package main

import (
	"container/list"
	"strconv"
	"sync"
	"time"
)

var endpoints *list.List           // Contains all active and ready endpoints
var delayedEndpoints *list.List    // Contains endpoints that are active, but not ready
var globalEndpointMutex sync.Mutex // A mutex for synchronizing Endpoint collections

func init() {
	endpoints = list.New()
	delayedEndpoints = list.New()

	registerParam("port", []int{8291}, "one or more default ports")
	registerParam("max-aps", 5, "maximum number of attempts per second for an endpoint")

	registerSwitch("keep-endpoint-on-good", "keep processing endpoint even if a good login/password was found")

	registerParam("conn-ratio", 0.15, "keep a failed endpoint if its bad/good connection ratio is lower than this value")
	registerParam("max-bad-after-good-conn", 5, "how many consecutive bad connections to allow after a good connection")
	registerParam("max-bad-conn", 20, "always remove endpoint after this many consecutive bad connections")
	registerParam("min-bad-conn", 1, "do not consider removing an endpoint if it does not have this many consecutive bad connections")

	registerParam("proto-error-ratio", 0.25, "keep endpoints with a protocol error if their protocol error ratio is lower than this value")
	registerParam("max-proto-errors", 20, "always remove endpoint after this many consecutive protocol errors")
	registerParam("min-proto-errors", 4, "do not consider removing an endpoint if it does not have this many consecutive protocol errors")

	registerParam("read-error-ratio", 0.25, "keep endpoints with a read error if their read error ratio is lower than this value")
	registerParam("max-read-errors", 20, "always remove endpoint after this many consecutive read errors")
	registerParam("min-read-errors", 3, "do not consider removing an endpoint if it does not have this many consecutive read errors")

	registerParam("no-response-delay-ms", 2000, "wait for this number of ms if an endpoint does not respond")
	registerParam("read-error-delay-ms", 5000, "wait for this number of ms if an endpoint returns a read error")
	registerParam("protocol-error-delay-ms", 5000, "wait for this number of ms if an endpoint returns a protocol error")

	registerParam("discover-percentage", 80, "percentage of threads that should be running host discovery")
	registerParam("discover-max-total-aps", 200, "max total attempts per second when discovery is not yet finished")
	registerParam("discover-max-endpoint-aps", 10, "max attempts per second for endpoints when discovery is not yet finished")
}

// FetchEndpoint retrieves an endpoint: first, a delayed list is queried,
// then, if nothing is found, a normal list is searched.
// If all endpoints are delayed, a wait time is returned.
func FetchEndpoint() (e *Endpoint, waitTime time.Duration) {
	globalEndpointMutex.Lock()
	defer globalEndpointMutex.Unlock()

	log("ep", 4, "fetching an endpoint")

	e, waitTime = GetDelayedEndpoint()
	if e != nil {
		log("ep", 4, "fetched a delayed endpoint: \"%v\"", e)
		return e, 0
	}

	el := endpoints.Front()
	if el == nil {
		if waitTime == 0 {
			log("ep", 4, "out of endpoints")
			return nil, 0
		}

		log("ep", 4, "all endpoints are delayed, waiting for %v", waitTime)
		return nil, waitTime
	}

	endpoints.MoveToBack(el)
	e = el.Value.(*Endpoint)

	if e.state == ES_Deleted {
		panic("fetched a deleted endpoint")
	}

	log("ep", 4, "fetched a normal endpoint: \"%v\"", e)
	return e, 0
}

// Event is a parameterless version of EventWithParm.
func (e *Endpoint) Event(event TaskEvent) bool {
	return e.EventWithParm(event, 0)
}

// EventWithParm tells an Endpoint that something important has happened,
// or a hint has been acquired.
// It is normally called from a Task handler.
// Returns False if an event resulted in a deletion of its Endpoint.
func (e *Endpoint) EventWithParm(event TaskEvent, parm any) bool {
	log("ep", 4, "endpoint event for \"%v\": %v", e, event)

	if event == TE_Generic {
		return true // do not process generic events
	}

	e.TakeMutex()
	defer e.ReleaseMutex()

	switch event {
	case TE_NoResponse:
		return e.NoResponse()

	case TE_ProtocolError:
		return e.ProtocolError()

	case TE_Good:
		e.Good(parm.(string))
		return false

	case TE_Bad:
		e.Bad()
	case TN_Connected:
		e.Connected()
	case TH_NoSuchLogin:
		e.NoSuchLogin(parm.(string))
	}

	return true // keep this endpoint
}

func (state EndpointState) String() string {
	switch state {
	case ES_Normal:
		return "normal"
	case ES_Delayed:
		return "delayed"
	case ES_Deleted:
		return "deleted"
	}

	return "unknown"
}

func (state EndpointState) GetList() *list.List {
	switch state {
	case ES_Normal:
		return endpoints
	case ES_Delayed:
		return delayedEndpoints
	}

	return nil
}

// String transforms an Endpoint to a string representation compatible with Dialer interface.
func (e *Endpoint) String() string {
	if e.addr.v6 {
		return "[" + e.addr.ip + "]:" + strconv.Itoa(e.addr.port)
	} else {
		return e.addr.ip + ":" + strconv.Itoa(e.addr.port)
	}
}

func (e *Endpoint) GetList() *list.List {
	return e.state.GetList()
}

// Delete deletes an endpoint from global storage.
// This method assumes that Endpoint's mutex was already taken.
func (e *Endpoint) Delete() {
	globalEndpointMutex.Lock()
	defer globalEndpointMutex.Unlock()

	list := e.GetList()
	if list == nil {
		log("ep", 3, "cannot delete endpoint \"%v\", not in the list", e)
	} else {
		log("ep", 3, "deleting endpoint \"%v\"", e)
	}

	e.delayUntil = time.Time{}
	e.SetStateEx(ES_Deleted, false)
}

// SetState changes an endpoint's state.
func (e *Endpoint) SetStateEx(newState EndpointState, takeMutex bool) {
	if e.state == newState {
		log("ep", 5, "ignoring state change for an endpoint \"%v\": already in state \"%v\"", e, e.state)
		return
	}

	oldList := e.GetList()
	newList := newState.GetList()

	if takeMutex {
		globalEndpointMutex.Lock()
		defer globalEndpointMutex.Unlock()
	}

	if e.listElement != nil && oldList != nil {
		oldList.Remove(e.listElement)
	}

	if newList == nil {
		e.listElement = nil
	} else {
		e.listElement = newList.PushBack(e)
	}

	e.state = newState
}

func (e *Endpoint) SetState(newState EndpointState) {
	e.SetStateEx(newState, true)
}

// Delay marks an Endpoint as "delayed" for a certain duration
// and migrates it to the delayed queue.
// This method assumes that Endpoint's mutex was already taken.
func (e *Endpoint) Delay(addTime time.Duration) {
	if e.state == ES_Normal {
		log("ep", 5, "delaying endpoint \"%v\" for %v", e, addTime)
		e.delayUntil = time.Now().Add(addTime)
		e.SetState(ES_Delayed)
	} else if e.state == ES_Delayed {
		// endpoints that are already delayed can have their delay time extended further

		tm := time.Now().Add(addTime)
		if e.delayUntil.Before(tm) {
			log("ep", 5, "extending delay deadline for endpoint \"%v\" from %v to %v", e, e.delayUntil, tm)
			e.delayUntil = tm
		}
	}
}

// SkipLogin gets the endpoint's current login,
// compares it with user-defined login and skips (advances) it if
// both logins are equal.
func (e *Endpoint) SkipLogin(login string) {
	// attempt to fetch next login
	curLogin, empty := SrcLogin.FetchOne(&e.loginPos, false)
	if curLogin == login && !empty { // this login has not yet been exhausted?
		// reset password pos
		e.passwordPos.Reset()

		// fetch but ignore result
		SrcLogin.FetchOne(&e.loginPos, true)

		log("ep", 3, "advanced to next login for \"%v\"", e)
	}
}

// NoResponse is an event handler that gets called when
// an Endpoint does not respond to a connection request.
func (e *Endpoint) NoResponse() bool {
	e.badConn++
	if e.consecutiveGoodConn == 0 {
		e.consecutiveBadConn++
	} else {
		e.consecutiveGoodConn = 0
		e.consecutiveBadConn = 1
	}

	// 1. always bail after X consecutive bad conns
	if e.consecutiveBadConn >= getParamInt("max-bad-conn") {
		log("ep", 3, "deleting \"%v\" due to max-bad-conn", e)
		e.Delete()
		return false
	}

	// 2. after a good conn, always allow at most X bad conns
	if e.goodConn > 0 && e.consecutiveBadConn <= getParamInt("max-bad-after-good-conn") {
		log("ep", 3, "keeping \"%v\" around due to max-bad-after-good-conn", e)
		e.Delay(getParamDurationMS("no-response-delay-ms"))
		return true
	}

	// 3. always allow at most X bad conns
	if e.consecutiveBadConn < getParamInt("min-bad-conn") {
		log("ep", 3, "keeping \"%v\" around due to min-bad-conn", e)
		e.Delay(getParamDurationMS("no-response-delay-ms"))
		return true
	}

	// 4. bad conn/good conn ratio must not be higher than X
	if e.goodConn > 0 && (float64(e.badConn)/float64(e.goodConn)) <= getParamFloat("conn-ratio") {
		log("ep", 3, "keeping \"%v\" around due to conn-ratio", e)
		e.Delay(getParamDurationMS("no-response-delay-ms"))
		return true
	}

	// otherwise, just delete it
	log("ep", 3, "deleting \"%v\" due to no applicable grace conditions", e)
	e.Delete()
	return false
}

// ProtocolError is an event handler that gets called when
// an Endpoint responds with wrong or missing data.
func (e *Endpoint) ProtocolError() bool {
	e.protoErrors++
	e.consecutiveProtoErrors++

	// 1. always bail after X consecutive protocol errors
	if e.consecutiveProtoErrors >= getParamInt("max-proto-errors") {
		log("ep", 3, "deleting \"%v\" due to max-proto-errors", e)
		e.Delete()
		return false
	}

	// 2. always allow at most X consecutive protocol errors
	if e.consecutiveProtoErrors < getParamInt("min-proto-errors") {
		log("ep", 3, "keeping \"%v\" around due to min-proto-errors", e)
		e.Delay(getParamDurationMS("protocol-error-delay-ms"))
		return true
	}

	// 3. bad conn/good conn ratio must not be higher than X
	if e.goodConn > 0 && (float64(e.protoErrors)/float64(e.goodConn)) <= getParamFloat("proto-error-ratio") {
		log("ep", 3, "keeping \"%v\" around due to proto-error-ratio", e)
		e.Delay(getParamDurationMS("protocol-error-delay-ms"))
		return true
	}

	// otherwise, just delete it
	log("ep", 3, "deleting \"%v\" due to no applicable grace conditions", e)
	e.Delete()
	return false
}

// Bad is an event handler that gets called when
// an authentication attempt to an Endpoint fails.
func (e *Endpoint) Bad() {
	e.consecutiveProtoErrors = 0

	// The endpoint may be in delayed queue, so push it back to the normal queue.
	e.SetState(ES_Normal)
}

// Good is an event handler that gets called when
// an authentication attempt to an Endpoint succeeds.
func (e *Endpoint) Good(login string) {
	e.consecutiveProtoErrors = 0

	if !getParamSwitch("keep-endpoint-on-good") {
		e.Delete()
	} else {
		e.SetState(ES_Normal)
		e.SkipLogin(login)
	}
}

// Connected is an event handler that gets called when
// a connection attempt to an Endpoint succeeds.
func (e *Endpoint) Connected() {
	e.goodConn++
	if e.consecutiveBadConn == 0 {
		e.consecutiveGoodConn++
	} else {
		e.consecutiveBadConn = 0
		e.consecutiveGoodConn = 1
	}
}

// NoSuchLogin is an event handler that gets called when
// a service module determines that a login does not present
// on an Endpoint and therefore can be excluded from processing.
func (e *Endpoint) NoSuchLogin(login string) {
	e.SkipLogin(login)
}

// Exhausted gets called when an endpoint no longer has any valid logins and passwords,
// thus it may be deleted.
func (e *Endpoint) Exhausted() {
	e.TakeMutex()
	defer e.ReleaseMutex()
	e.Delete()
}

// GetDelayedEndpoint retrieves an Endpoint from the delayed list.
// globalEndpointMutex must be already taken.
func GetDelayedEndpoint() (e *Endpoint, waitTime time.Duration) {
	currentTime := time.Now()

	if delayedEndpoints.Len() == 0 {
		log("ep", 5, "delayed endpoint list is empty")
		return nil, 0
	}

	minWaitTime := time.Time{}

	for e := delayedEndpoints.Front(); e != nil; e = e.Next() {
		dt := e.Value.(*Endpoint)
		if minWaitTime.IsZero() || (dt.delayUntil.Before(minWaitTime) && dt.delayUntil.After(currentTime)) {
			minWaitTime = dt.delayUntil
		}

		if dt.delayUntil.Before(currentTime) {
			dt.delayUntil = time.Time{}
			dt.SetStateEx(ES_Normal, false)
			return dt, 0
		}
	}

	if minWaitTime.Before(currentTime) {
		return nil, 0
	} else {
		return nil, minWaitTime.Sub(currentTime)
	}
}

func (e *Endpoint) TakeMutex() {
	e.mutex.Lock()
}

func (e *Endpoint) ReleaseMutex() {
	e.mutex.Unlock()
}

func (e *Endpoint) RegisterRTT(rtt time.Duration) {
	const rttAverage = 8

	if e.rttCount == 0 {
		e.rtt = rtt
	} else {
		e.rtt = e.rtt*(rttAverage-1)/rttAverage + rtt/rttAverage
	}

	e.rttCount++
}

type Address struct {
	ip   string // TODO: switch to a static 16-byte array
	port int
	v6   bool
}

type EndpointState int

const (
	ES_Normal EndpointState = iota
	ES_Delayed
	ES_Deleted
)

// An Endpoint represents a remote target and stores its persistent data between multiple connections.
type Endpoint struct {
	addr Address // IP address of an endpoint

	loginPos    SourcePos
	passwordPos SourcePos     // login/password cursors
	listElement *list.Element // position in list

	state      EndpointState // which state an endpoint is in
	delayUntil time.Time     // when this endpoint can be used again

	// endpoint stats
	goodConn, badConn, protoErrors, readErrors int
	consecutiveGoodConn, consecutiveBadConn, consecutiveProtoErrors,
	consecutiveReadErrors int

	mutex sync.Mutex // sync primitive

	rtt      time.Duration
	rttCount uint

	lastSentAt     time.Time
	lastAttemptAt  time.Time
	lastReceivedAt time.Time
}