From 09665c3b885fb7643b79f4214129d3d907a52a6b Mon Sep 17 00:00:00 2001
From: AYM1607 <u.g.a.mariano@gmail.com>
Date: Sun, 21 Jun 2020 11:02:00 -0500
Subject: [PATCH] Create: Finished code exercises for the 6th chapter

---
 chapter6/key_value_gen_server.ex            |  38 ++++++
 chapter6/key_value_gen_server_registered.ex |  40 ++++++
 chapter6/server_process_cast.ex             |  68 ++++++++++
 chapter6/server_process_todo.ex             | 133 ++++++++++++++++++++
 chapter6/todo_server.ex                     |  96 ++++++++++++++
 5 files changed, 375 insertions(+)
 create mode 100644 chapter6/key_value_gen_server.ex
 create mode 100644 chapter6/key_value_gen_server_registered.ex
 create mode 100644 chapter6/server_process_cast.ex
 create mode 100644 chapter6/server_process_todo.ex
 create mode 100644 chapter6/todo_server.ex

diff --git a/chapter6/key_value_gen_server.ex b/chapter6/key_value_gen_server.ex
new file mode 100644
index 0000000..f19db5b
--- /dev/null
+++ b/chapter6/key_value_gen_server.ex
@@ -0,0 +1,38 @@
+defmodule KeyValueStore do
+  use GenServer
+
+  def start do
+    GenServer.start(KeyValueStore, nil)
+  end
+
+  def put(pid, key, value) do
+    GenServer.cast(pid, {:put, key, value})
+  end
+
+  def get(pid, key) do
+    GenServer.call(pid, {:get, key})
+  end
+
+  @impl true
+  def init(_) do
+    # Set up the process to send itself a cleanup message every 5 secs.
+    :timer.send_interval(5000, :cleanup)
+    {:ok, %{}}
+  end
+
+  @impl true
+  def handle_cast({:put, key, value}, state) do
+    {:noreply, Map.put(state, key, value)}
+  end
+
+  @impl true
+  def handle_call({:get, key}, state) do
+    {:reply, Map.get(state, key), state}
+  end
+
+  @impl true
+  def handle_info(:cleanup, state) do
+    IO.puts("Performing cleanup...")
+    {:noreply, state}
+  end
+end
diff --git a/chapter6/key_value_gen_server_registered.ex b/chapter6/key_value_gen_server_registered.ex
new file mode 100644
index 0000000..dd41a34
--- /dev/null
+++ b/chapter6/key_value_gen_server_registered.ex
@@ -0,0 +1,40 @@
+defmodule KeyValueStore do
+  use GenServer
+
+  def start do
+    # At compile time, __MODULE__ is replaced with KeyValueStore
+    # This makes refactoring easier.
+    GenServer.start(__MODULE__, nil, name: __MODULE__)
+  end
+
+  def put(key, value) do
+    GenServer.cast(__MODULE__, {:put, key, value})
+  end
+
+  def get(key) do
+    GenServer.call(__MODULE__, {:get, key})
+  end
+
+  @impl true
+  def init(_) do
+    # Set up the process to send itself a cleanup message every 5 secs.
+    :timer.send_interval(5000, :cleanup)
+    {:ok, %{}}
+  end
+
+  @impl true
+  def handle_cast({:put, key, value}, state) do
+    {:noreply, Map.put(state, key, value)}
+  end
+
+  @impl true
+  def handle_call({:get, key}, _, state) do
+    {:reply, Map.get(state, key), state}
+  end
+
+  @impl true
+  def handle_info(:cleanup, state) do
+    IO.puts("Performing cleanup...")
+    {:noreply, state}
+  end
+end
diff --git a/chapter6/server_process_cast.ex b/chapter6/server_process_cast.ex
new file mode 100644
index 0000000..721f08d
--- /dev/null
+++ b/chapter6/server_process_cast.ex
@@ -0,0 +1,68 @@
+defmodule ServerProcess do
+  def start(callback_module) do
+    spawn(fn ->
+      initial_state = callback_module.init()
+      loop(callback_module, initial_state)
+    end)
+  end
+
+  def loop(callback_module, current_state) do
+    receive do
+      {:call, request, caller} ->
+        {response, new_state} =
+          callback_module.handle_call(
+            request,
+            current_state
+          )
+
+        send(caller, {:response, response})
+        loop(callback_module, new_state)
+
+      {:cast, request} ->
+        new_state =
+          callback_module.handle_cast(
+            request,
+            current_state
+          )
+
+        loop(callback_module, new_state)
+    end
+  end
+
+  def call(server_pid, request) do
+    send(server_pid, {:call, request, self()})
+
+    receive do
+      {:response, response} ->
+        response
+    end
+  end
+
+  def cast(server_pid, request) do
+    send(server_pid, {:cast, request})
+  end
+end
+
+defmodule KeyValueStore do
+  def init, do: %{}
+
+  def start do
+    ServerProcess.start(KeyValueStore)
+  end
+
+  def put(pid, key, value) do
+    ServerProcess.cast(pid, {:put, key, value})
+  end
+
+  def get(pid, key) do
+    ServerProcess.call(pid, {:get, key})
+  end
+
+  def handle_call({:get, key}, state) do
+    {Map.get(state, key), state}
+  end
+
+  def handle_cast({:put, key, value}, state) do
+    Map.put(state, key, value)
+  end
+end
diff --git a/chapter6/server_process_todo.ex b/chapter6/server_process_todo.ex
new file mode 100644
index 0000000..2bdb3a8
--- /dev/null
+++ b/chapter6/server_process_todo.ex
@@ -0,0 +1,133 @@
+defmodule ServerProcess do
+  def start(callback_module) do
+    spawn(fn ->
+      initial_state = callback_module.init()
+      loop(callback_module, initial_state)
+    end)
+  end
+
+  def loop(callback_module, current_state) do
+    receive do
+      {:call, request, caller} ->
+        {response, new_state} =
+          callback_module.handle_call(
+            request,
+            current_state
+          )
+
+        send(caller, {:response, response})
+        loop(callback_module, new_state)
+
+      {:cast, request} ->
+        new_state =
+          callback_module.handle_cast(
+            request,
+            current_state
+          )
+
+        loop(callback_module, new_state)
+    end
+  end
+
+  def call(server_pid, request) do
+    send(server_pid, {:call, request, self()})
+
+    receive do
+      {:response, response} ->
+        response
+    end
+  end
+
+  def cast(server_pid, request) do
+    send(server_pid, {:cast, request})
+  end
+end
+
+defmodule TodoServer do
+  def start do
+    ServerProcess.start(TodoServer)
+  end
+
+  def init, do: TodoList.new()
+
+  def entries(server_pid, date) do
+    ServerProcess.call(server_pid, {:entries, date})
+  end
+
+  def add_entry(server_pid, entry) do
+    ServerProcess.cast(server_pid, {:add_entry, entry})
+  end
+
+  def delete_entry(server_pid, entry_id) do
+    ServerProcess.cast(server_pid, {:delete_entry, entry_id})
+  end
+
+  def update_entry(server_pid, entry_id, updater_fun) do
+    ServerProcess.cast(server_pid, {:update_entry, entry_id, updater_fun})
+  end
+
+  def handle_cast({:add_entry, entry}, state) do
+    TodoList.add_entry(state, entry)
+  end
+
+  def handle_cast({:delete_entry, entry_id}, state) do
+    TodoList.delete_entry(state, entry_id)
+  end
+
+  def handle_cast({:update_entry, entry_id, updater_fun}, state) do
+    TodoList.update_entry(state, entry_id, updater_fun)
+  end
+
+  def handle_call({:entries, date}, state) do
+    entries = TodoList.entries(state, date)
+    {entries, state}
+  end
+end
+
+defmodule TodoList do
+  defstruct auto_id: 1, entries: %{}
+
+  def new(), do: %TodoList{}
+
+  def add_entry(todo_list, entry) do
+    entry = Map.put(entry, :id, todo_list.auto_id)
+
+    new_entries =
+      Map.put(
+        todo_list.entries,
+        todo_list.auto_id,
+        entry
+      )
+
+    %TodoList{todo_list | entries: new_entries, auto_id: todo_list.auto_id + 1}
+  end
+
+  def entries(todo_list, date) do
+    todo_list.entries
+    |> Stream.filter(fn {_, entry} -> entry.date == date end)
+    |> Enum.map(fn {_, entry} -> entry end)
+  end
+
+  def update_entry(todo_list, %{} = new_entry) do
+    update_entry(todo_list, new_entry.id, fn _ -> new_entry end)
+  end
+
+  def update_entry(todo_list, entry_id, updater_fun) do
+    case Map.fetch(todo_list.entries, entry_id) do
+      :error ->
+        todo_list
+
+      {:ok, old_entry} ->
+        old_entry_id = old_entry.id
+        # Make sure that the result of the updater is a map and the
+        # id remains unchanged.
+        new_entry = %{id: ^old_entry_id} = updater_fun.(old_entry)
+        new_entries = Map.put(todo_list.entries, new_entry.id, new_entry)
+        %TodoList{todo_list | entries: new_entries}
+    end
+  end
+
+  def delete_entry(todo_list, entry_id) do
+    %TodoList{todo_list | entries: Map.delete(todo_list.entries, entry_id)}
+  end
+end
diff --git a/chapter6/todo_server.ex b/chapter6/todo_server.ex
new file mode 100644
index 0000000..08d111f
--- /dev/null
+++ b/chapter6/todo_server.ex
@@ -0,0 +1,96 @@
+defmodule TodoServer do
+  use GenServer
+
+  def start do
+    GenServer.start(__MODULE__, nil)
+  end
+
+  def add_entry(pid, entry) do
+    GenServer.cast(pid, {:add_entry, entry})
+  end
+
+  def delete_entry(pid, entry_id) do
+    GenServer.cast(pid, {:delete_entry, entry_id})
+  end
+
+  def update_entry(pid, entry_id, updater_fun) do
+    GenServer.cast(pid, {:update_entry, entry_id, updater_fun})
+  end
+
+  def entries(pid, date) do
+    GenServer.call(pid, {:entries, date})
+  end
+
+  @impl true
+  def init(_) do
+    {:ok, TodoList.new()}
+  end
+
+  @impl true
+  def handle_cast({:add_entry, entry}, state) do
+    {:noreply, TodoList.add_entry(state, entry)}
+  end
+
+  @impl true
+  def handle_cast({:delete_entry, entry_id}, state) do
+    {:noreply, TodoList.delete_entry(state, entry_id)}
+  end
+
+  @impl true
+  def handle_cast({:update_entry, entry_id, updater_fun}, state) do
+    {:noreply, TodoList.update_entry(state, entry_id, updater_fun)}
+  end
+
+  @impl true
+  def handle_call({:entries, date}, _, state) do
+    {:reply, TodoList.entries(state, date), state}
+  end
+end
+
+defmodule TodoList do
+  defstruct auto_id: 1, entries: %{}
+
+  def new(), do: %TodoList{}
+
+  def add_entry(todo_list, entry) do
+    entry = Map.put(entry, :id, todo_list.auto_id)
+
+    new_entries =
+      Map.put(
+        todo_list.entries,
+        todo_list.auto_id,
+        entry
+      )
+
+    %TodoList{todo_list | entries: new_entries, auto_id: todo_list.auto_id + 1}
+  end
+
+  def entries(todo_list, date) do
+    todo_list.entries
+    |> Stream.filter(fn {_, entry} -> entry.date == date end)
+    |> Enum.map(fn {_, entry} -> entry end)
+  end
+
+  def update_entry(todo_list, %{} = new_entry) do
+    update_entry(todo_list, new_entry.id, fn _ -> new_entry end)
+  end
+
+  def update_entry(todo_list, entry_id, updater_fun) do
+    case Map.fetch(todo_list.entries, entry_id) do
+      :error ->
+        todo_list
+
+      {:ok, old_entry} ->
+        old_entry_id = old_entry.id
+        # Make sure that the result of the updater is a map and the
+        # id remains unchanged.
+        new_entry = %{id: ^old_entry_id} = updater_fun.(old_entry)
+        new_entries = Map.put(todo_list.entries, new_entry.id, new_entry)
+        %TodoList{todo_list | entries: new_entries}
+    end
+  end
+
+  def delete_entry(todo_list, entry_id) do
+    %TodoList{todo_list | entries: Map.delete(todo_list.entries, entry_id)}
+  end
+end