From c9bb113ce61c2dbf3a246b38d0863c76bec9c800 Mon Sep 17 00:00:00 2001
From: Arran Schlosberg <me@arranschlosberg.com>
Date: Mon, 7 Apr 2025 23:11:05 +0100
Subject: [PATCH] feat: `snowman/adaptor` package

---
 snow/engine/snowman/adaptor/adaptor.go | 87 ++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 snow/engine/snowman/adaptor/adaptor.go

diff --git a/snow/engine/snowman/adaptor/adaptor.go b/snow/engine/snowman/adaptor/adaptor.go
new file mode 100644
index 000000000000..a1aafd505a42
--- /dev/null
+++ b/snow/engine/snowman/adaptor/adaptor.go
@@ -0,0 +1,87 @@
+// Package adaptor provides a generic alternative to the Snowman [block.ChainVM]
+// interface, which doesn't require the block to be aware of the VM
+// implementation.
+package adaptor
+
+import (
+	"context"
+	"time"
+
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/snow/consensus/snowman"
+	"github.com/ava-labs/avalanchego/snow/engine/common"
+	"github.com/ava-labs/avalanchego/snow/engine/snowman/block"
+)
+
+// ChainVM defines the required functionality to be converted into a Snowman VM.
+// See the respective methods on [block.ChainVM] and [snowman.Block] for
+// detailed documentation.
+type ChainVM[B Block] interface {
+	common.VM
+
+	GetBlock(context.Context, ids.ID) (B, error)
+	ParseBlock(context.Context, []byte) (B, error)
+	BuildBlock(context.Context) (B, error)
+
+	// Transferred from [snowman.Block].
+	VerifyBlock(context.Context, B) error
+	AcceptBlock(context.Context, B) error
+	RejectBlock(context.Context, B) error
+
+	SetPreference(context.Context, ids.ID) error
+	LastAccepted(context.Context) (ids.ID, error)
+	GetBlockIDAtHeight(context.Context, uint64) (ids.ID, error)
+}
+
+// Block is a read-only subset of [snowman.Block]. The state-modifying methods
+// required by Snowman consensus are, instead, present on [ChainVM].
+type Block interface {
+	ID() ids.ID
+	Parent() ids.ID
+	Bytes() []byte
+	Height() uint64
+	Timestamp() time.Time
+}
+
+// Convert transforms a generic [ChainVM] into a standard [block.ChainVM].
+func Convert[B Block](vm ChainVM[B]) block.ChainVM {
+	return &adaptor[B]{vm}
+}
+
+type adaptor[B Block] struct {
+	ChainVM[B]
+}
+
+func (vm adaptor[B]) newBlock(b B, err error) (snowman.Block, error) {
+	if err != nil {
+		return nil, err
+	}
+	return blk[B]{b, vm.ChainVM}, nil
+}
+
+func (vm adaptor[B]) GetBlock(ctx context.Context, blkID ids.ID) (snowman.Block, error) {
+	return vm.newBlock(vm.ChainVM.GetBlock(ctx, blkID))
+}
+
+func (vm adaptor[B]) ParseBlock(ctx context.Context, blockBytes []byte) (snowman.Block, error) {
+	return vm.newBlock(vm.ChainVM.ParseBlock(ctx, blockBytes))
+}
+
+func (vm adaptor[B]) BuildBlock(ctx context.Context) (snowman.Block, error) {
+	return vm.newBlock(vm.ChainVM.BuildBlock(ctx))
+}
+
+type blk[B Block] struct {
+	b  B
+	vm ChainVM[B]
+}
+
+func (b blk[B]) Verify(ctx context.Context) error { return b.vm.VerifyBlock(ctx, b.b) }
+func (b blk[B]) Accept(ctx context.Context) error { return b.vm.AcceptBlock(ctx, b.b) }
+func (b blk[B]) Reject(ctx context.Context) error { return b.vm.RejectBlock(ctx, b.b) }
+
+func (b blk[B]) ID() ids.ID           { return b.b.ID() }
+func (b blk[B]) Parent() ids.ID       { return b.b.Parent() }
+func (b blk[B]) Bytes() []byte        { return b.b.Bytes() }
+func (b blk[B]) Height() uint64       { return b.b.Height() }
+func (b blk[B]) Timestamp() time.Time { return b.b.Timestamp() }