defmodule Rox do
  @moduledoc """
  Elixir wrapper for RocksDB.

  """

  alias __MODULE__.{DB,ColumnFamily,Native,Utils,Cursor}

  @type compaction_style :: :level | :universal | :fifo | :none
  @type compression_type :: :snappy | :zlib | :bzip2 | :lz4 | :lz4h | :none

  @type key :: String.t | binary
  @type value :: any

  @opaque snapshot_handle :: :erocksdb.snapshot_handle

  @type file_path :: String.t


  @type block_based_table_options :: [
    {:no_block_cache, boolean} |
    {:block_size, pos_integer} |
    {:block_cache_size, pos_integer} |
    {:bloom_filter_policy, bits_per_key :: pos_integer} |
    {:format_version, 0 | 1 | 2} |
    {:skip_table_builder_flush, boolean} |
    {:cache_index_and_filter_blocks, boolean}
  ]

  @type access_hint :: :normal | :sequential | :willneed | :none
  @type wal_recovery_mode ::
    :tolerate_corrupted_tail_records |
    :absolute_consistency |
    :point_in_time_recovery |
    :skip_any_corrupted_records

  @type db_options :: [
    {:total_threads, pos_integer} |
    {:optimize_level_type_compaction_memtable_memory_budget, integer} |
    {:auto_create_column_families, boolean} |
    {:create_if_missing, boolean} |
    {:max_open_files, pos_integer} |
    {:compression_type, compression_type} |
    {:use_fsync, boolean} |
    {:bytes_per_sync, pos_integer} |
    {:allow_os_buffer, boolean} |
    {:table_cache_num_shard_bits, pos_integer} |
    {:min_write_buffer_number, pos_integer} |
    {:max_write_buffer_number, pos_integer} |
    {:write_buffer_size, pos_integer} |
    {:max_bytes_for_level_base, pos_integer} |
    {:max_bytes_for_level_multiplier, pos_integer} |
    {:max_manifest_file_size, pos_integer} |
    {:target_file_size_base, pos_integer} |
    {:min_write_buffer_number_to_merge, pos_integer} |
    {:level_zero_file_num_compaction_trigger, non_neg_integer} |
    {:level_zero_slowdown_writes_trigger, non_neg_integer} |
    {:level_zero_stop_writes_trigger, non_neg_integer} |
    {:compaction_style, compaction_style} |
    {:max_background_compactions, pos_integer} |
    {:max_background_flushes, pos_integer} |
    {:disable_auto_compactions, boolean} |
    {:report_bg_io_stats, boolean} |
    {:num_levels, pos_integer} |
    {:use_direct_io_for_flush_and_compaction, boolean}
  ]

  @type read_options :: [
    {:fill_cache, boolean} |
    {:iterate_upper_bound, binary}
    # {:snapshot, snapshot_handle} |
  ]

  @type write_options :: [
    {:sync, boolean} |
    {:disable_wal, boolean}
  ]

  @doc """
  Open a RocksDB with the optional `db_opts` and `column_families`.

  If `column_families` are provided, a 3 element tuple will be returned with
  the second element being a map of column family names to `Rox.ColumnFamily` handles.
  The column families must have already been created via `create_cf` or the option
  `auto_create_column_families` can be set to `true`. If it is, the `db_opts` will be
  used to create the column families.


  The database will automatically be closed when the BEAM VM releases it for garbage collection.

  """
  @spec open(file_path, db_options, [ColumnFamily.name]) ::
    {:ok, DB.t} |
    {:ok, DB.t, %{ColumnFamily.name => ColumnFamily.t}} |
    {:error, any}
  def open(path, db_opts \\ [], column_families \\ []) when is_binary(path) and is_list(db_opts) and is_list(column_families) do
    auto_create_cfs? =
      db_opts[:auto_create_column_families]

    case column_families do
      [] ->
        do_open_db_with_no_cf(path, db_opts)

      _ ->
        # First try opening with existing column families
        with {:ok, db}         <- Native.open(path, to_map(db_opts), column_families),
                   db          <- DB.wrap_resource(db),
             {:ok, cf_handles} <- map_or_error(column_families, &cf_handle(db, &1)) do

            cf_map =
              Enum.zip(column_families, cf_handles)
              |> Enum.into(%{})

            {:ok, db, cf_map}
        else
          {:error, << "Invalid argument: Column family not found:", _rest :: binary >>} when auto_create_cfs? ->
            do_open_db_and_create_cfs(path, db_opts, column_families)
          other ->
           other
        end
    end
  end

  defp do_open_db_with_no_cf(path, opts) do
    with {:ok, db} <- Native.open(path, to_map(opts), []) do
      {:ok, DB.wrap_resource(db)}
    end
  end

  defp do_open_db_and_create_cfs(path, opts, column_families) do
    with {:ok, db} <- do_open_db_with_no_cf(path, opts),
         {:ok, cf_handles} <- map_or_error(column_families, &create_cf(db, &1, opts)) do

      cf_map =
        Enum.zip(column_families, cf_handles)
        |> Enum.into(%{})

      {:ok, db, cf_map}
    end
  end

  @doc """
  Create a column family in `db` with `name` and `opts`.

  """
  @spec create_cf(DB.t, ColumnFamily.name, db_options) :: {:ok, ColumnFamily.t} | {:error, any}
  def create_cf(%DB{resource: raw_db} = db, name, opts \\ []) do
    with {:ok, result} <- Native.create_cf(raw_db, name, to_map(opts)) do
      {:ok, ColumnFamily.wrap_resource(db, result, name)}
    end
  end

  @doc """
  Gets an existing `ColumnFamily.t` from the database.

  The column family must have been created via `create_cf/2` or from `open/3` with the `auto_create_column_families` option.

  """
  @spec cf_handle(DB.t, ColumnFamily.name) :: {:ok, ColumnFamily.t} | {:error, any}
  def cf_handle(%DB{resource: raw_db} = db, name) do
    with {:ok, result} <- Native.cf_handle(raw_db, name) do
      {:ok, ColumnFamily.wrap_resource(db, result, name)}
    end
  end


  @doc """
  Put a key/value pair into the specified database or column family.

  Optionally takes a list of `write_options`.

  Non-binary values will automatically be encoded using the `:erlang.term_to_binary/1` function.

  """
  @spec put(DB.t | ColumnFamily.t, key, value, write_options) :: :ok | {:error, any}
  def put(db_or_cf, key, value, write_opts \\[])
  def put(%DB{resource: db}, key, value, write_opts) when is_binary(key) and is_list(write_opts), do:
    Native.put(db, key, Utils.encode(value), to_map(write_opts))
  def put(%ColumnFamily{db_resource: db, cf_resource: cf}, key, value, write_opts) when is_binary(key), do:
    Native.put_cf(db, cf, key, Utils.encode(value), to_map(write_opts))


  @doc """
  Get a key/value pair in the databse or column family with the specified `key`.

  Optionally takes a list of `read_options`.

  For non-binary terms that were stored, they will be automatically decoded.

  """
  @spec get(DB.t | ColumnFamily.t, key, read_options) :: {:ok, binary} | {:ok, value} | :not_found | {:error, any}
  def get(db_or_cf, key, opts \\ [])
  def get(%DB{resource: db}, key, opts) when is_binary(key) and is_list(opts) do
    Native.get(db, key, to_map(opts))
    |> Utils.decode
  end
  def get(%ColumnFamily{db_resource: db, cf_resource: cf}, key, opts) when is_binary(key) and is_list(opts) do
    Native.get_cf(db, cf, key, to_map(opts))
    |> Utils.decode
  end

  @doc """
  Returns a `Cursor.t` which will iterate records from the provided database or
  column family.

  Optionally takes an `Rox.Cursor.mode`. Defaults to `:start`.

  The default arguments of this function is used for the `Enumerable` implementation
  for `DB` and `ColumnFamily` structs.

  Note: The result of stream is a cursor which is *not* meant to be shared across processes.
  Iterating over the cursor will result in an internal state in RocksDB being modified.
  If two processes try and use the same cursor, they will consume
  each others results. This may or may not be desired.

  """
  @spec stream(DB.t | ColumnFamily.t, Rox.Cursor.mode) :: Cursor.t | {:error, any}
  def stream(db_or_cf, mode \\ :start)
  def stream(%DB{resource: db}, mode) do
    with {:ok, resource} = Native.iterate(db, mode) do
      Cursor.wrap_resource(resource, mode)
    end
  end
  def stream(%ColumnFamily{db_resource: db, cf_resource: cf}, mode) do
    with {:ok, resource} = Native.iterate_cf(db, cf, mode) do
      Cursor.wrap_resource(resource, mode)
    end
  end


  @doc """
  Returns a `Cursor.t` which will iterate *keys* from the provided database or column family.

  Optionally takes a `Rox.Cursor.mode`, which defaults to `:start`.

  Note: The result of `stream_keys` is a cursor which is *not* meant to be shared across processes.
  Iterating over the cursor will result in an internal state in RocksDB being modified.
  If two processes try and use the same cursor, they will consume
  each others results. This may or may not be desired.

  """
  @spec stream_keys(DB.t | ColumnFamily.t, Rox.Cursor.mode) :: Cursor.t | {:error, any}
  def stream_keys(db_or_cf, mode \\ :start)
  def stream_keys(%DB{resource: db}, mode) do
    with {:ok, resource} = Native.iterate(db, mode) do
      Cursor.wrap_resource(resource, mode, decode_values: false)
      |> Stream.map(&elem(&1, 0))
    end
  end
  def stream_keys(%ColumnFamily{db_resource: db, cf_resource: cf}, mode) do
    with {:ok, resource} = Native.iterate_cf(db, cf, mode) do
      Cursor.wrap_resource(resource, mode, decode_values: false)
      |> Stream.map(&elem(&1, 0))
    end
  end


  @doc """
  Return the approximate number of keys in the database or specified column family.

  Implemented by calling GetIntProperty with `rocksdb.estimate-num-keys`

  """
  @spec count(DB.t | ColumnFamily.t) :: non_neg_integer | {:error, any}
  def count(%DB{resource: db}) do
    Native.count(db)
  end
  def count(%ColumnFamily{db_resource: db, cf_resource: cf}) do
    Native.count_cf(db, cf)
  end


  @doc """
  Deletes the specified `key` from the provided database or column family.

  Optionally takes a list of `write_opts`.

  """
  @spec delete(DB.t | ColumnFamily.t, key, write_options) :: :ok | {:error, any}
  def delete(db_or_cf, key, write_opts \\ [])
  def delete(%DB{resource: db}, key, write_opts) do
    Native.delete(db, key, to_map(write_opts))
  end
  def delete(%ColumnFamily{db_resource: db, cf_resource: cf}, key, write_opts) do
    Native.delete_cf(db, cf, key, to_map(write_opts))
  end

  defp to_map(map) when is_map(map), do: map
  defp to_map([]), do: %{}
  defp to_map(enum), do: Enum.into(enum, %{})


  defp map_or_error(list, fun) do
    do_map_or_error(list, fun, [])
  end

  defp do_map_or_error([], _fun, results), do: {:ok, :lists.reverse(results)}
  defp do_map_or_error([item | rest], fun, results) do
    case fun.(item) do
      {:error, _} = err ->
        err

      {:ok, result} ->
        do_map_or_error(rest, fun, [result | results])
    end
  end

end