ecs on lua

--- Just a template for component
function Component_Empty()
    local self = {
        name = "put_unique_name"
        -- properties ...
        }
    return self
end

function Component_Position(_x, _y)
    local self = {
        name = "position",
        x = _x or 0,
        y = _y or 0 }
    return self
end

function Component_Velocity(_vx, _vy)
    local s = {
        name = "velocity",
        vx = _vx or 0,
        vy = _vy or 0 }
    return s
end

-- Systems --

Systems = {}

function Systems.Base()
    local self = {}
    self.name = "base"
    local entities = {}

    function self.subscribe(entity)
        table.insert(entities, entity)
    end

    function self.get_entities()
        return entities
    end

    return self
end

function Systems.Moving()
    local self = Systems.Base()
    self.name = "moving"

    function self.update(dt)
        local entities = self.get_entities()
        for i, e in pairs(entities) do
            local p = e.position
            local v = e.velocity
            p.x = p.x + v.vx * dt
            p.y = p.y + v.vy * dt
        end
    end

    return self
end

function Systems.Handling()
    local self = Systems.Base()
    self.name = "handling"

    function self.update(dt)
        local entities = self.get_entities()
        for i, e in pairs(entities) do
            local v = e.velocity
            v.vx, v.vy = 0, 0
            if      love.keyboard.isDown("up")      then v.vy = -100
            elseif  love.keyboard.isDown("down")    then v.vy = 100
            end
            if      love.keyboard.isDown("right")   then v.vx = 100
            elseif  love.keyboard.isDown("left")    then v.vx = -100
            end
        end
    end

    return self
end

function Systems.Drawing()
    local self = Systems.Base()
    self.name = "drawing"

    function self.draw()
        local entities = self.get_entities()
        for i, e in pairs(entities) do
            local p = e.position
            love.graphics.circle("fill", p.x, p.y, 10)
        end
    end

    return self
end

function SystemManager()
    local self = {}
    local systems = {}

    -- registering systems
    for i, s in pairs(Systems) do
        local sys = s()
        systems[sys.name] = sys
    end

    function self.update(dt)
        for k, system in pairs(systems) do
            local upd = system.update
            if upd then upd(dt) end
        end
    end

    function self.draw()
        for k, system in pairs(systems) do
            local drw = system.draw
            if drw then drw(dt) end
        end
    end

    function self.subscribe(entity, system)
        local sys = systems[system]
        sys.subscribe(entity)
    end

    return self
end

-- Entity class --

Entity = {}
function Entity.new()
    local self = {}
    local updates = {}
    local draws = {}

    function self.add(component)
        self[component.name] = component
    end

    function self.subscribe(system)
        if system.update then table.insert(updates, system.update)
        elseif system.draw then table.insert(draws, system.draw)
        end
    end

    function self.update(dt)
        for k, update in pairs(updates) do
            update(self, dt)
        end
    end

    function self.draw()
        for k, draw in pairs(draws) do
            draw(self)
        end
    end

    return self
end

--- Assembling custom entity
function create_player(x, y, vx, vy)
    entity = Entity.new()
    entity.add(Component_Position(x, y))
    entity.add(Component_Velocity(vx, vy))
    ecs.subscribe(entity, "moving")
    ecs.subscribe(entity, "handling")
    ecs.subscribe(entity, "drawing")
    return entity
end

function create_moving_dot(x, y, vx, vy)
    entity = Entity.new()
    entity.add(Component_Position(x, y))
    entity.add(Component_Velocity(vx, vy))
    ecs.subscribe(entity, "moving")
    ecs.subscribe(entity, "drawing")
    return entity
end

function create_static_dot(x, y)
    entity = Entity.new()
    entity.add(Component_Position(x, y))
    ecs.subscribe(entity, "drawing")
    return entity
end

-- Main --
-- testing ECS framework

function love.load()
    ecs = SystemManager()
    e1 = create_player(400, 300)
    create_player(100, 100)
    create_moving_dot(200, 100, 50, 0)
    create_static_dot(500, 400)
end

function love.update(dt)
    ecs.update(dt)
end

function love.draw()
    ecs.draw()
end