Add practice exercise ledger (#1367)

* Add practice exercise `ledger`

* Format config file

* Fix bad solution

* type for locale

config.json

@@ -2314,6 +2314,25 @@
         "practices": [],
         "difficulty": 6
       },
+      {
+        "slug": "ledger",
+        "name": "Ledger",
+        "uuid": "a3134be3-ac2f-4612-9cd2-4f2a6a4de48f",
+        "prerequisites": [
+          "if",
+          "lists",
+          "atoms",
+          "strings",
+          "maps",
+          "dates-and-time",
+          "multiple-clause-functions",
+          "pattern-matching"
+        ],
+        "practices": [
+          "multiple-clause-functions"
+        ],
+        "difficulty": 6
+      },
       {
         "slug": "list-ops",
         "name": "List Ops",

exercises/practice/ledger/.docs/instructions.md

@@ -0,0 +1,14 @@
+# Instructions
+
+Refactor a ledger printer.
+
+The ledger exercise is a refactoring exercise.
+There is code that prints a nicely formatted ledger, given a locale (American or Dutch) and a currency (US dollar or euro).
+The code however is rather badly written, though (somewhat surprisingly) it consistently passes the test suite.
+
+Rewrite this code.
+Remember that in refactoring the trick is to make small steps that keep the tests passing.
+That way you can always quickly go back to a working version.
+Version control tools like git can help here as well.
+
+Please keep a log of what changes you've made and make a comment on the exercise containing that log, this will help reviewers.

exercises/practice/ledger/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

exercises/practice/ledger/.gitignore

@@ -0,0 +1,26 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+ledger-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

exercises/practice/ledger/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "jiegillet"
+  ],
+  "files": {
+    "solution": [
+      "lib/ledger.ex"
+    ],
+    "test": [
+      "test/ledger_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Refactor a ledger printer."
+}

exercises/practice/ledger/.meta/example.ex

@@ -0,0 +1,127 @@
+defmodule Ledger do
+  @doc """
+  Format the given entries given a currency and locale
+  """
+  @type currency :: :usd | :eur
+  @type locale :: :en_US | :nl_NL
+  @type entry :: %{amount_in_cents: integer(), date: Date.t(), description: String.t()}
+
+  @spec format_entries(currency(), locale(), list(entry())) :: String.t()
+  def format_entries(currency, locale, entries) do
+    header = header(locale)
+
+    entries =
+      entries
+      |> Enum.sort(&compare_entries/2)
+      |> Enum.map(fn entry -> format_entry(currency, locale, entry) end)
+
+    Enum.join([header | entries], "\n") <> "\n"
+  end
+
+  defp header(:en_US), do: "Date       | Description               | Change       "
+  defp header(:nl_NL), do: "Datum      | Omschrijving              | Verandering  "
+
+  defp compare_entries(a, b) do
+    case Date.compare(a.date, b.date) do
+      :lt ->
+        true
+
+      :gt ->
+        false
+
+      :eq ->
+        cond do
+          a.description < b.description -> true
+          a.description > b.description -> false
+          true -> a.amount_in_cents <= b.amount_in_cents
+        end
+    end
+  end
+
+  @description_width 25
+  @amount_width 13
+  defp format_entry(currency, locale, %{
+         amount_in_cents: amount,
+         date: date,
+         description: description
+       }) do
+    date = format_date(date, locale)
+
+    amount =
+      amount
+      |> format_amount(currency, locale)
+      |> String.pad_leading(@amount_width, " ")
+
+    description =
+      if String.length(description) > @description_width do
+        String.slice(description, 0, @description_width - 3) <> "..."
+      else
+        String.pad_trailing(description, @description_width, " ")
+      end
+
+    Enum.join([date, description, amount], " | ")
+  end
+
+  defp format_date(date, :en_US) do
+    year = date.year
+    month = date.month |> to_string() |> String.pad_leading(2, "0")
+    day = date.day |> to_string() |> String.pad_leading(2, "0")
+    Enum.join([month, day, year], "/")
+  end
+
+  defp format_date(date, :nl_NL) do
+    year = date.year
+    month = date.month |> to_string() |> String.pad_leading(2, "0")
+    day = date.day |> to_string() |> String.pad_leading(2, "0")
+    Enum.join([day, month, year], "-")
+  end
+
+  defp format_amount(amount, currency, :en_US) do
+    currency = format_currency(currency)
+    number = format_number(abs(amount), ".", ",")
+
+    if amount >= 0 do
+      " #{currency}#{number} "
+    else
+      "(#{currency}#{number})"
+    end
+  end
+
+  defp format_amount(amount, currency, :nl_NL) do
+    currency = format_currency(currency)
+    number = format_number(abs(amount), ",", ".")
+
+    if amount >= 0 do
+      "#{currency} #{number} "
+    else
+      "#{currency} -#{number} "
+    end
+  end
+
+  defp format_currency(:usd), do: "$"
+  defp format_currency(:eur), do: "€"
+
+  defp format_number(number, decimal_separator, thousand_separator) do
+    decimal = number |> rem(100) |> to_string() |> String.pad_leading(2, "0")
+    whole = number |> div(100) |> to_string() |> chunk() |> Enum.join(thousand_separator)
+    whole <> decimal_separator <> decimal
+  end
+
+  defp chunk(number) do
+    case String.length(number) do
+      0 ->
+        []
+
+      n when n < 3 ->
+        [number]
+
+      n when rem(n, 3) == 0 ->
+        {chunk, rest} = String.split_at(number, 3)
+        [chunk | chunk(rest)]
+
+      n ->
+        {chunk, rest} = String.split_at(number, rem(n, 3))
+        [chunk | chunk(rest)]
+    end
+  end
+end

exercises/practice/ledger/.meta/tests.toml

@@ -0,0 +1,43 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[d131ecae-a30e-436c-b8f3-858039a27234]
+description = "empty ledger"
+
+[ce4618d2-9379-4eca-b207-9df1c4ec8aaa]
+description = "one entry"
+
+[8d02e9cb-e6ee-4b77-9ce4-e5aec8eb5ccb]
+description = "credit and debit"
+
+[502c4106-0371-4e7c-a7d8-9ce33f16ccb1]
+description = "multiple entries on same date ordered by description"
+
+[29dd3659-6c2d-4380-94a8-6d96086e28e1]
+description = "final order tie breaker is change"
+
+[9b9712a6-f779-4f5c-a759-af65615fcbb9]
+description = "overlong description is truncated"
+
+[67318aad-af53-4f3d-aa19-1293b4d4c924]
+description = "euros"
+
+[bdc499b6-51f5-4117-95f2-43cb6737208e]
+description = "Dutch locale"
+
+[86591cd4-1379-4208-ae54-0ee2652b4670]
+description = "Dutch locale and euros"
+
+[876bcec8-d7d7-4ba4-82bd-b836ac87c5d2]
+description = "Dutch negative number with 3 digits before decimal point"
+
+[29670d1c-56be-492a-9c5e-427e4b766309]
+description = "American negative number with 3 digits before decimal point"

exercises/practice/ledger/lib/ledger.ex

@@ -0,0 +1,104 @@
+defmodule Ledger do
+  @doc """
+  Format the given entries given a currency and locale
+  """
+  @type currency :: :usd | :eur
+  @type locale :: :en_US | :nl_NL
+  @type entry :: %{amount_in_cents: integer(), date: Date.t(), description: String.t()}
+
+  @spec format_entries(currency(), locale(), list(entry())) :: String.t()
+  def format_entries(currency, locale, entries) do
+    header =
+      if locale == :en_US do
+        "Date       | Description               | Change       \n"
+      else
+        "Datum      | Omschrijving              | Verandering  \n"
+      end
+
+    if entries == [] do
+      header
+    else
+      entries =
+        Enum.sort(entries, fn a, b ->
+          cond do
+            a.date.day < b.date.day -> true
+            a.date.day > b.date.day -> false
+            a.description < b.description -> true
+            a.description > b.description -> false
+            true -> a.amount_in_cents <= b.amount_in_cents
+          end
+        end)
+        |> Enum.map(fn entry -> format_entry(currency, locale, entry) end)
+        |> Enum.join("\n")
+
+      header <> entries <> "\n"
+    end
+  end
+
+  defp format_entry(currency, locale, entry) do
+    year = entry.date.year |> to_string()
+    month = entry.date.month |> to_string() |> String.pad_leading(2, "0")
+    day = entry.date.day |> to_string() |> String.pad_leading(2, "0")
+
+    date =
+      if locale == :en_US do
+        month <> "/" <> day <> "/" <> year <> " "
+      else
+        day <> "-" <> month <> "-" <> year <> " "
+      end
+
+    number =
+      if locale == :en_US do
+        decimal =
+          entry.amount_in_cents |> abs |> rem(100) |> to_string() |> String.pad_leading(2, "0")
+
+        whole =
+          if abs(div(entry.amount_in_cents, 100)) < 1000 do
+            abs(div(entry.amount_in_cents, 100)) |> to_string()
+          else
+            to_string(div(abs(div(entry.amount_in_cents, 100)), 1000)) <>
+              "," <> to_string(rem(abs(div(entry.amount_in_cents, 100)), 1000))
+          end
+
+        whole <> "." <> decimal
+      else
+        decimal =
+          entry.amount_in_cents |> abs |> rem(100) |> to_string() |> String.pad_leading(2, "0")
+
+        whole =
+          if abs(div(entry.amount_in_cents, 100)) < 1000 do
+            abs(div(entry.amount_in_cents, 100)) |> to_string()
+          else
+            to_string(div(abs(div(entry.amount_in_cents, 100)), 1000)) <>
+              "." <> to_string(rem(abs(div(entry.amount_in_cents, 100)), 1000))
+          end
+
+        whole <> "," <> decimal
+      end
+
+    amount =
+      if entry.amount_in_cents >= 0 do
+        if locale == :en_US do
+          "  #{if(currency == :eur, do: "€", else: "$")}#{number} "
+        else
+          " #{if(currency == :eur, do: "€", else: "$")} #{number} "
+        end
+      else
+        if locale == :en_US do
+          " (#{if(currency == :eur, do: "€", else: "$")}#{number})"
+        else
+          " #{if(currency == :eur, do: "€", else: "$")} -#{number} "
+        end
+      end
+      |> String.pad_leading(14, " ")
+
+    description =
+      if entry.description |> String.length() > 26 do
+        " " <> String.slice(entry.description, 0, 22) <> "..."
+      else
+        " " <> String.pad_trailing(entry.description, 25, " ")
+      end
+
+    date <> "|" <> description <> " |" <> amount
+  end
+end

exercises/practice/ledger/mix.exs

@@ -0,0 +1,28 @@
+defmodule Ledger.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :ledger,
+      version: "0.1.0",
+      # elixir: "~> 1.10",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end