feat(collections): add sequence

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
+* [#14351](https://github.com/cosmos/cosmos-sdk/pull/14351) Add keyset
+* [#14364](https://github.com/cosmos/cosmos-sdk/pull/14364) Add sequence

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)
+}

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))
+}