From 4ed0046971e9c3c2397ff46cb193996116f248f1 Mon Sep 17 00:00:00 2001
From: "Dr. Carsten Leue" <carsten.leue@de.ibm.com>
Date: Thu, 3 Aug 2023 14:32:46 +0200
Subject: [PATCH] fix: add uniq

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>
---
 iterator/stateless/generic/uniq.go | 62 ++++++++++++++++++++++++++++++
 iterator/stateless/uniq.go         | 32 +++++++++++++++
 iterator/stateless/uniq_test.go    | 31 +++++++++++++++
 3 files changed, 125 insertions(+)
 create mode 100644 iterator/stateless/generic/uniq.go
 create mode 100644 iterator/stateless/uniq.go
 create mode 100644 iterator/stateless/uniq_test.go

diff --git a/iterator/stateless/generic/uniq.go b/iterator/stateless/generic/uniq.go
new file mode 100644
index 0000000..315d677
--- /dev/null
+++ b/iterator/stateless/generic/uniq.go
@@ -0,0 +1,62 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package generic
+
+import (
+	F "github.com/IBM/fp-go/function"
+	O "github.com/IBM/fp-go/option"
+	T "github.com/IBM/fp-go/tuple"
+)
+
+// addToMap makes a deep copy of a map and adds a value
+func addToMap[A comparable](a A, m map[A]bool) map[A]bool {
+	cpy := make(map[A]bool, len(m)+1)
+	for k, v := range m {
+		cpy[k] = v
+	}
+	cpy[a] = true
+	return cpy
+}
+
+func Uniq[AS ~func() O.Option[T.Tuple2[AS, A]], K comparable, A any](f func(A) K) func(as AS) AS {
+
+	var recurse func(as AS, mp map[K]bool) AS
+
+	recurse = func(as AS, mp map[K]bool) AS {
+		return F.Nullary2(
+			as,
+			O.Chain(func(a T.Tuple2[AS, A]) O.Option[T.Tuple2[AS, A]] {
+				return F.Pipe3(
+					a.F2,
+					f,
+					O.FromPredicate(func(k K) bool {
+						_, ok := mp[k]
+						return !ok
+					}),
+					O.Fold(recurse(a.F1, mp), func(k K) O.Option[T.Tuple2[AS, A]] {
+						return O.Of(T.MakeTuple2(recurse(a.F1, addToMap(k, mp)), a.F2))
+					}),
+				)
+			}),
+		)
+	}
+
+	return F.Bind2nd(recurse, make(map[K]bool, 0))
+}
+
+func StrictUniq[AS ~func() O.Option[T.Tuple2[AS, A]], A comparable](as AS) AS {
+	return Uniq[AS](F.Identity[A])(as)
+}
diff --git a/iterator/stateless/uniq.go b/iterator/stateless/uniq.go
new file mode 100644
index 0000000..02a80e4
--- /dev/null
+++ b/iterator/stateless/uniq.go
@@ -0,0 +1,32 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package stateless
+
+import (
+	G "github.com/IBM/fp-go/iterator/stateless/generic"
+)
+
+// StrictUniq converts an [Iterator] or arbitrary items into an [Iterator] or unique items
+// where uniqueness is determined by the built-in uniqueness constraint
+func StrictUniq[A comparable](as Iterator[A]) Iterator[A] {
+	return G.StrictUniq[Iterator[A]](as)
+}
+
+// Uniq converts an [Iterator] or arbitrary items into an [Iterator] or unique items
+// where uniqueness is determined based on a key extractor function
+func Uniq[A any, K comparable](f func(A) K) func(as Iterator[A]) Iterator[A] {
+	return G.Uniq[Iterator[A], K](f)
+}
diff --git a/iterator/stateless/uniq_test.go b/iterator/stateless/uniq_test.go
new file mode 100644
index 0000000..3507cd6
--- /dev/null
+++ b/iterator/stateless/uniq_test.go
@@ -0,0 +1,31 @@
+// Copyright (c) 2023 IBM Corp.
+// All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package stateless
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUniq(t *testing.T) {
+	// iterator with duplicate items
+	dups := From(1, 2, 3, 1, 4, 5, 2)
+
+	u := StrictUniq(dups)
+
+	assert.Equal(t, ToArray(From(1, 2, 3, 4, 5)), ToArray(u))
+}