First commit

chapter4/files/todos.csv

@@ -0,0 +1,3 @@
+2018/12/19,Dentist
+2018/12/20,Shopping
+2018/12/19,Movies

chapter4/fraction.ex

@@ -0,0 +1,16 @@
+defmodule Fraction do
+  defstruct a: nil, b: nil
+
+  def new(a, b), do: %Fraction{a: a, b: b}
+
+  def value(%Fraction{a: a, b: b}) do
+    a / b
+  end
+
+  def add(%Fraction{a: a1, b: b1}, %Fraction{a: a2, b: b2}) do
+    new(
+      a1 * b2 + a2 * b1,
+      b1 * b2
+    )
+  end
+end

chapter4/simple_todo.ex

@@ -0,0 +1,16 @@
+defmodule TodoList do
+  def new(), do: %{}
+
+  def add_entry(todo_list, date, title) do
+    Map.update(
+      todo_list,
+      date,
+      [title],
+      &[title | &1]
+    )
+  end
+
+  def entries(todo_list, date) do
+    Map.get(todo_list, date, [])
+  end
+end

chapter4/todo_builder.ex

@@ -0,0 +1,59 @@
+defmodule TodoList do
+  defstruct auto_id: 1, entries: %{}
+
+  def new(), do: %TodoList{}
+
+  def new(entries \\ []) do
+    Enum.reduce(
+      entries,
+      %TodoList{},
+      fn entry, todo_list_acc ->
+        add_entry(todo_list_acc, entry)
+      end
+      # Alternative definition
+      # &add_entry(&2, &1)
+    )
+  end
+
+  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

chapter4/todo_crud.ex

@@ -0,0 +1,47 @@
+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

chapter4/todo_import.ex

@@ -0,0 +1,126 @@
+defmodule TodoList do
+  defstruct auto_id: 1, entries: %{}
+
+  def new(entries \\ []) do
+    Enum.reduce(
+      entries,
+      %TodoList{},
+      fn entry, todo_list_acc ->
+        add_entry(todo_list_acc, entry)
+      end
+      # Alternative definition
+      # &add_entry(&2, &1)
+    )
+  end
+
+  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
+
+defmodule TodoList.CsvImporter do
+  def import(path) do
+    File.stream!(path)
+    |> Stream.map(&String.replace(&1, "\n", ""))
+    |> Stream.map(fn string ->
+      [date, title] = String.split(string, ",")
+      {date, title}
+    end)
+    |> Stream.map(fn {date, title} ->
+      [year, month, day] =
+        date
+        |> String.split("/")
+        |> Enum.map(&String.to_integer(&1))
+
+      {{year, month, day}, title}
+    end)
+    |> Stream.map(fn {{year, month, day}, title} ->
+      {:ok, date} = Date.new(year, month, day)
+      %{date: date, title: title}
+    end)
+    |> TodoList.new()
+  end
+end
+
+defmodule TodoList.CsvImporterAlternative do
+  def import(path) do
+    path
+    |> read_lines
+    |> create_entires
+    |> TodoList.new()
+  end
+
+  defp read_lines(path) do
+    path
+    |> File.stream!()
+    |> Stream.map(&String.replace(&1, "\n", ""))
+  end
+
+  defp create_entires(lines) do
+    lines
+    |> Stream.map(&extract_fileds/1)
+    |> Stream.map(&create_entry/1)
+  end
+
+  defp extract_fileds(line) do
+    line
+    |> String.split(",")
+    |> convert_date
+  end
+
+  defp convert_date([date_string, title]) do
+    {parse_date(date_string), title}
+  end
+
+  defp parse_date(date_string) do
+    [year, month, day] =
+      date_string
+      |> String.split("/")
+      |> Enum.map(&String.to_integer/1)
+
+    {:ok, date = Date.new(year, month, day)}
+    date
+  end
+
+  defp create_entry({date, title}) do
+    %{date: date, title: title}
+  end
+end

chapter4/todo_map_entry.ex

@@ -0,0 +1,28 @@
+defmodule MultiDict do
+  def new(), do: %{}
+
+  def add(dict, key, value) do
+    Map.update(
+      dict,
+      key,
+      [value],
+      &[value | &1]
+    )
+  end
+
+  def get(dict, key) do
+    Map.get(dict, key, [])
+  end
+end
+
+defmodule TodoList do
+  def new(), do: MultiDict.new()
+
+  def add_entry(todo_list, entry) do
+    MultiDict.add(todo_list, entry.date, entry)
+  end
+
+  def entries(todo_list, date) do
+    MultiDict.get(todo_list, date)
+  end
+end

chapter4/todo_multi_dict.ex

@@ -0,0 +1,28 @@
+defmodule MultiDict do
+  def new(), do: %{}
+
+  def add(dict, key, value) do
+    Map.update(
+      dict,
+      key,
+      [value],
+      &[value | &1]
+    )
+  end
+
+  def get(dict, key) do
+    Map.get(dict, key, [])
+  end
+end
+
+defmodule TodoList do
+  def new(), do: MultiDict.new()
+
+  def add_entry(todo_list, date, title) do
+    MultiDict.add(todo_list, date, title)
+  end
+
+  def entries(todo_list, date) do
+    MultiDict.get(todo_list, date)
+  end
+end