From 8e77ababa95035e65fddbc8e331d62ceb7ab4507 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Fri, 20 Jul 2018 09:44:42 +0200
Subject: Merkle list not a separate process, it makes no sense

---
 lib/app/chat.ex        |  22 +++++++---
 lib/data/merklelist.ex | 117 ++++++++++++++++++++++++++++---------------------
 lib/manager.ex         |   9 +++-
 test/mkllst_test.exs   |  14 +++---
 4 files changed, 98 insertions(+), 64 deletions(-)

diff --git a/lib/app/chat.ex b/lib/app/chat.ex
index 696e53c..b93e7b3 100644
--- a/lib/app/chat.ex
+++ b/lib/app/chat.ex
@@ -19,6 +19,8 @@ defmodule SApp.Chat do
 
   use GenServer
 
+  alias SData.MerkleList, as: ML
+
   @doc """
   Start a process that connects to a given channel
   """
@@ -30,7 +32,7 @@ defmodule SApp.Chat do
   Initialize channel process.
   """
   def init(channel) do
-    {:ok, store} = SData.MerkleList.start_link(&msg_cmp/2)
+    store = ML.new(&msg_cmp/2)
     manifest = {:chat, channel}
     id = SData.term_hash manifest
 
@@ -76,13 +78,13 @@ defmodule SApp.Chat do
     msgitem = {(System.os_time :seconds),
                Shard.Identity.get_nickname(),
                msg}
-    GenServer.cast(state.store, {:insert, msgitem})
+    new_state = %{state | store: ML.insert(state.store, msgitem)}
 
     for peer <- state.peers do
-      push_messages(state, peer, nil, 5)
+      push_messages(new_state, peer, nil, 5)
     end
 
-    {:noreply, state}
+    {:noreply, new_state}
   end
 
   @doc """
@@ -110,12 +112,13 @@ defmodule SApp.Chat do
         Shard.Manager.send(peer_id, {state.id, {:manifest, state.manifest}})
       {:get, start} -> push_messages(peer_id, state, start, 20)
       {:info, _start, list, rest} ->
-        if rest != nil and not GenServer.call(state.store, {:has, rest}) do
+        if rest != nil and not ML.has(state.store, rest) do
           Shard.Manager.send(peer_id, {state.id, {:get, rest}})
         end
+        who = self()
         spawn_link(fn ->
           Process.sleep 1000
-          GenServer.cast(state.store, {:insert_many, list, (fn msg -> msg_callback(state.channel, msg) end)})
+          GenServer.cast(who, {:deferred_insert, list})
         end)
       _ -> nil
     end
@@ -127,8 +130,13 @@ defmodule SApp.Chat do
     end
   end
 
+  def handle_cast({:deferred_insert, list}, state) do
+    new_store = ML.insert_many(state.store, list, (fn msg -> msg_callback(state.channel, msg) end))
+    %{state | store: new_store}
+  end
+
   defp push_messages(state, to, start, num) do
-    case GenServer.call(state.store, {:read, start, num}) do
+    case ML.read(state.store, start, num) do
       {:ok, list, rest} ->
         Shard.Manager.send(to, {state.id, {:info, start, list, rest}})
       _ -> nil
diff --git a/lib/data/merklelist.ex b/lib/data/merklelist.ex
index 727f2a8..71483bd 100644
--- a/lib/data/merklelist.ex
+++ b/lib/data/merklelist.ex
@@ -1,50 +1,45 @@
 defmodule SData.MerkleList do
-  @moduledoc """
+  @moduledoc"""
   A simple Merkle list store.
 
   Future improvements:
-  - When messages are inserted other than at the top, all intermediate hashes
-    change. Keep track of the mapping from old hashes to new hashes so that get
-    requests can work even for hashes that are not valid anymore.
-  - group items in "pages" (bigger bundles)
+    - When messages are inserted other than at the top, all intermediate hashes
+      change. Keep track of the mapping from old hashes to new hashes so that get
+      requests can work even for hashes that are not valid anymore.
+    - group items in "pages" (bigger bundles)
   """
 
-  use GenServer
+  defstruct [:root, :top, :cmp, :store]
 
-  @doc """
-    Start a Merkle List storage process.
+  @doc"""
+  Create a Merkle list store.
 
-
-    `cmp` is a function that compares stored items and provides a total order.
-    It must return:
-      - `:after` if the first argument is more recent
-      - `:duplicate` if the two items are the same
-      - `:before` if the first argument is older
+  `cmp` is a function that compares stored items and provides a total order.
+  It must return:
+    - `:after` if the first argument is more recent
+    - `:duplicate` if the two items are the same
+    - `:before` if the first argument is older
   """
-  def start_link(cmp) do
-    GenServer.start_link(__MODULE__, cmp)
-  end
-
-  def init(cmp) do
+  def new(cmp) do
     root_item = :root
     root_hash = SData.term_hash root_item
-    state = %{
+    state = %SData.MerkleList{
               root:  root_hash,
               top:   root_hash,
               cmp:   cmp,
               store: %{ root_hash => root_item }
             }
-    {:ok, state}
+    state
   end
 
-  defp state_push(item, state) do
+  defp push(state, item) do
     new_item = {item, state.top}
     new_item_hash = SData.term_hash new_item
     new_store = Map.put(state.store, new_item_hash, new_item)
     %{ state | :top => new_item_hash, :store => new_store }
   end
 
-  defp state_pop(state) do
+  defp pop(state) do
     if state.top == state.root do
       :error
     else
@@ -55,59 +50,81 @@ defmodule SData.MerkleList do
     end
   end
 
-  defp insert_many(state, [], _callback) do
+  @doc"""
+  Insert a list of items in the store.
+
+  A callback function may be specified that is called on any item
+  that is sucessfully added, i.e. that wasn't present in the store before.
+  """
+  def insert_many(state, items, callback \\ (fn _ -> nil end)) do
+    items_sorted = Enum.sort(items, fn (x, y) -> state.cmp.(x, y) == :after end)
+    insert_many_aux(state, items_sorted, callback)
+  end
+
+  defp insert_many_aux(state, [], _callback) do
     state
   end
 
-  defp insert_many(state, [item | rest], callback) do
-    case state_pop(state) do
+  defp insert_many_aux(state, [item | rest], callback) do
+    case pop(state) do
       :error ->
-        new_state = state_push(item, insert_many(state, rest, callback))
+        new_state = push(insert_many_aux(state, rest, callback), item)
         callback.(item)
         new_state
       {:ok, front, state_rest} ->
         case state.cmp.(item, front) do
           :after ->
-            new_state = state_push(item, insert_many(state, rest, callback))
+            new_state = push(insert_many_aux(state, rest, callback), item)
             callback.(item)
             new_state
-          :duplicate -> insert_many(state, rest, callback)
-          :before -> state_push(front, insert_many(state_rest, [item | rest], callback))
+          :duplicate -> insert_many_aux(state, rest, callback)
+          :before -> push(insert_many_aux(state_rest, [item | rest], callback), item)
         end
     end
   end
 
-  def handle_cast({:insert, item}, state) do
-    handle_cast({:insert_many, [item]}, state)
-  end
+  @doc"""
+  Insert a single item in the store.
 
-  def handle_cast({:insert_many, items}, state) do
-    handle_cast({:insert_many, items, fn _ -> nil end}, state)
+  A callback function may be specified that is called on the item
+  if it is sucessfully added, i.e. it wasn't present in the store before.
+  """
+  def insert(state, item, callback \\ (fn _ -> nil end)) do
+    insert_many(state, [item], callback)
   end
 
-  def handle_cast({:insert_many, items, callback}, state) do
-    items_sorted = Enum.sort(items, fn (x, y) -> state.cmp.(x, y) == :after end)
-    new_state = insert_many(state, items_sorted, callback)
-    {:noreply, new_state}
-  end
+  @doc"""
+  Read some items from the state.
 
-  def handle_call({:read, qbegin, qlimit}, _from, state) do
+  The two parameters are optional:
+  - qbegin : hash of the first item to read
+  - qlimit : number of items to read
+  """
+  def read(state, qbegin \\ nil, qlimit \\ nil) do
     begin = qbegin || state.top
     limit = qlimit || 20
-    items = get_items_list(state, begin, limit)
-    {:reply, items, state}
+    get_items_list(state, begin, limit)
   end
 
-  def handle_call(:top, _from, state) do
-    {:reply, state.top, state}
+  @doc"""
+  Get the hash of the last item
+  """
+  def top(state) do
+    state.top
   end
 
-  def handle_call(:root, _from, state) do
-    {:reply, state.root, state}
+  @doc"""
+  Get the hash of the root item
+  """
+  def root(state) do
+    state.root
   end
 
-  def handle_call({:has, hash}, _from, state) do
-    {:reply, Map.has_key?(state.store, hash), state}
+  @doc"""
+  Check if the store holds a certain item
+  """
+  def has(state, hash) do
+    Map.has_key?(state.store, hash)
   end
 
   defp get_items_list(state, begin, limit) do
@@ -128,7 +145,7 @@ defmodule SData.MerkleList do
     end
   end
 
-  @doc """
+  @doc"""
     Compare function for timestamped strings
   """
   def cmp_ts_str({ts1, str1}, {ts2, str2}) do
diff --git a/lib/manager.ex b/lib/manager.ex
index 07295fa..45aae5f 100644
--- a/lib/manager.ex
+++ b/lib/manager.ex
@@ -1,6 +1,6 @@
 defmodule Shard.Manager do
   @moduledoc"""
-    Maintains three tables :
+    Maintains two important tables :
 
     - :peer_db
       
@@ -12,11 +12,18 @@ defmodule Shard.Manager do
       List of
         { id, manifest, shard_pid }
 
+    And also some others :
+
     - :peer_shard_db
 
       Mult-list of
         { peer_id, shard_id }
 
+    - :outbox
+      
+      Multi-list of
+        { peer_id, message }
+
   """
 
   use GenServer
diff --git a/test/mkllst_test.exs b/test/mkllst_test.exs
index 4df25df..ac13795 100644
--- a/test/mkllst_test.exs
+++ b/test/mkllst_test.exs
@@ -3,14 +3,16 @@ defmodule ShardTest.MklLst do
   doctest Shard.Application
 
   test "merkle list" do
-    {:ok, pid} = GenServer.start(SData.MerkleList, &SData.MerkleList.cmp_ts_str/2)
+    alias SData.MerkleList, as: ML
 
-    {:ok, [], nil} = GenServer.call(pid, {:read, nil, nil})
+    mkl = ML.new(&ML.cmp_ts_str/2)
 
-    GenServer.cast(pid, {:insert, {12, "aa, bb"}})
-    GenServer.cast(pid, {:insert_many, [{14, "qwerty"}, {8, "haha"}]})
-    GenServer.cast(pid, {:insert, {14, "qwerty"}})
-    {:ok, list, nil} = GenServer.call(pid, {:read, nil, nil})
+    {:ok, [], nil} = ML.read(mkl)
+
+    mkl = ML.insert(mkl, {12, "aa, bb"})
+    mkl = ML.insert_many(mkl, [{14, "qwerty"}, {8, "haha"}])
+    mkl = ML.insert(mkl, {14, "qwerty"})
+    {:ok, list, nil} = ML.read(mkl, nil, nil)
     assert length(list) == 3
   end
 end
-- 
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