function world_init()
  worldtiles = {}
  --test start
  bob = build(3,2,buildings.jam_workshop)
  bob = replace(bob, buildings.city)
  destroy(bob)
  --test end
end

function world_update()
    if (btnp(4)) build(3,2,buildings.jam_workshop)
    if (btnp(5)) compute_effect_array(worldtiles)
end

function world_draw()
  draw_array(worldtiles)
end


buildings = 
{
  jam_workshop = 
  {
    sprite = 1,
    inputs = 
    {
        {
            type = "fruit",
            quantity = 2
        }
    },
    outputs = 
    {
        {
            type = "jam",
            quantity = 3
        }
    }
  },
  city = 
  {
    sprite = 5,
    inputs = 
    {
        {
            type = "jam",
            quantity = 1
        }
    },
    outputs = 
    {
        {
            type = "money",
            quantity = 2
        }
    }
  },
}

function compute_effect_array(array)
  for obj in all(array) do
    obj.compute_effet(obj)
  end
end

function draw_array(array)
  for obj in all(array) do
    obj.draw(obj)
  end
end

function new_worldtile(x, y, building)
    local worldtile = {}
    worldtile.x = x
    worldtile.y = y
    worldtile.building = building
    worldtile.draw = function(this)
      spr(worldtile.building.sprite,worldtile.x*2*8,8+worldtile.y*2*8, 2, 2)
    end
    worldtile.compute_effet = function(this)
        has_ressource = true
        for _,input in pairs(worldtile.building.inputs) do
          if (ressources[input.type].quantity < input.quantity) has_ressource = false
        end
        if (has_ressource) then
            for _,input in pairs(worldtile.building.inputs) do
                ressources[input.type].quantity-=input.quantity
            end
            for _,output in pairs(worldtile.building.outputs) do
                ressources[output.type].quantity+=output.quantity
            end
        end
    end
    return worldtile
end

function build(x, y, building)
    newtile = new_worldtile(x,y,building)
    add(worldtiles, newtile)
    return newtile
end

function destroy(worldtile)
    del(worldtiles, worldtile)
end

function replace(worldtile, building)
    destroy(worldtile)
    return build(worldtile.x, worldtile.y, building)
end

function get_worldtile(x,y)
    for _,tile in pairs(worldtiles) do
        if (tile.x == x and tile.y == y) then 
            return tile
        end
    end
end