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

package common

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

// Engine describes the standard interface of a consensus engine
type Engine interface {
	Handler

	// Return the context of the chain this engine is working on
	Context() *snow.Context
}

// Handler defines the functions that are acted on the node
type Handler interface {
	ExternalHandler
	InternalHandler
}

// ExternalHandler defines how a consensus engine reacts to messages and
// requests from other validators
type ExternalHandler interface {
	FrontierHandler
	AcceptedHandler
	FetchHandler
	QueryHandler
}

// FrontierHandler defines how a consensus engine reacts to frontier messages
// from other validators. Functions only return fatal errors if they occur.
type FrontierHandler interface {
	// Notify this engine of a request for the accepted frontier of vertices.
	//
	// The accepted frontier is the set of accepted vertices that do not have
	// any accepted descendants.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID. However, the validatorID is
	// assumed to be authenticated.
	//
	// This engine should respond with an AcceptedFrontier message with the same
	// requestID, and the engine's current accepted frontier.
	GetAcceptedFrontier(validatorID ids.ShortID, requestID uint32) error

	// Notify this engine of an accepted frontier.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is in response to a GetAcceptedFrontier message, is
	// utilizing a unique requestID, or that the containerIDs from a valid
	// frontier. However, the validatorID is  assumed to be authenticated.
	AcceptedFrontier(
		validatorID ids.ShortID,
		requestID uint32,
		containerIDs ids.Set,
	) error

	// Notify this engine that a get accepted frontier request it issued has
	// failed.
	//
	// This function will be called if the engine sent a GetAcceptedFrontier
	// message that is not anticipated to be responded to. This could be because
	// the recipient of the message is unknown or if the message request has
	// timed out.
	//
	// The validatorID, and requestID, are assumed to be the same as those sent
	// in the GetAcceptedFrontier message.
	GetAcceptedFrontierFailed(validatorID ids.ShortID, requestID uint32) error
}

// AcceptedHandler defines how a consensus engine reacts to messages pertaining
// to accepted containers from other validators. Functions only return fatal
// errors if they occur.
type AcceptedHandler interface {
	// Notify this engine of a request to filter non-accepted vertices.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID. However, the validatorID is
	// assumed to be authenticated.
	//
	// This engine should respond with an Accepted message with the same
	// requestID, and the subset of the containerIDs that this node has decided
	// are accepted.
	GetAccepted(
		validatorID ids.ShortID,
		requestID uint32,
		containerIDs ids.Set,
	) error

	// Notify this engine of a set of accepted vertices.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is in response to a GetAccepted message, is utilizing a
	// unique requestID, or that the containerIDs are a subset of the
	// containerIDs from a GetAccepted message. However, the validatorID is
	// assumed to be authenticated.
	Accepted(
		validatorID ids.ShortID,
		requestID uint32,
		containerIDs ids.Set,
	) error

	// Notify this engine that a get accepted request it issued has failed.
	//
	// This function will be called if the engine sent a GetAccepted message
	// that is not anticipated to be responded to. This could be because the
	// recipient of the message is unknown or if the message request has timed
	// out.
	//
	// The validatorID, and requestID, are assumed to be the same as those sent
	// in the GetAccepted message.
	GetAcceptedFailed(validatorID ids.ShortID, requestID uint32) error
}

// FetchHandler defines how a consensus engine reacts to retrieval messages from
// other validators. Functions only return fatal errors if they occur.
type FetchHandler interface {
	// Notify this engine of a request for a container.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID. It is also not safe to
	// assume the requested containerID exists. However, the validatorID is
	// assumed to be authenticated.
	//
	// There should never be a situation where a virtuous node sends a Get
	// request to another virtuous node that does not have the requested
	// container. Unless that container was pruned from the active set.
	//
	// This engine should respond with a Put message with the same requestID if
	// the container was locally avaliable. Otherwise, the message can be safely
	// dropped.
	Get(validatorID ids.ShortID, requestID uint32, containerID ids.ID) error

	// Notify this engine of a container.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID or even that the containerID
	// matches the ID of the container bytes. However, the validatorID is
	// assumed to be authenticated.
	//
	// This engine needs to request and receive missing ancestors of the
	// container before adding the container to consensus. Once all ancestor
	// containers are added, pushes the container into the consensus.
	Put(
		validatorID ids.ShortID,
		requestID uint32,
		containerID ids.ID,
		container []byte,
	) error

	// Notify this engine that a get request it issued has failed.
	//
	// This function will be called if the engine sent a Get message that is not
	// anticipated to be responded to. This could be because the recipient of
	// the message is unknown or if the message request has timed out.
	//
	// The validatorID and requestID are assumed to be the same as those sent in
	// the Get message.
	GetFailed(validatorID ids.ShortID, requestID uint32) error
}

// QueryHandler defines how a consensus engine reacts to query messages from
// other validators. Functions only return fatal errors if they occur.
type QueryHandler interface {
	// Notify this engine of a request for our preferences.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID. However, the validatorID is
	// assumed to be authenticated.
	//
	// If the container or its ancestry is incomplete, this engine is expected
	// to request the missing containers from the validator. Once the ancestry
	// is complete, this engine should send this validator the current
	// preferences in a Chits message. The Chits message should have the same
	// requestID that was passed in here.
	PullQuery(
		validatorID ids.ShortID,
		requestID uint32,
		containerID ids.ID,
	) error

	// Notify this engine of a request for our preferences.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is utilizing a unique requestID or even that the containerID
	// matches the ID of the container bytes. However, the validatorID is
	// assumed to be authenticated.
	//
	// This function is meant to behave the same way as PullQuery, except the
	// container is optimistically provided to potentially remove the need for
	// a series of Get/Put messages.
	//
	// If the ancestry of the container is incomplete, this engine is expected
	// to request the ancestry from the validator. Once the ancestry is
	// complete, this engine should send this validator the current preferences
	// in a Chits message. The Chits message should have the same requestID that
	// was passed in here.
	PushQuery(
		validatorID ids.ShortID,
		requestID uint32,
		containerID ids.ID,
		container []byte,
	) error

	// Notify this engine of the specified validators preferences.
	//
	// This function can be called by any validator. It is not safe to assume
	// this message is in response to a PullQuery or a PushQuery message.
	// However, the validatorID is assumed to be authenticated.
	Chits(validatorID ids.ShortID, requestID uint32, containerIDs ids.Set) error

	// Notify this engine that a query it issued has failed.
	//
	// This function will be called if the engine sent a PullQuery or PushQuery
	// message that is not anticipated to be responded to. This could be because
	// the recipient of the message is unknown or if the message request has
	// timed out.
	//
	// The validatorID and the requestID are assumed to be the same as those
	// sent in the Query message.
	QueryFailed(validatorID ids.ShortID, requestID uint32) error
}

// InternalHandler defines how this consensus engine reacts to messages from
// other components of this validator. Functions only return fatal errors if
// they occur.
type InternalHandler interface {
	// Startup this engine.
	//
	// This function will be called once the environment is configured to be
	// able to run the engine.
	Startup() error

	// Gossip to the network a container on the accepted frontier
	Gossip() error

	// Shutdown this engine.
	//
	// This function will be called when the environment is exiting.
	Shutdown() error

	// Notify this engine of a message from the virtual machine.
	Notify(Message) error
}