exbitcask.ex

defmodule ExBitcask do
  use Application
  alias ExBitcask.Database, as: DB

  defmodule Config do
    @moduledoc false
    def set_defaults() do
      defaults = [
        {:max_file_size, 2147483648},
        {:tombstone_version, 2},
        {:open_timeout, 4},
        {:sync_strategy, :none},
        {:require_hint_crc, false},
        {:merge_window, :always},
        {:frag_merge_trigger, 60},
        {:dead_bytes_merge_trigger, 536870912},
        {:frag_threshold, 40},
        {:dead_bytes_threshold, 134217728},
        {:small_file_threshold, 10485760},
        {:max_fold_age, -1},
        {:max_fold_puts, 0},
        {:expiry_secs, -1}
      ]
      for {key, val} <- defaults do
        if Application.get_env(:bitcask, key) == nil do
          Application.put_env(:bitcask, key, val)
        end
      end
    end
  end

  def start(_type, _args) do
    Config.set_defaults
    import Supervisor.Spec, warn: false
    children = [
      worker(:bitcask_merge_worker, []),
      worker(:bitcask_merge_delete, [])
    ]
    opts = [strategy: :one_for_one, name: ExBitcask.Supervisor]
    Supervisor.start_link(children, opts)
  end
  @moduledoc ~S"""
  Elixir wrapper of [Basho's Bitcask](https://github.com/basho/bitcask) Key/Value store.

  ExBitcask currently uses version **2.0.0** of bitcask.

  *[Wikipedia](https://en.wikipedia.org/wiki/Bitcask)*: Bitcask is an Erlang application that provides an API for
  storing and retrieving key/value data into a log-structured  hash table that provides very fast access. The design
  owes a lot to the principles found in log-structured file systems and draws inspiration from a number of designs that
  involve log file merging.

  ## Setup

  First, add ExBitcask to your mix.exs dependencies:

      def deps do
        [{:ex_bitcask, "~> VERSION"}]
      end

  and run $ `mix deps.get`. Now, list the :ex_bitcask application as your application dependency:

      def application do
        [applications: [:ex_bitcask]]
      end

  ## Usage

      db = ExBitcask.open("my.db", [:read_write])
      ExBitcask.put(db, "Foo", "bar")
      ExBitcask.put(db, "Hello", "world")
      ExBitcask.get(db, "Hello")
      # {:ok, "world"}

  ### Streams

  Lazy Streams can be generated for both the keys and the {key, val} of the database.

      ExBitcask.stream_keys(db) |> Stream.map(&(String.upcase(&1))) |> Enum.to_list
      # ["FOO", "HELLO"]
      ExBitcask.stream_keyvals(db) |> Enum.to_list
      # [{"Foo", "bar"}, {"Hello", "world"}]


  ### Serialization

  If a value is in binary or String format it will be put in as is.
  Other terms will be serialized into binary using `:erlang.term_to_binary/1` with a prefix so ExBitcask knows when to de-serialize a value.

  This means a value can be any complex Elixir object. Like the database connection itself.

      ExBitcask.put(db, "myown_db", db)
      db_from_db = ExBitcask.get!(db, "myown_db")
      ExBitcask.get(db_from_db, "Hello")
      # {:ok, "world"}

  """

  @doc ~S"""
  Opens up a Bitcask database in the given folder.

  To open up the database for writing into use options `[:read_write]`
  """
  @spec open(String.t, DB.options) :: DB.t
  def open(folder, options \\ []) do
    ref = :bitcask.open(to_char_list(folder), options)
    %DB{
      ref: ref,
      folder: folder,
      options: options
    }
  end

  @doc ~S"""
  Closes the access to a given database.
  """
  @spec close(DB.t) :: :ok
  def close(db), do: :bitcask.close(db.ref)

  @doc ~S"""
  Closes the write lock a connection has to the database.
  """
  @spec close_write_file(DB.t) :: :ok
  def close_write_file(db), do: :bitcask.close_write_file(db.ref)

  @doc ~S"""
  Retreives a value by key.

  If the value was a serialized term it will be de-serialized before returning.
  """
  @spec get(DB.t, String.t) :: {:ok, binary()} | :not_found
  def get(db, key) when is_binary(key), do: decode(:bitcask.get(db.ref, key))

  @doc ~S"""
  Retreives a value by key. Throws if key is not found.

  If the value was a serialized term it will be de-serialized before returning.
  """
  @spec get!(DB.t, String.t) :: binary()
  def get!(db, key) do
    {:ok, val} = get(db, key)
    val
  end

  @doc ~S"""
  Puts a given value into the key.

  If a value is in binary or String format it will be put in as is.
  Other terms will be serialized into binary.
  """
  @spec put(DB.t, String.t, binary()) :: :ok
  def put(db, key, val) when is_binary(key), do: :bitcask.put(db.ref, key, encode(val))

  @doc ~S"""
  Delete the key. Bet you weren't expecting that.
  """
  @spec delete(DB.t, String.t) :: :ok
  def delete(db, key) when is_binary(key), do: :bitcask.delete(db.ref, key)

  @doc ~S"""
  Forces a sync of the database.
  """
  @spec sync(DB.t) :: :ok
  def sync(db), do: :bitcask.sync(db.ref)

  @doc ~S"""
  List all keys in the database.

  Consider using `ExBitcask.stream_keys/3` instead.
  """
  @spec list_keys(DB.t) :: [binary()]
  def list_keys(db), do: :bitcask.list_keys(db.ref)

  @doc ~S"""
  Gets the status of a database.
  """
  @spec status(DB.t) :: any()
  def status(db), do: :bitcask.status(db.ref)

  @doc ~S"""
  Does the db need to be merged?
  """
  @spec needs_merge?(DB.t, List.t) :: :ok
  def needs_merge?(db, options \\ []), do: :bitcask.needs_merge(db.ref, options)

  @doc ~S"""
  Merge the data files of the database.
  """
  @spec merge(String.t | DB.t, List.t) :: :ok
  def merge(folder_or_db, options \\ [])
  def merge(folder, options) when is_binary(folder), do: :bitcask.merge(to_char_list(folder), options)
  def merge(db, options) when is_map(db), do: :bitcask.merge(to_char_list(db.folder), options)

  # TODO: fold_keys(Ref, Fun, Acc0, MaxAge, MaxPut, SeeTombstonesP)
  @doc ~S"""
  Fold over the keys in the database.

  Consider using `ExBitcask.stream_keys/3` instead.
  """
  @spec fold_keys(DB.t, function(), List.t) :: :ok
  def fold_keys(db, func, options \\ []), do: :bitcask.fold_keys(db.ref, func, options)

  # TODO: fold(Ref, Fun, Acc0, MaxAge, MaxPut, SeeTombstonesP)
  @doc ~S"""
  Fold over the keys and values.

  Consider using `ExBitcask.stream_keys/3` instead.
  """
  @spec fold(DB.t, function(), List.t) :: :ok
  def fold(db, func, options \\ []) do
    :bitcask.fold(db.ref, &(func.(&1, encode(&2), &3)), options)
  end

  @doc ~S"""
  Is the DB frozen?
  """
  @spec is_frozen?(DB.t) :: boolean()
  def is_frozen?(db), do: :bitcask.is_frozen(db.ref)

  @doc ~S"""
  Creates a Stream object with all the keys in the database.

  Same as calling `ExBitcask.stream_keys(db, -1, -1)`.
  """
  @spec stream_keys(DB.t) :: Stream.t
  def stream_keys(db), do: do_stream(db, -1, -1, false)

  @doc ~S"""
  Creates a Stream object with all the keys in the database.

  Check the number of updates since pending was created is less than the maximum
  and that the current view is not too old.
  Call with ts set to zero to force a wait on any pending keydir.
  Set maxage or maxputs negative to ignore them.  Set both negative to force
  using the keydir - useful when a process has waited once and needs to run
  next time.
  """
  @spec stream_keys(DB.t, Integer.t, Integer.t) :: Stream.t
  def stream_keys(db, max_age, max_puts), do: do_stream(db, max_age, max_puts, false)

  @doc ~S"""
  Creates a Stream object with all the {key, val} objects in the database.

  Same as calling `ExBitcask.stream_keyvals(db, -1, -1)`.
  """
  @spec stream_keyvals(DB.t) :: Stream.t
  def stream_keyvals(db), do: do_stream(db, -1, -1, true)

  @doc ~S"""
  Creates a Stream object with all the {key, val} objects in the database.

  Check the number of updates since pending was created is less than the maximum
  and that the current view is not too old.
  Call with ts set to zero to force a wait on any pending keydir.
  Set maxage or maxputs negative to ignore them.  Set both negative to force
  using the keydir - useful when a process has waited once and needs to run
  next time.
  """
  @spec stream_keyvals(DB.t, Integer.t, Integer.t) :: Stream.t
  def stream_keyvals(db, max_age, max_puts), do: do_stream(db, max_age, max_puts, true)


  defp do_stream(db, max_age, max_puts, get_value) do
    Stream.resource(
      fn ->
        iterator_db = open(db.folder)
        :ok = :bitcask.iterator(iterator_db.ref, max_age, max_puts)
        iterator_db
      end,
      fn iterator_db ->
        case :bitcask.iterator_next iterator_db.ref do
          :not_found -> {:halt, iterator_db}
          {:bitcask_entry, key, _, _, _, _} ->
            if get_value do
              {[{key, get!(iterator_db, key)}], iterator_db}
            else
              {[key], iterator_db}
            end
        end
      end,
      fn iterator_db ->
        :bitcask.iterator_release iterator_db.ref
        close(iterator_db)
      end
    )
  end

  defp encode(val) when is_binary(val), do: val
  defp encode(val), do: "ETERM"<>:erlang.term_to_binary(val)

  defp decode({:ok, val}), do: {:ok, decode(val)}
  defp decode("ETERM"<>term), do: :erlang.binary_to_term(term)
  defp decode(val), do: val


end