defmodule RNS.Packet.Announce do
  @moduledoc """
  Module for the announce packet.
  """
  @type t() :: RNS.Packet.t()

  require Logger

  require RNS.Packet

  @doc """
  Handles received announce packets.
  If an announce is valid, its identity will be added to the `RNS.IdentityStore` and its destination to `RNS.DestinationStore`.
  """
  @spec handle(t(),  RNS.Interface.t()) ::
          :ok | {:error, :invalid_hash | :invalid_signature}
  def handle(packet, interface_id) do
    context_flag = RNS.Packet.context_flag(packet)
    hops = RNS.Packet.hops(packet)
    destination_hash = RNS.Packet.destination_hash(packet)
    data = RNS.Packet.encrypted_data(packet)

    # The ratchet size will be 0 if the context flag is unset, meaning that no ratchet is present.
    ratchet_size = if context_flag, do: 32, else: 0

    <<
      encryption_key::binary-size(32),
      signature_key::binary-size(32),
      name_hash::binary-size(10),
      random_hash::binary-size(10),
      ratchet::binary-size(ratchet_size),
      signature::binary-size(64),
      app_data::binary
    >> = data

    identity =
      RNS.Identity.new(
        create_keys: false,
        encryption_public: encryption_key,
        signature_public: signature_key,
        expiry: NaiveDateTime.add(NaiveDateTime.utc_now(), 30, :day),
        store: false
      )

    signed_data =
      <<destination_hash::binary, encryption_key::binary, signature_key::binary,
        name_hash::binary, random_hash::binary, ratchet::binary, app_data::binary>>

    if RNS.Identity.validate?(signed_data, signature, identity) do
      identity_hash = RNS.Identity.hash(identity)
      hash_material = <<name_hash::binary, identity_hash::binary>>

      expected_hash = RNS.Crypto.truncated_sha256(hash_material)

      if destination_hash == expected_hash do
        # Add the ratchet
        if ratchet != "" do
          RNS.DestinationStore.put_ratchet(ratchet, destination_hash)
        end

        # Add the identity to the identity store, the entry will expire in 14 days.
        # If the entry is already present, this will just update the expiry.
        RNS.IdentityStore.put(identity)

        if should_store?(destination_hash, hops) do
          Logger.debug(
            "Received announce for #{RNS.Destination.to_string(destination_hash)}, which is #{hops} hops away through #{interface_id}."
          )

          # Create and store the destination, will expire in 7 days.
          destination =
            RNS.Destination.new(
              hash: destination_hash,
              hops: hops,
              expiry: NaiveDateTime.add(NaiveDateTime.utc_now(), 7, :day),
              name_hash: name_hash,
              identity: identity,
              interface: interface_id,
              app_data: app_data,
              announce: packet,
              store: true
            )

          # Run the handlers
          for handler <- RNS.AnnounceHashStore.handlers(destination_hash, name_hash) do
            send(handler, {:announce, destination})
          end
        end
      else
        {:error, :invalid_hash}
      end
    else
      {:error, :invalid_signature}
    end
  end

  @spec should_store?(RNS.Destination.hash(), RNS.Packet.hops()) :: boolean()
  # No destination in store -> true
  # Announced destination closer or equal than stored one -> true
  # Stored destination interface dead -> true
  defp should_store?(destination_hash, hops) do
    case RNS.DestinationStore.fetch(destination_hash) do
      {:ok, store_destination} ->
        if RNS.Destination.hops(store_destination) >= hops or
             not RNS.Interface.alive?(RNS.Destination.interface(store_destination)) do
          true
        else
          false
        end

      {:error, :not_found} ->
        true
    end
  end

  @doc "Create a new announce from a destination(private keys need to be present)."
  @spec new(RNS.Destination.t()) ::
          {:ok, t()} | {:error, :not_all_identity_keys}
  def new(destination) do
    random_hash =
      RNS.Identity.random_hash()
      |> RNS.Crypto.truncate(10)

    name_hash = RNS.Destination.name_hash(destination)
    destination_hash = RNS.Destination.hash(destination)
    app_data = RNS.Destination.app_data(destination)

    identity = RNS.Destination.identity(destination)

    encryption_public = RNS.Identity.encryption_public(identity)
    signature_public = RNS.Identity.signature_public(identity)
    encryption_secret = RNS.Identity.encryption_secret(identity)
    signature_secret = RNS.Identity.signature_secret(identity)

    if encryption_public != nil and signature_public != nil and encryption_secret != nil and
         signature_secret != nil do
      signed_data =
        <<destination_hash::binary, encryption_public::binary, signature_public::binary,
          name_hash::binary, random_hash::binary, app_data::binary>>

      signature = RNS.Identity.sign(signed_data, signature_secret)

      data = <<
        encryption_public::binary-size(32),
        signature_public::binary-size(32),
        name_hash::binary-size(10),
        random_hash::binary-size(10),
        signature::binary-size(64),
        app_data::binary
      >>

      packet = RNS.Packet.new(
        data,
        destination_hash,
        destination_type: :plain,
        packet_type: :announce,
        propagation_type: :broadcast
      )
      {:ok, packet}
    else
      {:error, :not_all_identity_keys}
    end
  end
end