From 1bb1ac07601074999a0a0539e077334da745d75e Mon Sep 17 00:00:00 2001
From: Georgios Konstantopoulos <me@gakonst.com>
Date: Wed, 20 Nov 2019 22:37:39 +0200
Subject: [PATCH] calculate uptime using the stored values

---
 consensus/istanbul/backend/engine.go |  5 +++
 consensus/istanbul/backend/pos.go    | 46 ++++++++++++++++++++++++----
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/consensus/istanbul/backend/engine.go b/consensus/istanbul/backend/engine.go
index 96b73015c5..e41f990c47 100644
--- a/consensus/istanbul/backend/engine.go
+++ b/consensus/istanbul/backend/engine.go
@@ -458,6 +458,11 @@ func (sb *Backend) EpochSize() uint64 {
 	return sb.config.Epoch
 }
 
+// Returns the size of the lookback window for calculating uptime (in blocks)
+func (sb *Backend) LookbackWindow() uint64 {
+	return sb.config.LookbackWindow
+}
+
 // Finalize runs any post-transaction state modifications (e.g. block rewards)
 // and assembles the final block.
 //
diff --git a/consensus/istanbul/backend/pos.go b/consensus/istanbul/backend/pos.go
index d1c0bbc6d1..164f8f0c5f 100644
--- a/consensus/istanbul/backend/pos.go
+++ b/consensus/istanbul/backend/pos.go
@@ -17,6 +17,8 @@
 package backend
 
 import (
+	"errors"
+	"fmt"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -29,6 +31,7 @@ import (
 	"github.com/ethereum/go-ethereum/contract_comm/gold_token"
 	"github.com/ethereum/go-ethereum/contract_comm/validators"
 	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/rawdb"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
@@ -78,12 +81,16 @@ func (sb *Backend) distributeEpochPaymentsAndRewards(header *types.Header, state
 }
 
 func (sb *Backend) updateValidatorScores(header *types.Header, state *state.StateDB, valSet []istanbul.Validator) error {
-	for _, val := range valSet {
-		// TODO: Use actual uptime metric.
-		// 1.0 in fixidity
-		uptime := math.BigPow(10, 24)
-		sb.logger.Info("Updating validator score for address", "address", val.Address(), "uptime", uptime.String())
-		err := validators.UpdateValidatorScore(header, state, val.Address(), uptime)
+	// we need to use the previous 
+	epoch := istanbul.GetEpochNumber(header.Number.Uint64(), sb.EpochSize())
+	log.Debug("uptime-trace: updateValidatorScores", "blocknum", header.Number.Uint64(), "epoch", epoch)
+	for i, val := range valSet {
+		uptime, err := sb.getUptime(i, epoch-1)
+		if err != nil {
+			return err
+		}
+		sb.logger.Info("Updating validator score for address", "index", i, "address", val.Address(), "uptime", uptime)
+		err = validators.UpdateValidatorScore(header, state, val.Address(), uptime)
 		if err != nil {
 			return err
 		}
@@ -91,6 +98,33 @@ func (sb *Backend) updateValidatorScores(header *types.Header, state *state.Stat
 	return nil
 }
 
+func (sb *Backend) getUptime(validatorIndex int, epoch uint64) (*big.Int, error) {
+	// try to get a handle on the core.blockchain's database
+	// sb.db is a different database (defined in CreateConsensusEngine) :/
+	// is there a better way than this? don't think we want to pollute the interface
+	c := sb.chain.(*core.BlockChain)
+	db := c.GetDatabase()
+	uptimes := rawdb.ReadAccumulatedEpochUptime(db, epoch)
+	if uptimes == nil {
+		panic(fmt.Sprintf("could not read uptimes, i: %v", validatorIndex))
+		return nil, errors.New("Invalid accumulated uptime")
+	}
+
+	// skip the math if we've counted more signatures than necessary for that epoch
+	// when does this happen?
+	if uptimes[validatorIndex].Score >= sb.EpochSize()-2+1 { // sb.LookbackWindow()+1 {
+		// 1.0 in fixidity
+		return math.BigPow(10, 24), nil
+	}
+
+	// this will end up being between 0 and 1 but in fixidty
+	numerator := big.NewInt(0).Mul(big.NewInt(int64(uptimes[validatorIndex].Score)), math.BigPow(10, 24))
+	denominator := big.NewInt(int64(sb.EpochSize() - 2 + 1)) //- sb.LookbackWindow() + 1))
+	validatorUptime := big.NewInt(0).Div(numerator, denominator)
+
+	return validatorUptime, nil
+}
+
 func (sb *Backend) distributeEpochPayments(header *types.Header, state *state.StateDB, valSet []istanbul.Validator, maxPayment *big.Int) (*big.Int, error) {
 	totalEpochPayments := big.NewInt(0)
 	for _, val := range valSet {