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#
# lkn.core: an entity-component-system (ecs) implementation for lyxan
# Copyright (C) 2017 Thomas Letan <contact@thomasletan.fr>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program 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 Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
defmodule Lkn.Core.System do
@moduledoc """
A behaviour module for implementing and querying a System.
**Note:** You are not supposed to spawn a System yourself. The
`Lkn.Core.Instance` takes care of that for you. This is why you
will not find any `start*` function here.
The core of this module is the `defsystem/2` macro. It is the
recommended way to implement of System, that is a Process that
handles one aspect of the gameplay. Before we going any further,
lets have a look at a following minimal example.
defsystem Sys do
# 1. Specify which 'Component's are required by this 'System'.
@map Sys.MapSpec
@puppet Sys.PuppetSpec
# 2. Implementation of the 'System' callbacks.
def init_state(_instance_key, _map_key) do
# return some state
end
def puppet_enter(state, _instance_key, _map_key, _puppets, _puppet_key)
# we do nothing, but we could
state
end
def puppet_leave(state, _instance_key, _map_key, _puppets, _puppet_key)
# we do nothing, but we could
state
end
# 3. Define some specific functions
cast func1(a :: integer, b :: boolean) do
# here you can use 'a' and 'b', but also 'state',
# 'puppets', 'map_key' and 'instance_key'
# you have to return the new state value
state
end
end
## Map and Puppet Components
A System handles one facet of the gameplay. Its purpose is to
manipulate the set of “compatible” of Puppets. A System is tied to
two Component Specification Modules (that is two modules defined
with the `Lkn.Core.Component.defcomponent/2` macro). A Component is
a Proxy to manipulate an Entity. It abstracts away its underlying
structure and expose a common interface. See `Lkn.Core.Component` to
learn how to specify then implement a Component.
To define which Component is required for a Map and which one is
required for a Puppet, we use the `@map` and `@puppet` annotations.
## The System Behaviour
The System callbacks can be divided into two categories. The
`init_map/2` function is called only one time to initialize the
inner state of the System. This state implementation is at the
discretion of the developer. The other callbacks are a set of hooks
which are called when a particular event occures.
## The `cast` Keyword
In addition to the System callbacks which are shared by all the
Systems, each System exposes a public interface the Puppeteer can
use to actually play. The function interface are defined using the
`cast` keyword.
You can use the `cast` keyword as follows: `cast
<func_name>([arg_name :: arg_type]*) do <block> end`. Inside the
block, you can use the arguments you have defined. In addition, you
also can use the following variables:
- `state` is the current state of the System, as initialized by
`init_state/2` and modified by the System callbacks and functions
- `instance_key` is the key to identify the Instance which spawns
the system, it can be used to reach its other systems
- `map_key` is the key to identify the map on which the puppets have
been spawned
- `puppets` is a `MapSet` of all the Puppets currently in the
Instance and “compatible” with the System
In addition to this variables, you also can use the `notify/1`
function. It takes a lambda of types `(Lkn.Core.Puppeteer.k ->
any)`. It can be used to reach all the Puppeteers that have
populated the Instance with their Puppets.
The block has to return the new system state.
The `defsystem` will generate a client function to use this
function. In addition to the specified arguments, it takes an
additional one: an Instance key.
"""
use Lkn.Prelude
alias Lkn.Core.Map
alias Lkn.Core.Name
alias Lkn.Core.Puppet
alias Lkn.Core.System
alias Lkn.Core.Instance
@typedoc "A System defined using the `defsystem/2` macro."
@type m :: module
@typedoc "A set of “compatible” puppets."
@type puppets :: MapSet.t(Puppet.t)
defmodule PrivateState do
@moduledoc false
defstruct [
:map_key,
:instance_key,
:puppets,
:state,
]
@type t :: %PrivateState{
map_key: Map.k,
instance_key: Instance.k,
puppets: System.puppets,
state: term,
}
@spec new(Instance.k, Map.k, term) :: t
def new(instance_key, map_key, public) do
%PrivateState{
puppets: MapSet.new(),
instance_key: instance_key,
map_key: map_key,
state: public,
}
end
def update(state, opts) do
st = Keyword.get(opts, :state, state.state)
%PrivateState{state|
state: st
}
end
@spec put(t, Puppet.k) :: t
def put(state, puppet_key) do
puppets = MapSet.put(state.puppets, puppet_key)
%PrivateState{state|
puppets: puppets
}
end
@spec delete(t, Puppet.k) :: t
def delete(state, puppet_key) do
%PrivateState{state|
puppets: MapSet.delete(state.puppets, puppet_key)
}
end
@spec population(t) :: integer
def population(state) do
MapSet.size(state.puppets)
end
@spec notify(t, any) :: :ok
def notify(state, notif) do
Lkn.Core.Instance.notify_puppeteers(state.instance_key, notif)
end
end
@typedoc """
The inner state of the Server process.
"""
@type state :: any
@doc """
Initialize the state of the system.
With the `instance_key`, you can trigger other systems of the same
instance. With the `map_key`, you can request through the Map
Component some information about the map.
"""
@callback init_state(instance_key :: Instance.k, map_key :: Map.k) :: state
@doc """
A hook function which is called when a “compatible” puppet enters the Instance.
"""
@callback puppet_enter(
state :: state,
instance_key :: Instance.k,
map_key :: Map.k,
puppets :: System.puppets,
puppet_key :: Puppet.k) :: term
@doc """
A hook function which is called when a “compatible” puppet leaves the Instance.
"""
@callback puppet_leave(
state :: state,
instance_key :: Instance.k,
map_key :: Map.k,
puppets :: System.puppets,
puppet_key :: Puppet.k) :: term
@doc """
A macro to ease the definition of a new System which provides the
[cast](#module-the-keyword) keyword.
"""
defmacro defsystem(name, do: block) do
alias Lkn.Core.Specs
state_type = quote do Lkn.Core.System.state end
key_type = quote do Lkn.Core.Instance.k end
key_to_name = quote do
&(Lkn.Core.Name.system(&1, unquote(name)))
end
quote do
defmodule unquote(name) do
use Lkn.Prelude
use GenServer
@behaviour Lkn.Core.System
unquote(Specs.gen_server_returns())
unquote(Specs.gen_server_from_specs(
block,
key_type,
key_to_name,
state_type,
key_name: Specs.var_name("instance_key"),
impl_suffix: "_impl",
allow_impl: true,
allow_specs: false,
additional_args: [
quote do unquote(Specs.var_name("map_key")) :: Lkn.Core.Map.k end,
quote do unquote(Specs.var_name("puppets")) :: Lkn.Core.System.puppets end,
],
))
@doc false
@spec component(:puppet|:map) :: module
def component(:puppet) do
@puppet
end
def component(:map) do
@map
end
def init(st) do
{:ok, st}
end
defp priv_handle_cast({:notify, notification}, state) do
PrivateState.notify(state, notification)
{:noreply, state}
end
defp priv_handle_call({:register_puppet, entity_key}, _from, state) do
if Lkn.Core.Entity.has_component?(entity_key, __MODULE__) do
state = PrivateState.put(state, entity_key)
opts = puppet_enter(state.state, state.instance_key, state.map_key, state.puppets, entity_key)
{:reply, true, PrivateState.update(state, opts)}
else
{:reply, false, state}
end
end
defp priv_handle_call({:unregister_puppet, entity_key}, _from, state) do
if Lkn.Core.Entity.has_component?(entity_key, __MODULE__) do
opts = puppet_leave(state.state, state.instance_key, state.map_key, state.puppets, entity_key)
state = PrivateState.delete(state, entity_key)
{:reply, true, PrivateState.update(state, opts)}
else
{:reply, false, state}
end
end
defp priv_handle_call(:population_size, _from, state) do
{:reply, PrivateState.population(state), state}
end
def handle_cast({:priv, cmd}, state) do
priv_handle_cast(cmd, state)
end
def handle_cast({:spec, {name, args}}, state) do
name = String.to_atom(String.replace_suffix(Atom.to_string(name), "", "_impl"))
opts = :erlang.apply(__MODULE__, name, [state.instance_key|args] ++ [state.map_key, state.puppets, state.state])
{:noreply, PrivateState.update(state, opts)}
end
def handle_call({:spec, {name, args}}, _call, state) do
name = String.to_atom(String.replace_suffix(Atom.to_string(name), "", "_impl"))
{res, opts} = :erlang.apply(__MODULE__, name, [state.instance_key|args] ++ [state.map_key, state.puppets, state.state])
{:reply, res, PrivateState.update(state, opts)}
end
def handle_call({:priv, cmd}, from, state) do
priv_handle_call(cmd, from, state)
end
@spec notify(any) :: :ok
defp notify(notification) do
GenServer.cast(self(), {:priv, {:notify, notification}})
end
end
end
end
@doc false
@spec start_link(m, Instance.k, Map.k) :: GenServer.on_start
def start_link(module, instance_key, map_key) do
pub = module.init_state(instance_key, map_key)
GenServer.start_link(
module,
PrivateState.new(instance_key, map_key, pub),
name: Name.system(instance_key, module)
)
end
@doc false
@spec register_puppet(Instance.k, m, Puppet.k) :: boolean
def register_puppet(instance_key, system, puppet_key) do
GenServer.call(Name.system(instance_key, system), {:priv, {:register_puppet, puppet_key}})
end
@doc false
@spec unregister_puppet(Instance.k, m, Puppet.k) :: boolean
def unregister_puppet(instance_key, system, puppet_key) do
GenServer.call(Name.system(instance_key, system), {:priv, {:unregister_puppet, puppet_key}})
end
@doc """
Returns the number of “compatible” Puppets of a given System
registered to a given Instance.
"""
@spec population_size(Instance.k, m) :: integer
def population_size(instance_key, system) do
GenServer.call(Name.system(instance_key, system), {:priv, :population_size})
end
end
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