// Copyright 2018 Google LLC

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

// http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#ifndef CC_GROUP_H_

#define CC_GROUP_H_

#include <cstdint>

#include "cc/constants.h"

#include "cc/inline_vector.h"

namespace minigo {

// GroupId is a unique identifier for a group (string) of stones.

using GroupId = uint16_t;

// Group represents a group (string) of stones.

// A group only keeps track of the count of its current liberties, not their

// location.

struct Group {

Group() = default;

Group(uint16_t size, uint16_t num_liberties)

: size(size), num_liberties(num_liberties) {}

// Maximum number of potential groups on the board.

// Used in various places to pre-allocate buffers.

// TODO(tommadams): We can probably reduce the space reserved for potential

// groups a bit: https://senseis.xmp.net/?MaximumNumberOfLiveGroups

static constexpr int kMaxNumGroups = kN * kN;

uint16_t size = 0;

uint16_t num_liberties = 0;

};

// GroupPool is a simple memory pool for Group objects.

class GroupPool {

public:

// Allocates a new Group with the given size and number of liberties, and

// returns the group's ID.

GroupId alloc(uint16_t size, uint16_t num_liberties) {

GroupId id;

if (!free_ids_.empty()) {

// We have at least one previously acclocated then freed group, return it.

id = free_ids_.back();

free_ids_.pop_back();

groups_[id] = {size, num_liberties};

} else {

// Allocate a new group from the pool.

id = static_cast<GroupId>(groups_.size());

groups_.emplace_back(size, num_liberties);

}

return id;

}

// Free the group, returning it the pool.

void free(GroupId id) { free_ids_.push_back(id); }

// Access the Group object by ID.

Group& operator[](GroupId id) { return groups_[id]; }

const Group& operator[](GroupId id) const { return groups_[id]; }

private:

inline_vector<Group, Group::kMaxNumGroups> groups_;

inline_vector<GroupId, Group::kMaxNumGroups> free_ids_;

};

} // namespace minigo

#endif // CC_GROUP_H_