package state

/* State module
 * 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 (
	"encoding/json"
	"errors"
	"os"
	"strconv"
	"sync"
	"time"

	"gitlab.com/whom/bingobot/internal/logging"
	"gitlab.com/whom/bingobot/pkg/docbuf"
)

/* 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: "
	BadEventNoUID              = "event data has no UID field"
	BadEventNoCreated          = "event data has no created field"
	BadEventStoreFilename      = "failed to open event store file"
	BadEventStreamInit         = "failed to initialize event stream"
	BadEventCreate             = "failed to create event"
	BadUserEventCreatedParse   = "failed to parse created time"
	BadChallengeEvent          = "failed to make Challenge Event"
	BadRestorationEvent        = "failed to make Restoration Event"
	BadUserActiveEvent         = "failed to make UserActive Event"
	BadTestEvent               = "failed to make Test Event"
	BadEventObjMarshal         = "error marshalling event"
	BadEventObjUnmarshal       = "failed to unmarshal event map"
	BadEventUnmarshal          = "failed to unmarshal event"
	BadEventMissingTypeKey     = "event map missing type key"
	StartBeforeInitError       = "state machine not initialized"
	ReopenStoreFileError       = "failed to reopen store file"

	EventTypeMapKey            = "type"

	TmpDocBufBackingFile       = "bingobot_events_processing"
)

var eventMutex sync.RWMutex
var eventSubscriptionCache = [NumEventTypes][]chan Event{}
var eventStorageFileName string
var eventStream docbuf.DocumentBuffer
var maxEventsInMemory int

// expect filename validations in config package
func Init(eventMemCacheSize int, eventStoreFileName string) error {
	file, err := os.OpenFile(eventStoreFileName, os.O_CREATE|os.O_RDWR, 0644)
	if err != nil {
		return errors.Join(errors.New(BadEventStoreFilename), err)
	}

	if eventStream, err = docbuf.NewDocumentBuffer(
		0, // temporary nil-cache buffer to replay events from
		file,
	); err != nil {
		return errors.Join(errors.New(BadEventStreamInit), err)
	}

	eventStorageFileName = eventStoreFileName
	maxEventsInMemory = eventMemCacheSize
	return nil
}

// replay events and begin state machine
func Start() error {
	if eventStream == nil {
		return errors.New(StartBeforeInitError)
	}

	tmpBackFile, err := os.CreateTemp("", TmpDocBufBackingFile)
	if err != nil {
		return err
	}

	tmpBuf, err := docbuf.NewDocumentBuffer(0, tmpBackFile)
	if err != nil {
		tmpBackFile.Close()
		return err
	}

	// filter out disposable events into a reverse ordered on disk stack
	var doc string
	for err == nil || err.Error() != docbuf.PopFromEmptyBufferError {
		doc, err = eventStream.Pop()
		if err != nil && err.Error() != docbuf.PopFromEmptyBufferError {
			return err
		}

		if doc == "" || 
		   (err != nil && err.Error() == docbuf.PopFromEmptyBufferError) {
			break
		}

		ev, err := EventFromString(doc)
		if err != nil {
			logging.Warn("Discarding the following event for not unmarshaling: %s", doc)
			continue
		}

		if !ev.Disposable() {
			tmpBuf.Push(doc)
		}
	}

	if err := os.Truncate(eventStorageFileName, 0); err != nil {
		return errors.Join(errors.New(ReopenStoreFileError), err)
	}

	file, err := os.OpenFile(eventStorageFileName, os.O_CREATE|os.O_RDWR, 0644)
	if err != nil {
		return errors.Join(errors.New(BadEventStoreFilename), err)
	}

	eventStream, err = docbuf.NewDocumentBuffer(maxEventsInMemory, file)
	if err != nil {
		// return error here will panic without truncating or writing to the file
		return err
	}

	// unravel tmp stack into properly ordered properly allocated buffer
	for err == nil || err.Error() != docbuf.PopFromEmptyBufferError {
		doc, err := tmpBuf.Pop()
		if err != nil && err.Error() != docbuf.PopFromEmptyBufferError {
			logging.Warn("Could not handle the following error: %s", err.Error())
			continue
		}

		if doc == "" || 
		   (err != nil && err.Error() == docbuf.PopFromEmptyBufferError) {
			break
		}

		ev, err := EventFromString(doc)
		if err != nil {
			logging.Warn("Could not handle the following error: %s", err.Error())
			continue
		}

		if err := PublishEvent(ev); err != nil {
			logging.Warn("Could not handle the following error: %s", err.Error())
		}
	}

	return nil
}

// return no error. we are handling SIGINT
func Teardown() {
	// riskily ignore all locking....
	// we are handling a termination signal after all
	i, e := eventStream.Close()
	if e != nil {
		logging.Warn("failed to close document buffer: %s", e.Error())
		logging.Warn("will attempt to truncate event store anyways")
	}

	e = os.Truncate(eventStorageFileName, i)
	if e != nil {
		logging.Error("FAILED TO TRUNCATE EVENT STORE!!")
		logging.Error("You will likely have garbage data at the end of it")
		logging.Error("Attempt manual correction!")
	}
}

type EventType int8

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

	// leave this last
	NumEventTypes
)

// either returns a valid event type or NumEventTypes
func EventTypeFromString(doc string) EventType {
	switch doc {
	case "Vote":
		return Vote
	case "Challenge":
		return Challenge
	case "Restoration":
		return Restoration
	case "UserActive":
		return UserActive
	case "Test":
		return Test
	case "ConfessionsChannelLink":
		return ConfessionsChannelLink
	default:
		// error case
		return NumEventTypes
	}
}

func (et EventType) String() string {
	events := []string{
		"Vote",
		"Challenge",
		"Restoration",
		"UserActive",
		"Test",
		"ConfessionsChannelLink",
	}

	if et < 0 || et >= NumEventTypes {
		return ""
	}

	return events[et]
}

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

	return nil
}

/* Allocates a specific event of type T from event type instance.
 * output event not guaranteed to be valid.
 * Call Validate() yourself.
 */
func (et EventType) MakeEvent(data map[string]string) (Event, error) {
	if err := et.Validate(); err != nil {
		return nil, errors.Join(errors.New(BadEventCreate), err)
	}

	MakeUserEvent := func(data map[string]string) (*UserEvent, error) {
		user, hasUser := data[UserEventUserKey]
		if !hasUser {
			return nil, errors.New(BadEventNoUID)
		}

		created, hasCreated := data[UserEventCreatedKey]
		if !hasCreated {
			return nil, errors.New(BadEventNoCreated)
		}

		createdTime, err := time.Parse(time.RFC3339, created)
		if err != nil {
			return nil, errors.Join(errors.New(BadUserEventCreatedParse), err)
		}

		return &UserEvent{
			uid: user,
			created: createdTime,
		}, nil
	}

	switch et {
	case Vote:
		return VoteEvent(data), nil

	case Challenge:
		e, err := MakeUserEvent(data)
		if err != nil {
			return nil, errors.Join(errors.New(BadChallengeEvent), err)
		}
		return ChallengeEvent{*e}, nil

	case Restoration:
		e, err := MakeUserEvent(data)
		if err != nil {
			return nil, errors.Join(errors.New(BadRestorationEvent), err)
		}
		return RestorationEvent{*e}, nil

	case UserActive:
		e, err := MakeUserEvent(data)
		if err != nil {
			return nil, errors.Join(errors.New(BadUserActiveEvent), err)
		}
		return UserActiveEvent{*e}, nil

	case Test:
		disp := false
		if v, ok := data[TestEventDisposeKey]; ok && v == "t" {
			disp = true
		}
		id := -1
		if v, ok := data[TestEventIDKey]; ok {
			var err error
			if id, err = strconv.Atoi(v); err != nil {
				return nil, errors.Join(errors.New(BadTestEvent), err)
			}
		}
		return TestEvent{
			Dispose: disp,
			ID:      id,
		}, nil

	case ConfessionsChannelLink:
		gid, ok := data[ConfessionsLinkEventGuildKey]
		if !ok {
			return nil, errors.New(BadConfessionsLinkEventError)
		}

		cid, ok := data[ConfessionsLinkEventChannelKey]
		if !ok {
			return nil, errors.New(BadConfessionsLinkEventError)
		}

		ti, ok := data[ConfessionsLinkEventCreatedKey]
		if !ok {
			return nil, errors.New(BadConfessionsLinkEventError)
		}
		t, err := time.Parse(time.RFC3339, ti)
		if err != nil {
			return nil, errors.Join(errors.New(BadConfessionsLinkEventError), err)
		}

		return ConfessionsChannelLinkEvent{
			GuildID: gid,
			ChannelID: cid,
			Created: t,
		}, nil

	default:
		return nil, errors.New(BadEventTypeError)
	}
}

/* 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, maxEventsInMemory)

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

	return ch, 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

	// returns true if event can be discarded
	Disposable() bool
}

func EventToString(e Event) (string, error) {
	m := e.Data()
	m[EventTypeMapKey] = e.Type().String()
	buf, err := json.Marshal(m)
	if err != nil {
		return "", errors.Join(errors.New(BadEventObjMarshal), err)
	}

	return string(buf), nil
}

func EventFromString(doc string) (Event, error) {
	var obj map[string]string
	if err := json.Unmarshal([]byte(doc), &obj); err != nil {
		return nil, errors.Join(errors.New(BadEventObjUnmarshal), err)
	}

	et, ok := obj[EventTypeMapKey]
	if !ok {
		return nil, errors.New(BadEventMissingTypeKey)
	}
	t := EventTypeFromString(et)
	ev, err := t.MakeEvent(obj)
	if err != nil {
		return nil, errors.Join(errors.New(BadEventCreate), err)
	}

	return ev, ev.Validate()
}

func PublishEvent(e Event) error {
	if err := ValidateEvent(e); err != nil {
		return errors.Join(errors.New(EventValidationFailedError), err)
	}

	doc, err := EventToString(e)
	if err != nil {
		return errors.New(BadEventUnmarshal)
	}

	eventMutex.Lock()
	eventStream.Push(doc)
	eventMutex.Unlock()
	eventMutex.RLock()
	defer eventMutex.RUnlock()

	blocking := false

	for _, c := range eventSubscriptionCache[e.Type()] {
		if float32(len(c)) > (float32(maxEventsInMemory) * 0.75) {
			if len(c) == maxEventsInMemory {
				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
}

/* Takes a filter and applies it to each individual event
 * The filter is a function/closure that accepts one event
 * and returns true if ApplyToEvents should continue iterating
 *
 * If the filter returns false then ApplyToEvents halts and returns.
 *
 * (this calls docbuf.Apply() under the hood)
 */
func ApplyToEvents(
	f func(Event)bool,
) error {
	// local variables enclosed by filter function filterWrap
	var err error
	var ev Event
	// wrap f() to be compatible with docbuf.Apply()
	filterWrap := func(doc string) bool {
		ev, err = EventFromString(doc)
		if err != nil {
			return false
		}
		return f(ev)
	}

	eventMutex.RLock()
	defer eventMutex.RUnlock()

	// cant reuse err or return val directly as err is set
	// by filter function if an error happens unmarshalling
	// an event. In this case apply might return nil
	err2 := eventStream.Apply(filterWrap)
	if err2 != nil {
		return err2
	}
	if 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
	}

	filter := func(e Event) bool {
		if e.Type() != t {
			return true
		}
		for k, v := range filters {
			val, found := e.Data()[k]
			if !found || val != v {
				return true
			}
		}

		matches = append(matches, e)
		return true
	}

	err := ApplyToEvents(filter)
	return matches, err
}