package state

/* STATE
 * This package encapsulates various state information
 * state is represented in various global singletons
 * Additionally, this package offers a pub/sub interface
 * for various aspects of state
 */

import (
	"fmt"
	"slices"
	"sync"
	"time"

	"gitlab.com/whom/bingobot/internal/discord"
	"gitlab.com/whom/bingobot/internal/logging"
)

/* Event interface is meant to encapsulate a general interface
 * extendable for any different action the bot takes or that a
 * user takes.
 */

const (
	BadEventTypeError          = "bad event type"
	EventValidationFailedError = "event failed validation: "
)

var eventMutex sync.RWMutex
var eventSubscriptionCache = [NumEventTypes][]chan Event{}
var eventCache = []Event{}

// TODO: Configurable
var eventChannelBufferSize = 256

// TODO: pruned events go to DISK
// ASSUMES eventCache is ordered by age (oldest first)
func pruneEventCache() {
	eventMutex.Lock()
	defer eventMutex.Unlock()

	oldCacheInvalid := false
	newCache := []Event{}
	for _, obj := range eventCache {
		if time.Since(obj.Time()).Hours() > 24*10 {
			oldCacheInvalid = true
		} else if oldCacheInvalid {
			newCache = append(newCache, obj)
		}
	}

	eventCache = newCache
}

type EventType int8

const (
	Vote EventType = iota
	Challenge
	Restoration
	UserActive
	// ...

	// leave this last
	NumEventTypes
)

func (et EventType) Validate() error {
	if et < 0 || et >= NumEventTypes {
		return stringErrorType(BadEventTypeError)
	}

	return nil
}

type Event interface {
	// gets EventType associated with event
	Type() EventType

	// gets time event created
	Time() time.Time

	// gets internal metadata associated with event
	// may be read only depending on event implementation
	Data() map[string]string

	// validates state of internal metadata per EventType
	Validate() error
}

// TODO: Something better than this
type stringErrorType string

func (s stringErrorType) Error() string {
	return string(s)
}

/* adds a new subscriber channel to the event subscription cache
 * and returns the channel that it will publish notifications on
 *
 * note: channel is prefilled with at most eventChannelBufferSize
 *  historical events. Truncated if history exceeds event channel
 *  buffer size.
 */
func (et EventType) SubscribeWithHistory() (chan Event, error) {
	if err := et.Validate(); err != nil {
		return nil, err
	}

	ch := make(chan Event, eventChannelBufferSize)

	eventMutex.Lock()
	eventSubscriptionCache[et] = append(
		eventSubscriptionCache[et],
		ch,
	)
	eventMutex.Unlock()

	eventMutex.RLock()
	defer eventMutex.RUnlock()
	numEventsAdded := 0
	for _, ev := range slices.Backward(eventCache) {
		if numEventsAdded >= eventChannelBufferSize {
			break
		}

		if ev.Type() == et {
			ch <- ev
			numEventsAdded += 1
		}
	}

	return ch, nil
}

/* adds a new subscriber channel to the event subscription cache
 * and returns the channel that it will publish notifications on
 */
func (et EventType) Subscribe() (chan Event, error) {
	if err := et.Validate(); err != nil {
		return nil, err
	}

	ch := make(chan Event, eventChannelBufferSize)

	eventMutex.Lock()
	defer eventMutex.Unlock()
	eventSubscriptionCache[et] = append(
		eventSubscriptionCache[et],
		ch,
	)

	return ch, nil
}

func PublishEvent(e Event) error {
	if err := ValidateEvent(e); err != nil {
		return stringErrorType(
			EventValidationFailedError + err.Error(),
		)
	}

	eventMutex.Lock()
	eventCache = append(eventCache, e)
	eventMutex.Unlock()
	eventMutex.RLock()
	defer eventMutex.RUnlock()

	blocking := false

	for _, c := range eventSubscriptionCache[e.Type()] {
		if float32(len(c)) > (float32(eventChannelBufferSize) * 0.25) {
			if len(c) == eventChannelBufferSize {
				logging.Warn(
					"PublishEvent() blocking -- event channel full",
					// log the event time to provide blockage timing information
					// in the logs
					"eventTime",
					e.Time(),
				)
				blocking = true
			}
		}
		c <- e

		if blocking {
			logging.Info("PublishEvent() no longer blocking")
			blocking = false
		}

	}

	return nil
}

func ValidateEvent(e Event) error {
	if err := e.Type().Validate(); err != nil {
		return err
	}

	if err := e.Validate(); err != nil {
		return err
	}

	return nil
}

/* gets all events of type T in cache
 * that also share all field values in
 * map 'filters'
 */
func GetMatchingEvents(
	t EventType,
	filters map[string]string,
) ([]Event, error) {
	matches := []Event{}

	if err := t.Validate(); err != nil {
		return matches, err
	}

	eventMutex.RLock()
	defer eventMutex.RUnlock()

Events:
	for _, e := range eventCache {
		if e.Type() != t {
			continue
		}
		for k, v := range filters {
			val, found := e.Data()[k]
			if !found || val != v {
				continue Events
			}
		}

		matches = append(matches, e)
	}

	return matches, nil
}

type VoteEvent map[string]string

const (
	VoteMissingKeyError = "vote data not found: "
	VoteCreatedKey      = "created"
	VoteRequesterKey    = "requester"
	VoteActionKey       = "action"

	VoteResultKey          = "result"
	VoteResultPass         = "pass"
	VoteResultFail         = "fail"
	VoteResultTie          = "tie"
	VoteResultTimeout      = "timeout"
	VoteBadResultError     = "vote has invalid result: "
	VoteNotFinishedError   = "vote has result but isnt finished"
	VoteMissingResultError = "vote finished but missing result"

	VoteStatusKey        = "status"
	VoteStatusInProgress = "in_progress"
	VoteStatusFinalized  = "finalized"
	VoteStatusTimeout    = "timed_out"
	VoteBadStatusError   = "vote has invalid status: "

	VeryOldVote = "1990-01-01T00:00:00Z"
)

func (ve VoteEvent) Type() EventType {
	return Vote
}

func (ve VoteEvent) Time() time.Time {
	t, e := time.Parse(time.RFC3339, ve[VoteCreatedKey])
	if e != nil {
		// we have a corrupted event
		// return old time so that this event gets
		// pruned from cache
		logging.Warn(
			"pruning corrupted vote event",
			"event",
			fmt.Sprintf("%+v", ve),
		)
		tooOld, _ := time.Parse(
			time.RFC3339,
			VeryOldVote,
		)
		return tooOld
	}
	return t
}

func (ve VoteEvent) Data() map[string]string {
	return map[string]string(ve)
}

func (ve VoteEvent) Validate() error {
	// make sure action, requester, and created are set
	for _, key := range []string{
		VoteActionKey,
		VoteRequesterKey,
		VoteCreatedKey,
		VoteStatusKey,
	} {
		if _, found := ve[key]; !found {
			return stringErrorType(
				VoteMissingKeyError + key)
		}
	}

	status := ve[VoteStatusKey]
	if status != VoteStatusTimeout &&
		status != VoteStatusInProgress &&
		status != VoteStatusFinalized {
		return stringErrorType(VoteBadStatusError + status)
	}

	result, hasResult := ve[VoteResultKey]
	if hasResult && status == VoteStatusInProgress {
		return stringErrorType(VoteNotFinishedError)
	}
	if status != VoteStatusInProgress && !hasResult {
		return stringErrorType(VoteMissingResultError)
	}

	if hasResult &&
		(result != VoteResultPass &&
			result != VoteResultFail &&
			result != VoteResultTie &&
			result != VoteResultTimeout) {

		return stringErrorType(VoteBadResultError + result)
	}

	return nil
}

type UserEvent struct {
	uid     string
	created time.Time
}

const (
	UserEventUserKey      = "user"
	UserEventCreatedKey   = "created"
	UserEventBadUserError = "event has bad user"
)

func (ue UserEvent) Time() time.Time {
	return ue.created
}

func (ue UserEvent) Data() map[string]string {
	return map[string]string{
		UserEventUserKey:    ue.uid,
		UserEventCreatedKey: ue.created.Local().String(),
	}
}

func (ue UserEvent) Validate() error {
	if discord.Connected() {
		_, err := discord.User(ue.uid)
		return err
	} else {
		// I would love to know how to actually fail here
		// and still have unit testable code.

		logging.Error(
			"can't validate UserEvent: nil discord session",
			"event",
			fmt.Sprintf("%+v", ue),
		)
		return nil
	}
}

type ChallengeEvent struct {
	UserEvent
}

func (ce ChallengeEvent) Type() EventType {
	return Challenge
}

func NewChallengeEvent(user string) ChallengeEvent {
	return ChallengeEvent{UserEvent{
		uid:     user,
		created: time.Now(),
	}}
}

type RestorationEvent struct {
	UserEvent
}

func (re RestorationEvent) Type() EventType {
	return Restoration
}

func NewRestorationEvent(user string) RestorationEvent {
	return RestorationEvent{UserEvent{
		uid:     user,
		created: time.Now(),
	}}
}

type UserActiveEvent struct {
	UserEvent
}

func (ua UserActiveEvent) Type() EventType {
	return UserActive
}

func NewUserActiveEvent(user string) UserActiveEvent {
	return UserActiveEvent{UserEvent{
		uid:     user,
		created: time.Now(),
	}}
}