From cdf605ca7cbe799ba782dd98063202b51c05566e Mon Sep 17 00:00:00 2001
From: Rafael Pili <rafael.pili@gobots.com.br>
Date: Sat, 31 Jul 2021 14:16:28 -0300
Subject: [PATCH] feat: add distinct operator and tests

---
 .../kwik/generator/api/GeneratorOperators.kt  | 26 +++++++++++++++++++
 .../kwik/generator/api/DistinctTest.kt        | 25 ++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 generator/api/src/commonTest/kotlin/com/github/jcornaz/kwik/generator/api/DistinctTest.kt

diff --git a/generator/api/src/commonMain/kotlin/com/github/jcornaz/kwik/generator/api/GeneratorOperators.kt b/generator/api/src/commonMain/kotlin/com/github/jcornaz/kwik/generator/api/GeneratorOperators.kt
index 4425f9c3..60fba7ba 100644
--- a/generator/api/src/commonMain/kotlin/com/github/jcornaz/kwik/generator/api/GeneratorOperators.kt
+++ b/generator/api/src/commonMain/kotlin/com/github/jcornaz/kwik/generator/api/GeneratorOperators.kt
@@ -3,6 +3,7 @@ package com.github.jcornaz.kwik.generator.api
 import kotlin.random.Random
 
 private const val DEFAULT_SAMPLE_PROBABILITY = 0.2
+private const val MAX_DISTINCT_TRIES = 100
 
 /**
  * Returns a generator containing the results of applying the given transform function to each element emitted by
@@ -40,6 +41,31 @@ public fun <T> Generator<T>.filter(predicate: (T) -> Boolean): Generator<T> =
 public fun <T, R> Generator<T>.andThen(transform: (T) -> Generator<R>): Generator<R> =
     Generator { transform(generate(it)).generate(it) }
 
+/**
+ * Returns a generator that emits items of the upstream generator only once (based on result of `hashCode` and `equals` method)
+ *
+ * Be sure to use a generator function that can generate a big set of values
+ * Be sure to not overuse it has it may slow down your tests
+ */
+public fun <T> Generator<T>.distinct(): Generator<T> {
+    var generatedValues = mutableListOf<T>()
+    return Generator {
+        var retries = 0
+        val genSize = generatedValues.size
+        generatedValues.add(generate(it))
+        generatedValues = generatedValues.toMutableSet().toMutableList()
+        while (genSize == generatedValues.size) {
+            if (retries > MAX_DISTINCT_TRIES) {
+                throw Exception("Number of retries exceeded maximum. Distinct cannot be applied to this resource")
+            }
+            generatedValues.add(generate(it))
+            generatedValues = generatedValues.toMutableSet().toMutableList()
+            retries++
+        }
+        generatedValues.last()
+    }
+}
+
 /**
  * @Deprecated Use `andThen` operator instead
  */
diff --git a/generator/api/src/commonTest/kotlin/com/github/jcornaz/kwik/generator/api/DistinctTest.kt b/generator/api/src/commonTest/kotlin/com/github/jcornaz/kwik/generator/api/DistinctTest.kt
new file mode 100644
index 00000000..183ebb08
--- /dev/null
+++ b/generator/api/src/commonTest/kotlin/com/github/jcornaz/kwik/generator/api/DistinctTest.kt
@@ -0,0 +1,25 @@
+package com.github.jcornaz.kwik.generator.api
+
+import com.github.jcornaz.kwik.generator.test.AbstractGeneratorTest
+import kotlin.math.absoluteValue
+import kotlin.random.Random
+import kotlin.test.Test
+import kotlin.test.assertTrue
+
+class DistinctTest : AbstractGeneratorTest() {
+    override val generator: Generator<String> = Generator { it: Random -> it.nextInt() }.map { it.toString() }
+
+    companion object {
+        const val COLLISION_TAKEN_VALUES = 2000
+    }
+
+    @Test
+    fun applyDistinction() {
+        val gen: Generator<Int> = Generator { it.nextInt().absoluteValue / 2000 }
+
+        // sequence known to produce collisions
+        val result = gen.distinct().randomSequence(1).take(COLLISION_TAKEN_VALUES)
+        assertTrue { COLLISION_TAKEN_VALUES == result.toList().size }
+
+    }
+}
\ No newline at end of file