Introduce ChannelPhase enum

We introduce the `ChannelPhase` enum which will contain the different
channel structs wrapped by each of its variants so that we can place
these within a single `channel_by_id` map in `peer_state` in the
following commits. This will reduce the number of map lookup operations
we need to do in `ChannelManager`'s various methods. It will also make
certain channel counting logic easier to reason about with less risk of
forgetting to modify logic when new channels structs are introduced for
V2 channel establishment.

Author: dunxen

lightning/src/ln/channel.rs

@@ -601,6 +601,32 @@ impl_writeable_tlv_based!(PendingChannelMonitorUpdate, {
 	(0, update, required),
 });
 
+/// The `ChannelPhase` enum describes the current phase in life of a lightning channel with each of
+/// its variants containing an appropriate channel struct.
+pub(super) enum ChannelPhase<Signer: ChannelSigner> {
+	UnfundedOutboundV1(OutboundV1Channel<Signer>),
+	UnfundedInboundV1(InboundV1Channel<Signer>),
+	Funded(Channel<Signer>),
+}
+
+impl<'a, Signer: ChannelSigner> ChannelPhase<Signer> {
+	pub fn context(&'a self) -> &'a ChannelContext<Signer> {
+		match self {
+			ChannelPhase::Funded(chan) => &chan.context,
+			ChannelPhase::UnfundedOutboundV1(chan) => &chan.context,
+			ChannelPhase::UnfundedInboundV1(chan) => &chan.context,
+		}
+	}
+
+	pub fn context_mut(&'a mut self) -> &'a mut ChannelContext<Signer> {
+		match self {
+			ChannelPhase::Funded(ref mut chan) => &mut chan.context,
+			ChannelPhase::UnfundedOutboundV1(ref mut chan) => &mut chan.context,
+			ChannelPhase::UnfundedInboundV1(ref mut chan) => &mut chan.context,
+		}
+	}
+}
+
 /// Contains all state common to unfunded inbound/outbound channels.
 pub(super) struct UnfundedChannelContext {
 	/// A counter tracking how many ticks have elapsed since this unfunded channel was