// Unless explicitly stated otherwise all files in this repository are licensed
// under the Apache License 2.0.
// This product includes software developed at Datadog (https://www.datadoghq.com/).
// Copyright 2021 Datadog, Inc.

package store

import (
	"errors"
	"sort"

	enc "github.com/DataDog/sketches-go/ddsketch/encoding"
	"github.com/DataDog/sketches-go/ddsketch/pb/sketchpb"
)

type SparseStore struct {
	counts map[int]float64
}

func NewSparseStore() *SparseStore {
	return &SparseStore{counts: make(map[int]float64)}
}

func (s *SparseStore) Add(index int) {
	s.counts[index]++
}

func (s *SparseStore) AddBin(bin Bin) {
	s.AddWithCount(bin.index, bin.count)
}

func (s *SparseStore) AddWithCount(index int, count float64) {
	if count == 0 {
		return
	}
	s.counts[index] += count
}

func (s *SparseStore) Bins() <-chan Bin {
	orderedBins := s.orderedBins()
	ch := make(chan Bin)
	go func() {
		defer close(ch)
		for _, bin := range orderedBins {
			ch <- bin
		}
	}()
	return ch
}

func (s *SparseStore) orderedBins() []Bin {
	bins := make([]Bin, 0, len(s.counts))
	for index, count := range s.counts {
		bins = append(bins, Bin{index: index, count: count})
	}
	sort.Slice(bins, func(i, j int) bool { return bins[i].index < bins[j].index })
	return bins
}

func (s *SparseStore) ForEach(f func(index int, count float64) (stop bool)) {
	for index, count := range s.counts {
		if f(index, count) {
			return
		}
	}
}

func (s *SparseStore) Copy() Store {
	countsCopy := make(map[int]float64)
	for index, count := range s.counts {
		countsCopy[index] = count
	}
	return &SparseStore{counts: countsCopy}
}

func (s *SparseStore) Clear() {
	for index := range s.counts {
		delete(s.counts, index)
	}
}

func (s *SparseStore) IsEmpty() bool {
	return len(s.counts) == 0
}

func (s *SparseStore) MaxIndex() (int, error) {
	if s.IsEmpty() {
		return 0, errUndefinedMaxIndex
	}
	maxIndex := minInt
	for index := range s.counts {
		if index > maxIndex {
			maxIndex = index
		}
	}
	return maxIndex, nil
}

func (s *SparseStore) MinIndex() (int, error) {
	if s.IsEmpty() {
		return 0, errUndefinedMinIndex
	}
	minIndex := maxInt
	for index := range s.counts {
		if index < minIndex {
			minIndex = index
		}
	}
	return minIndex, nil
}

func (s *SparseStore) TotalCount() float64 {
	totalCount := float64(0)
	for _, count := range s.counts {
		totalCount += count
	}
	return totalCount
}

func (s *SparseStore) KeyAtRank(rank float64) int {
	orderedBins := s.orderedBins()
	cumulCount := float64(0)
	for _, bin := range orderedBins {
		cumulCount += bin.count
		if cumulCount > rank {
			return bin.index
		}
	}
	maxIndex, err := s.MaxIndex()
	if err == nil {
		return maxIndex
	} else {
		// FIXME: make Store's KeyAtRank consistent with MinIndex and MaxIndex
		return 0
	}
}

func (s *SparseStore) MergeWith(store Store) {
	store.ForEach(func(index int, count float64) (stop bool) {
		s.AddWithCount(index, count)
		return false
	})
}

func (s *SparseStore) ToProto() *sketchpb.Store {
	binCounts := make(map[int32]float64)
	for index, count := range s.counts {
		binCounts[int32(index)] = count
	}
	return &sketchpb.Store{BinCounts: binCounts}
}

func (s *SparseStore) Reweight(w float64) error {
	if w <= 0 {
		return errors.New("can't reweight by a negative factor")
	}
	if w == 1 {
		return nil
	}
	for index := range s.counts {
		s.counts[index] *= w
	}
	return nil
}

func (s *SparseStore) Encode(b *[]byte, t enc.FlagType) {
	if s.IsEmpty() {
		return
	}
	enc.EncodeFlag(b, enc.NewFlag(t, enc.BinEncodingIndexDeltasAndCounts))
	enc.EncodeUvarint64(b, uint64(len(s.counts)))
	previousIndex := 0
	for index, count := range s.counts {
		enc.EncodeVarint64(b, int64(index-previousIndex))
		enc.EncodeVarfloat64(b, count)
		previousIndex = index
	}
}

func (s *SparseStore) DecodeAndMergeWith(b *[]byte, encodingMode enc.SubFlag) error {
	return DecodeAndMergeWith(s, b, encodingMode)
}

var _ Store = (*SparseStore)(nil)