//  Copyright (c) 2015 Couchbase, Inc.
//  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.

// +build go1.4

package cznicb

import (
	"errors"

	"github.com/cznic/b"
)

var iteratorDoneErr = errors.New("iteratorDoneErr") // A sentinel value.

type Iterator struct { // Assuming that iterators are used single-threaded.
	s *Store
	e *b.Enumerator

	currK   interface{}
	currV   interface{}
	currErr error
}

func (i *Iterator) SeekFirst() {
	i.currK = nil
	i.currV = nil
	i.currErr = nil

	var err error
	i.s.m.RLock()
	i.e, err = i.s.t.SeekFirst()
	i.s.m.RUnlock() // cannot defer, must unlock before Next
	if err != nil {
		i.currK = nil
		i.currV = nil
		i.currErr = iteratorDoneErr
	}

	i.Next()
}

func (i *Iterator) Seek(k []byte) {
	i.currK = nil
	i.currV = nil
	i.currErr = nil

	i.s.m.RLock()
	i.e, _ = i.s.t.Seek(k)
	i.s.m.RUnlock() // cannot defer, must unlock before Next

	i.Next()
}

func (i *Iterator) Next() {
	if i.currErr != nil {
		i.currK = nil
		i.currV = nil
		i.currErr = iteratorDoneErr
		return
	}

	i.s.m.RLock()
	defer i.s.m.RUnlock()
	i.currK, i.currV, i.currErr = i.e.Next()
}

func (i *Iterator) Current() ([]byte, []byte, bool) {
	if i.currErr == iteratorDoneErr ||
		i.currK == nil ||
		i.currV == nil {
		return nil, nil, false
	}

	return i.currK.([]byte), i.currV.([]byte), true
}

func (i *Iterator) Key() []byte {
	k, _, ok := i.Current()
	if !ok {
		return nil
	}
	return k
}

func (i *Iterator) Value() []byte {
	_, v, ok := i.Current()
	if !ok {
		return nil
	}
	return v
}

func (i *Iterator) Valid() bool {
	_, _, ok := i.Current()
	return ok
}

func (i *Iterator) Close() error {
	if i.e != nil {
		i.e.Close()
	}
	i.e = nil
	return nil
}