Add server crdt

assets/js/app.js

@@ -277,3 +277,14 @@ return `
     </div>
 `
 }
+
+// Check if local CRDT consistent with server CRDT
+var check_btn = document.getElementById("check_btn");
+check_btn.onclick = function() {
+    channel.push("check", {
+        value: crdt.toString()
+    }).receive("ok", resp => {
+        console.log(`Response: ${resp["flag"]}`)
+    })
+}
+

lib/codeshare/application.ex

@@ -14,7 +14,10 @@ defmodule Codeshare.Application do
       CodeshareWeb.Endpoint,
       # Starts a worker by calling: Codeshare.Worker.start_link(arg)
       # {Codeshare.Worker, arg},
-      CodeshareWeb.Presence
+      # Start Presence
+      CodeshareWeb.Presence,
+      # Start CRDT Supervisor
+      Codeshare.CRDT.Supervisor
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/codeshare/crdt/character.ex

@@ -0,0 +1,170 @@
+defmodule Codeshare.Identifier do
+  @moduledoc """
+  List of identifiers define the 'position'
+  of a character in CRDT
+  """
+  alias __MODULE__
+
+  defstruct [
+    position: 0,
+    siteID: -1
+  ]
+
+  @doc """
+  Helper to convert payload from channel
+  to struct
+  """
+  def to_struct(identifier_map) do
+    map = identifier_map
+    %Identifier{
+      position: map["position"],
+      siteID: map["siteID"]
+    }
+  end
+
+  @doc """
+  Convert to string representation
+  """
+  def to_string(identifier) do
+    # Client and server have diff infinity values!
+    if identifier.siteID == 16777216 do
+      "[#{identifier.position}, Infinity]"
+    else
+      "[#{identifier.position}, #{identifier.siteID}]"
+    end
+  end
+
+  @doc """
+  Check if two identifiers are equal
+  """
+  def is_equal(id1, id2) do
+    id1.position == id2.position && id1.siteID == id2.siteID
+  end
+
+  @doc """
+  is `id1` > `id2` ? [Identifiers]
+  """
+  def is_greater(id1, id2) do
+    if id1.position == id2.position do
+      id1.siteID > id2.siteID
+    else
+      id1.position > id2.position
+    end
+  end
+
+  # TODO: Add struct validation?
+end
+
+defmodule Codeshare.Character do
+  @moduledoc """
+  Represensts each 'character' in
+  the CRDT text
+  """
+  alias __MODULE__
+  alias Codeshare.Identifier
+
+  defstruct [
+    ch: "",
+    identifiers: [%Identifier{}]
+  ]
+
+  @doc """
+  Helper to convert payload from channel
+  to struct
+  """
+  def to_struct(character_map) do
+    map = character_map
+    %Character{
+      ch: map["ch"],
+      identifiers: to_identifiers_struct_list(map["identifiers"])
+    }
+  end
+
+  @doc """
+  Convert to string representation
+  """
+  def to_string(character) do
+    "{#{character.ch}: [#{to_string_id_list(character.identifiers)}]}"
+  end
+
+  @doc """
+  Check if two characters are equal
+  """
+  def is_equal(character1, character2) do
+    if character1.ch != character2.ch || 
+        length(character1.identifiers) != length(character2.identifiers) do
+      false      
+    else
+      is_identifier_list_equal(character1.identifiers, 
+        character2.identifiers)
+    end
+  end
+
+  @doc """
+  is `character1` > `character2` ?
+  """
+  def is_greater(character1, character2) do
+    is_identifier_list_greater(character1.identifiers, 
+                                character2.identifiers)
+  end
+
+  # Helper functions
+
+  defp to_identifiers_struct_list(identifiers_map_list) do
+    if identifiers_map_list == [] do
+      []
+    else
+      [h | t] = identifiers_map_list
+      [Identifier.to_struct(h) | to_identifiers_struct_list(t)]
+    end
+  end 
+
+  defp is_identifier_list_equal(id_list1, id_list2) do
+    if id_list1 == [] && id_list2 == [] do
+      true
+    else
+      [id1 | id_list1] = id_list1
+      [id2 | id_list2] = id_list2
+
+      if Identifier.is_equal(id1, id2) do
+        is_identifier_list_equal(id_list1, id_list2)
+      else
+        false
+      end
+    end
+  end
+
+  defp is_identifier_list_greater(id_list1, id_list2) do
+
+    cond do
+      id_list1 == [] ->
+        false
+      id_list2 == [] ->
+        true
+      true ->
+        [id1 | id_list1] = id_list1
+        [id2 | id_list2] = id_list2
+
+        cond do
+          Identifier.is_greater(id1, id2) ->
+            true
+          Identifier.is_greater(id2, id1) ->
+            false
+          Identifier.is_equal(id1, id2) ->
+            is_identifier_list_greater(id_list1, id_list2)
+        end
+    end
+
+  end
+
+  defp to_string_id_list(id_list) do
+    [first_id | id_list] = id_list
+    if id_list == [] do
+      "#{Identifier.to_string(first_id)}"
+    else
+      "#{Identifier.to_string(first_id)}, #{to_string_id_list(id_list)}"
+    end
+  end
+
+  # TODO: Add struct validation?
+end

lib/codeshare/crdt/crdt.ex

@@ -0,0 +1,196 @@
+defmodule Codeshare.CRDT do
+  @moduledoc """
+  Manages the server-side CRDT
+  """
+  use Agent
+  alias Codeshare.{Character, Identifier}
+
+  # [] arg required by supervisor
+  def start_link(_opts) do
+    fn -> [[
+      %Character{
+        ch: "",
+        identifiers: [%Identifier{
+          position: 0,
+          siteID: -1
+        }]
+      },
+      %Character{
+        ch: "",
+        identifiers: [%Identifier{
+            position: 1,
+            siteID: 16777216 #TODO: Infinity for now; think of something
+          }]
+      }
+    ]]
+    end |> Agent.start_link()
+    # TODO: Registered with module name, which doesn't allow server crdt per session
+    # (It allows for only one server crdt process)
+    # Need another process to map session id with corresponding server crdt pid
+  end
+
+  @doc """
+  Put payload data recived from channel
+  into CRDT
+  """
+  def put(crdt, payload) do
+    character = Character.to_struct(payload["character"])
+    case Map.get(payload, "type") do
+      "input" -> 
+        remote_insert(crdt, character)
+      "delete" ->
+        remote_delete(crdt, character)
+      "inputnewline" ->
+        remote_insert_newline(crdt, character)
+      "deletenewline" ->
+        remote_delete_newline(crdt, character)
+    end
+  end
+
+  @doc """
+  Get CRDT data
+  """
+  def get(crdt) do
+    Agent.get(crdt, & &1)
+  end
+
+  @doc """
+  Get CRDT string representation
+  """
+  def get_string(crdt) do
+    Agent.get(crdt, & convert_to_string(&1))
+  end
+
+  def stop(crdt) do
+    Agent.stop(crdt)
+  end
+
+  # Helper functions
+
+  defp remote_insert(crdt, character) do
+    Agent.update(crdt, fn crdt -> insert_character(crdt, character) end)
+  end
+
+  defp remote_delete(crdt, character) do
+    Agent.update(crdt, fn crdt -> delete_character(crdt, character) end)
+  end
+
+  defp remote_insert_newline(crdt, character) do
+    Agent.update(crdt, fn crdt -> insert_newline(crdt, character) end)
+  end
+
+  defp remote_delete_newline(crdt, character) do
+    Agent.update(crdt, fn crdt -> delete_newline(crdt, character) end)
+  end
+
+  defp insert_character(crdt, character) do
+
+    [first_line | crdt] = crdt
+    last_ch = List.last(first_line) # NOTE: Takes linear time :(
+
+    if Character.is_greater(last_ch, character) do
+      [insert_character_on_line(first_line, character) | crdt]
+    else
+      [first_line | insert_character(crdt, character)]
+    end
+  end
+
+  defp insert_character_on_line(line, character) do
+
+    [first_ch | line] = line
+
+    if Character.is_greater(first_ch, character) do
+      [character | [ first_ch | line] ]
+    else
+      [first_ch | insert_character_on_line(line, character)]
+    end
+  end
+
+  defp delete_character(crdt, character) do
+
+    [first_line | crdt] = crdt
+    last_ch = List.last(first_line) # NOTE: Takes linear time :(
+
+    if Character.is_greater(last_ch, character) do
+      [delete_character_on_line(first_line, character) | crdt]
+    else
+      [first_line | delete_character(crdt, character)]
+    end
+  end
+
+  defp delete_character_on_line(line, character) do
+
+    [first_ch | line] = line
+
+    if Character.is_equal(first_ch, character) do
+      line
+    else
+      [first_ch | delete_character_on_line(line, character)]
+    end
+  end
+
+  defp insert_newline(crdt, character) do
+
+    [first_line | crdt] = crdt
+    last_ch = List.last(first_line) # NOTE: Takes linear time :(
+
+    if Character.is_greater(last_ch, character) do
+      insert_newline_on_line(first_line, character) ++ crdt
+    else
+      [first_line | insert_newline(crdt, character)]
+    end
+  end
+
+  defp insert_newline_on_line(line, character) do
+
+    [first_ch | line] = line
+
+    if Character.is_greater(first_ch, character) do
+      delimeter_ch = %Character{
+        ch: "",
+        identifiers: character.identifiers
+      }
+      line1 = [delimeter_ch]
+      line2 = [delimeter_ch | [first_ch | line] ]
+      [line1, line2]
+    else
+      lines = insert_newline_on_line(line, character)
+      [line1 | [line2]] = lines
+      line1 = [first_ch | line1]
+      [line1 | [line2]]
+    end
+  end
+
+  defp delete_newline(crdt, character) do
+
+    [first_line | crdt] = crdt
+    last_ch = List.last(first_line) # NOTE: Takes linear time :(
+
+    if Character.is_equal(last_ch, character) do
+      line1 = first_line |> Enum.reverse |> tl |> Enum.reverse
+      [[_ | line2] | crdt] = crdt
+      [line1++line2 | crdt]
+    else
+      [first_line | delete_newline(crdt, character)]
+    end
+  end
+
+  defp convert_to_string(crdt) do
+    if crdt == [] do
+      ""
+    else
+      [first_line | crdt] = crdt
+      "#{convert_line_to_string(first_line)}\n#{convert_to_string(crdt)}"
+    end
+  end
+
+  defp convert_line_to_string(line) do
+    [first_ch | line] = line
+    if line == [] do
+      "#{Character.to_string(first_ch)}"
+    else
+      "#{Character.to_string(first_ch)}, #{convert_line_to_string(line)}"
+    end
+  end
+
+end