liquidity: use builder in single place

In preparation of supporting multiple swap types, we move our swap
builder into a single place, so that we can check our `maySwap`
restriction per-swap (since we'll now have different checks for
different swap types.

To save ourselves from making multiple calls to the loop server for
the restrictions placed on each swap type, we still pass a single
set of restrictions in.

liquidity/liquidity.go

@@ -386,10 +386,6 @@ type Manager struct {
 	// current liquidity balance.
 	cfg *Config
 
-	// builder is the swap builder responsible for creating swaps of our
-	// chosen type for us.
-	builder swapBuilder
-
 	// params is the set of parameters we are currently using. These may be
 	// updated at runtime.
 	params Parameters
@@ -428,9 +424,8 @@ func (m *Manager) Run(ctx context.Context) error {
 // NewManager creates a liquidity manager which has no rules set.
 func NewManager(cfg *Config) *Manager {
 	return &Manager{
-		cfg:     cfg,
-		params:  defaultParameters,
-		builder: newLoopOutBuilder(cfg),
+		cfg:    cfg,
+		params: defaultParameters,
 	}
 }
 
@@ -617,23 +612,8 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 		return m.singleReasonSuggestion(ReasonBudgetNotStarted), nil
 	}
 
-	// Before we get any swap suggestions, we check what the current fee
-	// estimate is to sweep within our target number of confirmations. If
-	// This fee exceeds the fee limit we have set, we will not suggest any
-	// swaps at present.
-	if err := m.builder.maySwap(ctx, m.params); err != nil {
-		var reasonErr *reasonError
-		if errors.As(err, &reasonErr) {
-			return m.singleReasonSuggestion(reasonErr.reason), nil
-
-		}
-
-		return nil, err
-	}
-
-	// Get the current server side restrictions, combined with the client
-	// set restrictions, if any.
-	restrictions, err := m.getSwapRestrictions(ctx, m.builder.swapType())
+	// Get restrictions placed on swaps by the server.
+	outRestrictions, err := m.getSwapRestrictions(ctx, swap.TypeOut)
 	if err != nil {
 		return nil, err
 	}
@@ -721,7 +701,8 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 		}
 
 		suggestion, err := m.suggestSwap(
-			ctx, traffic, balances, rule, restrictions, autoloop,
+			ctx, traffic, balances, rule, outRestrictions,
+			autoloop,
 		)
 		var reasonErr *reasonError
 		if errors.As(err, &reasonErr) {
@@ -746,7 +727,8 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 		}
 
 		suggestion, err := m.suggestSwap(
-			ctx, traffic, balance, rule, restrictions, autoloop,
+			ctx, traffic, balance, rule, outRestrictions,
+			autoloop,
 		)
 
 		var reasonErr *reasonError
@@ -841,12 +823,34 @@ func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
 // suggestSwap checks whether we can currently perform a swap, and creates a
 // swap request for the rule provided.
 func (m *Manager) suggestSwap(ctx context.Context, traffic *swapTraffic,
-	balance *balances, rule *SwapRule, restrictions *Restrictions,
+	balance *balances, rule *SwapRule, outRestrictions *Restrictions,
 	autoloop bool) (swapSuggestion, error) {
 
+	var (
+		builder      swapBuilder
+		restrictions *Restrictions
+	)
+
+	switch rule.Type {
+	case swap.TypeOut:
+		builder = newLoopOutBuilder(m.cfg)
+		restrictions = outRestrictions
+
+	default:
+		return nil, fmt.Errorf("unsupported swap type: %v", rule.Type)
+	}
+
+	// Before we get any swap suggestions, we check what the current fee
+	// estimate is to sweep within our target number of confirmations. If
+	// This fee exceeds the fee limit we have set, we will not suggest any
+	// swaps at present.
+	if err := builder.maySwap(ctx, m.params); err != nil {
+		return nil, err
+	}
+
 	// First, check whether this peer/channel combination is already in use
 	// for our swap.
-	err := m.builder.inUse(traffic, balance.pubkey, balance.channels)
+	err := builder.inUse(traffic, balance.pubkey, balance.channels)
 	if err != nil {
 		return nil, err
 	}
@@ -858,7 +862,7 @@ func (m *Manager) suggestSwap(ctx context.Context, traffic *swapTraffic,
 		return nil, newReasonError(ReasonLiquidityOk)
 	}
 
-	return m.builder.buildSwap(
+	return builder.buildSwap(
 		ctx, balance.pubkey, balance.channels, amount, autoloop,
 		m.params,
 	)