city.erl

-module(city).
-include("city.hrl").
-author("Yvan").

%% ------------------------------------------------------------------
%% API Function Exports
%% ------------------------------------------------------------------

-export([new/0,plague/1,preturnPopulation/1,preturnHealth/1]).

-define(IS_HEALTH_LOW(X), X < 4).
-define(IS_HEALTH_VERYLOW(X), X < 2).
-define(IS_HEALTH_HIGH(X), X > 8).

-define(LOW_FOOD,3).
-define(VERYLOW_FOOD,1).
-define(HIGH_FOOD,8).

%% ------------------------------------------------------------------
%% API Function Definitions
%% ------------------------------------------------------------------

new() -> #city{}.

plague(#city{health = CurrentHealth} = City) ->
  City#city{health = gauge:decrement(CurrentHealth)}.

nextPopulation(CurrentPopulation, CurrentHealth)
  when ?IS_HEALTH_VERYLOW(CurrentHealth)
      -> gauge:decrement(gauge:decrement(CurrentPopulation));
nextPopulation(CurrentPopulation, CurrentHealth)
  when ?IS_HEALTH_LOW(CurrentHealth)
      -> gauge:decrement(CurrentPopulation);
nextPopulation(CurrentPopulation, CurrentHealth)
  when  ?IS_HEALTH_HIGH(CurrentHealth)
      -> gauge:increment(CurrentPopulation);
nextPopulation(CurrentPopulation, _)
      -> CurrentPopulation.


preturnPopulation(#city{population = CurrentPopulation, health = CurrentHealth} = City) ->
  City#city{population = nextPopulation(CurrentPopulation, CurrentHealth)}.

preturnHealth(#city{health = CurrentHealth, food = CurrentFood} = City) ->
  case City of
    _ when CurrentFood < ?VERYLOW_FOOD ->
      NewHealth = gauge:decrement(gauge:decrement(CurrentHealth));
    _ when CurrentFood < ?LOW_FOOD ->
      NewHealth = gauge:decrement(CurrentHealth);
    _ when CurrentFood >= ?HIGH_FOOD ->
      NewHealth = gauge:increment(CurrentHealth);
    _ ->
      NewHealth = CurrentHealth
  end,
  City#city{health = NewHealth}.