// Copyright 2014 The Cayley Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package graph

// Defines the interface for consistent replication of a graph instance.
//
// Separate from the backend, this dictates how individual triples get
// identified and replicated consistently across (potentially) multiple
// instances. The simplest case is to keep an append-only log of triple
// changes.

import (
	"errors"
)

type Procedure byte

// The different types of actions a transaction can do.
const (
	Add Procedure = iota
	Delete
)

type Transaction struct {
	ID     int64
	Triple *Triple
	Action Procedure
}

type Replication interface {
	// Get a unique range of triple IDs from the Replication strategy.
	// Returns the inclusive set of unique ids.
	AcquireNextIds(size int64) (start int64, end int64)

	// Returns the highest current ID.
	GetLastID() int64

	// Sends the transactions to the replicas.
	Replicate([]*Transaction)

	// Attempt to acquire the given range of triples from other replicated sources.
	RequestTransactionRange(start int64, end int64)
}

type NewReplicationFunc func(TripleStore, Options) (Replication, error)

var replicationRegistry = make(map[string]NewReplicationFunc)

func RegisterReplication(name string, newFunc NewReplicationFunc) {
	if _, found := replicationRegistry[name]; found {
		panic("already registered Replication " + name)
	}
	replicationRegistry[name] = newFunc
}

func NewReplication(name string, ts TripleStore, opts Options) (Replication, error) {
	newFunc, hasNew := replicationRegistry[name]
	if !hasNew {
		return nil, errors.New("replication: name '" + name + "' is not registered")
	}
	return newFunc(ts, opts)
}

func ReplicationMethods() []string {
	t := make([]string, 0, len(replicationRegistry))
	for n := range replicationRegistry {
		t = append(t, n)
	}
	return t
}