Add flatMap for Result type (#51)

app/src/main/java/com/x8bit/bitwarden/data/platform/util/ResultExtensions.kt

@@ -0,0 +1,10 @@
+package com.x8bit.bitwarden.data.platform.util
+
+/**
+ * Flat maps a successful [Result] with the given [transform] to another [Result], and leaves
+ * failures untouched.
+ */
+inline fun <T, R> Result<T>.flatMap(transform: (T) -> Result<R>): Result<R> =
+    this.exceptionOrNull()
+        ?.let { Result.failure(it) }
+        ?: transform(this.getOrThrow())

app/src/test/java/com/x8bit/bitwarden/data/platform/util/ResultTest.kt

@@ -0,0 +1,52 @@
+package com.x8bit.bitwarden.data.platform.util
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+
+class ResultTest {
+
+    @Test
+    fun `flatMap where receiver is success and argument is success should be argument success`() {
+        val intResult = Result.success(1)
+        val stringResult = intResult.flatMap {
+            Result.success(it.toString())
+        }
+        assertTrue(stringResult.isSuccess)
+        assertEquals("1", stringResult.getOrNull())
+    }
+
+    @Test
+    fun `flatMap where receiver is success and argument is failure should be argument failure`() {
+        val expectedException = IllegalStateException("Exception in transform")
+        val intResult = Result.success(1)
+        val stringResult = intResult.flatMap {
+            Result.failure<String>(expectedException)
+        }
+        assertTrue(stringResult.isFailure)
+        assertEquals(expectedException, stringResult.exceptionOrNull())
+    }
+
+    @Test
+    @Suppress("TooGenericExceptionThrown")
+    fun `flatMap where receiver is failure and argument is failure should be receiver failure`() {
+        val expectedException = RuntimeException("Exception on int result.")
+        val intResult = Result.failure<Int>(expectedException)
+        val stringResult = intResult.flatMap<Int, String> {
+            throw RuntimeException("transform function should not be called for failed Results")
+        }
+        assertTrue(stringResult.isFailure)
+        assertEquals(expectedException, stringResult.exceptionOrNull())
+    }
+
+    @Test
+    fun `flatMap where receiver is failure and argument is success should be receiver failure`() {
+        val expectedException = RuntimeException("Exception on int result.")
+        val intResult = Result.failure<Int>(expectedException)
+        val stringResult = intResult.flatMap {
+            Result.success("1")
+        }
+        assertTrue(stringResult.isFailure)
+        assertEquals(expectedException, stringResult.exceptionOrNull())
+    }
+}