//  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 searcher

import (
	"fmt"
	"math"
	"sort"

	"github.com/blevesearch/bleve/index"
	"github.com/blevesearch/bleve/search"
	"github.com/blevesearch/bleve/search/scorer"
)

// DisjunctionMaxClauseCount is a compile time setting that applications can
// adjust to non-zero value to cause the DisjunctionSearcher to return an
// error instead of exeucting searches when the size exceeds this value.
var DisjunctionMaxClauseCount = 0

type DisjunctionSearcher struct {
	indexReader  index.IndexReader
	searchers    OrderedSearcherList
	numSearchers int
	queryNorm    float64
	currs        []*search.DocumentMatch
	scorer       *scorer.DisjunctionQueryScorer
	min          int
	matching     []*search.DocumentMatch
	matchingIdxs []int
	initialized  bool
}

func tooManyClauses(count int) bool {
	if DisjunctionMaxClauseCount != 0 && count > DisjunctionMaxClauseCount {
		return true
	}
	return false
}

func tooManyClausesErr() error {
	return fmt.Errorf("TooManyClauses[maxClauseCount is set to %d]", DisjunctionMaxClauseCount)
}

func NewDisjunctionSearcher(indexReader index.IndexReader, qsearchers []search.Searcher, min float64, explain bool) (*DisjunctionSearcher, error) {
	if tooManyClauses(len(qsearchers)) {
		return nil, tooManyClausesErr()
	}
	// build the downstream searchers
	searchers := make(OrderedSearcherList, len(qsearchers))
	for i, searcher := range qsearchers {
		searchers[i] = searcher
	}
	// sort the searchers
	sort.Sort(sort.Reverse(searchers))
	// build our searcher
	rv := DisjunctionSearcher{
		indexReader:  indexReader,
		searchers:    searchers,
		numSearchers: len(searchers),
		currs:        make([]*search.DocumentMatch, len(searchers)),
		scorer:       scorer.NewDisjunctionQueryScorer(explain),
		min:          int(min),
		matching:     make([]*search.DocumentMatch, len(searchers)),
		matchingIdxs: make([]int, len(searchers)),
	}
	rv.computeQueryNorm()
	return &rv, nil
}

func (s *DisjunctionSearcher) computeQueryNorm() {
	// first calculate sum of squared weights
	sumOfSquaredWeights := 0.0
	for _, termSearcher := range s.searchers {
		sumOfSquaredWeights += termSearcher.Weight()
	}
	// now compute query norm from this
	s.queryNorm = 1.0 / math.Sqrt(sumOfSquaredWeights)
	// finally tell all the downstream searchers the norm
	for _, termSearcher := range s.searchers {
		termSearcher.SetQueryNorm(s.queryNorm)
	}
}

func (s *DisjunctionSearcher) initSearchers(ctx *search.SearchContext) error {
	var err error
	// get all searchers pointing at their first match
	for i, termSearcher := range s.searchers {
		if s.currs[i] != nil {
			ctx.DocumentMatchPool.Put(s.currs[i])
		}
		s.currs[i], err = termSearcher.Next(ctx)
		if err != nil {
			return err
		}
	}

	err = s.updateMatches()
	if err != nil {
		return err
	}

	s.initialized = true
	return nil
}

func (s *DisjunctionSearcher) updateMatches() error {
	matching := s.matching[:0]
	matchingIdxs := s.matchingIdxs[:0]

	for i := 0; i < len(s.currs); i++ {
		curr := s.currs[i]
		if curr == nil {
			continue
		}

		if len(matching) > 0 {
			cmp := curr.IndexInternalID.Compare(matching[0].IndexInternalID)
			if cmp > 0 {
				continue
			}

			if cmp < 0 {
				matching = matching[:0]
				matchingIdxs = matchingIdxs[:0]
			}
		}

		matching = append(matching, curr)
		matchingIdxs = append(matchingIdxs, i)
	}

	s.matching = matching
	s.matchingIdxs = matchingIdxs

	return nil
}

func (s *DisjunctionSearcher) Weight() float64 {
	var rv float64
	for _, searcher := range s.searchers {
		rv += searcher.Weight()
	}
	return rv
}

func (s *DisjunctionSearcher) SetQueryNorm(qnorm float64) {
	for _, searcher := range s.searchers {
		searcher.SetQueryNorm(qnorm)
	}
}

func (s *DisjunctionSearcher) Next(ctx *search.SearchContext) (*search.DocumentMatch, error) {
	if !s.initialized {
		err := s.initSearchers(ctx)
		if err != nil {
			return nil, err
		}
	}
	var err error
	var rv *search.DocumentMatch

	found := false
	for !found && len(s.matching) > 0 {
		if len(s.matching) >= s.min {
			found = true
			// score this match
			rv = s.scorer.Score(ctx, s.matching, len(s.matching), s.numSearchers)
		}

		// invoke next on all the matching searchers
		for _, i := range s.matchingIdxs {
			searcher := s.searchers[i]
			if s.currs[i] != rv {
				ctx.DocumentMatchPool.Put(s.currs[i])
			}
			s.currs[i], err = searcher.Next(ctx)
			if err != nil {
				return nil, err
			}
		}

		err = s.updateMatches()
		if err != nil {
			return nil, err
		}
	}
	return rv, nil
}

func (s *DisjunctionSearcher) Advance(ctx *search.SearchContext, ID index.IndexInternalID) (*search.DocumentMatch, error) {
	if !s.initialized {
		err := s.initSearchers(ctx)
		if err != nil {
			return nil, err
		}
	}
	// get all searchers pointing at their first match
	var err error
	for i, termSearcher := range s.searchers {
		if s.currs[i] != nil {
			ctx.DocumentMatchPool.Put(s.currs[i])
		}
		s.currs[i], err = termSearcher.Advance(ctx, ID)
		if err != nil {
			return nil, err
		}
	}

	err = s.updateMatches()
	if err != nil {
		return nil, err
	}

	return s.Next(ctx)
}

func (s *DisjunctionSearcher) Count() uint64 {
	// for now return a worst case
	var sum uint64
	for _, searcher := range s.searchers {
		sum += searcher.Count()
	}
	return sum
}

func (s *DisjunctionSearcher) Close() (rv error) {
	for _, searcher := range s.searchers {
		err := searcher.Close()
		if err != nil && rv == nil {
			rv = err
		}
	}
	return rv
}

func (s *DisjunctionSearcher) Min() int {
	return s.min
}

func (s *DisjunctionSearcher) DocumentMatchPoolSize() int {
	rv := len(s.currs)
	for _, s := range s.searchers {
		rv += s.DocumentMatchPoolSize()
	}
	return rv
}
