feat(bitswap:strategy) add interfaces

refac(bitswap:strategy) update interface

bitswap/strategy/interface.go

+package strategy
+
+import (
+	bsmsg "github.com/jbenet/go-ipfs/bitswap/message"
+	peer "github.com/jbenet/go-ipfs/peer"
+	u "github.com/jbenet/go-ipfs/util"
+)
+
+type Strategist interface {
+	Accountant
+
+	// Returns a slice of Peers that
+	Peers() []*peer.Peer
+
+	// WantList returns the WantList for the given Peer
+	IsWantedByPeer(u.Key, *peer.Peer) bool
+
+	// ShouldSendTo(Peer) decides whether to send data to this Peer
+	ShouldSendToPeer(u.Key, *peer.Peer) bool
+
+	// Seed initializes the decider to a deterministic state
+	Seed(int64)
+}
+
+type Accountant interface {
+	// MessageReceived records receipt of message for accounting purposes
+	MessageReceived(*peer.Peer, bsmsg.BitSwapMessage) error
+
+	// MessageSent records sending of message for accounting purposes
+	MessageSent(*peer.Peer, bsmsg.BitSwapMessage) error
+}
+
+type WantList interface {
+	// Peer returns the owner of the WantList
+	Peer() *peer.Peer
+
+	// Intersection returns the keys common to both WantLists
+	Intersection(WantList) WantList
+
+	KeySet
+}
+
+// TODO(brian): potentially move this somewhere more generic. For now, it's
+// useful in BitSwap operations.
+
+type KeySet interface {
+	Contains(u.Key) bool
+	Keys() []u.Key
+}