From b5b2f49e81b32a155c422a5f98223fc9a00cd61d Mon Sep 17 00:00:00 2001
From: oren-lava <111131399+oren-lava@users.noreply.github.com>
Date: Wed, 27 Nov 2024 13:54:45 +0200
Subject: [PATCH] feat(collections): add collections reverse triple helpers
 (#22641)

---
 collections/CHANGELOG.md   |  1 +
 collections/triple.go      | 33 +++++++++++++++++++++++++++++++++
 collections/triple_test.go | 22 +++++++++++++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/collections/CHANGELOG.md b/collections/CHANGELOG.md
index d0da0dcfa5..844df7e785 100644
--- a/collections/CHANGELOG.md
+++ b/collections/CHANGELOG.md
@@ -33,6 +33,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Features
 
+* [#22641](https://github.com/cosmos/cosmos-sdk/pull/22641) Add reverse iterator support for `Triple`.
 * [#17656](https://github.com/cosmos/cosmos-sdk/pull/17656) Introduces `Vec`, a collection type that allows to represent a growable array on top of a KVStore.
 * [#18933](https://github.com/cosmos/cosmos-sdk/pull/18933) Add LookupMap implementation. It is basic wrapping of the standard Map methods but is not iterable.
 * [#19343](https://github.com/cosmos/cosmos-sdk/pull/19343) Simplify IndexedMap creation by allowing to infer indexes through reflection.
diff --git a/collections/triple.go b/collections/triple.go
index d7dcb36056..7474e01ccd 100644
--- a/collections/triple.go
+++ b/collections/triple.go
@@ -352,3 +352,36 @@ func NewSuperPrefixedTripleRange[K1, K2, K3 any](k1 K1, k2 K2) Ranger[Triple[K1,
 		end:   RangeKeyPrefixEnd(key),
 	}
 }
+
+// NewPrefixUntilTripleRangeReversed defines a collection query which ranges until the provided Pair prefix
+// in reverse order.
+// Unstable: this API might change in the future.
+func NewPrefixUntilTripleRangeReversed[K1, K2, K3 any](k1 K1) Ranger[Triple[K1, K2, K3]] {
+	key := TriplePrefix[K1, K2, K3](k1)
+	return &Range[Triple[K1, K2, K3]]{
+		end:   RangeKeyPrefixEnd(key),
+		order: OrderDescending,
+	}
+}
+
+// NewPrefixedTripleRangeReversed provides a Range for all keys prefixed with the given
+// first part of the Triple key in reverse order.
+func NewPrefixedTripleRangeReversed[K1, K2, K3 any](k1 K1) Ranger[Triple[K1, K2, K3]] {
+	key := TriplePrefix[K1, K2, K3](k1)
+	return &Range[Triple[K1, K2, K3]]{
+		start: RangeKeyExact(key),
+		end:   RangeKeyPrefixEnd(key),
+		order: OrderDescending,
+	}
+}
+
+// NewSuperPrefixedTripleRangeReversed provides a Range for all keys prefixed with the given
+// first and second parts of the Triple key in reverse order.
+func NewSuperPrefixedTripleRangeReversed[K1, K2, K3 any](k1 K1, k2 K2) Ranger[Triple[K1, K2, K3]] {
+	key := TripleSuperPrefix[K1, K2, K3](k1, k2)
+	return &Range[Triple[K1, K2, K3]]{
+		start: RangeKeyExact(key),
+		end:   RangeKeyPrefixEnd(key),
+		order: OrderDescending,
+	}
+}
diff --git a/collections/triple_test.go b/collections/triple_test.go
index 5ea53b3fe6..c605a7aeab 100644
--- a/collections/triple_test.go
+++ b/collections/triple_test.go
@@ -7,7 +7,7 @@ import (
 
 	"cosmossdk.io/collections"
 	"cosmossdk.io/collections/colltest"
-	"cosmossdk.io/core/testing"
+	coretesting "cosmossdk.io/core/testing"
 )
 
 func TestTriple(t *testing.T) {
@@ -45,10 +45,30 @@ func TestTripleRange(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, keys[:3], gotKeys)
 
+	// we prefix over (1) with "reverse" enabled, we expect 3 results in reverse order
+	iter, err = keySet.Iterate(ctx, collections.NewPrefixedTripleRangeReversed[uint64, string, []byte](uint64(1)))
+	require.NoError(t, err)
+	gotKeys, err = iter.Keys()
+	require.NoError(t, err)
+	require.Len(t, gotKeys, 3)
+	for i := range gotKeys {
+		require.Equal(t, gotKeys[i], keys[len(gotKeys)-i-1])
+	}
+
 	// we super prefix over Join(1, "A") we expect 2 results
 	iter, err = keySet.Iterate(ctx, collections.NewSuperPrefixedTripleRange[uint64, string, []byte](1, "A"))
 	require.NoError(t, err)
 	gotKeys, err = iter.Keys()
 	require.NoError(t, err)
 	require.Equal(t, keys[:2], gotKeys)
+
+	// we prefix over Join(1, "A") with "reverse" enabled, we expect 2 results in reverse order
+	iter, err = keySet.Iterate(ctx, collections.NewSuperPrefixedTripleRangeReversed[uint64, string, []byte](1, "A"))
+	require.NoError(t, err)
+	gotKeys, err = iter.Keys()
+	require.NoError(t, err)
+	require.Len(t, gotKeys, 2)
+	for i := range gotKeys {
+		require.Equal(t, gotKeys[i], keys[len(gotKeys)-i-1])
+	}
 }