package store

import (
	"fmt"
	"strings"
	"sync"
	"time"

	etcdErr "github.com/coreos/etcd/error"
)

const (
	Get        = "get"
	Create     = "create"
	Update     = "update"
	Delete     = "delete"
	TestAndSet = "testAndSet"
	Expire     = "expire"
)

const (
	UndefIndex = 0
	UndefTerm  = 0
)

type Event struct {
	Action     string     `json:"action"`
	Key        string     `json:"key, omitempty"`
	Dir        bool       `json:"dir,omitempty"`
	PrevValue  string     `json:"prevValue,omitempty"`
	Value      string     `json:"value,omitempty"`
	KVPairs    kvPairs    `json:"kvs,omitempty"`
	Expiration *time.Time `json:"expiration,omitempty"`
	TTL        int64      `json:"ttl,omitempty"` // Time to live in second
	// The command index of the raft machine when the command is executed
	Index uint64 `json:"index"`
	Term  uint64 `json:"term"`
}

func newEvent(action string, key string, index uint64, term uint64) *Event {
	return &Event{
		Action: action,
		Key:    key,
		Index:  index,
		Term:   term,
	}
}

type eventQueue struct {
	Events   []*Event
	Size     int
	Front    int
	Capacity int
}

func (eq *eventQueue) back() int {
	return (eq.Front + eq.Size - 1 + eq.Capacity) % eq.Capacity
}

func (eq *eventQueue) insert(e *Event) {
	index := (eq.back() + 1) % eq.Capacity

	eq.Events[index] = e

	if eq.Size == eq.Capacity { //dequeue
		eq.Front = (index + 1) % eq.Capacity
	} else {
		eq.Size++
	}

}

type EventHistory struct {
	Queue      eventQueue
	StartIndex uint64
	LastIndex  uint64
	LastTerm   uint64
	DupCnt     uint64 // help to compute the watching point with duplicated indexes in the queue
	rwl        sync.RWMutex
}

func newEventHistory(capacity int) *EventHistory {
	return &EventHistory{
		Queue: eventQueue{
			Capacity: capacity,
			Events:   make([]*Event, capacity),
		},
	}
}

// addEvent function adds event into the eventHistory
func (eh *EventHistory) addEvent(e *Event) *Event {
	eh.rwl.Lock()
	defer eh.rwl.Unlock()

	var duped uint64

	if e.Index == UndefIndex {
		e.Index = eh.LastIndex
		e.Term = eh.LastTerm
		duped = 1
	}

	eh.Queue.insert(e)

	eh.LastIndex = e.Index
	eh.LastTerm = e.Term
	eh.DupCnt += duped

	eh.StartIndex = eh.Queue.Events[eh.Queue.Front].Index

	return e
}

// scan function is enumerating events from the index in history and
// stops till the first point where the key has identified prefix
func (eh *EventHistory) scan(prefix string, index uint64) (*Event, *etcdErr.Error) {
	eh.rwl.RLock()
	defer eh.rwl.RUnlock()

	start := index - eh.StartIndex

	// the index should locate after the event history's StartIndex
	if start < 0 {
		return nil,
			etcdErr.NewError(etcdErr.EcodeEventIndexCleared,
				fmt.Sprintf("the requested history has been cleared [%v/%v]",
					eh.StartIndex, index), UndefIndex, UndefTerm)
	}

	// the index should locate before the size of the queue minus the duplicate count
	if start >= (uint64(eh.Queue.Size) - eh.DupCnt) { // future index
		return nil, nil
	}

	i := int((start + uint64(eh.Queue.Front)) % uint64(eh.Queue.Capacity))

	for {
		e := eh.Queue.Events[i]
		if strings.HasPrefix(e.Key, prefix) && index <= e.Index { // make sure we bypass the smaller one
			return e, nil
		}

		i = (i + 1) % eh.Queue.Capacity

		if i == eh.Queue.back() { // find nothing, return and watch from current index
			return nil, nil
		}
	}
}

// clone will be protected by a stop-world lock
// do not need to obtain internal lock
func (eh *EventHistory) clone() *EventHistory {
	clonedQueue := eventQueue{
		Capacity: eh.Queue.Capacity,
		Events:   make([]*Event, eh.Queue.Capacity),
		Size:     eh.Queue.Size,
		Front:    eh.Queue.Front,
	}

	for i, e := range eh.Queue.Events {
		clonedQueue.Events[i] = e
	}

	return &EventHistory{
		StartIndex: eh.StartIndex,
		Queue:      clonedQueue,
		LastIndex:  eh.LastIndex,
		LastTerm:   eh.LastTerm,
		DupCnt:     eh.DupCnt,
	}

}