accounts, consensus, core, eth: make chain maker consensus agnostic (#15497)

* accounts, consensus, core, eth: make chain maker consensus agnostic

* consensus, core: move CalcDifficulty to Engine interface

* consensus: add docs for calcDifficulty function

* consensus, core: minor comment fixups

1 files changed, 23 insertions, 5 deletions

diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index a98058141..2bdad9092 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -510,7 +510,6 @@ func (c *Clique) Prepare(chain consensus.ChainReader, header *types.Header) erro
 	header.Nonce = types.BlockNonce{}
 
 	number := header.Number.Uint64()
-
 	// Assemble the voting snapshot to check which votes make sense
 	snap, err := c.snapshot(chain, number-1, header.ParentHash, nil)
 	if err != nil {
@@ -538,10 +537,8 @@ func (c *Clique) Prepare(chain consensus.ChainReader, header *types.Header) erro
 		c.lock.RUnlock()
 	}
 	// Set the correct difficulty
-	header.Difficulty = diffNoTurn
-	if snap.inturn(header.Number.Uint64(), c.signer) {
-		header.Difficulty = diffInTurn
-	}
+	header.Difficulty = CalcDifficulty(snap, c.signer)
+
 	// Ensure the extra data has all it's components
 	if len(header.Extra) < extraVanity {
 		header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, extraVanity-len(header.Extra))...)
@@ -655,6 +652,27 @@ func (c *Clique) Seal(chain consensus.ChainReader, block *types.Block, stop <-ch
 	return block.WithSeal(header), nil
 }
 
+// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+// that a new block should have based on the previous blocks in the chain and the
+// current signer.
+func (c *Clique) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
+	snap, err := c.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil)
+	if err != nil {
+		return nil
+	}
+	return CalcDifficulty(snap, c.signer)
+}
+
+// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+// that a new block should have based on the previous blocks in the chain and the
+// current signer.
+func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
+	if snap.inturn(snap.Number+1, signer) {
+		return new(big.Int).Set(diffInTurn)
+	}
+	return new(big.Int).Set(diffNoTurn)
+}
+
 // APIs implements consensus.Engine, returning the user facing RPC API to allow
 // controlling the signer voting.
 func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {