Let’s use the “Creating a Tic-Tac-Toe Smart Contract” tutorial and sample contract from the EOS.IO blockchain.
The challenge: Code a contract for a 3x3 tic-tac-toe player vs player game using sruby :-).
Here’s the EOS.IO C++ “monster” in its full glory:
#include <eosiolib/eosio.hpp>
/**
* @defgroup tictactoecontract Tic Tac Toe Contract
* @brief Defines the PvP tic tac toe contract example
* @ingroup examplecontract
*
* @details
* For the following tic-tac-toe game:
* - Each pair of player can have 2 unique game, one where player_1 become host and player_2 become challenger and vice versa
* - The game data is stored in the "host" scope and use the "challenger" as the key
*
* (0,0) coordinate is on the top left corner of the board
* @code
* (0,2)
* (0,0) - | o | x where - = empty cell
* - | x | - x = move by host
* (2,0) x | o | o o = move by challenger
* @endcode
*
* Board is represented with number:
* - 0 represents empty cell
* - 1 represents cell filled by host
* - 2 represents cell filled by challenger
* Therefore, assuming x is host, the above board will have the following representation: [0, 2, 1, 0, 1, 0, 1, 2, 2] inside the game object
*
* In order to deploy this contract:
* - Create an account called tic.tac.toe
* - Add tic.tac.toe key to your wallet
* - Set the contract on the tic.tac.toe account
*
* How to play the game:
* - Create a game using `create` action, with you as the host and other account as the challenger.
* - The first move needs to be done by the host, use the `move` action to make a move by specifying which row and column to fill.
* - Then ask the challenger to make a move, after that it's back to the host turn again, repeat until the winner is determined.
* - If you want to restart the game, use the `restart` action
* - If you want to clear the game from the database to save up some space after the game has ended, use the `close` action
* @{
*/
class tic_tac_toe : public eosio::contract {
public:
tic_tac_toe( account_name self ):contract(self){}
/**
* @brief Information related to a game
* @abi table games i64
*/
struct game {
static const uint16_t board_width = 3;
static const uint16_t board_height = board_width;
game() {
initialize_board();
}
account_name challenger;
account_name host;
account_name turn; // = account name of host/ challenger
account_name winner = N(none); // = none/ draw/ name of host/ name of challenger
std::vector<uint8_t> board;
// Initialize board with empty cell
void initialize_board() {
board = std::vector<uint8_t>(board_width * board_height, 0);
}
// Reset game
void reset_game() {
initialize_board();
turn = host;
winner = N(none);
}
auto primary_key() const { return challenger; }
EOSLIB_SERIALIZE( game, (challenger)(host)(turn)(winner)(board))
};
/**
* @brief The table definition, used to store existing games and their current state
*/
typedef eosio::multi_index< N(games), game> games;
/// @abi action
/// Create a new game
void create(const account_name& challenger, const account_name& host);
/// @abi action
/// Restart a game
/// @param by the account who wants to restart the game
void restart(const account_name& challenger, const account_name& host, const account_name& by);
/// @abi action
/// Close an existing game, and remove it from storage
void close(const account_name& challenger, const account_name& host);
/// @abi action
/// Make movement
/// @param by the account who wants to make the move
void move(const account_name& challenger, const account_name& host, const account_name& by, const uint16_t& row, const uint16_t& column);
};
(Source: EOSIO/eos/contracts/tic_tac_toe/tic_tac_toe.hpp)
#include "tic_tac_toe.hpp"
using namespace eosio;
/**
* @brief Check if cell is empty
* @param cell - value of the cell (should be either 0, 1, or 2)
* @return true if cell is empty
*/
bool is_empty_cell(const uint8_t& cell) {
return cell == 0;
}
/**
* @brief Check for valid movement
* @detail Movement is considered valid if it is inside the board and done on empty cell
* @param row - the row of movement made by the player
* @param column - the column of movement made by the player
* @param board - the board on which the movement is being made
* @return true if movement is valid
*/
bool is_valid_movement(const uint16_t& row, const uint16_t& column, const vector<uint8_t>& board) {
uint16_t board_width = tic_tac_toe::game::board_width;
uint16_t board_height = tic_tac_toe::game::board_height;
uint32_t movement_location = row * board_width + column;
bool is_valid = column < board_width && row < board_height && is_empty_cell(board[movement_location]);
return is_valid;
}
/**
* @brief Get winner of the game
* @detail Winner of the game is the first player who made three consecutive aligned movement
* @param current_game - the game which we want to determine the winner of
* @return winner of the game (can be either none/ draw/ account name of host/ account name of challenger)
*/
account_name get_winner(const tic_tac_toe::game& current_game) {
auto& board = current_game.board;
bool is_board_full = true;
// Use bitwise AND operator to determine the consecutive values of each column, row and diagonal
// Since 3 == 0b11, 2 == 0b10, 1 = 0b01, 0 = 0b00
vector<uint32_t> consecutive_column(tic_tac_toe::game::board_width, 3 );
vector<uint32_t> consecutive_row(tic_tac_toe::game::board_height, 3 );
uint32_t consecutive_diagonal_backslash = 3;
uint32_t consecutive_diagonal_slash = 3;
for (uint32_t i = 0; i < board.size(); i++) {
is_board_full &= !is_empty_cell(board[i]);
uint16_t row = uint16_t(i / tic_tac_toe::game::board_width);
uint16_t column = uint16_t(i % tic_tac_toe::game::board_width);
// Calculate consecutive row and column value
consecutive_row[column] = consecutive_row[column] & board[i];
consecutive_column[row] = consecutive_column[row] & board[i];
// Calculate consecutive diagonal \ value
if (row == column) {
consecutive_diagonal_backslash = consecutive_diagonal_backslash & board[i];
}
// Calculate consecutive diagonal / value
if ( row + column == tic_tac_toe::game::board_width - 1) {
consecutive_diagonal_slash = consecutive_diagonal_slash & board[i];
}
}
// Inspect the value of all consecutive row, column, and diagonal and determine winner
vector<uint32_t> aggregate = { consecutive_diagonal_backslash, consecutive_diagonal_slash };
aggregate.insert(aggregate.end(), consecutive_column.begin(), consecutive_column.end());
aggregate.insert(aggregate.end(), consecutive_row.begin(), consecutive_row.end());
for (auto value: aggregate) {
if (value == 1) {
return current_game.host;
} else if (value == 2) {
return current_game.challenger;
}
}
// Draw if the board is full, otherwise the winner is not determined yet
return is_board_full ? N(draw) : N(none);
}
/**
* @brief Apply create action
*/
void tic_tac_toe::create(const account_name& challenger, const account_name& host) {
require_auth(host);
eosio_assert(challenger != host, "challenger shouldn't be the same as host");
// Check if game already exists
games existing_host_games(_self, host);
auto itr = existing_host_games.find( challenger );
eosio_assert(itr == existing_host_games.end(), "game already exists");
existing_host_games.emplace(host, [&]( auto& g ) {
g.challenger = challenger;
g.host = host;
g.turn = host;
});
}
/**
* @brief Apply restart action
*/
void tic_tac_toe::restart(const account_name& challenger, const account_name& host, const account_name& by) {
require_auth(by);
// Check if game exists
games existing_host_games(_self, host);
auto itr = existing_host_games.find( challenger );
eosio_assert(itr != existing_host_games.end(), "game doesn't exists");
// Check if this game belongs to the action sender
eosio_assert(by == itr->host || by == itr->challenger, "this is not your game!");
// Reset game
existing_host_games.modify(itr, itr->host, []( auto& g ) {
g.reset_game();
});
}
/**
* @brief Apply close action
*/
void tic_tac_toe::close(const account_name& challenger, const account_name& host) {
require_auth(host);
// Check if game exists
games existing_host_games(_self, host);
auto itr = existing_host_games.find( challenger );
eosio_assert(itr != existing_host_games.end(), "game doesn't exists");
// Remove game
existing_host_games.erase(itr);
}
/**
* @brief Apply move action
*/
void tic_tac_toe::move(const account_name& challenger, const account_name& host, const account_name& by, const uint16_t& row, const uint16_t& column ) {
require_auth(by);
// Check if game exists
games existing_host_games(_self, host);
auto itr = existing_host_games.find( challenger );
eosio_assert(itr != existing_host_games.end(), "game doesn't exists");
// Check if this game hasn't ended yet
eosio_assert(itr->winner == N(none), "the game has ended!");
// Check if this game belongs to the action sender
eosio_assert(by == itr->host || by == itr->challenger, "this is not your game!");
// Check if this is the action sender's turn
eosio_assert(by == itr->turn, "it's not your turn yet!");
// Check if user makes a valid movement
eosio_assert(is_valid_movement(row, column, itr->board), "not a valid movement!");
// Fill the cell, 1 for host, 2 for challenger
const uint8_t cell_value = itr->turn == itr->host ? 1 : 2;
const auto turn = itr->turn == itr->host ? itr->challenger : itr->host;
existing_host_games.modify(itr, itr->host, [&]( auto& g ) {
g.board[row * tic_tac_toe::game::board_width + column] = cell_value;
g.turn = turn;
g.winner = get_winner(g);
});
}
EOSIO_ABI( tic_tac_toe, (create)(restart)(close)(move))
(Source: EOSIO/eos/contracts/tic_tac_toe/tic_tac_toe.cpp)
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Happy hacking and (crypto) blockchain contract scripting with sruby.