package structs

import (
	"bytes"
	"fmt"
	"time"

	"github.com/hashicorp/go-msgpack/codec"
)

var (
	ErrNoLeader     = fmt.Errorf("No cluster leader")
	ErrNoRegionPath = fmt.Errorf("No path to region")
)

type MessageType uint8

const (
	RegisterRequestType MessageType = iota
)

const (
	// IgnoreUnknownTypeFlag is set along with a MessageType
	// to indicate that the message type can be safely ignored
	// if it is not recognized. This is for future proofing, so
	// that new commands can be added in a way that won't cause
	// old servers to crash when the FSM attempts to process them.
	IgnoreUnknownTypeFlag MessageType = 128
)

// RPCInfo is used to describe common information about query
type RPCInfo interface {
	RequestRegion() string
	IsRead() bool
	AllowStaleRead() bool
}

// QueryOptions is used to specify various flags for read queries
type QueryOptions struct {
	// The target region for this query
	Region string

	// If set, any follower can service the request. Results
	// may be arbitrarily stale.
	AllowStale bool
}

func (q QueryOptions) RequestRegion() string {
	return q.Region
}

// QueryOption only applies to reads, so always true
func (q QueryOptions) IsRead() bool {
	return true
}

func (q QueryOptions) AllowStaleRead() bool {
	return q.AllowStale
}

type WriteRequest struct {
	Region string
}

func (w WriteRequest) RequestRegion() string {
	// The target region for this request
	return w.Region
}

// WriteRequest only applies to writes, always false
func (w WriteRequest) IsRead() bool {
	return false
}

func (w WriteRequest) AllowStaleRead() bool {
	return false
}

// QueryMeta allows a query response to include potentially
// useful metadata about a query
type QueryMeta struct {
	// This is the index associated with the read
	Index uint64

	// If AllowStale is used, this is time elapsed since
	// last contact between the follower and leader. This
	// can be used to gauge staleness.
	LastContact time.Duration

	// Used to indicate if there is a known leader node
	KnownLeader bool
}

// msgpackHandle is a shared handle for encoding/decoding of structs
var msgpackHandle = &codec.MsgpackHandle{}

// Decode is used to decode a MsgPack encoded object
func Decode(buf []byte, out interface{}) error {
	return codec.NewDecoder(bytes.NewReader(buf), msgpackHandle).Decode(out)
}

// Encode is used to encode a MsgPack object with type prefix
func Encode(t MessageType, msg interface{}) ([]byte, error) {
	var buf bytes.Buffer
	buf.WriteByte(uint8(t))
	err := codec.NewEncoder(&buf, msgpackHandle).Encode(msg)
	return buf.Bytes(), err
}