package mapstate

// To add a new state format
// - implement the previous format's "next" function to the new format
// - implement the new format's unmarshal function
// - add a case to the switch statement for the previous format version
// - update the code copying the from mapStateVx to mapState
import (
	"context"
	"errors"
	"io"

	"github.com/ipfs/ipfs-cluster/api"

	msgpack "github.com/multiformats/go-multicodec/msgpack"
)

// Instances of migrateable can be read from a serialized format and migrated
// to other state formats
type migrateable interface {
	next() migrateable
	unmarshal(io.Reader) error
}

/* V1 */

type mapStateV1 struct {
	Version int
	PinMap  map[string]struct{}
}

// Unmarshal the serialization of a v1 state
func (st *mapStateV1) unmarshal(r io.Reader) error {
	dec := msgpack.Multicodec(msgpack.DefaultMsgpackHandle()).Decoder(r)
	return dec.Decode(st)
}

// Migrate from v1 to v2
func (st *mapStateV1) next() migrateable {
	var mst2 mapStateV2
	mst2.PinMap = make(map[string]pinSerialV2)
	for k := range st.PinMap {
		mst2.PinMap[k] = pinSerialV2{
			Cid:               k,
			Allocations:       []string{},
			ReplicationFactor: -1,
		}
	}
	return &mst2
}

/* V2 */

type pinSerialV2 struct {
	Cid               string   `json:"cid"`
	Name              string   `json:"name"`
	Allocations       []string `json:"allocations"`
	ReplicationFactor int      `json:"replication_factor"`
}

type mapStateV2 struct {
	PinMap  map[string]pinSerialV2
	Version int
}

func (st *mapStateV2) unmarshal(r io.Reader) error {
	dec := msgpack.Multicodec(msgpack.DefaultMsgpackHandle()).Decoder(r)
	return dec.Decode(st)
}

func (st *mapStateV2) next() migrateable {
	var mst3 mapStateV3
	mst3.PinMap = make(map[string]pinSerialV3)
	for k, v := range st.PinMap {
		mst3.PinMap[k] = pinSerialV3{
			Cid:                  v.Cid,
			Name:                 v.Name,
			Allocations:          v.Allocations,
			ReplicationFactorMin: v.ReplicationFactor,
			ReplicationFactorMax: v.ReplicationFactor,
		}
	}
	return &mst3
}

/* V3 */

type pinSerialV3 struct {
	Cid                  string   `json:"cid"`
	Name                 string   `json:"name"`
	Allocations          []string `json:"allocations"`
	ReplicationFactorMin int      `json:"replication_factor_min"`
	ReplicationFactorMax int      `json:"replication_factor_max"`
}

type mapStateV3 struct {
	PinMap  map[string]pinSerialV3
	Version int
}

func (st *mapStateV3) unmarshal(r io.Reader) error {
	dec := msgpack.Multicodec(msgpack.DefaultMsgpackHandle()).Decoder(r)
	return dec.Decode(st)
}

func (st *mapStateV3) next() migrateable {
	var mst4 mapStateV4
	mst4.PinMap = make(map[string]pinSerialV4)
	for k, v := range st.PinMap {
		mst4.PinMap[k] = pinSerialV4{
			Cid:                  v.Cid,
			Name:                 v.Name,
			Allocations:          v.Allocations,
			ReplicationFactorMin: v.ReplicationFactorMin,
			ReplicationFactorMax: v.ReplicationFactorMax,
			Recursive:            true,
		}
	}
	return &mst4
}

/* V4 */

type pinSerialV4 struct {
	Cid                  string   `json:"cid"`
	Name                 string   `json:"name"`
	Allocations          []string `json:"allocations"`
	ReplicationFactorMin int      `json:"replication_factor_min"`
	ReplicationFactorMax int      `json:"replication_factor_max"`
	Recursive            bool     `json:"recursive"`
}

type mapStateV4 struct {
	PinMap  map[string]pinSerialV4
	Version int
}

func (st *mapStateV4) unmarshal(r io.Reader) error {
	dec := msgpack.Multicodec(msgpack.DefaultMsgpackHandle()).Decoder(r)
	return dec.Decode(st)
}

func (st *mapStateV4) next() migrateable {
	var mst5 mapStateV5
	mst5.PinMap = make(map[string]pinSerialV5)
	for k, v := range st.PinMap {
		pinsv5 := pinSerialV5{}
		pinsv5.Cid = v.Cid
		pinsv5.Type = uint64(api.DataType)
		pinsv5.Allocations = v.Allocations

		// Encountered pins with Recursive=false
		// in previous states. Since we do not support
		// non recursive pins yet, we fix it by
		// harcoding MaxDepth.
		pinsv5.MaxDepth = -1

		// Options
		pinsv5.Name = v.Name
		pinsv5.ReplicationFactorMin = v.ReplicationFactorMin
		pinsv5.ReplicationFactorMax = v.ReplicationFactorMax

		mst5.PinMap[k] = pinsv5
	}
	return &mst5
}

/* V5 */

type pinOptionsV5 struct {
	ReplicationFactorMin int    `json:"replication_factor_min"`
	ReplicationFactorMax int    `json:"replication_factor_max"`
	Name                 string `json:"name"`
	ShardSize            uint64 `json:"shard_size"`
}

type pinSerialV5 struct {
	pinOptionsV5

	Cid         string   `json:"cid"`
	Type        uint64   `json:"type"`
	Allocations []string `json:"allocations"`
	MaxDepth    int      `json:"max_depth"`
	Reference   string   `json:"reference"`
}

type mapStateV5 struct {
	PinMap  map[string]pinSerialV5
	Version int
}

func (st *mapStateV5) unmarshal(r io.Reader) error {
	dec := msgpack.Multicodec(msgpack.DefaultMsgpackHandle()).Decoder(r)
	return dec.Decode(st)
}

func (st *mapStateV5) next() migrateable {
	v6 := NewMapState()
	for k, v := range st.PinMap {
		logger.Infof("migrating", k, v.Cid)
		// we need to convert because we added codec struct fields
		// and thus serialization is not the same.
		p := api.PinSerial{}
		p.Cid = v.Cid
		p.Type = v.Type
		p.Allocations = v.Allocations
		p.MaxDepth = v.MaxDepth
		p.Reference = v.Reference
		p.ReplicationFactorMax = v.ReplicationFactorMax
		p.ReplicationFactorMin = v.ReplicationFactorMin
		p.Name = v.Name
		p.ShardSize = v.ShardSize

		v6.Add(context.Background(), p.ToPin())
	}
	return v6.(*MapState)
}

// Last time we use this migration approach.
func (st *MapState) next() migrateable { return nil }
func (st *MapState) unmarshal(r io.Reader) error {
	return st.dst.Unmarshal(r)
}

// Migrate code

func finalCopy(st *MapState, internal *MapState) {
	st.dst = internal.dst
}

func (st *MapState) migrateFrom(version int, snap io.Reader) error {
	var m, next migrateable
	switch version {
	case 1:
		var mst1 mapStateV1
		m = &mst1
	case 2:
		var mst2 mapStateV2
		m = &mst2
	case 3:
		var mst3 mapStateV3
		m = &mst3
	case 4:
		var mst4 mapStateV4
		m = &mst4
	case 5:
		var mst5 mapStateV5
		m = &mst5
	default:
		return errors.New("version migration not supported")
	}

	err := m.unmarshal(snap)
	if err != nil {
		return err
	}

	for {
		next = m.next()
		if next == nil {
			mst6, ok := m.(*MapState)
			if !ok {
				return errors.New("migration ended prematurely")
			}
			finalCopy(st, mst6)
			return nil
		}
		m = next
	}
}