fix(RepositoryCache): Reduce cache key collisions (#247)

* fix(RepositoryCache): Reduce cache key collisions

* style: use RepositoryCache alias

* refactor(RepositoryCache): implement KeyGenerator behavior directly

lib/mbta_v3_api/repository.ex

@@ -60,28 +60,32 @@ defmodule MBTAV3API.Repository.Impl do
 
   use Nebulex.Caching.Decorators
 
-  alias MBTAV3API.JsonApi
+  alias MBTAV3API.{JsonApi, RepositoryCache}
 
   @ttl :timer.hours(1)
 
   @impl true
+  @decorate cacheable(cache: RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   def route_patterns(params, opts \\ []), do: all(MBTAV3API.RoutePattern, params, opts)
 
   @impl true
+  @decorate cacheable(cache: RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   def routes(params, opts \\ []), do: all(MBTAV3API.Route, params, opts)
 
   @impl true
+  @decorate cacheable(cache: RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   def schedules(params, opts \\ []), do: all(MBTAV3API.Schedule, params, opts)
 
   @impl true
+  @decorate cacheable(cache: RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   def stops(params, opts \\ []), do: all(MBTAV3API.Stop, params, opts)
 
   @impl true
+  @decorate cacheable(cache: RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   def trips(params, opts \\ []), do: all(MBTAV3API.Trip, params, opts)
 
   @spec all(module(), JsonApi.Params.t(), Keyword.t()) ::
           {:ok, JsonApi.Response.t(JsonApi.Object.t())} | {:error, term()}
-  @decorate cacheable(cache: MBTAV3API.RepositoryCache, on_error: :nothing, opts: [ttl: @ttl])
   defp all(module, params, opts) do
     params = JsonApi.Params.flatten_params(params, module)
     url = "/#{JsonApi.Object.plural_type(module.jsonapi_type())}"

lib/mbta_v3_api/repository_cache.ex

@@ -2,5 +2,23 @@ defmodule MBTAV3API.RepositoryCache do
   @moduledoc """
   Cache used to reduce the number of calls to the V3 API.
   """
-  use Nebulex.Cache, otp_app: :mobile_app_backend, adapter: Nebulex.Adapters.Local
+  use Nebulex.Cache,
+    otp_app: :mobile_app_backend,
+    adapter: Nebulex.Adapters.Local,
+    default_key_generator: __MODULE__
+
+  @behaviour Nebulex.Caching.KeyGenerator
+
+  @impl Nebulex.Caching.KeyGenerator
+  def generate(mod, fun, []) do
+    "#{mod}|#{fun}"
+  end
+
+  def generate(mod, fun, [arg]) do
+    "#{mod}|#{fun}|#{:erlang.phash2(arg)}"
+  end
+
+  def generate(mod, fun, args) do
+    "#{mod}|#{fun}|#{:erlang.phash2(args)}"
+  end
 end