-- data shared between modules goes here, both constants and mutable data.
-- also contains some functions that act solely on the data
--
-- also has commented "fake constants" that are replaced by actual values, for
-- reference.
--
-- also see index_map.md for more "constant" values

function init_data()
   -- block_size = 64
   -- biome_size = 128

   -- the indices here are sprite numbers.
   object_interaction_map = {
      -- bush
      [3] = {
         replacement = 17,
         sfx = 13,
         drop = 68
      },

      -- tree
      [4] = {
         replacement = 14,
         sfx = 11,
         drop = 64
      },

      -- big mushroom
      [8] = {
         replacement = 16,
         sfx = 12,
         drop = 65
      },

      -- cactus w/ flower
      [10] = {
         replacement = 15,
         sfx = 12,
         drop = 67
      },

      -- cactus
      [13] = {
         replacement = 15,
         sfx = 12,
         drop = 66
      }
   }

   -- initialize a ring buffer of changed positions. In use, this will be keyed
   -- using strings of the form mod_buffer["x:y"], using absolute world
   -- coordinates. this is to flatten the buffer so that #mod_cache is useful
   -- for checking against max_mod_entries.
   max_mod_entries = 4096
   mod_buffer = {}
end

-- x and y are global coords
function get_mod_key(x, y)
   return tostr(x) .. ":" .. tostr(y)
end

-- x and y are map-local coords
function write_map_change(new_sprite, x, y)
   local global_x, global_y = calculate_world_pos(x, y)
   if #mod_buffer >= max_mod_entries then
      cull_mod_buffer()
   end

   mod_buffer[get_mod_key(global_x, global_y)] = new_sprite
end

function cull_mod_buffer()
   -- we cull 10% of the mod buffer at a time
   -- todo: implement this
end

function calculate_world_pos(x, y)
   -- player_pos_[xy] is world absolute, so we can get the world pos of map 0,0,
   -- then add x and y back in.
   return player_pos_x - camera_pos_x - 8 + x,
          player_pos_y - camera_pos_y - 8 + y
end