feat: add OneOf API

Author: tksimeji

modules/core/src/main/kotlin/net/azisaba/data/NumberProvider.kt

@@ -3,5 +3,5 @@ package net.azisaba.data
 import kotlin.random.Random
 
 interface NumberProvider<T : Number> {
-    fun sample(random: Random): T
+    fun sample(random: Random = Random.Default): T
 }

modules/core/src/main/kotlin/net/azisaba/data/OneOf.kt

@@ -0,0 +1,57 @@
+package net.azisaba.data
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlin.random.Random
+
+@Serializable
+sealed interface OneOf<T : Any> {
+    fun choice(random: Random = Random.Default): T
+
+    @Serializable
+    @SerialName("Fixed")
+    data class Fixed<T : Any>(val value: T) : OneOf<T> {
+        override fun choice(random: Random): T = value
+    }
+
+    @Serializable
+    @SerialName("Uniform")
+    data class Uniform<T : Any>(val values: List<T>) : OneOf<T> {
+        init {
+            require(values.isNotEmpty()) { "values must not be empty" }
+        }
+
+        override fun choice(random: Random): T = values[random.nextInt(values.size)]
+    }
+
+    @Serializable
+    @SerialName("Weighted")
+    data class Weighted<T : Any>(val entries: List<Entry<T>>) : OneOf<T> {
+        private val totalWeight: Int = entries.sumOf(Entry<T>::weight)
+
+        init {
+            require(entries.isNotEmpty()) { "entries must not be empty" }
+            require(totalWeight > 0) { "total weight must be greater than 0" }
+        }
+
+        override fun choice(random: Random): T {
+            var r = random.nextInt(totalWeight)
+
+            for (entry in entries) {
+                if (r < entry.weight) {
+                    return entry.value
+                }
+                r -= entry.weight
+            }
+
+            return entries.last().value
+        }
+
+        @Serializable
+        data class Entry<T : Any>(val value: T, val weight: Int) {
+            init {
+                require(weight > 0) { "weight must be greater than 0" }
+            }
+        }
+    }
+}