defmodule Fsdb.Server do
  @moduledoc """
    Fsdb.Server module.

    ```elixir
    #run with: mix sample_server

    path = Path.expand("_build/dev/.fsdb")

    {:ok, db} = Fsdb.Server.start_link([path: path])

    #drop to start over
    :ok = Fsdb.Server.drop(db, "table1")

    :ok = Fsdb.Server.create(db, "table1")

    #insert generates and returns an autoincrementing id
    {:ok, 1} = Fsdb.Server.insert(db, "table1", "row1")
    {:ok, "row1"} = Fsdb.Server.fetch(db, "table1", 1)

    #operation on nonexisting ids return not found
    :nf = Fsdb.Server.delete(db, "table1", 5)
    :nf = Fsdb.Server.update(db, "table1", 5, "row5+")

    #save overrides and updates id generator
    :ok = Fsdb.Server.save(db, "table1", 5, "row5")
    :ok = Fsdb.Server.save(db, "table1", 3, "row3")
    #continue +1 of largest id used/generated before
    {:ok, 6} = Fsdb.Server.insert(db, "table1", "row6")

    #operations that get back previous value
    {:ok, "row5"} = Fsdb.Server.update(db, "table1", 5, "row5+")
    {:ok, "row5+"} = Fsdb.Server.save(db, "table1", 5, "row5++")
    {:ok, "row5++"} = Fsdb.Server.delete(db, "table1", 5)

    #tuples may not be id ordered
    [{1, "row1"}, {3, "row3"}, {6, "row6"}] = Fsdb.Server.list(db, "table1")
    ```
  """
  use GenServer

  ##########################################
  # Public API
  ##########################################

  @doc """
  Starts the GenServer.

  `params` *must* contain a valid path in the `:path` key.

  `opts` is optional and is passed verbatim to GenServer.

  Returns `{:ok, pid}`.

  ## Example

    ```
    Fsdb.Server.start_link([path: ".fsdb"], [name: Fsdb.Server])
    ```
  """
  def start_link(params, opts \\ []) do
    GenServer.start_link(__MODULE__, params, opts)
  end

  @doc """
  Stops the GenServer.

  Returns `:ok`.
  """
  def stop(pid) do
    GenServer.stop(pid)
  end

  @doc """
  Creates a table with name `table`.
  Returns `:ok`.
  """
  def create(pid, table) do
    GenServer.call(pid, {:create, table})
  end

  @doc """
  Drops the table named `table`.
  Returns `:ok`.
  """
  def drop(pid, table) do
    GenServer.call(pid, {:drop, table})
  end

  @doc """
  Returns all rows in table `table`.
  Returns `[{id, row}, ...]`.
  """
  def list(pid, table) do
    GenServer.call(pid, {:list, table})
  end

  @doc """
  Inserts row `row` in table `table` with auto generated id.
  Returns `{:ok, id}`.
  """
  def insert(pid, table, row) do
    GenServer.call(pid, {:insert, table, row})
  end

  @doc """
  Inserts or updates row `row` in table `table` with specific id `id`.
  If the provided id is greater than the last autogenerated id then
  the autogenerated id is updated to the provided one.
  Returns `:ok | {:ok, previous_row}`.
  """
  def save(pid, table, id, row) when is_integer(id) do
    GenServer.call(pid, {:save, table, id, row})
  end

  @doc """
  Fetches the row in table `table` having the id `id`.
  Returns `{:ok, row} | :nf`.
  """
  def fetch(pid, table, id) do
    GenServer.call(pid, {:fetch, table, id})
  end

  @doc """
  Updates the row in table `table` having the id `id`.
  Returns `{:ok, previous_row} | :nf`.
  """
  def update(pid, table, id, row) do
    GenServer.call(pid, {:update, table, id, row})
  end

  @doc """
  Deletes the row in table `table` having the id `id`.
  Returns `{:ok, previous_row} | :nf`.
  """
  def delete(pid, table, id) do
    GenServer.call(pid, {:delete, table, id})
  end

  ##########################################
  # GenServer Implementation
  ##########################################

  def init(params) do
    path = Keyword.fetch!(params, :path)
    Fsdb.init(path)
    {:ok, path}
  end

  def handle_call({:create, table}, _from, path) do
    {:reply, Fsdb.create(path, table), path}
  end

  def handle_call({:drop, table}, _from, path) do
    {:reply, Fsdb.drop(path, table), path}
  end

  def handle_call({:list, table}, _from, path) do
    {:reply, Fsdb.list(path, table), path}
  end

  def handle_call({:insert, table, row}, _from, path) do
    {:reply, Fsdb.insert(path, table, row), path}
  end

  def handle_call({:save, table, id, row}, _from, path) do
    {:reply, Fsdb.save(path, table, id, row), path}
  end

  def handle_call({:fetch, table, id}, _from, path) do
    {:reply, Fsdb.fetch(path, table, id), path}
  end

  def handle_call({:update, table, id, row}, _from, path) do
    {:reply, Fsdb.update(path, table, id, row), path}
  end

  def handle_call({:delete, table, id}, _from, path) do
    {:reply, Fsdb.delete(path, table, id), path}
  end

end