feat: Adds implementation for NegativeBigDecimal.

src/Internal/Exceptions/NonNegativeValue.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace TinyBlocks\Math\Internal\Exceptions;
+
+use RuntimeException;
+use TinyBlocks\Math\Internal\Number;
+
+final class NonNegativeValue extends RuntimeException
+{
+    public function __construct(Number $number)
+    {
+        $template = 'Value <%s> is not valid. Must be a negative number less than zero.';
+        parent::__construct(message: sprintf($template, $number->value));
+    }
+}

src/Internal/Number.php

@@ -66,6 +66,11 @@ public function isNegative(): bool
         return $this->value < self::ZERO;
     }
 
+    public function isPositiveOrZero(): bool
+    {
+        return $this->isZero() || !$this->isNegative();
+    }
+
     public function isNegativeOrZero(): bool
     {
         return $this->isZero() || $this->isNegative();

src/Internal/Operations/Adapters/BcMathAdapter.php

@@ -12,7 +12,7 @@
 use TinyBlocks\Math\Internal\Operations\Adapters\Scales\Subtraction;
 use TinyBlocks\Math\Internal\Operations\MathOperations;
 
-final class BcMathAdapter implements MathOperations
+final readonly class BcMathAdapter implements MathOperations
 {
     public function add(BigNumber $augend, BigNumber $addend): Result
     {

src/Internal/Operations/Extension/ExtensionAdapter.php

@@ -4,7 +4,7 @@
 
 namespace TinyBlocks\Math\Internal\Operations\Extension;
 
-final class ExtensionAdapter implements Extension
+final readonly class ExtensionAdapter implements Extension
 {
     public function isAvailable(string $extension): bool
     {

src/Internal/Scale.php

@@ -7,13 +7,13 @@
 use TinyBlocks\Math\BigNumber;
 use TinyBlocks\Math\Internal\Exceptions\InvalidScale;
 
-final class Scale
+final readonly class Scale
 {
     private const MINIMUM = 0;
     private const MAXIMUM = 2147483647;
     private const ZERO_DECIMAL_PLACE = 0;
 
-    private function __construct(public readonly ?int $value)
+    private function __construct(public ?int $value)
     {
         if (!$this->hasAutomaticScale() && ($this->value < self::MINIMUM || $this->value > self::MAXIMUM)) {
             throw new InvalidScale(value: $this->value, minimum: self::MINIMUM, maximum: self::MAXIMUM);

src/NegativeBigDecimal.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace TinyBlocks\Math;
+
+use TinyBlocks\Math\Internal\BigNumberBehavior;
+use TinyBlocks\Math\Internal\Exceptions\NonNegativeValue;
+use TinyBlocks\Math\Internal\Number;
+use TinyBlocks\Math\Internal\Scale;
+
+class NegativeBigDecimal extends BigNumberBehavior implements BigNumber
+{
+    protected function __construct(string|float $value, ?int $scale = null)
+    {
+        $scale = Scale::from(value: $scale);
+        $number = Number::from(value: $value);
+
+        if ($number->isPositiveOrZero()) {
+            throw new NonNegativeValue(number: $number);
+        }
+
+        parent::__construct(number: $number, scale: $scale);
+    }
+
+    public static function fromFloat(float $value, ?int $scale = BigNumber::AUTOMATIC_SCALE): NegativeBigDecimal
+    {
+        return new NegativeBigDecimal(value: $value, scale: $scale);
+    }
+
+    public static function fromString(string $value, ?int $scale = BigNumber::AUTOMATIC_SCALE): NegativeBigDecimal
+    {
+        return new NegativeBigDecimal(value: $value, scale: $scale);
+    }
+}

tests/NegativeBigDecimalTest.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+namespace TinyBlocks\Math;
+
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use TinyBlocks\Math\Internal\Exceptions\NonNegativeValue;
+
+final class NegativeBigDecimalTest extends TestCase
+{
+    public function testFromFloat(): void
+    {
+        /** @Given a negative float value */
+        $value = -1.0;
+
+        /** @When creating a NegativeBigDecimal from the float */
+        $actual = NegativeBigDecimal::fromFloat(value: $value);
+
+        /** @Then the created object should be an instance of both BigNumber and NegativeBigDecimal */
+        self::assertInstanceOf(BigNumber::class, $actual);
+        self::assertInstanceOf(NegativeBigDecimal::class, $actual);
+    }
+
+    public function testFromString(): void
+    {
+        /** @Given a negative string value */
+        $value = '-0.3333333333333333333333';
+
+        /** @When creating a NegativeBigDecimal from the string */
+        $actual = NegativeBigDecimal::fromString(value: $value);
+
+        /** @Then the created object should be an instance of both BigNumber and NegativeBigDecimal */
+        self::assertInstanceOf(BigNumber::class, $actual);
+        self::assertInstanceOf(NegativeBigDecimal::class, $actual);
+    }
+
+    #[DataProvider('dataProviderForTestNonNegativeValue')]
+    public function testNonNegativeValue(mixed $value): void
+    {
+        /** @Given a non-negative value */
+        $template = 'Value <%s> is not valid. Must be a negative number less than zero.';
+
+        /** @Then a NonNegativeValue exception should be thrown with the correct message */
+        $this->expectException(NonNegativeValue::class);
+        $this->expectExceptionMessage(sprintf($template, $value));
+
+        /** @When attempting to create a NegativeBigDecimal with a non-negative value */
+        NegativeBigDecimal::fromFloat(value: $value);
+    }
+
+    public function testNonNegativeValueWithNegate(): void
+    {
+        /** @Given a NegativeBigDecimal value */
+        $template = 'Value <%s> is not valid. Must be a negative number less than zero.';
+
+        /** @Then a NonNegativeValue exception should be thrown when the value is negated */
+        $this->expectException(NonNegativeValue::class);
+        $this->expectExceptionMessage(sprintf($template, 10.155));
+
+        /** @When negating a negative number, it should trigger an exception */
+        $negative = NegativeBigDecimal::fromFloat(value: -10.155);
+        $negative->negate();
+    }
+
+    public static function dataProviderForTestNonNegativeValue(): array
+    {
+        return [
+            'Zero value'       => ['value' => 0],
+            'Positive integer' => ['value' => 1]
+        ];
+    }
+}