server/asset/eth: refactor coins

Separate swapCoin from redeemCoin. Switch (*rpcclient).swap method to
return a *dexeth.SwapState.

dex/networks/eth/params.go

@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"decred.org/dcrdex/dex"
+	v0 "decred.org/dcrdex/dex/networks/eth/contracts/v0"
 	"github.com/ethereum/go-ethereum/common"
 )
 
@@ -130,7 +131,11 @@ func GweiToWei(v uint64) *big.Int {
 
 // GweiToWei converts *big.Int Wei to uint64 Gwei.
 func WeiToGwei(v *big.Int) uint64 {
-	return new(big.Int).Div(v, BigGweiFactor).Uint64()
+	vGwei := new(big.Int).Div(v, BigGweiFactor)
+	if vGwei.IsUint64() {
+		return vGwei.Uint64()
+	}
+	return 0
 }
 
 // SwapStep is the state of a swap and corresponds to values in the Solidity
@@ -197,3 +202,20 @@ type Redemption struct {
 	Secret     [32]byte
 	SecretHash [32]byte
 }
+
+// SwapStateFromV0 converts a v0.ETHSwapSwap to a *SwapState.
+func SwapStateFromV0(state *v0.ETHSwapSwap) *SwapState {
+	var blockTime int64
+	if state.RefundBlockTimestamp.IsInt64() {
+		blockTime = state.RefundBlockTimestamp.Int64()
+	}
+	return &SwapState{
+		BlockHeight: state.InitBlockNumber.Uint64(),
+		LockTime:    time.Unix(blockTime, 0),
+		Secret:      state.Secret,
+		Initiator:   state.Initiator,
+		Participant: state.Participant,
+		Value:       WeiToGwei(state.Value),
+		State:       SwapStep(state.State),
+	}
+}