Part 2 of proto array fork choice - proto array types (#4616)

* Docs

* Interface definitions

* Fmt and gazelle

* Rename interface to interfaces

* Define all the type for protoarray

* Gaz

beacon-chain/forkchoice/protoarray/BUILD.bazel

@@ -2,7 +2,10 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library")
 
 go_library(
     name = "go_default_library",
-    srcs = ["doc.go"],
+    srcs = [
+        "doc.go",
+        "types.go",
+    ],
     importpath = "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray",
     visibility = ["//beacon-chain:__subpackages__"],
 )

beacon-chain/forkchoice/protoarray/types.go

@@ -0,0 +1,44 @@
+package protoarray
+
+import "sync"
+
+// ForkChoice defines the overall fork choice store which includes all block nodes, validator's latest votes and balances.
+type ForkChoice struct {
+	store    *Store
+	votes    []Vote   // tracks individual validator's last vote.
+	balances []uint64 // tracks individual validator's last justified balances.
+}
+
+// Store defines the fork choice store which includes block nodes and the last view of checkpoint information.
+type Store struct {
+	pruneThreshold  uint64              // do not prune tree unless threshold is reached.
+	justifiedEpoch  uint64              // latest justified epoch in store.
+	finalizedEpoch  uint64              // latest finalized epoch in store.
+	finalizedRoot   [32]byte            // latest finalized root in store.
+	nodes           []*Node             // list of block nodes, each node is a representation of one block.
+	nodeIndices     map[[32]byte]uint64 // the root of block node and the nodes index in the list.
+	nodeIndicesLock sync.RWMutex
+}
+
+// Node defines the individual block which includes its block parent, ancestor and how much weight accounted for it.
+// This is used as an array based stateful DAG for efficient fork choice look up.
+type Node struct {
+	slot           uint64   // slot of the block converted to the node.
+	root           [32]byte // root of the block converted to the node.
+	parent         uint64   // the parent index of this node.
+	justifiedEpoch uint64   // justified epoch of this node.
+	finalizedEpoch uint64   // finalized epoch of this node.
+	weight         uint64   // weight of this node.
+	bestChild      uint64   // best child index of this node.
+	bestDescendant uint64   // head index of this node.
+}
+
+// Vote defines an individual validator's vote.
+type Vote struct {
+	currentRoot [32]byte // current voting root.
+	nextRoot    [32]byte // next voting root.
+	nextEpoch   uint64   // epoch of next voting period.
+}
+
+// This defines an unknown node which is used for the array based stateful DAG.
+const nonExistentNode = ^uint64(0)