Grade school

src/GradeSchool.php

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+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+use Assert\Assert;
+use Tightenco\Collect\Support\Collection;
+
+final class GradeSchool
+{
+    private Collection $students;
+
+    public function __construct()
+    {
+        $this->students = new Collection();
+    }
+
+    public function addStudentToGrade(string $name, int $grade): void
+    {
+        Assert::that($name)->notEmpty('Name cannot be blank');
+
+        Assert::that($grade)
+            ->greaterOrEqualThan(1, 'Grade must be greater than or equal to 1');
+
+        $this->students->push(['name' => $name, 'grade' => $grade]);
+    }
+
+    public function getAllStudents(): Collection
+    {
+        return $this->students->pluck('grade')
+            ->unique()
+            ->map(fn (int $grade): Collection => new Collection([
+                'grade' => $grade,
+                'students' => $this->getStudentsByGrade($grade),
+            ]))
+            ->sortBy('grade')
+            ->values();
+    }
+
+    public function getStudentsByGrade(int $grade): Collection
+    {
+        return $this->students
+            ->filter(fn (array $student): bool => $grade == $student['grade'])
+            ->pluck('name')
+            ->sort()
+            ->values();
+    }
+}

tests/GradeSchoolTest.php

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+<?php
+
+declare(strict_types=1);
+
+use App\GradeSchool;
+use Assert\AssertionFailedException;
+
+beforeEach(function (): void {
+    $this->school = new GradeSchool();
+});
+
+it('gets all students', function (): void {
+    $this->school->addStudentToGrade('Anna', 1);
+    $this->school->addStudentToGrade('Jim', 2);
+    $this->school->addStudentToGrade('Charlie', 3);
+
+    $expected = [
+        ['grade' => 1, 'students' => ['Anna']],
+        ['grade' => 2, 'students' => ['Jim']],
+        ['grade' => 3, 'students' => ['Charlie']],
+    ];
+
+    assertSame($expected, $this->school->getAllStudents()->toArray());
+});
+
+it('can get students by grade', function (): void {
+    $this->school->addStudentToGrade('Jim', 2);
+
+    assertSame(['Jim'], $this->school->getStudentsByGrade(2)->toArray());
+});
+
+it('should order grades numerically', function (): void {
+    $this->school->addStudentToGrade('Anna', 1);
+    $this->school->addStudentToGrade('Charlie', 3);
+    $this->school->addStudentToGrade('Jim', 2);
+    $this->school->addStudentToGrade('Harry', 4);
+
+    $expected = [
+        ['grade' => 1, 'students' => ['Anna']],
+        ['grade' => 2, 'students' => ['Jim']],
+        ['grade' => 3, 'students' => ['Charlie']],
+        ['grade' => 4, 'students' => ['Harry']],
+    ];
+
+    assertSame($expected, $this->school->getAllStudents()->toArray());
+});
+
+it('names within a grade are ordered alphabetically', function (): void {
+    $this->school->addStudentToGrade('Charlie', 1);
+    $this->school->addStudentToGrade('Barb', 1);
+    $this->school->addStudentToGrade('Anna', 1);
+
+    $this->school->addStudentToGrade('Peter', 2);
+    $this->school->addStudentToGrade('Alex', 2);
+    $this->school->addStudentToGrade('Zoe', 2);
+
+    $expected = [
+        [
+            'grade' => 1,
+            'students' => ['Anna', 'Barb', 'Charlie'],
+        ],
+        [
+            'grade' => 2,
+            'students' => ['Alex', 'Peter', 'Zoe'],
+        ]
+    ];
+
+    assertSame($expected, $this->school->getAllStudents()->toArray());
+});
+
+test('name cannot be empty', function (): void {
+    $this->school->addStudentToGrade('', 1);
+})->throws(
+    AssertionFailedException::class,
+    'Name cannot be blank'
+);
+
+test('grade cannot be zero or negative', function (int $grade): void {
+    $this->school->addStudentToGrade('Fred', $grade);
+})->with([0, -1])->throws(
+    AssertionFailedException::class,
+    'Grade must be greater than or equal to 1'
+);