Add formula database property

src/Databases/Properties/Factory.php

@@ -20,6 +20,7 @@ public static function fromArray(array $array): PropertyInterface
             Property::TYPE_SELECT => Select::fromArray($array),
             Property::TYPE_MULTI_SELECT => MultiSelect::fromArray($array),
             Property::TYPE_DATE => Date::fromArray($array),
+            Property::TYPE_FORMULA => Formula::fromArray($array),
             Property::TYPE_PEOPLE => People::fromArray($array),
             Property::TYPE_FILES => Files::fromArray($array),
             Property::TYPE_CHECKBOX => Checkbox::fromArray($array),

src/Databases/Properties/Formula.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace Notion\Databases\Properties;
+
+/**
+ * @psalm-type FormulaJson = array{
+ *      id: string,
+ *      name: string,
+ *      type: "formula",
+ *      formula: array{ expression: string },
+ * }
+ */
+class Formula implements PropertyInterface
+{
+    private const TYPE = Property::TYPE_FORMULA;
+
+    private Property $property;
+    private string $expression;
+
+    private function __construct(Property $property, string $expression)
+    {
+        $this->property = $property;
+        $this->expression = $expression;
+    }
+
+    public static function create(string $propertyName = "Formula", string $expression = ""): self
+    {
+        $property = Property::create("", $propertyName, self::TYPE);
+
+        return new self($property, $expression);
+    }
+
+    public function property(): Property
+    {
+        return $this->property;
+    }
+
+    public function expression(): string
+    {
+        return $this->expression;
+    }
+
+    public function withExpression(string $expression): self
+    {
+        return new self($this->property, $expression);
+    }
+
+    public static function fromArray(array $array): self
+    {
+        /** @psalm-var FormulaJson $array */
+        $property = Property::fromArray($array);
+        $expression = $array[self::TYPE]["expression"];
+
+        return new self($property, $expression);
+    }
+
+    public function toArray(): array
+    {
+        $array = $this->property->toArray();
+        $array[self::TYPE] = [
+            "expression" => $this->expression,
+        ];
+
+        return $array;
+    }
+}

src/Databases/Properties/Property.php

@@ -105,10 +105,10 @@ public function isDate(): bool
         return $this->type === self::TYPE_DATE;
     }
 
-    // public function isFormula(): bool
-    // {
-    //     return $this->type === self::TYPE_FORMULA;
-    // }
+    public function isFormula(): bool
+    {
+        return $this->type === self::TYPE_FORMULA;
+    }
 
     // public function isRelation(): bool
     // {

tests/Unit/Databases/Properties/FormulaTest.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Notion\Test\Unit\Databases\Properties;
+
+use Notion\Databases\Properties\Factory;
+use Notion\Databases\Properties\Formula;
+use PHPUnit\Framework\TestCase;
+
+class FormulaTest extends TestCase
+{
+    public function test_create(): void
+    {
+        $expression = "if(prop(\"In stock\"), 0, prop(\"Price\"))";
+        $formula = Formula::create("Dummy prop name", $expression);
+
+        $this->assertEquals("Dummy prop name", $formula->property()->name());
+        $this->assertTrue($formula->property()->isFormula());
+        $this->assertEquals($expression, $formula->expression());
+    }
+
+    public function test_change_expression(): void
+    {
+        $expression = "if(prop(\"In stock\"), 0, prop(\"Price\"))";
+        $formula = Formula::create()->withExpression($expression);
+
+        $this->assertEquals($expression, $formula->expression());
+    }
+
+    public function test_array_conversion(): void
+    {
+        $array = [
+            "id"    => "abc",
+            "name"  => "dummy",
+            "type"  => "formula",
+            "formula" => [
+                "expression" => "if(prop(\"In stock\"), 0, prop(\"Price\"))",
+            ],
+        ];
+        $formula = Formula::fromArray($array);
+        $fromFactory = Factory::fromArray($array);
+
+        $this->assertEquals($array, $formula->toArray());
+        $this->assertEquals($array, $fromFactory->toArray());
+    }
+}