isbn-verifier

elixir/isbn-verifier/.exercism/config.json

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+{
+  "authors": [
+    "stfnsr"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "devonestes",
+    "herminiotorres",
+    "neenjaw",
+    "sotojuan"
+  ],
+  "files": {
+    "solution": [
+      "lib/isbn_verifier.ex"
+    ],
+    "test": [
+      "test/isbn_verifier_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Check if a given string is a valid ISBN-10 number.",
+  "source": "Converting a string into a number and some basic processing utilizing a relatable real world example.",
+  "source_url": "https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation"
+}

elixir/isbn-verifier/.exercism/metadata.json

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+{"track":"elixir","exercise":"isbn-verifier","id":"6c4a3518e48f4c1595cc3d84835d58f8","url":"https://exercism.org/tracks/elixir/exercises/isbn-verifier","handle":"negrienko","is_requester":true,"auto_approve":false}

elixir/isbn-verifier/.formatter.exs

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

elixir/isbn-verifier/.gitignore

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+# 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").
+isbn_verifier-*.tar
+

elixir/isbn-verifier/HELP.md

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+# Help
+
+## Running the tests
+
+From the terminal, change to the base directory of the exercise then execute the tests with:
+
+```bash
+$ mix test
+```
+
+This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
+
+Documentation:
+
+* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
+* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
+
+## Pending tests
+
+In test suites of practice exercises, all but the first test have been tagged to be skipped.
+
+Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
+
+For example:
+
+```elixir
+# @tag :pending
+test "shouting" do
+  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
+end
+```
+
+If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
+
+```bash
+$ mix test --include pending
+```
+
+Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
+
+```elixir
+# ExUnit.configure(exclude: :pending, trace: true)
+```
+
+## Useful `mix test` options
+
+* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
+* `--failed` - runs only tests that failed the last time they ran
+* `--max-failures` - the suite stops evaluating tests when this number of test failures
+is reached
+* `--seed 0` - disables randomization so the tests in a single file will always be ran
+in the same order they were defined in
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/isbn_verifier.ex` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
+- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.

elixir/isbn-verifier/README.md

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+# ISBN Verifier
+
+Welcome to ISBN Verifier on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+The [ISBN-10 verification process][isbn-verification] is used to validate book identification numbers.
+These normally contain dashes and look like: `3-598-21508-8`
+
+## ISBN
+
+The ISBN-10 format is 9 digits (0 to 9) plus one check character (either a digit or an X only).
+In the case the check character is an X, this represents the value '10'.
+These may be communicated with or without hyphens, and can be checked for their validity by the following formula:
+
+```text
+(d₁ * 10 + d₂ * 9 + d₃ * 8 + d₄ * 7 + d₅ * 6 + d₆ * 5 + d₇ * 4 + d₈ * 3 + d₉ * 2 + d₁₀ * 1) mod 11 == 0
+```
+
+If the result is 0, then it is a valid ISBN-10, otherwise it is invalid.
+
+## Example
+
+Let's take the ISBN-10 `3-598-21508-8`.
+We plug it in to the formula, and get:
+
+```text
+(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 == 0
+```
+
+Since the result is 0, this proves that our ISBN is valid.
+
+## Task
+
+Given a string the program should check if the provided string is a valid ISBN-10.
+Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.
+
+The program should be able to verify ISBN-10 both with and without separating dashes.
+
+## Caveats
+
+Converting from strings to numbers can be tricky in certain languages.
+Now, it's even trickier since the check digit of an ISBN-10 may be 'X' (representing '10').
+For instance `3-598-21507-X` is a valid ISBN-10.
+
+[isbn-verification]: https://en.wikipedia.org/wiki/International_Standard_Book_Number
+
+## Source
+
+### Created by
+
+- @stfnsr
+
+### Contributed to by
+
+- @angelikatyborska
+- @Cohen-Carlisle
+- @devonestes
+- @herminiotorres
+- @neenjaw
+- @sotojuan
+
+### Based on
+
+Converting a string into a number and some basic processing utilizing a relatable real world example. - https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation

elixir/isbn-verifier/lib/isbn_verifier.ex

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+defmodule IsbnVerifier do
+  @doc """
+    Checks if a string is a valid ISBN-10 identifier
+
+    ## Examples
+
+      iex> IsbnVerifier.isbn?("3-598-21507-X")
+      true
+
+      iex> IsbnVerifier.isbn?("3-598-2K507-0")
+      false
+
+  """
+
+  @regex ~r/^(?<digits>\d{9})(?<check_digit>[0-9X])$/
+
+  @spec isbn?(String.t()) :: boolean
+  def isbn?(isbn) do
+    with isbn_without_dashes <- String.replace(isbn, "-", ""),
+         %{"digits" => digits, "check_digit" => check_digit} <-
+           Regex.named_captures(@regex, isbn_without_dashes) do
+      rem(check_sum(digits) + check_digit(check_digit), 11) == 0
+    else
+      _ -> false
+    end
+  end
+
+  defp check_sum(digits) do
+    {1, check_sum} =
+      digits
+      |> String.graphemes()
+      |> Enum.reduce({10, 0}, fn digit, {index, acc} ->
+        {index - 1, acc + String.to_integer(digit) * index}
+      end)
+
+    check_sum
+  end
+
+  defp check_digit("X"), do: 10
+  defp check_digit(string), do: String.to_integer(string)
+end

elixir/isbn-verifier/mix.exs

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+defmodule IsbnVerifier.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :isbn_verifier,
+      version: "0.1.0",
+      # elixir: "~> 1.8",
+      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

elixir/isbn-verifier/test/isbn_verifier_test.exs

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+defmodule IsbnVerifierTest do
+  use ExUnit.Case
+
+  test "valid isbn number" do
+    assert IsbnVerifier.isbn?("3-598-21508-8")
+  end
+
+  test "invalid isbn check digit" do
+    refute IsbnVerifier.isbn?("3-598-21508-9")
+  end
+
+  test "valid isbn number with a check digit of 10" do
+    assert IsbnVerifier.isbn?("3-598-21507-X")
+  end
+
+  test "check digit is a character other than X" do
+    refute IsbnVerifier.isbn?("3-598-21507-A")
+  end
+
+  test "check digit in isbn is not treated as zero" do
+    refute IsbnVerifier.isbn?("4-598-21507-B")
+  end
+
+  test "invalid character in isbn" do
+    refute IsbnVerifier.isbn?("3-598-P1581-X")
+  end
+
+  test "X is only valid as a check digit" do
+    refute IsbnVerifier.isbn?("3-598-2X507-9")
+  end
+
+  test "valid isbn without separating dashes" do
+    assert IsbnVerifier.isbn?("3598215088")
+  end
+
+  test "isbn without separating dashes and X as check digit" do
+    assert IsbnVerifier.isbn?("359821507X")
+  end
+
+  test "isbn without check digit and dashes" do
+    refute IsbnVerifier.isbn?("359821507")
+  end
+
+  test "too long isbn and no dashes" do
+    refute IsbnVerifier.isbn?("3598215078X")
+  end
+
+  test "too short isbn" do
+    refute IsbnVerifier.isbn?("00")
+  end
+
+  test "isbn without check digit" do
+    refute IsbnVerifier.isbn?("3-598-21507")
+  end
+
+  test "too long isbn" do
+    refute IsbnVerifier.isbn?("3-598-21507-XA")
+  end
+
+  test "check digit of X should not be used for 0" do
+    refute IsbnVerifier.isbn?("3-598-21515-X")
+  end
+
+  test "input is 9 characters" do
+    refute IsbnVerifier.isbn?("134456729")
+  end
+
+  test "invalid characters are not ignored" do
+    refute IsbnVerifier.isbn?("3132P34035")
+  end
+
+  test "invalid characters are not ignored before checking length" do
+    refute IsbnVerifier.isbn?("3598P215088")
+  end
+
+  test "input is too long but contains a valid isbn" do
+    refute IsbnVerifier.isbn?("98245726788")
+  end
+
+  # Test cases from international ISBN to test variable dash placement
+  # Adapted from https://en.wikipedia.org/wiki/International_Standard_Book_Number#Registrant_element
+
+  test "Qatar	NCCAH, Doha" do
+    assert IsbnVerifier.isbn?("99921-58-10-7")
+  end
+
+  test "Singapore	World Scientific" do
+    assert IsbnVerifier.isbn?("9971-5-0210-0")
+  end
+
+  test "Greece	Sigma Publications" do
+    assert IsbnVerifier.isbn?("960-425-059-0")
+  end
+
+  test "Czech Republic; Slovakia	Taita Publishers" do
+    assert IsbnVerifier.isbn?("80-902734-1-6")
+  end
+
+  test "Brazil	Companhia das Letras" do
+    assert IsbnVerifier.isbn?("85-359-0277-5")
+  end
+
+  test "English-speaking area	Simon Wallenberg Press" do
+    assert IsbnVerifier.isbn?("1-84356-028-3")
+  end
+
+  test "English-speaking area	Scribner" do
+    assert IsbnVerifier.isbn?("0-684-84328-5")
+  end
+
+  test "English-speaking area	Frederick Ungar" do
+    assert IsbnVerifier.isbn?("0-8044-2957-X")
+  end
+
+  test "English-speaking area	J. A. Allen & Co." do
+    assert IsbnVerifier.isbn?("0-85131-041-9")
+  end
+
+  test "English-speaking area	Edupedia Publications Pvt Ltd." do
+    assert IsbnVerifier.isbn?("93-86954-21-4")
+  end
+
+  test "English-speaking area Willmann-Bell" do
+    assert IsbnVerifier.isbn?("0-943396-04-2")
+  end
+
+  test "English-speaking area	KT Publishing" do
+    assert IsbnVerifier.isbn?("0-9752298-0-X")
+  end
+end

elixir/isbn-verifier/test/test_helper.exs

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+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true)