// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package snowman

import (
	"github.com/ava-labs/gecko/snow/choices"
)

// Block is a possible decision that dictates the next canonical block.
//
// Blocks are guaranteed to be Verified, Accepted, and Rejected in topological
// order. Specifically, if Verify is called, then the parent has already been
// verified. If Accept is called, then the parent has already been accepted. If
// Reject is called, the parent has already been accepted or rejected.
//
// If the status of the block is Unknown, ID is assumed to be able to be called.
// If the status of the block is Accepted or Rejected; Parent, Verify, Accept,
// and Reject will never be called.
type Block interface {
	choices.Decidable

	// Parent returns the block that this block points to.
	//
	// If the parent block is not known, a Block should be returned with the
	// status Unknown.
	Parent() Block

	// Verify that the state transition this block would make if accepted is
	// valid. If the state transition is invalid, a non-nil error should be
	// returned.
	//
	// It is guaranteed that the Parent has been successfully verified.
	Verify() error

	// Bytes returns the binary representation of this block.
	//
	// This is used for sending blocks to peers. The bytes should be able to be
	// parsed into the same block on another node.
	Bytes() []byte
}