];
		int index = p.index;
		int prev_priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(prev_priority < int(m_piece_info.size()));

		TORRENT_ASSERT(p.peer_count < piece_pos::max_peer_count);
		p.peer_count++;
		TORRENT_ASSERT(p.peer_count != 0);	

		// if we have the piece or if it's filtered
		// we don't have to move any entries in the piece_info vector
		if (p.priority(m_sequenced_download_threshold) == prev_priority) return;

		if (prev_priority == 0)
		{
			add(i);
		}
		else
		{
			move(prev_priority, index);
		}

#ifndef NDEBUG
//		integrity_check();
#endif
		return;
	}

	void piece_picker::dec_refcount(int i)
	{
//		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		TORRENT_ASSERT(m_files_checked_called);
		TORRENT_ASSERT(i >= 0);
		TORRENT_ASSERT(i < (int)m_piece_map.size());

		piece_pos& p = m_piece_map[i];
		int prev_priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(prev_priority < int(m_piece_info.size()));
		int index = p.index;
		TORRENT_ASSERT(p.peer_count > 0);

		if (p.peer_count > 0)
			p.peer_count--;

		if (p.priority(m_sequenced_download_threshold) == prev_priority) return;

		move(prev_priority, index);
	}

	// this is used to indicate that we succesfully have
	// downloaded a piece, and that no further attempts
	// to pick that piece should be made. The piece will
	// be removed from the available piece list.
	void piece_picker::we_have(int index)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < (int)m_piece_map.size());

		piece_pos& p = m_piece_map[index];
		int info_index = p.index;
		int priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(priority < int(m_piece_info.size()));

		if (p.downloading)
		{
			std::vector<downloading_piece>::iterator i
				= std::find_if(m_downloads.begin()
				, m_downloads.end()
				, has_index(index));
			TORRENT_ASSERT(i != m_downloads.end());
			erase_download_piece(i);
			p.downloading = 0;
		}

		TORRENT_ASSERT(std::find_if(m_downloads.begin(), m_downloads.end()
			, has_index(index)) == m_downloads.end());

		if (p.have()) return;
		if (p.filtered())
		{
			--m_num_filtered;
			++m_num_have_filtered;
		}
		++m_num_have;
		p.set_have();
		if (priority == 0) return;
		TORRENT_ASSERT(p.priority(m_sequenced_download_threshold) == 0);
		move(priority, info_index);
	}


	bool piece_picker::set_piece_priority(int index, int new_piece_priority)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(new_piece_priority >= 0);
		TORRENT_ASSERT(new_piece_priority <= 7);
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < (int)m_piece_map.size());
		
		piece_pos& p = m_piece_map[index];

		// if the priority isn't changed, don't do anything
		if (new_piece_priority == int(p.piece_priority)) return false;
		
		int prev_priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(prev_priority < int(m_piece_info.size()));

		bool ret = false;
		if (new_piece_priority == piece_pos::filter_priority
			&& p.piece_priority != piece_pos::filter_priority)
		{
			// the piece just got filtered
			if (p.have()) ++m_num_have_filtered;
			else ++m_num_filtered;
			ret = true;
		}
		else if (new_piece_priority != piece_pos::filter_priority
			&& p.piece_priority == piece_pos::filter_priority)
		{
			// the piece just got unfiltered
			if (p.have()) --m_num_have_filtered;
			else --m_num_filtered;
			ret = true;
		}
		TORRENT_ASSERT(m_num_filtered >= 0);
		TORRENT_ASSERT(m_num_have_filtered >= 0);
		
		p.piece_priority = new_piece_priority;
		int new_priority = p.priority(m_sequenced_download_threshold);
		TORRENT_ASSERT(prev_priority < int(m_piece_info.size()));

		if (new_priority == prev_priority) return false;
		
		if (prev_priority == 0)
		{
			add(index);
		}
		else
		{
			move(prev_priority, p.index);
		}
		return ret;
	}

	int piece_picker::piece_priority(int index) const
	{
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < (int)m_piece_map.size());

		return m_piece_map[index].piece_priority;
	}

	void piece_picker::piece_priorities(std::vector<int>& pieces) const
	{
		pieces.resize(m_piece_map.size());
		std::vector<int>::iterator j = pieces.begin();
		for (std::vector<piece_pos>::const_iterator i = m_piece_map.begin(),
			end(m_piece_map.end()); i != end; ++i, ++j)
		{
			*j = i->piece_priority;
		}
	}

	// ============ start deprecation ==============

	void piece_picker::filtered_pieces(std::vector<bool>& mask) const
	{
		mask.resize(m_piece_map.size());
		std::vector<bool>::iterator j = mask.begin();
		for (std::vector<piece_pos>::const_iterator i = m_piece_map.begin(),
			end(m_piece_map.end()); i != end; ++i, ++j)
		{
			*j = i->filtered();
		}
	}

	// ============ end deprecation ==============

	// pieces describes which pieces the peer we're requesting from
	// has.
	// interesting_blocks is an out parameter, and will be filled
	// with (up to) num_blocks of interesting blocks that the peer has.
	// prefer_whole_pieces can be set if this peer should download
	// whole pieces rather than trying to download blocks from the
	// same piece as other peers.
	//	the void* is the pointer to the policy::peer of the peer we're
	// picking pieces from. This is used when downloading whole pieces,
	// to only pick from the same piece the same peer is downloading
	// from. state is supposed to be set to fast if the peer is downloading
	// relatively fast, by some notion. Slow peers will prefer not
	// to pick blocks from the same pieces as fast peers, and vice
	// versa. Downloading pieces are marked as being fast, medium
	// or slow once they're started.
	void piece_picker::pick_pieces(const std::vector<bool>& pieces
		, std::vector<piece_block>& interesting_blocks
		, int num_blocks, int prefer_whole_pieces
		, void* peer, piece_state_t speed, bool rarest_first
		, bool on_parole, std::vector<int> const& suggested_pieces) const
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
		TORRENT_ASSERT(num_blocks > 0);
		TORRENT_ASSERT(pieces.size() == m_piece_map.size());
		TORRENT_ASSERT(m_files_checked_called);

		TORRENT_ASSERT(m_piece_info.begin() != m_piece_info.end());

		// this will be filled with blocks that we should not request
		// unless we can't find num_blocks among the other ones.
		// blocks that belong to pieces with a mismatching speed
		// category for instance, or if we prefer whole pieces,
		// blocks belonging to a piece that others have
		// downloaded to
		std::vector<piece_block> backup_blocks;
		// suggested pieces for each vector is put in this vector
		std::vector<int> suggested_bucket;
		const std::vector<int> empty_vector;
	
		// When prefer_whole_pieces is set (usually set when downloading from
		// fast peers) the partial pieces will not be prioritized, but actually
		// ignored as long as possible. All blocks found in downloading
		// pieces are regarded as backup blocks

		num_blocks = add_blocks_downloading(pieces
			, interesting_blocks, backup_blocks, num_blocks
			, prefer_whole_pieces, peer, speed, on_parole);

		if (num_blocks <= 0) return;

		if (rarest_first)
		{
			// this loop will loop from pieces with priority 1 and up
			// until we either reach the end of the piece list or
			// has filled the interesting_blocks with num_blocks
			// blocks.

			// +1 is to ignore pieces that no peer has. The bucket with index 0 contains
			// pieces that 0 other peers have. bucket will point to a bucket with
			// pieces with the same priority. It will be iterated in priority
			// order (high priority/rare pices first). The content of each
			// bucket is randomized
			for (std::vector<std::vector<int> >::const_iterator bucket
				= m_piece_info.begin() + 1; num_blocks > 0 && bucket != m_piece_info.end();
				++bucket)
			{
				if (bucket->empty()) continue;
				if (!suggested_pieces.empty())
				{
					int bucket_index = bucket - m_piece_info.begin();
					suggested_bucket.clear();
					for (std::vector<int>::const_iterator i = suggested_pieces.begin()
						, end(suggested_pieces.end()); i != end; ++i)
					{
						TORRENT_ASSERT(*i >= 0);
						TORRENT_ASSERT(*i < int(m_piece_map.size()));
						if (!can_pick(*i, pieces)) continue;
						if (m_piece_map[*i].priority(m_sequenced_download_threshold) == bucket_index)
							suggested_bucket.push_back(*i);
					}
					if (!suggested_bucket.empty())
					{
						num_blocks = add_blocks(suggested_bucket, pieces
							, interesting_blocks, num_blocks
							, prefer_whole_pieces, peer, empty_vector);
						if (num_blocks == 0) break;
					}
				}
				num_blocks = add_blocks(*bucket, pieces
					, interesting_blocks, num_blocks
					, prefer_whole_pieces, peer, suggested_bucket);
				TORRENT_ASSERT(num_blocks >= 0);
			}
		}
		else
		{
			// we're not using rarest first (only for the first
			// bucket, since that's where the currently downloading
			// pieces are)
			int start_piece = rand() % m_piece_map.size();

			// if we have suggested pieces, try to find one of those instead
			for (std::vector<int>::const_iterator i = suggested_pieces.begin()
				, end(suggested_pieces.end()); i != end; ++i)
			{
				if (!can_pick(*i, pieces)) continue;
				start_piece = *i;
				break;
			}
			int piece = start_piece;
			while (num_blocks > 0)
			{
				while (!can_pick(piece, pieces))
				{
					++piece;
					if (piece == int(m_piece_map.size())) piece = 0;
					// could not find any more pieces
					if (piece == start_piece) return;
				}

				int start, end;
				boost::tie(start, end) = expand_piece(piece, prefer_whole_pieces, pieces);
				for (int k = start; k < end; ++k)
				{
					TORRENT_ASSERT(m_piece_map[piece].downloading == false);
					TORRENT_ASSERT(m_piece_map[k].priority(m_sequenced_download_threshold) > 0);
					int num_blocks_in_piece = blocks_in_piece(k);
					if (prefer_whole_pieces == 0 && num_blocks_in_piece > num_blocks)
						num_blocks_in_piece = num_blocks;
					for (int j = 0; j < num_blocks_in_piece; ++j)
					{
						interesting_blocks.push_back(piece_block(k, j));
						--num_blocks;
					}
				}
				piece = end;
				if (piece == int(m_piece_map.size())) piece = 0;
				// could not find any more pieces
				if (piece == start_piece) return;
			}
		
		}

		if (num_blocks <= 0) return;

		if (!backup_blocks.empty())
			interesting_blocks.insert(interesting_blocks.end()
				, backup_blocks.begin(), backup_blocks.end());
	}

	bool piece_picker::can_pick(int piece, std::vector<bool> const& bitmask) const
	{
		TORRENT_ASSERT(piece >= 0 && piece < int(m_piece_map.size()));
		return bitmask[piece]
			&& !m_piece_map[piece].have()
			&& !m_piece_map[piece].downloading
			&& !m_piece_map[piece].filtered();
	}

	void piece_picker::clear_peer(void* peer)
	{
		for (std::vector<block_info>::iterator i = m_block_info.begin()
			, end(m_block_info.end()); i != end; ++i)
			if (i->peer == peer) i->peer = 0;
	}

	namespace
	{
		// the first bool is true if this is the only peer that has requested and downloaded
		// blocks from this piece.
		// the second bool is true if this is the only active peer that is requesting
		// and downloading blocks from this piece. Active means having a connection.
		boost::tuple<bool, bool> requested_from(piece_picker::downloading_piece const& p
			, int num_blocks_in_piece, void* peer)
		{
			bool exclusive = true;
			bool exclusive_active = true;
			for (int j = 0; j < num_blocks_in_piece; ++j)
			{
				piece_picker::block_info const& info = p.info[j];
				if (info.state != piece_picker::block_info::state_none
					&& info.peer != peer)
				{
					exclusive = false;
					if (info.state == piece_picker::block_info::state_requested
						&& info.peer != 0)
					{
						exclusive_active = false;
						return boost::make_tuple(exclusive, exclusive_active);
					}
				}
			}
			return boost::make_tuple(exclusive, exclusive_active);
		}
	}

	int piece_picker::add_blocks(std::vector<int> const& piece_list
		, std::vector<bool> const& pieces
		, std::vector<piece_block>& interesting_blocks
		, int num_blocks, int prefer_whole_pieces
		, void* peer, std::vector<int> const& ignore) const
	{
		for (std::vector<int>::const_iterator i = piece_list.begin();
			i != piece_list.end(); ++i)
		{
			TORRENT_ASSERT(*i >= 0);
			TORRENT_ASSERT(*i < (int)m_piece_map.size());

			// if the peer doesn't have the piece
			// skip it
			if (!pieces[*i]) continue;

			// ignore pieces found in the ignore list
			if (std::find(ignore.begin(), ignore.end(), *i) != ignore.end()) continue;

			// skip the piece is the priority is 0
			TORRENT_ASSERT(m_piece_map[*i].priority(m_sequenced_download_threshold) > 0);

			int num_blocks_in_piece = blocks_in_piece(*i);

			TORRENT_ASSERT(m_piece_map[*i].downloading == 0);
			TORRENT_ASSERT(m_piece_map[*i].priority(m_sequenced_download_threshold) > 0);

			// pick a new piece
			if (prefer_whole_pieces == 0)
			{
				if (num_blocks_in_piece > num_blocks)
					num_blocks_in_piece = num_blocks;
				for (int j = 0; j < num_blocks_in_piece; ++j)
					interesting_blocks.push_back(piece_block(*i, j));
				num_blocks -= num_blocks_in_piece;
			}
			else
			{
				int start, end;
				boost::tie(start, end) = expand_piece(*i, prefer_whole_pieces, pieces);
				for (int k = start; k < end; ++k)
				{
					TORRENT_ASSERT(m_piece_map[k].priority(m_sequenced_download_threshold) > 0);
					num_blocks_in_piece = blocks_in_piece(k);
					for (int j = 0; j < num_blocks_in_piece; ++j)
					{
						interesting_blocks.push_back(piece_block(k, j));
						--num_blocks;
					}
				}
			}
			if (num_blocks <= 0)
			{
#ifndef NDEBUG
				verify_pick(interesting_blocks, pieces);
#endif
				return 0;
			}
		}
#ifndef NDEBUG
		verify_pick(interesting_blocks, pieces);
#endif
		return num_blocks;
	}

	int piece_picker::add_blocks_downloading(std::vector<bool> const& pieces
		, std::vector<piece_block>& interesting_blocks
		, std::vector<piece_block>& backup_blocks
		, int num_blocks, int prefer_whole_pieces
		, void* peer, piece_state_t speed, bool on_parole) const
	{
		for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin()
			, end(m_downloads.end()); i != end; ++i)
		{
			if (!pieces[i->index]) continue;

			int num_blocks_in_piece = blocks_in_piece(i->index);

			// is true if all the other pieces that are currently
			// requested from this piece are from the same
			// peer as 'peer'.
			bool exclusive;
			bool exclusive_active;
			boost::tie(exclusive, exclusive_active)
				= requested_from(*i, num_blocks_in_piece, peer);

			// peers on parole are only allowed to pick blocks from
			// pieces that only they have downloaded/requested from
			if (on_parole && !exclusive) continue;

			if (prefer_whole_pieces > 0 && !exclusive_active) continue;

			// don't pick too many back-up blocks
			if (i->state != none
				&& i->state != speed
				&& !exclusive_active
				&& int(backup_blocks.size()) >= num_blocks)
				continue;

			for (int j = 0; j < num_blocks_in_piece; ++j)
			{
				// ignore completed blocks and already requested blocks
				block_info const& info = i->info[j];
				if (info.state != block_info::state_none)
					continue;

				TORRENT_ASSERT(i->info[j].state == block_info::state_none);

				// if the piece is fast and the peer is slow, or vice versa,
				// add the block as a backup.
				// override this behavior if all the other blocks
				// have been requested from the same peer or
				// if the state of the piece is none (the
				// piece will in that case change state).
				if (i->state != none && i->state != speed
					&& !exclusive_active)
				{
					backup_blocks.push_back(piece_block(i->index, j));
					continue;
				}
				
				// this block is interesting (we don't have it
				// yet).
				interesting_blocks.push_back(piece_block(i->index, j));
				// we have found a block that's free to download
				num_blocks--;
				// if we prefer whole pieces, continue picking from this
				// piece even though we have num_blocks
				if (prefer_whole_pieces > 0) continue;
				TORRENT_ASSERT(num_blocks >= 0);
				if (num_blocks <= 0) break;
			}
			if (num_blocks <= 0) break;
		}
	
		TORRENT_ASSERT(num_blocks >= 0 || prefer_whole_pieces > 0);

#ifndef NDEBUG
		verify_pick(interesting_blocks, pieces);
		verify_pick(backup_blocks, pieces);
#endif

		if (num_blocks <= 0) return 0;
		if (on_parole) return num_blocks;

		int to_copy;
		if (prefer_whole_pieces == 0)
			to_copy = (std::min)(int(backup_blocks.size()), num_blocks);
		else
			to_copy = int(backup_blocks.size());

		interesting_blocks.insert(interesting_blocks.end()
			, backup_blocks.begin(), backup_blocks.begin() + to_copy);
		num_blocks -= to_copy;
		backup_blocks.clear();

		if (num_blocks <= 0) return 0;

		if (prefer_whole_pieces > 0)
		{
			for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin()
				, end(m_downloads.end()); i != end; ++i)
			{
				if (!pieces[i->index]) continue;
				int num_blocks_in_piece = blocks_in_piece(i->index);
				bool exclusive;
				bool exclusive_active;
				boost::tie(exclusive, exclusive_active)
					= requested_from(*i, num_blocks_in_piece, peer);

				if (exclusive_active) continue;
				
				for (int j = 0; j < num_blocks_in_piece; ++j)
				{
					block_info const& info = i->info[j];
					if (info.state != block_info::state_none) continue;
					backup_blocks.push_back(piece_block(i->index, j));
				}
			}
		}

		if (int(backup_blocks.size()) >= num_blocks) return num_blocks;


#ifndef NDEBUG
//		make sure that we at this point has added requests to all unrequested blocks
//		in all downloading pieces

		for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin()
			, end(m_downloads.end()); i != end; ++i)
		{
			if (!pieces[i->index]) continue;
				
			int num_blocks_in_piece = blocks_in_piece(i->index);
			for (int j = 0; j < num_blocks_in_piece; ++j)
			{
				block_info const& info = i->info[j];
				if (info.state != block_info::state_none) continue;
				std::vector<piece_block>::iterator k = std::find(
					interesting_blocks.begin(), interesting_blocks.end()
					, piece_block(i->index, j));
				if (k != interesting_blocks.end()) continue;
				
				k = std::find(backup_blocks.begin()
					, backup_blocks.end(), piece_block(i->index, j));
				if (k != backup_blocks.end()) continue;

				std::cerr << "interesting blocks:" << std::endl;
				for (k = interesting_blocks.begin(); k != interesting_blocks.end(); ++k)
					std::cerr << "(" << k->piece_index << ", " << k->block_index << ") ";
				std::cerr << std::endl;
				std::cerr << "backup blocks:" << std::endl;
				for (k = backup_blocks.begin(); k != backup_blocks.end(); ++k)
					std::cerr << "(" << k->piece_index << ", " << k->block_index << ") ";
				std::cerr << std::endl;
				std::cerr << "num_blocks: " << num_blocks << std::endl;
				
				for (std::vector<downloading_piece>::const_iterator l = m_downloads.begin()
					, end(m_downloads.end()); l != end; ++l)
				{
					std::cerr << l->index << " : ";
					int num_blocks_in_piece = blocks_in_piece(l->index);
					for (int m = 0; m < num_blocks_in_piece; ++m)
						std::cerr << l->info[m].state;
					std::cerr << std::endl;
				}

				TORRENT_ASSERT(false);
			}
		}
#endif

		for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin()
			, end(m_downloads.end()); i != end; ++i)
		{
			if (!pieces[i->index]) continue;

			int num_blocks_in_piece = blocks_in_piece(i->index);

			// fill in with blocks requested from other peers
			// as backups
			for (int j = 0; j < num_blocks_in_piece; ++j)
			{
				block_info const& info = i->info[j];
				if (info.state != block_info::state_requested
					|| info.peer == peer)
					continue;
				backup_blocks.push_back(piece_block(i->index, j));
			}
		}
#ifndef NDEBUG
		verify_pick(backup_blocks, pieces);
#endif
		return num_blocks;
	}
	
	std::pair<int, int> piece_picker::expand_piece(int piece, int whole_pieces
		, std::vector<bool> const& have) const
	{
		if (whole_pieces == 0) return std::make_pair(piece, piece + 1);

		int start = piece - 1;
		int lower_limit = piece - whole_pieces;
		if (lower_limit < -1) lower_limit = -1;
		while (start > lower_limit
			&& can_pick(start, have))
			--start;
		++start;
		TORRENT_ASSERT(start >= 0);
		int end = piece + 1;
		int upper_limit = start + whole_pieces;
		if (upper_limit > int(m_piece_map.size())) upper_limit = int(m_piece_map.size());
		while (end < upper_limit
			&& can_pick(end, have))
			++end;
		return std::make_pair(start, end);
	}

	bool piece_picker::is_piece_finished(int index) const
	{
		TORRENT_ASSERT(index < (int)m_piece_map.size());
		TORRENT_ASSERT(index >= 0);

		if (m_piece_map[index].downloading == 0)
		{
			TORRENT_ASSERT(std::find_if(m_downloads.begin(), m_downloads.end()
				, has_index(index)) == m_downloads.end());
			return false;
		}
		std::vector<downloading_piece>::const_iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(index));
		TORRENT_ASSERT(i != m_downloads.end());
		TORRENT_ASSERT((int)i->finished <= m_blocks_per_piece);
		int max_blocks = blocks_in_piece(index);
		if ((int)i->finished < max_blocks) return false;

#ifndef NDEBUG
		for (int k = 0; k < max_blocks; ++k)
		{
			TORRENT_ASSERT(i->info[k].state == block_info::state_finished);
		}
#endif

		TORRENT_ASSERT((int)i->finished == max_blocks);
		return true;
	}

	bool piece_picker::is_requested(piece_block block) const
	{
		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());

		if (m_piece_map[block.piece_index].downloading == 0) return false;
		std::vector<downloading_piece>::const_iterator i
			= std::find_if(
				m_downloads.begin()
				, m_downloads.end()
				, has_index(block.piece_index));

		TORRENT_ASSERT(i != m_downloads.end());
		return i->info[block.block_index].state == block_info::state_requested;
	}

	bool piece_picker::is_downloaded(piece_block block) const
	{
		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());

		if (m_piece_map[block.piece_index].index == piece_pos::we_have_index) return true;
		if (m_piece_map[block.piece_index].downloading == 0) return false;
		std::vector<downloading_piece>::const_iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
		TORRENT_ASSERT(i != m_downloads.end());
		return i->info[block.block_index].state == block_info::state_finished
			|| i->info[block.block_index].state == block_info::state_writing;
	}

	bool piece_picker::is_finished(piece_block block) const
	{
		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());

		if (m_piece_map[block.piece_index].index == piece_pos::we_have_index) return true;
		if (m_piece_map[block.piece_index].downloading == 0) return false;
		std::vector<downloading_piece>::const_iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
		TORRENT_ASSERT(i != m_downloads.end());
		return i->info[block.block_index].state == block_info::state_finished;
	}


	bool piece_picker::mark_as_downloading(piece_block block
		, void* peer, piece_state_t state)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());
		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));
		TORRENT_ASSERT(!m_piece_map[block.piece_index].have());

		piece_pos& p = m_piece_map[block.piece_index];
		if (p.downloading == 0)
		{
			int prio = p.priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(prio < int(m_piece_info.size()));
			TORRENT_ASSERT(prio > 0);
			p.downloading = 1;
			move(prio, p.index);

			downloading_piece& dp = add_download_piece();
			dp.state = state;
			dp.index = block.piece_index;
			block_info& info = dp.info[block.block_index];
			info.state = block_info::state_requested;
			info.peer = peer;
			info.num_peers = 1;
			++dp.requested;
		}
		else
		{
			std::vector<downloading_piece>::iterator i
				= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
			TORRENT_ASSERT(i != m_downloads.end());
			block_info& info = i->info[block.block_index];
			if (info.state == block_info::state_writing
				|| info.state == block_info::state_finished)
				return false;
			TORRENT_ASSERT(info.state == block_info::state_none
				|| (info.state == block_info::state_requested
					&& (info.num_peers > 0)));
			info.peer = peer;
			if (info.state != block_info::state_requested)
			{
				info.state = block_info::state_requested;
				++i->requested;
			}
			++info.num_peers;
			if (i->state == none) i->state = state;
		}
		return true;
	}

	int piece_picker::num_peers(piece_block block) const
	{
		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());
		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));

		piece_pos const& p = m_piece_map[block.piece_index];
		if (!p.downloading) return 0;

		std::vector<downloading_piece>::const_iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
		TORRENT_ASSERT(i != m_downloads.end());

		block_info const& info = i->info[block.block_index];
		return info.num_peers;
	}
	
	void piece_picker::get_availability(std::vector<int>& avail) const
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;
	
		avail.resize(m_piece_map.size());
		std::vector<int>::iterator j = avail.begin();
		for (std::vector<piece_pos>::const_iterator i = m_piece_map.begin()
			, end(m_piece_map.end()); i != end; ++i, ++j)
			*j = i->peer_count;
	}

	void piece_picker::mark_as_writing(piece_block block, void* peer)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());
		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));

		// this might be the case if a piece fails, is restored, and then
		// completed from a different peer (from which the piece was requested
		// before it failed the hash check)

		TORRENT_ASSERT(m_piece_map[block.piece_index].downloading);

		std::vector<downloading_piece>::iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
		TORRENT_ASSERT(i != m_downloads.end());
		block_info& info = i->info[block.block_index];

		info.peer = peer;
		TORRENT_ASSERT(info.state == block_info::state_requested);
		if (info.state == block_info::state_requested) --i->requested;
		TORRENT_ASSERT(i->requested >= 0);
		TORRENT_ASSERT(info.state != block_info::state_writing);
		++i->writing;
		info.state = block_info::state_writing;
		if (info.num_peers > 0) --info.num_peers;

		if (i->requested == 0)
		{
			// there are no blocks requested in this piece.
			// remove the fast/slow state from it
			i->state = none;
		}
		sort_piece(i);
	}
	
	void piece_picker::mark_as_finished(piece_block block, void* peer)
	{
		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());
		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));

		piece_pos& p = m_piece_map[block.piece_index];

		if (p.downloading == 0)
		{
			TORRENT_PIECE_PICKER_INVARIANT_CHECK;
			
			TORRENT_ASSERT(peer == 0);
			int prio = p.priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(prio < int(m_piece_info.size()));
			p.downloading = 1;
			if (prio > 0) move(prio, p.index);
			else TORRENT_ASSERT(p.priority(m_sequenced_download_threshold) == 0);

			downloading_piece& dp = add_download_piece();
			dp.state = none;
			dp.index = block.piece_index;
			block_info& info = dp.info[block.block_index];
			info.peer = peer;
			TORRENT_ASSERT(info.state == block_info::state_none);
			if (info.state != block_info::state_finished)
			{
				++dp.finished;
				sort_piece(m_downloads.end() - 1);
			}
			info.state = block_info::state_finished;
		}
		else
		{
			TORRENT_PIECE_PICKER_INVARIANT_CHECK;
			
			std::vector<downloading_piece>::iterator i
				= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(block.piece_index));
			TORRENT_ASSERT(i != m_downloads.end());
			block_info& info = i->info[block.block_index];
			info.peer = peer;
			TORRENT_ASSERT(info.state == block_info::state_writing
				|| peer == 0);
			TORRENT_ASSERT(i->writing >= 0);
			++i->finished;
			if (info.state == block_info::state_writing)
			{
				--i->writing;
				info.state = block_info::state_finished;
			}
			else
			{
				info.state = block_info::state_finished;
				sort_piece(i);
			}
		}
	}

	void piece_picker::get_downloaders(std::vector<void*>& d, int index) const
	{
		TORRENT_ASSERT(index >= 0 && index <= (int)m_piece_map.size());
		std::vector<downloading_piece>::const_iterator i
			= std::find_if(m_downloads.begin(), m_downloads.end(), has_index(index));
		TORRENT_ASSERT(i != m_downloads.end());

		d.clear();
		for (int j = 0; j < blocks_in_piece(index); ++j)
		{
			d.push_back(i->info[j].peer);
		}
	}

	void* piece_picker::get_downloader(piece_block block) const
	{
		std::vector<downloading_piece>::const_iterator i = std::find_if(
			m_downloads.begin()
			, m_downloads.end()
			, has_index(block.piece_index));

		if (i == m_downloads.end()) return 0;

		TORRENT_ASSERT(block.block_index >= 0);

		if (i->info[block.block_index].state == block_info::state_none)
			return 0;

		return i->info[block.block_index].peer;
	}

	void piece_picker::abort_download(piece_block block)
	{
		TORRENT_PIECE_PICKER_INVARIANT_CHECK;

		TORRENT_ASSERT(block.piece_index >= 0);
		TORRENT_ASSERT(block.block_index >= 0);
		TORRENT_ASSERT(block.piece_index < (int)m_piece_map.size());
		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));

		if (m_piece_map[block.piece_index].downloading == 0)
		{
			TORRENT_ASSERT(std::find_if(m_downloads.begin(), m_downloads.end()
				, has_index(block.piece_index)) == m_downloads.end());
			return;
		}

		std::vector<downloading_piece>::iterator i = std::find_if(m_downloads.begin()
			, m_downloads.end(), has_index(block.piece_index));
		TORRENT_ASSERT(i != m_downloads.end());

		block_info& info = i->info[block.block_index];
		--info.num_peers;
		if (info.num_peers > 0) return;

		if (i->info[block.block_index].state == block_info::state_finished
			|| i->info[block.block_index].state == block_info::state_writing)
		{
			return;
		}

		TORRENT_ASSERT(block.block_index < blocks_in_piece(block.piece_index));
		TORRENT_ASSERT(i->info[block.block_index].state == block_info::state_requested);

		// clear this block as being downloaded
		info.state = block_info::state_none;
		--i->requested;
		
		// clear the downloader of this block
		info.peer = 0;

		// if there are no other blocks in this piece
		// that's being downloaded, remove it from the list
		if (i->requested + i->finished + i->writing == 0)
		{
			erase_download_piece(i);
			piece_pos& p = m_piece_map[block.piece_index];
			int prev_prio = p.priority(m_sequenced_download_threshold);
			TORRENT_ASSERT(prev_prio < int(m_piece_info.size()));
			p.downloading = 0;
			int prio = p.priority(m_sequenced_download_threshold);
			if (prev_prio == 0 && prio > 0) add(block.piece_index);
			else if (prio > 0) move(prio, p.index);

			TORRENT_ASSERT(std::find_if(m_downloads.begin(), m_downloads.end()
				, has_index(block.piece_index)) == m_downloads.end());
		}
		else if (i->requested == 0)
		{
			// there are no blocks requested in this piece.
			// remove the fast/slow state from it
			i->state = none;
		}
	}

	int piece_picker::unverified_blocks() const
	{
		int counter = 0;
		for (std::vector<downloading_piece>::const_iterator i = m_downloads.begin();
			i != m_downloads.end(); ++i)
		{
			counter += (int)i->finished;
		}
		return counter;
	}

}

