// Copyright 2016 Apcera Inc. All rights reserved.

package stores

import (
	"sort"
	"sync"
	"time"

	"github.com/nats-io/go-nats-streaming/pb"
)

// MemoryStore is a factory for message and subscription stores.
type MemoryStore struct {
	genericStore
}

// MemorySubStore is a subscription store in memory
type MemorySubStore struct {
	genericSubStore
}

// MemoryMsgStore is a per channel message store in memory
type MemoryMsgStore struct {
	genericMsgStore
	msgs     map[uint64]*pb.MsgProto
	ageTimer *time.Timer
	wg       sync.WaitGroup
}

////////////////////////////////////////////////////////////////////////////
// MemoryStore methods
////////////////////////////////////////////////////////////////////////////

// NewMemoryStore returns a factory for stores held in memory.
// If not limits are provided, the store will be created with
// DefaultStoreLimits.
func NewMemoryStore(limits *StoreLimits) (*MemoryStore, error) {
	ms := &MemoryStore{}
	ms.init(TypeMemory, limits)
	return ms, nil
}

// CreateChannel creates a ChannelStore for the given channel, and returns
// `true` to indicate that the channel is new, false if it already exists.
func (ms *MemoryStore) CreateChannel(channel string, userData interface{}) (*ChannelStore, bool, error) {
	ms.Lock()
	defer ms.Unlock()
	channelStore := ms.channels[channel]
	if channelStore != nil {
		return channelStore, false, nil
	}

	if err := ms.canAddChannel(); err != nil {
		return nil, false, err
	}

	// Defaults to the global limits
	msgStoreLimits := ms.limits.MsgStoreLimits
	subStoreLimits := ms.limits.SubStoreLimits
	// See if there is an override
	thisChannelLimits, exists := ms.limits.PerChannel[channel]
	if exists {
		// Use this channel specific limits
		msgStoreLimits = thisChannelLimits.MsgStoreLimits
		subStoreLimits = thisChannelLimits.SubStoreLimits
	}

	msgStore := &MemoryMsgStore{msgs: make(map[uint64]*pb.MsgProto, 64)}
	msgStore.init(channel, &msgStoreLimits)

	subStore := &MemorySubStore{}
	subStore.init(channel, &subStoreLimits)

	channelStore = &ChannelStore{
		Subs:     subStore,
		Msgs:     msgStore,
		UserData: userData,
	}

	ms.channels[channel] = channelStore

	return channelStore, true, nil
}

////////////////////////////////////////////////////////////////////////////
// MemoryMsgStore methods
////////////////////////////////////////////////////////////////////////////

// Store a given message.
func (ms *MemoryMsgStore) Store(data []byte) (uint64, error) {
	ms.Lock()
	defer ms.Unlock()

	if ms.first == 0 {
		ms.first = 1
	}
	ms.last++
	m := &pb.MsgProto{
		Sequence:  ms.last,
		Subject:   ms.subject,
		Data:      data,
		Timestamp: time.Now().UnixNano(),
	}
	ms.msgs[ms.last] = m
	ms.totalCount++
	ms.totalBytes += uint64(m.Size())
	// If there is an age limit and no timer yet created, do so now
	if ms.limits.MaxAge > time.Duration(0) && ms.ageTimer == nil {
		ms.wg.Add(1)
		ms.ageTimer = time.AfterFunc(ms.limits.MaxAge, ms.expireMsgs)
	}

	// Check if we need to remove any (but leave at least the last added)
	maxMsgs := ms.limits.MaxMsgs
	maxBytes := ms.limits.MaxBytes
	if maxMsgs > 0 || maxBytes > 0 {
		for ms.totalCount > 1 &&
			((maxMsgs > 0 && ms.totalCount > maxMsgs) ||
				(maxBytes > 0 && (ms.totalBytes > uint64(maxBytes)))) {
			ms.removeFirstMsg()
			if !ms.hitLimit {
				ms.hitLimit = true
				Noticef(droppingMsgsFmt, ms.subject, ms.totalCount, ms.limits.MaxMsgs, ms.totalBytes, ms.limits.MaxBytes)
			}
		}
	}

	return ms.last, nil
}

// Lookup returns the stored message with given sequence number.
func (ms *MemoryMsgStore) Lookup(seq uint64) *pb.MsgProto {
	ms.RLock()
	m := ms.msgs[seq]
	ms.RUnlock()
	return m
}

// FirstMsg returns the first message stored.
func (ms *MemoryMsgStore) FirstMsg() *pb.MsgProto {
	ms.RLock()
	m := ms.msgs[ms.first]
	ms.RUnlock()
	return m
}

// LastMsg returns the last message stored.
func (ms *MemoryMsgStore) LastMsg() *pb.MsgProto {
	ms.RLock()
	m := ms.msgs[ms.last]
	ms.RUnlock()
	return m
}

// GetSequenceFromTimestamp returns the sequence of the first message whose
// timestamp is greater or equal to given timestamp.
func (ms *MemoryMsgStore) GetSequenceFromTimestamp(timestamp int64) uint64 {
	ms.RLock()
	defer ms.RUnlock()

	index := sort.Search(len(ms.msgs), func(i int) bool {
		m := ms.msgs[uint64(i)+ms.first]
		if m.Timestamp >= timestamp {
			return true
		}
		return false
	})

	return uint64(index) + ms.first
}

// expireMsgs ensures that messages don't stay in the log longer than the
// limit's MaxAge.
func (ms *MemoryMsgStore) expireMsgs() {
	ms.Lock()
	if ms.closed {
		ms.Unlock()
		ms.wg.Done()
		return
	}
	defer ms.Unlock()

	now := time.Now().UnixNano()
	maxAge := int64(ms.limits.MaxAge)
	for {
		m, ok := ms.msgs[ms.first]
		if !ok {
			ms.ageTimer = nil
			ms.wg.Done()
			return
		}
		elapsed := now - m.Timestamp
		if elapsed >= maxAge {
			ms.removeFirstMsg()
		} else {
			ms.ageTimer.Reset(time.Duration(maxAge - elapsed))
			return
		}
	}
}

// removeFirstMsg removes the first message and updates totals.
func (ms *MemoryMsgStore) removeFirstMsg() {
	firstMsg := ms.msgs[ms.first]
	ms.totalBytes -= uint64(firstMsg.Size())
	ms.totalCount--
	delete(ms.msgs, ms.first)
	ms.first++
}

// Close implements the MsgStore interface
func (ms *MemoryMsgStore) Close() error {
	ms.Lock()
	if ms.closed {
		ms.Unlock()
		return nil
	}
	ms.closed = true
	if ms.ageTimer != nil {
		if ms.ageTimer.Stop() {
			ms.wg.Done()
		}
	}
	ms.Unlock()

	ms.wg.Wait()
	return nil
}

////////////////////////////////////////////////////////////////////////////
// MemorySubStore methods
////////////////////////////////////////////////////////////////////////////

// AddSeqPending adds the given message seqno to the given subscription.
func (*MemorySubStore) AddSeqPending(subid, seqno uint64) error {
	// Overrides in case genericSubStore does something. For the memory
	// based store, we want to minimize the cost of this to a minimum.
	return nil
}

// AckSeqPending records that the given message seqno has been acknowledged
// by the given subscription.
func (*MemorySubStore) AckSeqPending(subid, seqno uint64) error {
	// Overrides in case genericSubStore does something. For the memory
	// based store, we want to minimize the cost of this to a minimum.
	return nil
}