//  Copyright (c) 2014 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.

package bleve

import (
	"context"
	"sort"
	"sync"
	"time"

	"github.com/blevesearch/bleve/document"
	"github.com/blevesearch/bleve/index"
	"github.com/blevesearch/bleve/index/store"
	"github.com/blevesearch/bleve/mapping"
	"github.com/blevesearch/bleve/search"
)

type indexAliasImpl struct {
	name    string
	indexes []Index
	mutex   sync.RWMutex
	open    bool
}

// NewIndexAlias creates a new IndexAlias over the provided
// Index objects.
func NewIndexAlias(indexes ...Index) *indexAliasImpl {
	return &indexAliasImpl{
		name:    "alias",
		indexes: indexes,
		open:    true,
	}
}

func (i *indexAliasImpl) isAliasToSingleIndex() error {
	if len(i.indexes) < 1 {
		return ErrorAliasEmpty
	} else if len(i.indexes) > 1 {
		return ErrorAliasMulti
	}
	return nil
}

func (i *indexAliasImpl) Index(id string, data interface{}) error {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return err
	}

	return i.indexes[0].Index(id, data)
}

func (i *indexAliasImpl) Delete(id string) error {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return err
	}

	return i.indexes[0].Delete(id)
}

func (i *indexAliasImpl) Batch(b *Batch) error {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return err
	}

	return i.indexes[0].Batch(b)
}

func (i *indexAliasImpl) Document(id string) (*document.Document, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil, err
	}

	return i.indexes[0].Document(id)
}

func (i *indexAliasImpl) DocCount() (uint64, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	rv := uint64(0)

	if !i.open {
		return 0, ErrorIndexClosed
	}

	for _, index := range i.indexes {
		otherCount, err := index.DocCount()
		if err == nil {
			rv += otherCount
		}
		// tolerate errors to produce partial counts
	}

	return rv, nil
}

func (i *indexAliasImpl) Search(req *SearchRequest) (*SearchResult, error) {
	return i.SearchInContext(context.Background(), req)
}

func (i *indexAliasImpl) SearchInContext(ctx context.Context, req *SearchRequest) (*SearchResult, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil, ErrorIndexClosed
	}

	if len(i.indexes) < 1 {
		return nil, ErrorAliasEmpty
	}

	// short circuit the simple case
	if len(i.indexes) == 1 {
		return i.indexes[0].SearchInContext(ctx, req)
	}

	return MultiSearch(ctx, req, i.indexes...)
}

func (i *indexAliasImpl) Fields() ([]string, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil, err
	}

	return i.indexes[0].Fields()
}

func (i *indexAliasImpl) FieldDict(field string) (index.FieldDict, error) {
	i.mutex.RLock()

	if !i.open {
		i.mutex.RUnlock()
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	fieldDict, err := i.indexes[0].FieldDict(field)
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	return &indexAliasImplFieldDict{
		index:     i,
		fieldDict: fieldDict,
	}, nil
}

func (i *indexAliasImpl) FieldDictRange(field string, startTerm []byte, endTerm []byte) (index.FieldDict, error) {
	i.mutex.RLock()

	if !i.open {
		i.mutex.RUnlock()
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	fieldDict, err := i.indexes[0].FieldDictRange(field, startTerm, endTerm)
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	return &indexAliasImplFieldDict{
		index:     i,
		fieldDict: fieldDict,
	}, nil
}

func (i *indexAliasImpl) FieldDictPrefix(field string, termPrefix []byte) (index.FieldDict, error) {
	i.mutex.RLock()

	if !i.open {
		i.mutex.RUnlock()
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	fieldDict, err := i.indexes[0].FieldDictPrefix(field, termPrefix)
	if err != nil {
		i.mutex.RUnlock()
		return nil, err
	}

	return &indexAliasImplFieldDict{
		index:     i,
		fieldDict: fieldDict,
	}, nil
}

func (i *indexAliasImpl) Close() error {
	i.mutex.Lock()
	defer i.mutex.Unlock()

	i.open = false
	return nil
}

func (i *indexAliasImpl) Mapping() mapping.IndexMapping {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil
	}

	return i.indexes[0].Mapping()
}

func (i *indexAliasImpl) Stats() *IndexStat {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil
	}

	return i.indexes[0].Stats()
}

func (i *indexAliasImpl) StatsMap() map[string]interface{} {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil
	}

	return i.indexes[0].StatsMap()
}

func (i *indexAliasImpl) GetInternal(key []byte) ([]byte, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil, err
	}

	return i.indexes[0].GetInternal(key)
}

func (i *indexAliasImpl) SetInternal(key, val []byte) error {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return err
	}

	return i.indexes[0].SetInternal(key, val)
}

func (i *indexAliasImpl) DeleteInternal(key []byte) error {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return err
	}

	return i.indexes[0].DeleteInternal(key)
}

func (i *indexAliasImpl) Advanced() (index.Index, store.KVStore, error) {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil, nil, ErrorIndexClosed
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil, nil, err
	}

	return i.indexes[0].Advanced()
}

func (i *indexAliasImpl) Add(indexes ...Index) {
	i.mutex.Lock()
	defer i.mutex.Unlock()

	i.indexes = append(i.indexes, indexes...)
}

func (i *indexAliasImpl) removeSingle(index Index) {
	for pos, in := range i.indexes {
		if in == index {
			i.indexes = append(i.indexes[:pos], i.indexes[pos+1:]...)
			break
		}
	}
}

func (i *indexAliasImpl) Remove(indexes ...Index) {
	i.mutex.Lock()
	defer i.mutex.Unlock()

	for _, in := range indexes {
		i.removeSingle(in)
	}
}

func (i *indexAliasImpl) Swap(in, out []Index) {
	i.mutex.Lock()
	defer i.mutex.Unlock()

	// add
	i.indexes = append(i.indexes, in...)

	// delete
	for _, ind := range out {
		i.removeSingle(ind)
	}
}

// createChildSearchRequest creates a separate
// request from the original
// For now, avoid data race on req structure.
// TODO disable highlight/field load on child
// requests, and add code to do this only on
// the actual final results.
// Perhaps that part needs to be optional,
// could be slower in remote usages.
func createChildSearchRequest(req *SearchRequest) *SearchRequest {
	rv := SearchRequest{
		Query:            req.Query,
		Size:             req.Size + req.From,
		From:             0,
		Highlight:        req.Highlight,
		Fields:           req.Fields,
		Facets:           req.Facets,
		Explain:          req.Explain,
		Sort:             req.Sort.Copy(),
		IncludeLocations: req.IncludeLocations,
		Score:            req.Score,
	}
	return &rv
}

type asyncSearchResult struct {
	Name   string
	Result *SearchResult
	Err    error
}

// MultiSearch executes a SearchRequest across multiple Index objects,
// then merges the results.  The indexes must honor any ctx deadline.
func MultiSearch(ctx context.Context, req *SearchRequest, indexes ...Index) (*SearchResult, error) {

	searchStart := time.Now()
	asyncResults := make(chan *asyncSearchResult, len(indexes))

	// run search on each index in separate go routine
	var waitGroup sync.WaitGroup

	var searchChildIndex = func(in Index, childReq *SearchRequest) {
		rv := asyncSearchResult{Name: in.Name()}
		rv.Result, rv.Err = in.SearchInContext(ctx, childReq)
		asyncResults <- &rv
		waitGroup.Done()
	}

	waitGroup.Add(len(indexes))
	for _, in := range indexes {
		go searchChildIndex(in, createChildSearchRequest(req))
	}

	// on another go routine, close after finished
	go func() {
		waitGroup.Wait()
		close(asyncResults)
	}()

	var sr *SearchResult
	indexErrors := make(map[string]error)

	for asr := range asyncResults {
		if asr.Err == nil {
			if sr == nil {
				// first result
				sr = asr.Result
			} else {
				// merge with previous
				sr.Merge(asr.Result)
			}
		} else {
			indexErrors[asr.Name] = asr.Err
		}
	}

	// merge just concatenated all the hits
	// now lets clean it up

	// handle case where no results were successful
	if sr == nil {
		sr = &SearchResult{
			Status: &SearchStatus{
				Errors: make(map[string]error),
			},
		}
	}

	// sort all hits with the requested order
	if len(req.Sort) > 0 {
		sorter := newMultiSearchHitSorter(req.Sort, sr.Hits)
		sort.Sort(sorter)
	}

	// now skip over the correct From
	if req.From > 0 && len(sr.Hits) > req.From {
		sr.Hits = sr.Hits[req.From:]
	} else if req.From > 0 {
		sr.Hits = search.DocumentMatchCollection{}
	}

	// now trim to the correct size
	if req.Size > 0 && len(sr.Hits) > req.Size {
		sr.Hits = sr.Hits[0:req.Size]
	}

	// fix up facets
	for name, fr := range req.Facets {
		sr.Facets.Fixup(name, fr.Size)
	}

	// fix up original request
	sr.Request = req
	searchDuration := time.Since(searchStart)
	sr.Took = searchDuration

	// fix up errors
	if len(indexErrors) > 0 {
		if sr.Status.Errors == nil {
			sr.Status.Errors = make(map[string]error)
		}
		for indexName, indexErr := range indexErrors {
			sr.Status.Errors[indexName] = indexErr
			sr.Status.Total++
			sr.Status.Failed++
		}
	}

	return sr, nil
}

func (i *indexAliasImpl) NewBatch() *Batch {
	i.mutex.RLock()
	defer i.mutex.RUnlock()

	if !i.open {
		return nil
	}

	err := i.isAliasToSingleIndex()
	if err != nil {
		return nil
	}

	return i.indexes[0].NewBatch()
}

func (i *indexAliasImpl) Name() string {
	return i.name
}

func (i *indexAliasImpl) SetName(name string) {
	i.name = name
}

type indexAliasImplFieldDict struct {
	index     *indexAliasImpl
	fieldDict index.FieldDict
}

func (f *indexAliasImplFieldDict) Next() (*index.DictEntry, error) {
	return f.fieldDict.Next()
}

func (f *indexAliasImplFieldDict) Close() error {
	defer f.index.mutex.RUnlock()
	return f.fieldDict.Close()
}

type multiSearchHitSorter struct {
	hits          search.DocumentMatchCollection
	sort          search.SortOrder
	cachedScoring []bool
	cachedDesc    []bool
}

func newMultiSearchHitSorter(sort search.SortOrder, hits search.DocumentMatchCollection) *multiSearchHitSorter {
	return &multiSearchHitSorter{
		sort:          sort,
		hits:          hits,
		cachedScoring: sort.CacheIsScore(),
		cachedDesc:    sort.CacheDescending(),
	}
}

func (m *multiSearchHitSorter) Len() int      { return len(m.hits) }
func (m *multiSearchHitSorter) Swap(i, j int) { m.hits[i], m.hits[j] = m.hits[j], m.hits[i] }
func (m *multiSearchHitSorter) Less(i, j int) bool {
	c := m.sort.Compare(m.cachedScoring, m.cachedDesc, m.hits[i], m.hits[j])
	return c < 0
}
