package vsync

import (
  "veyron/services/store/raw"

  "veyron2/storage"
)

// DeviceID is the globally unique ID of a device.
type DeviceID string
// GenID is the unique ID per generation per device.
type GenID uint64
// LSN is the log sequence number.
type LSN uint64
// GenVector is the generation vector.
type GenVector map[DeviceID]GenID

const (
      // NodeRec type log record adds a new node in the dag.
      NodeRec = byte(0)
      // LinkRec type log record adds a new link in the dag.
      LinkRec = byte(1)
)

// LogRec represents a single log record that is exchanged between two
// peers.
//
// It contains log related metadata: DevID is the id of the
// device that created the log record, GNum is the ID of the
// generation that the log record is part of, LSN is the log
// sequence number of the log record in the generation GNum,
// and RecType is the type of log record.
//
// It also contains information relevant to the updates to an object
// in the store: ObjID is the id of the object that was
// updated. CurVers is the current version number of the
// object. Parents can contain 0, 1 or 2 parent versions that the
// current version is derived from, and Value is the actual value of
// the object mutation.
type LogRec struct {
  // Log related information.
  DevID    DeviceID
  GNum     GenID
  LSN      LSN
  RecType  byte
  // Object related information.
  ObjID    storage.ID
  CurVers  raw.Version
  Parents  []raw.Version
  Value    LogValue
}

// LogValue represents an object mutation within a transaction.
type LogValue struct {
  // Mutation is the store mutation representing the change in the object.
  Mutation raw.Mutation
  // SyncTime is the timestamp of the mutation when it arrives at the Sync server.
  SyncTime int64
  // Delete indicates whether the mutation resulted in the object being
  // deleted from the store.
  Delete   bool
  // Continued tracks the transaction boundaries in a range of mutations.
  // It is set to true in all transaction mutations except the last one
  // in which it is set to false to mark the end of the transaction.
  Continued bool
}

// Sync allows a device to GetDeltas from another device.
type Sync interface {
  // GetDeltas returns a device's current generation vector and all the missing log records
  // when compared to the incoming generation vector.
  GetDeltas(In GenVector, ClientID DeviceID) stream<_, LogRec> (Out GenVector, Err error)
}