aprs.me/lib/aprsme/cache.ex

defmodule Aprsme.Cache do
  @moduledoc """
  Cache abstraction layer using ETS (Erlang Term Storage).
  Provides a unified API for in-memory caching with optional TTL support.

  Entries are stored as `{key, value, expires_at}` tuples where `expires_at`
  is a monotonic time in milliseconds, or `:infinity` for no expiration.
  Expired entries are lazily evicted on read.
  """

  use GenServer

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  @impl true
  def init(_opts) do
    {:ok, %{}}
  end

  @doc """
  Get a value from cache. Returns `{:ok, nil}` for expired entries.
  """
  def get(cache_name, key) do
    GenServer.call(__MODULE__, {:get, cache_name, key})
  end

  @doc """
  Put a value in cache with optional TTL.

  ## Options
    * `:ttl` - Time to live in milliseconds. Use `Cache.to_timeout/1` for convenience.
  """
  def put(cache_name, key, value, opts \\ []) do
    GenServer.call(__MODULE__, {:put, cache_name, key, value, opts})
  end

  @doc """
  Delete a key from cache
  """
  def del(cache_name, key) do
    GenServer.call(__MODULE__, {:del, cache_name, key})
  end

  @doc """
  Clear all keys from cache
  """
  def clear(cache_name) do
    GenServer.call(__MODULE__, {:clear, cache_name})
  end

  @doc """
  Get cache statistics (simplified for ETS)
  """
  def stats(cache_name) do
    GenServer.call(__MODULE__, {:stats, cache_name})
  end

  @doc """
  Check if key exists and is not expired.
  """
  def exists?(cache_name, key) do
    case get(cache_name, key) do
      {:ok, nil} -> false
      {:ok, _} -> true
      _ -> false
    end
  end

  @doc """
  Get TTL for a key. Returns remaining milliseconds or nil if no TTL.
  """
  def ttl(cache_name, key) do
    GenServer.call(__MODULE__, {:ttl, cache_name, key})
  end

  @doc """
  Convert timeout keyword list to milliseconds.
  """
  def to_timeout(opts) do
    Enum.reduce(opts, 0, fn
      {:second, n}, acc -> acc + n * 1000
      {:seconds, n}, acc -> acc + n * 1000
      {:minute, n}, acc -> acc + n * 60 * 1000
      {:minutes, n}, acc -> acc + n * 60 * 1000
      {:hour, n}, acc -> acc + n * 60 * 60 * 1000
      {:hours, n}, acc -> acc + n * 60 * 60 * 1000
      {:day, n}, acc -> acc + n * 24 * 60 * 60 * 1000
      {:days, n}, acc -> acc + n * 24 * 60 * 60 * 1000
      {:millisecond, n}, acc -> acc + n
      {:milliseconds, n}, acc -> acc + n
    end)
  end

  @impl true
  def handle_call({:get, cache_name, key}, _from, state) do
    result =
      try do
        case :ets.lookup(cache_name, key) do
          [{^key, value, :infinity}] ->
            {:ok, value}

          [{^key, value, expires_at}] ->
            if System.monotonic_time(:millisecond) < expires_at do
              {:ok, value}
            else
              :ets.delete(cache_name, key)
              {:ok, nil}
            end

          [{^key, value}] ->
            {:ok, value}

          [] ->
            {:ok, nil}
        end
      rescue
        ArgumentError ->
          {:error, :no_cache}
      end

    {:reply, result, state}
  end

  @impl true
  def handle_call({:put, cache_name, key, value, opts}, _from, state) do
    result =
      try do
        expires_at =
          case Keyword.get(opts, :ttl) do
            nil -> :infinity
            ttl when is_integer(ttl) and ttl > 0 -> System.monotonic_time(:millisecond) + ttl
            _ -> :infinity
          end

        :ets.insert(cache_name, {key, value, expires_at})
        {:ok, true}
      rescue
        ArgumentError -> {:error, :no_cache}
      end

    {:reply, result, state}
  end

  @impl true
  def handle_call({:del, cache_name, key}, _from, state) do
    result =
      try do
        :ets.delete(cache_name, key)
        {:ok, true}
      rescue
        ArgumentError -> {:error, :no_cache}
      end

    {:reply, result, state}
  end

  @impl true
  def handle_call({:clear, cache_name}, _from, state) do
    result =
      try do
        :ets.delete_all_objects(cache_name)
        {:ok, true}
      rescue
        ArgumentError -> {:error, :no_cache}
      end

    {:reply, result, state}
  end

  @impl true
  def handle_call({:stats, cache_name}, _from, state) do
    result =
      case :ets.info(cache_name) do
        :undefined -> {:error, :no_cache}
        info when is_list(info) -> {:ok, %{size: Keyword.get(info, :size, 0)}}
      end

    {:reply, result, state}
  end

  @impl true
  def handle_call({:ttl, cache_name, key}, _from, state) do
    result =
      try do
        case :ets.lookup(cache_name, key) do
          [{^key, _value, :infinity}] -> {:ok, nil}
          [{^key, _value, expires_at}] -> {:ok, max(0, expires_at - System.monotonic_time(:millisecond))}
          [{^key, _value}] -> {:ok, nil}
          [] -> {:ok, nil}
        end
      rescue
        ArgumentError -> {:ok, nil}
      end

    {:reply, result, state}
  end
end