Add ISBN Verifier Exercise (#641)

Author: tomasnorre

config.json

@@ -1140,6 +1140,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "isbn-verifier",
+        "name": "ISBN Verifier",
+        "uuid": "f7309216-0ba7-4990-acd7-4a47eca949fb",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "say",
         "name": "Say",

exercises/practice/isbn-verifier/.docs/instructions.md

@@ -0,0 +1,42 @@
+# 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

exercises/practice/isbn-verifier/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "tomasnorre"
+  ],
+  "files": {
+    "solution": [
+      "IsbnVerifier.php"
+    ],
+    "test": [
+      "IsbnVerifierTest.php"
+    ],
+    "example": [
+      ".meta/example.php"
+    ]
+  },
+  "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"
+}

exercises/practice/isbn-verifier/.meta/example.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+class IsbnVerifier
+{
+    public function isValid(string $isbn): bool
+    {
+        $isbn = str_replace("-", "", $isbn);
+        if (strlen($isbn) !== 10) {
+            return false;
+        }
+
+        $i = 10;
+        $isbnSum = 0;
+
+        if ($isbn[strlen($isbn) - 1] === 'X') {
+            $isbnSum = 10;
+            $isbn = substr($isbn, 0, -1);
+        }
+
+        if (!is_numeric($isbn)) {
+            return false;
+        }
+
+        for ($j = 0, $jMax = strlen($isbn); $j < $jMax; $j++) {
+            $intV = (int) $isbn[$j];
+            $isbnSum += $i * $intV;
+            $i--;
+        }
+
+        return $isbnSum % 11 === 0;
+    }
+}

exercises/practice/isbn-verifier/.meta/tests.toml

@@ -0,0 +1,67 @@
+# 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.
+
+[0caa3eac-d2e3-4c29-8df8-b188bc8c9292]
+description = "valid isbn"
+
+[19f76b53-7c24-45f8-87b8-4604d0ccd248]
+description = "invalid isbn check digit"
+
+[4164bfee-fb0a-4a1c-9f70-64c6a1903dcd]
+description = "valid isbn with a check digit of 10"
+
+[3ed50db1-8982-4423-a993-93174a20825c]
+description = "check digit is a character other than X"
+
+[9416f4a5-fe01-4b61-a07b-eb75892ef562]
+description = "invalid check digit in isbn is not treated as zero"
+
+[c19ba0c4-014f-4dc3-a63f-ff9aefc9b5ec]
+description = "invalid character in isbn is not treated as zero"
+
+[28025280-2c39-4092-9719-f3234b89c627]
+description = "X is only valid as a check digit"
+
+[f6294e61-7e79-46b3-977b-f48789a4945b]
+description = "valid isbn without separating dashes"
+
+[185ab99b-3a1b-45f3-aeec-b80d80b07f0b]
+description = "isbn without separating dashes and X as check digit"
+
+[7725a837-ec8e-4528-a92a-d981dd8cf3e2]
+description = "isbn without check digit and dashes"
+
+[47e4dfba-9c20-46ed-9958-4d3190630bdf]
+description = "too long isbn and no dashes"
+
+[737f4e91-cbba-4175-95bf-ae630b41fb60]
+description = "too short isbn"
+
+[5458a128-a9b6-4ff8-8afb-674e74567cef]
+description = "isbn without check digit"
+
+[70b6ad83-d0a2-4ca7-a4d5-a9ab731800f7]
+description = "check digit of X should not be used for 0"
+
+[94610459-55ab-4c35-9b93-ff6ea1a8e562]
+description = "empty isbn"
+
+[7bff28d4-d770-48cc-80d6-b20b3a0fb46c]
+description = "input is 9 characters"
+
+[ed6e8d1b-382c-4081-8326-8b772c581fec]
+description = "invalid characters are not ignored after checking length"
+
+[daad3e58-ce00-4395-8a8e-e3eded1cdc86]
+description = "invalid characters are not ignored before checking length"
+
+[fb5e48d8-7c03-4bfb-a088-b101df16fdc3]
+description = "input is too long but contains a valid isbn"

exercises/practice/isbn-verifier/IsbnVerifier.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * By adding type hints and enabling strict type checking, code can become
+ * easier to read, self-documenting and reduce the number of potential bugs.
+ * By default, type declarations are non-strict, which means they will attempt
+ * to change the original type to match the type specified by the
+ * type-declaration.
+ *
+ * In other words, if you pass a string to a function requiring a float,
+ * it will attempt to convert the string value to a float.
+ *
+ * To enable strict mode, a single declare directive must be placed at the top
+ * of the file.
+ * This means that the strictness of typing is configured on a per-file basis.
+ * This directive not only affects the type declarations of parameters, but also
+ * a function's return type.
+ *
+ * For more info review the Concept on strict type checking in the PHP track
+ * <link>.
+ *
+ * To disable strict typing, comment out the directive below.
+ */
+
+declare(strict_types=1);
+
+class IsbnVerifier
+{
+    public function isValid(string $isbn): bool
+    {
+        throw new \BadMethodCallException(sprintf('Implement the %s method', __FUNCTION__));
+    }
+}

exercises/practice/isbn-verifier/IsbnVerifierTest.php

@@ -0,0 +1,170 @@
+<?php
+
+declare(strict_types=1);
+
+class IsbnVerifierTest extends PHPUnit\Framework\TestCase
+{
+    private IsbnVerifier $isbnVerifier;
+
+    public static function setUpBeforeClass(): void
+    {
+        require_once 'IsbnVerifier.php';
+    }
+
+    public function setUp(): void
+    {
+        $this->isbnVerifier = new IsbnVerifier();
+    }
+
+    /**
+     * uuid: 0caa3eac-d2e3-4c29-8df8-b188bc8c9292
+     */
+    public function testValidIsbn(): void
+    {
+        $this->assertTrue($this->isbnVerifier->isValid('3-598-21508-8'));
+    }
+
+    /**
+     * uuid: 19f76b53-7c24-45f8-87b8-4604d0ccd248
+     */
+    public function testInvalidIsbnCheckDigit(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-21508-9'));
+    }
+
+    /**
+     * uuid: 4164bfee-fb0a-4a1c-9f70-64c6a1903dcd
+     */
+    public function testValidIsbnWithACheckDigitOf10(): void
+    {
+        $this->assertTrue($this->isbnVerifier->isValid('3-598-21507-X'));
+    }
+
+    /**
+     * uuid: 3ed50db1-8982-4423-a993-93174a20825c
+     */
+    public function testCheckDigitIsACharacterOtherThanX(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-21507-A'));
+    }
+
+    /**
+     * uuid: 9416f4a5-fe01-4b61-a07b-eb75892ef562
+     */
+    public function testInvalidCheckDigitInIsbnIsNotTreatedAsZero(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('4-598-21507-B'));
+    }
+
+    /**
+     * uuid: c19ba0c4-014f-4dc3-a63f-ff9aefc9b5ec
+     */
+    public function testInvalidCharacterInIsbnIsNotTreatedAsZero(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-P1581-X'));
+    }
+
+    /**
+     * uuid: 28025280-2c39-4092-9719-f3234b89c627
+     */
+    public function testXIsOnlyValidAsACheckDigit(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-2X507-9'));
+    }
+
+    /**
+     * uuid: f6294e61-7e79-46b3-977b-f48789a4945b
+     */
+    public function testValidIsbnWithoutSeparatingDashes(): void
+    {
+        $this->assertTrue($this->isbnVerifier->isValid('3598215088'));
+    }
+
+    /**
+     * uuid: 185ab99b-3a1b-45f3-aeec-b80d80b07f0b
+     */
+    public function testIsbnWithoutSeparatingDashesAndXAsCheckDigit(): void
+    {
+        $this->assertTrue($this->isbnVerifier->isValid('359821507X'));
+    }
+
+    /**
+     * uuid: 7725a837-ec8e-4528-a92a-d981dd8cf3e2
+     */
+    public function testIsbnWithoutCheckDigitAndDashes(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('359821507'));
+    }
+
+    /**
+     * uuid: 47e4dfba-9c20-46ed-9958-4d3190630bdf
+     */
+    public function testTooLongIsbnAndNoDashes(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3598215078X'));
+    }
+
+    /**
+     * uuid: 737f4e91-cbba-4175-95bf-ae630b41fb60
+     */
+    public function testTooShortIsbn(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('00'));
+    }
+
+    /**
+     * uuid: 5458a128-a9b6-4ff8-8afb-674e74567cef
+     */
+    public function testIsbnWithoutCheckDigit(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-21507'));
+    }
+
+    /**
+     * uuid: 70b6ad83-d0a2-4ca7-a4d5-a9ab731800f7
+     */
+    public function testCheckDigitOfXShouldNotBeUsedForZero(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3-598-21515-X'));
+    }
+
+    /**
+     * uuid: 94610459-55ab-4c35-9b93-ff6ea1a8e562
+     */
+    public function testEmptyIsbn(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid(''));
+    }
+
+    /**
+     * uuid: 7bff28d4-d770-48cc-80d6-b20b3a0fb46c
+     */
+    public function testInputIs9Characters(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('134456729'));
+    }
+
+    /**
+     * uuid: ed6e8d1b-382c-4081-8326-8b772c581fec
+     */
+    public function testInvalidCharactersAreNotIgnoredAfterCheckingLength(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3132P34035'));
+    }
+
+    /**
+     * uuid: daad3e58-ce00-4395-8a8e-e3eded1cdc86
+     */
+    public function testCatchInvalidCharactersInOnOtherwiseValidIsbn(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('3598P215088'));
+    }
+
+    /**
+     * uuid: fb5e48d8-7c03-4bfb-a088-b101df16fdc3
+     */
+    public function testInputIsTooLongButContainsAValidIsbn(): void
+    {
+        $this->assertFalse($this->isbnVerifier->isValid('98245726788'));
+    }
+}