From 1d16adce8a2ca38a3f04bf7bf2ae5985657cf552 Mon Sep 17 00:00:00 2001
From: testinginprod <98415576+testinginprod@users.noreply.github.com>
Date: Wed, 21 Dec 2022 16:26:00 +0100
Subject: [PATCH] feat(collections): add sequence (#14364)

Co-authored-by: testinginprod <testinginprod@somewhere.idk>
Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>
---
 collections/CHANGELOG.md     |  3 ++-
 collections/sequence.go      | 49 ++++++++++++++++++++++++++++++++++++
 collections/sequence_test.go | 32 +++++++++++++++++++++++
 3 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 collections/sequence.go
 create mode 100644 collections/sequence_test.go

diff --git a/collections/CHANGELOG.md b/collections/CHANGELOG.md
index d49418598a79..b69be22353e9 100644
--- a/collections/CHANGELOG.md
+++ b/collections/CHANGELOG.md
@@ -32,4 +32,5 @@ Ref: https://keepachangelog.com/en/1.0.0/
 ## [Unreleased]
 
 * [#14134](https://github.com/cosmos/cosmos-sdk/pull/14134) Initialise core (Prefix, KeyEncoder, ValueEncoder, Map).
-* [#14351](https://github.com/cosmos/cosmos-sdk/pull/14351) Add keyset
\ No newline at end of file
+* [#14351](https://github.com/cosmos/cosmos-sdk/pull/14351) Add keyset
+* [#14364](https://github.com/cosmos/cosmos-sdk/pull/14364) Add sequence
\ No newline at end of file
diff --git a/collections/sequence.go b/collections/sequence.go
new file mode 100644
index 000000000000..61be844fa45d
--- /dev/null
+++ b/collections/sequence.go
@@ -0,0 +1,49 @@
+package collections
+
+import (
+	"context"
+	"errors"
+)
+
+// DefaultSequenceStart defines the default starting number of a sequence.
+const DefaultSequenceStart uint64 = 1
+
+// Sequence builds on top of an Item, and represents a monotonically increasing number.
+type Sequence Item[uint64]
+
+// NewSequence instantiates a new sequence given
+// a Schema, a Prefix and humanised name for the sequence.
+func NewSequence(schema Schema, prefix Prefix, name string) Sequence {
+	return (Sequence)(NewItem(schema, prefix, name, Uint64Value))
+}
+
+// Peek returns the current sequence value, if no number
+// is set then the DefaultSequenceStart is returned.
+// Errors on encoding issues.
+func (s Sequence) Peek(ctx context.Context) (uint64, error) {
+	n, err := (Item[uint64])(s).Get(ctx)
+	switch {
+	case err == nil:
+		return n, nil
+	case errors.Is(err, ErrNotFound):
+		return DefaultSequenceStart, nil
+	default:
+		return 0, err
+	}
+}
+
+// Next returns the next sequence number, and sets the next expected sequence.
+// Errors on encoding issues.
+func (s Sequence) Next(ctx context.Context) (uint64, error) {
+	seq, err := s.Peek(ctx)
+	if err != nil {
+		return 0, err
+	}
+	return seq, s.Set(ctx, seq+1)
+}
+
+// Set hard resets the sequence to the provided value.
+// Errors on encoding issues.
+func (s Sequence) Set(ctx context.Context, value uint64) error {
+	return (Item[uint64])(s).Set(ctx, value)
+}
diff --git a/collections/sequence_test.go b/collections/sequence_test.go
new file mode 100644
index 000000000000..082e3000669c
--- /dev/null
+++ b/collections/sequence_test.go
@@ -0,0 +1,32 @@
+package collections
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestSequence(t *testing.T) {
+	sk, ctx := deps()
+	schema := NewSchema(sk)
+	seq := NewSequence(schema, NewPrefix(0), "sequence")
+	// initially the first available number is DefaultSequenceStart
+	n, err := seq.Peek(ctx)
+	require.NoError(t, err)
+	require.Equal(t, DefaultSequenceStart, n)
+
+	// when we call next when sequence is still unset the first expected value is DefaultSequenceStart
+	n, err = seq.Next(ctx)
+	require.NoError(t, err)
+	require.Equal(t, DefaultSequenceStart, n)
+	// when we call peek after the first number is set, then the next expected sequence is DefaultSequenceStart + 1
+	n, err = seq.Peek(ctx)
+	require.NoError(t, err)
+	require.Equal(t, DefaultSequenceStart+1, n)
+
+	// set
+	err = seq.Set(ctx, 10)
+	require.NoError(t, err)
+	n, err = seq.Peek(ctx)
+	require.NoError(t, err)
+	require.Equal(t, n, uint64(10))
+}