def Plant(World world):
    int NUM_LEVELS = 5;           # 5 levels displayed plant state.
    int NUM_UNITS = 72;           # 1 level is 72 units water
    int FRACTION_MULTIPLY = 1024; # 1 unit water is 1024/1024 water
    int INITIAL_LEVEL = (NUM_LEVELS * NUM_UNITS - 1) * FRACTION_MULTIPLY;
    int WARN_LEVEL = 1;           # Level to reach before the user is warned.

    XY position = nullptr; # Position of the plant in the world (if any).
    int water;             # Fractions of water for all levels.
    bool warned;           # Whether the user was warned about low level.


    # Return the level of water available for the plant. Used for drawing the plant.
    function int GetLevel():
        return water // (NUM_UNITS * FRACTION_MULTIPLY);
    end


    state initial:
        do  water = INITIAL_LEVEL;
            warned = false;
            SetAnimation(GetLevel());
        goto wait_drop;

    state wait_drop:
        recv drop_down(XY newpos)
        do  position = newpos;
        goto alive;

        recv time_tick; # Ignore time while in inventory.

    state alive:
        recv time_tick
        do  if refreshing:
                water = water + REFRESH_AMOUNT;
                if water >= INITIAL_LEVEL:
                    water = INITIAL_LEVEL;
                    refreshing = false;
                    warned = false;
                end
            else:
                water = water - position.GetTemperature();
                if water < 0: water = 0; end;
            end;
            SetAnimation(GetLevel());

            if not warned and GetLevel() <= WARN_LEVEL:
                ui.WarnUser("Plant at %s has low water level", position);
            end;

        recv refresh_water:
            refreshing = true;

        recv pick_up:
        do  position = nullptr;
        goto wait_drop;

end