feat(desktop): create interface MutableSchoolSupply

desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/MutableSchoolSupply.kt

@@ -0,0 +1,54 @@
+package com.intelligentbackpack.desktopdomain.entities
+
+/**
+ * Interface for a mutable school supply.
+ */
+interface MutableSchoolSupply<T : SchoolSupply> : SchoolSupply {
+
+    /**
+     * The school supply that replaces this one.
+     */
+    val replacedBy: Set<T>
+
+    /**
+     * The school supply that this one replaces.
+     */
+    val replace: Set<T>
+
+    /**
+     * Adds the given school supply to the school supplies that replace this one.
+     * @param schoolSupply The school supply to add.
+     * @return The school supply with the given school supply added.
+     */
+    fun addReplacedBy(schoolSupply: T): MutableSchoolSupply<T>
+
+    /**
+     * Adds the given school supplies to the school supplies that replace this one.
+     * @param schoolSupplies The school supplies to add.
+     * @return The school supply with the given school supplies added.
+     */
+    fun addReplacesBy(schoolSupplies: Set<T>): MutableSchoolSupply<T> =
+        schoolSupplies.fold(this) { acc, schoolSupply -> acc.addReplacedBy(schoolSupply) }
+
+    /**
+     * Adds the given school supply to the school supplies that this one replaces.
+     * @param schoolSupply The school supply to add.
+     * @return The school supply with the given school supply added.
+     */
+    fun addReplace(schoolSupply: T): MutableSchoolSupply<T>
+
+    /**
+     * Adds the given school supplies to the school supplies that this one replaces.
+     * @param schoolSupplies The school supplies to add.
+     * @return The school supply with the given school supplies added.
+     */
+    fun addReplaces(schoolSupplies: Set<T>): MutableSchoolSupply<T> =
+        schoolSupplies.fold(this) { acc, schoolSupply -> acc.addReplace(schoolSupply) }
+
+    /**
+     * Adds the given subjects to the school supply.
+     * @param subjects The subjects to add.
+     * @return The school supply with the given subjects added.
+     */
+    override fun addSubjects(subjects: Set<Subject>): MutableSchoolSupply<T>
+}