defmodule IRC.Account do
  alias IRC.UserTrack.User

  @moduledoc """
  Account registry....

  Maps a network predicate:
    * `{net, {:nick, nickname}}`
    * `{net, {:account, account}}`
    * `{net, {:mask, user@host}}`
  to an unique identifier, that can be shared over multiple networks.

  If a predicate cannot be found for an existing account, a new account will be made in the database.

  To link two existing accounts from different network onto a different one, a merge operation is provided.

  """

  # FIXME: Ensure uniqueness of name?

  @derive {Poison.Encoder, except: [:token]}
  defstruct [:id, :name, :token]
  @type t :: %__MODULE__{id: id(), name: String.t()}
  @type id :: String.t()

  defimpl Inspect, for: __MODULE__ do
    import Inspect.Algebra

    def inspect(%{id: id, name: name}, opts) do
      concat(["#IRC.Account[", id, " ", name, "]"])
    end
  end

  def file(base) do
    to_charlist(Nola.data_path() <> "/account_#{base}.dets")
  end

  defp from_struct(%__MODULE__{id: id, name: name, token: token}) do
    {id, name, token}
  end

  defp from_tuple({id, name, token}) do
    %__MODULE__{id: id, name: name, token: token}
  end

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

  def init(_) do
    {:ok, accounts} = :dets.open_file(file("db"), [])
    {:ok, meta} = :dets.open_file(file("meta"), [])
    {:ok, predicates} = :dets.open_file(file("predicates"), [{:type, :set}])
    {:ok, %{accounts: accounts, meta: meta, predicates: predicates}}
  end

  def get(id) do
    case :dets.lookup(file("db"), id) do
      [account] -> from_tuple(account)
      _ -> nil
    end
  end

  def get_by_name(name) do
    spec = [{{:_, :"$1", :_}, [{:==, :"$1", {:const, name}}], [:"$_"]}]
    case :dets.select(file("db"), spec) do
      [account] -> from_tuple(account)
      _ -> nil
    end
  end

  def get_meta(%__MODULE__{id: id}, key, default \\ nil) do
    case :dets.lookup(file("meta"), {id, key}) do
      [{_, value}] -> (value || default)
      _ -> default
    end
  end

  @spec find_meta_accounts(String.t()) :: [{account :: t(), value :: String.t()}, ...]
  @doc "Find all accounts that have a meta of `key`."
  def find_meta_accounts(key) do
    spec = [{{{:"$1", :"$2"}, :"$3"}, [{:==, :"$2", {:const, key}}], [{{:"$1", :"$3"}}]}]
    for {id, val} <- :dets.select(file("meta"), spec), do: {get(id), val}
  end

  @doc "Find an account given a specific meta `key` and `value`."
  @spec find_meta_account(String.t(), String.t()) :: t() | nil
  def find_meta_account(key, value) do
    #spec = [{{{:"$1", :"$2"}, :"$3"}, [:andalso, {:==, :"$2", {:const, key}}, {:==, :"$3", {:const, value}}], [:"$1"]}]
    spec = [{{{:"$1", :"$2"}, :"$3"}, [{:andalso, {:==, :"$2", {:const, key}}, {:==, {:const, value}, :"$3"}}], [:"$1"]}]
    case :dets.select(file("meta"), spec) do
      [id] -> get(id)
      _ -> nil
    end
  end

  def get_all_meta(%__MODULE__{id: id}) do
    spec = [{{{:"$1", :"$2"}, :"$3"}, [{:==, :"$1", {:const, id}}], [{{:"$2", :"$3"}}]}]
    :dets.select(file("meta"), spec)
  end

  def put_user_meta(account = %__MODULE__{}, key, value) do
    put_meta(account, "u:"<>key, value)
  end

  def put_meta(%__MODULE__{id: id}, key, value) do
    :dets.insert(file("meta"), {{id, key}, value})
  end

  def delete_meta(%__MODULE__{id: id}, key) do
    :dets.delete(file("meta"), {id, key})
  end

  def all_accounts() do
    :dets.traverse(file("db"), fn(obj) -> {:continue, from_tuple(obj)} end)
  end

  def all_predicates() do
    :dets.traverse(file("predicates"), fn(obj) -> {:continue, obj} end)
  end

  def all_meta() do
    :dets.traverse(file("meta"), fn(obj) -> {:continue, obj} end)
  end

  def merge_account(old_id, new_id) do
    if old_id != new_id do
      spec = [{{:"$1", :"$2"}, [{:==, :"$2", {:const, old_id}}], [:"$1"]}]
      predicates = :dets.select(file("predicates"), spec)
      for pred <- predicates, do: :ok = :dets.insert(file("predicates"), {pred, new_id})
      spec = [{{{:"$1", :"$2"}, :"$3"}, [{:==, :"$1", {:const, old_id}}], [{{:"$2", :"$3"}}]}]
      metas = :dets.select(file("meta"), spec)
      for {k,v} <- metas do
        :dets.delete(file("meta"), {{old_id, k}})
        :ok = :dets.insert(file("meta"), {{new_id, k}, v})
      end
      :dets.delete(file("db"), old_id)
      IRC.Membership.merge_account(old_id, new_id)
      IRC.UserTrack.merge_account(old_id, new_id)
      IRC.Connection.dispatch("account", {:account_change, old_id, new_id})
      IRC.Connection.dispatch("conn", {:account_change, old_id, new_id})
    end
    :ok
  end

  @doc "Find an account by a logged in user"
  def find_by_nick(network, nick) do
    do_lookup(%ExIRC.SenderInfo{nick: nick, network: network}, false)
  end

  @doc "Always find an account by nickname, even if offline. Uses predicates and then account name."
  def find_always_by_nick(network, chan, nick) do
    with \
      nil <- find_by_nick(network, nick),
         nil <- do_lookup(%User{network: network, nick: nick}, false),
         nil <- get_by_name(nick)
    do
      nil
    else
      %__MODULE__{} = account ->
        memberships = IRC.Membership.of_account(account)
        if Enum.any?(memberships, fn({net, ch}) -> (net == network) or (chan && chan == ch) end) do
          account
        else
          nil
        end
    end
  end

  def find(something) do
    do_lookup(something, false)
  end

  def lookup(something, make_default \\ true) do
    account = do_lookup(something, make_default)
    if account && Map.get(something, :nick) do
      IRC.Connection.dispatch("account", {:account_auth, Map.get(something, :nick), account.id})
    end
    account
  end

  def handle_info(_, state) do
    {:noreply, state}
  end

  def handle_cast(_, state) do
    {:noreply, state}
  end

  def handle_call(_, _, state) do
    {:noreply, state}
  end

  def terminate(_, state) do
    for {_, dets} <- state do
      :dets.sync(dets)
      :dets.close(dets)
    end
  end

  defp do_lookup(message = %IRC.Message{account: account_id}, make_default) when is_binary(account_id) do
    get(account_id)
  end

  defp do_lookup(sender = %ExIRC.Who{}, make_default) do
    if user = IRC.UserTrack.find_by_nick(sender) do
      lookup(user, make_default)
    else
      #FIXME this will never work with continued lookup by other methods as Who isn't compatible
      lookup_by_nick(sender, :dets.lookup(file("predicates"), {sender.network,{:nick, sender.nick}}), make_default)
    end
  end

  defp do_lookup(sender = %ExIRC.SenderInfo{}, make_default) do
    lookup(IRC.UserTrack.find_by_nick(sender), make_default)
  end

  defp do_lookup(user = %User{account: id}, make_default) when is_binary(id) do
    get(id)
  end

  defp do_lookup(user = %User{network: server, nick: nick}, make_default) do
    lookup_by_nick(user, :dets.lookup(file("predicates"), {server,{:nick, nick}}), make_default)
  end

  defp do_lookup(nil, _) do
    nil
  end

  defp lookup_by_nick(_, [{_, id}], _make_default) do
    get(id)
  end

  defp lookup_by_nick(user, _, make_default) do
    #authenticate_by_host(user)
    if make_default, do: new_account(user), else: nil
  end

  def new_account(nick) do
    id = EntropyString.large_id()
    :dets.insert(file("db"), {id, nick, EntropyString.token()})
    get(id)
  end

  def new_account(%{nick: nick, network: server}) do
    id = EntropyString.large_id()
    :dets.insert(file("db"), {id, nick, EntropyString.token()})
    :dets.insert(file("predicates"), {{server, {:nick, nick}}, id})
    get(id)
  end

  def update_account_name(account = %__MODULE__{id: id}, name) do
    account = %__MODULE__{account | name: name}
    :dets.insert(file("db"), from_struct(account))
    get(id)
  end

  def get_predicates(%__MODULE__{} = account) do
    spec = [{{:"$1", :"$2"}, [{:==, :"$2", {:const, account.id}}], [:"$1"]}]
    :dets.select(file("predicates"), spec)
  end

end