From 7095ec6c5147fac08bb036f65d386b61690f49a5 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Tue, 25 Feb 2020 16:15:17 +0300
Subject: [PATCH] core: implement (*Blockchain).CalculateClaimable

Calculating amount of GAS that can be claimed is required
for getclaimable RPC.
---
 pkg/core/blockchain.go      | 55 +++++++++++++++++++++++++++++++++++++
 pkg/core/blockchain_test.go | 40 +++++++++++++++++++++++++++
 pkg/core/blockchainer.go    |  1 +
 pkg/network/helper_test.go  |  3 ++
 4 files changed, 99 insertions(+)

diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index 29ee9a4c6..6239ad89f 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -93,6 +93,9 @@ type Blockchain struct {
 	// Number of headers stored in the chain file.
 	storedHeaderCount uint32
 
+	generationAmount  []int
+	decrementInterval int
+
 	// All operations on headerList must be called from an
 	// headersOp to be routine safe.
 	headerList *HeaderHashList
@@ -154,6 +157,9 @@ func NewBlockchain(s storage.Store, cfg config.ProtocolConfiguration, log *zap.L
 		memPool:       mempool.NewMemPool(cfg.MemPoolSize),
 		keyCache:      make(map[util.Uint160]map[string]*keys.PublicKey),
 		log:           log,
+
+		generationAmount:  genAmount,
+		decrementInterval: decrementInterval,
 	}
 
 	if err := bc.init(); err != nil {
@@ -1033,6 +1039,55 @@ func (bc *Blockchain) GetConfig() config.ProtocolConfiguration {
 	return bc.config
 }
 
+// CalculateClaimable calculates the amount of GAS which can be claimed for a transaction with value.
+// First return value is GAS generated between startHeight and endHeight.
+// Second return value is GAS returned from accumulated SystemFees between startHeight and endHeight.
+func (bc *Blockchain) CalculateClaimable(value util.Fixed8, startHeight, endHeight uint32) (util.Fixed8, util.Fixed8, error) {
+	var amount util.Fixed8
+	di := uint32(bc.decrementInterval)
+
+	ustart := startHeight / di
+	if genSize := uint32(len(bc.generationAmount)); ustart < genSize {
+		uend := endHeight / di
+		iend := endHeight % di
+		if uend >= genSize {
+			uend = genSize - 1
+			iend = di
+		} else if iend == 0 {
+			uend--
+			iend = di
+		}
+
+		istart := startHeight % di
+		for ustart < uend {
+			amount += util.Fixed8(di-istart) * util.Fixed8(bc.generationAmount[ustart])
+			ustart++
+			istart = 0
+		}
+
+		amount += util.Fixed8(iend-istart) * util.Fixed8(bc.generationAmount[ustart])
+	}
+
+	var sysFeeTotal util.Fixed8
+	if startHeight == 0 {
+		startHeight++
+	}
+	for i := startHeight; i < endHeight; i++ {
+		h := bc.GetHeaderHash(int(i))
+		b, err := bc.GetBlock(h)
+		if err != nil {
+			return 0, 0, err
+		}
+		for _, tx := range b.Transactions {
+			sysFeeTotal += bc.SystemFee(tx)
+		}
+	}
+
+	sysFeeTotal /= 100000000
+	ratio := value / 100000000
+	return amount * ratio, sysFeeTotal * ratio, nil
+}
+
 // References maps transaction's inputs into a slice of InOuts, effectively
 // joining each Input with the corresponding Output.
 // @TODO: unfortunately we couldn't attach this method to the Transaction struct in the
diff --git a/pkg/core/blockchain_test.go b/pkg/core/blockchain_test.go
index 523f3b448..0f1f38888 100644
--- a/pkg/core/blockchain_test.go
+++ b/pkg/core/blockchain_test.go
@@ -175,6 +175,46 @@ func TestGetTransaction(t *testing.T) {
 	}
 }
 
+func TestGetClaimable(t *testing.T) {
+	bc := newTestChain(t)
+
+	_, _, err := bc.CalculateClaimable(util.Fixed8FromInt64(1), 0, 2)
+	require.Error(t, err)
+
+	bc.generationAmount = []int{4, 3, 2, 1}
+	bc.decrementInterval = 2
+	_, err = bc.genBlocks(10)
+	require.NoError(t, err)
+
+	t.Run("first generation period", func(t *testing.T) {
+		amount, sysfee, err := bc.CalculateClaimable(util.Fixed8FromInt64(1), 0, 2)
+		require.NoError(t, err)
+		require.EqualValues(t, 8, amount)
+		require.EqualValues(t, 0, sysfee)
+	})
+
+	t.Run("a number of full periods", func(t *testing.T) {
+		amount, sysfee, err := bc.CalculateClaimable(util.Fixed8FromInt64(1), 0, 6)
+		require.NoError(t, err)
+		require.EqualValues(t, 4+4+3+3+2+2, amount)
+		require.EqualValues(t, 0, sysfee)
+	})
+
+	t.Run("start from the 2-nd block", func(t *testing.T) {
+		amount, sysfee, err := bc.CalculateClaimable(util.Fixed8FromInt64(1), 1, 7)
+		require.NoError(t, err)
+		require.EqualValues(t, 4+3+3+2+2+1, amount)
+		require.EqualValues(t, 0, sysfee)
+	})
+
+	t.Run("end height after generation has ended", func(t *testing.T) {
+		amount, sysfee, err := bc.CalculateClaimable(util.Fixed8FromInt64(1), 1, 10)
+		require.NoError(t, err)
+		require.EqualValues(t, 4+3+3+2+2+1+1, amount)
+		require.EqualValues(t, 0, sysfee)
+	})
+}
+
 func TestClose(t *testing.T) {
 	defer func() {
 		r := recover()
diff --git a/pkg/core/blockchainer.go b/pkg/core/blockchainer.go
index bbe3b0c6b..d5368dd28 100644
--- a/pkg/core/blockchainer.go
+++ b/pkg/core/blockchainer.go
@@ -20,6 +20,7 @@ type Blockchainer interface {
 	AddHeaders(...*block.Header) error
 	AddBlock(*block.Block) error
 	BlockHeight() uint32
+	CalculateClaimable(value util.Fixed8, startHeight, endHeight uint32) (util.Fixed8, util.Fixed8, error)
 	Close()
 	HeaderHeight() uint32
 	GetBlock(hash util.Uint256) (*block.Block, error)
diff --git a/pkg/network/helper_test.go b/pkg/network/helper_test.go
index 1f72bee0d..3133a9f5c 100644
--- a/pkg/network/helper_test.go
+++ b/pkg/network/helper_test.go
@@ -32,6 +32,9 @@ func (chain testChain) ApplyPolicyToTxSet([]mempool.TxWithFee) []mempool.TxWithF
 func (chain testChain) GetConfig() config.ProtocolConfiguration {
 	panic("TODO")
 }
+func (chain testChain) CalculateClaimable(util.Fixed8, uint32, uint32) (util.Fixed8, util.Fixed8, error) {
+	panic("TODO")
+}
 
 func (chain testChain) References(t *transaction.Transaction) ([]transaction.InOut, error) {
 	panic("TODO")