distributed_system_coursework/README.md

# Application Coperative "Atomas" Game

The application that this project implements is a coperative version of the game [Atomas](https://play.google.com/store/apps/details?id=com.sirnic.atomas&hl=en&gl=US&pli=1). 
Atomas is a simple single player mobile phone game which allows players to combine atomns to make new attoms with heigher atomic numbers.

The Server application inplements a coperative, and simplified version of this game that allows players to play a game of Atomas in the same board at the same time.

The Server uses Paxos to guanratee that the only user can play at the time and that a player can not make  a move on a diferent game state than another player.

Ther `server.ex` file both provides some `Server` Module that runs this service and a `Client` Module that can be used to display some the game state in the terminal with nicer representation.

# API

The server provides the following API:

```elixir
    {:start_game, participants, pid_to_inform}
    {:get_game_state, game_id, pid_to_inform}
    {:make_move, game_id, move, pid_to_inform}
```

## Important Concepts

The `game_id` is a number and is an identifier for the game, this can be a number because paxos guanratees that the there can not be two games with same number, as the server would have learned about that  decision and whould have not incremented the number.

The `game_state` is a representation of a game state that corresponds to an array of numbers, and some special atoms, where the number represents the atomic number of an atom the max length of this array is 16 when array gets bigger then that the game is over.

## Start Game

The `:start_game` message causes the server to create a new game.

The `:start_game` message takes as arguments `participants` and `pid_to_inform`. 
 - `participants` which is a list of names of the servers that are participating in the game.
 - `pid_to_inform` which is a pid of the process that needs to be informed of the success or failure of this action.

For example to request the start of a game a user might do somethig like:

```elixir
send(server_pid, {:start_game, [:p0, :p1], self()})
# use recieve do to wait for the message

# Or, assuming the server was started with the name :p0

Server.start_game(:p0, [:p0, :p1])
```

The server will answer with:
```
    {:start_game_ans, game_id}
```

This request will always create a new game (with the exception of crashes).


## Get Game State

The `:get_game_state` message causes the server to return the current state of a game.

The `:get_game_state` message takes as arguments `game_id`, and `pid_to_inform`.
 - `game_id` which is the game_id returned by the `:start_game` request
 - `pid_to_inform` which is a pid of the process that needs to be informed of the success or failure of this action.

For example to request the current state of a agame:

```elixir
send(server_pid, {:get_game_state, 1, self()})
# use recieve do to wait for the message

# Or, assuming the server was started with the name :p0

Server.get_game_state(:p0, 1)
```

The server will answer with one of the following:
```elixir
    {:game_state, game_id, :not_playing} # When the player is not playing in the game
    {:game_state, game_id, :game_does_not_exist} # When the game was never created
    {:game_state, game_id, :game_finished, score} # When the game is already over
    {:game_state, game_id, game_state, hand} # When the player is in the game and the game has not finished
                                             # Returns the current game state of the game, 
                                             # and the current "atom" on the hand of the player
```

## Make a move

The `:make_move` message causes the server to try to play the move that the player is requesting.

The `:make_move` message takes as arguments `game_id`, `move`, and `pid_to_inform`.
 - `game_id` which is the game_id returned by the `:start_game` request
 - `move` which is the position in the game state array the play wants to insert their "atom"
 - `pid_to_inform` which is a pid of the process that needs to be informed of the success or failure of this action.

For example to request the current state of a agame:

```elixir
send(server_pid, {:make_move, 1, 3, self()})
# use recieve do to wait for the message

# Or, assuming the server was started with the name :p0

Server.make_move(:p0, 1, 3)
```

The server will answer with one of the following:
```elixir
    {:make_move, game_id, :not_playing} # When the player is not playing in the game
    {:make_move, game_id, :game_does_not_exist} # When the game was never created
    {:make_move, game_id, :game_finished, score} # When the game is already over
    {:make_move, game_id, :invalid_move} # When the move requested by the player is an invalid move
    {:make_move, game_id, :player_moved_before, game_state, hand} # When the player is in the game and the game has not finished,
                                                                  # but another player has played before this request was male
                                                                  # Returns the current game state of the game, 
                                                                  # and the current "atom" on the hand of the player
    {:make_move, game_id, game_state, hand} # When the player is in the game and the game has not finished
                                            # and the move is valid
                                            # Returns the current game state of the game, 
                                            # and the current "atom" on the hand of the player
```

# Properties

- If a game exists then there was a process that create it.
- Eventually all processes would will be in the same game state
- A player cannot make a move in a game state unless it's updated to the last game state
- If two players make a move at the same time for the same game only one of the moves happens and the other player eventually gets notified

# Assumptions

- Processes won't be behave in a byzantine way
- Only a minority of processes can fail
- Will be run in a partial synchronous system

# Usage instructions

There is two ways of interacting with the server via the API or the `Client` Module

## Notes

By default all the logs are disabled to enable all the logs inside the paxos file there is a module variable called `@min_print_level`,
by setting it to 0 it enables all the logs

## API

Start a new iex session and compilie `paxos.ex` and `server.ex`:

```elixir
c "paxos.ex"; c "server.ex"
```

** Paxos needs to be compiled before the server as the server requires macros written in the paxos file **

Now start 3 instances of the server:

```elixir
procs = Enum.to_list(1..3) |> Enum.map(fn x -> :"p#{x}" end)
pids = procs |> Enum.map(fn x -> Server.start(x, procs) end)
```

After the 3 instances have been started you can use Server helper functions to communicate with the Server:

```elixir
Server.start_game(:p1, [:p1, :p2])
Server.get_game_state(:p1, 1)
Server.make_move(:p1, 1, 0)
```

## Using the Client

Open 2 different terminals. One terminal will be the display game and the other will be used to control the game

In the first terminal start an iex session with a session name:
```
iex --sname c1
```

In the second terminal start an iex session with a session name:
```
iex --sname c2
```

On the first terminal connect to the second terminal:
```elixir
# In c1
Node.connect(:"c2@<computer_name>")
```

On both terminals compile paxos and server:
```elixir
# In both run
c "paxos.ex"; c "server.ex"
```

On the first terminal start the servers, create a game and enter display mode:
```elixir
# In c1
procs = Enum.to_list(1..3) |> Enum.map(fn x -> :"p#{x}" end)
pids = procs |> Enum.map(fn x -> Server.start(x, procs) end)

Server.start_game(:p1, [:p1, :p2])
Client.display_game(:p1, 1)
```

You now should see something like:

```
                    0         H

                                    1
           Be
                                       H

         5                               2
                        Be

         Be                            Li


              4                     3


                        Be
```

The Center "Atom" is your hand, while the Letters arround are the game_state or board,
the number represents where you can put the "Atom" in your hand


On the second terminal start enter control mode:
```elixir
# In c2
Client.control_game(:p1, 1)
```

You should see:
```
Type the number you want to play or q to exit:
```

Keep your mouse in the second terminal, and insert the number, where you want to make your move, and hit enter!

The map should update on the top screen and now you can play the game!