package instance

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"net/http"
	"strings"
	"sync"
	"time"

	"git.eeqj.de/sneak/feta/jsonapis"
	"git.eeqj.de/sneak/feta/toot"
	"github.com/google/uuid"
	"github.com/looplab/fsm"
	"github.com/rs/zerolog/log"
)

const nodeInfoSchemaVersionTwoName = "http://nodeinfo.diaspora.software/ns/schema/2.0"
const instanceNodeinfoTimeout = time.Second * 60 * 2        // 2m
const instanceHTTPTimeout = time.Second * 60 * 2            // 2m
const instanceSpiderInterval = time.Second * 60 * 2         // 2m
const instanceErrorInterval = time.Second * 60 * 60         // 1h
const instancePersistentErrorInterval = time.Second * 86400 // 1d
const zeroInterval = time.Second * 0                        // 0s

// Instance stores all the information we know about an instance
type Instance struct {
	Disabled                   bool
	ErrorCount                 uint
	ConsecutiveErrorCount      uint
	FSM                        *fsm.FSM
	Fetching                   bool
	HighestID                  uint
	Hostname                   string
	Identified                 bool
	Implementation             string
	InitialFSMState            string
	NextFetch                  time.Time
	LastError                  string
	NodeInfoURL                string
	ServerImplementationString string
	ServerVersionString        string
	SuccessCount               uint
	UUID                       uuid.UUID
	fetchingLock               sync.Mutex
	fsmLock                    sync.Mutex
	structLock                 sync.Mutex
	tootDestination            chan *toot.Toot
}

// New returns a new instance, argument is a function that operates on the
// new instance
func New(options ...func(i *Instance)) *Instance {
	i := new(Instance)
	i.UUID = uuid.New()
	i.setNextFetchAfter(1 * time.Second)
	i.InitialFSMState = "STATUS_UNKNOWN"

	for _, opt := range options {
		opt(i)
	}

	if i.InitialFSMState == "FETCHING" {
		i.InitialFSMState = "READY_FOR_TOOTFETCH"
	}

	i.FSM = fsm.NewFSM(
		i.InitialFSMState,
		fsm.Events{
			{Name: "BEGIN_NODEINFO_URL_FETCH", Src: []string{"STATUS_UNKNOWN"}, Dst: "FETCHING_NODEINFO_URL"},
			{Name: "GOT_NODEINFO_URL", Src: []string{"FETCHING_NODEINFO_URL"}, Dst: "PRE_NODEINFO_FETCH"},
			{Name: "BEGIN_NODEINFO_FETCH", Src: []string{"PRE_NODEINFO_FETCH"}, Dst: "FETCHING_NODEINFO"},
			{Name: "GOT_NODEINFO", Src: []string{"FETCHING_NODEINFO"}, Dst: "READY_FOR_TOOTFETCH"},
			{Name: "FETCH_TIME_REACHED", Src: []string{"READY_FOR_TOOTFETCH"}, Dst: "READY_AND_DUE_FETCH"},
			{Name: "BEGIN_TOOT_FETCH", Src: []string{"READY_AND_DUE_FETCH"}, Dst: "FETCHING"},
			{Name: "WEIRD_NODE_RESPONSE", Src: []string{"FETCHING_NODEINFO_URL", "PRE_NODEINFO_FETCH", "FETCHING_NODEINFO"}, Dst: "WEIRD_NODE"},
			{Name: "EARLY_FETCH_ERROR", Src: []string{"FETCHING_NODEINFO_URL", "PRE_NODEINFO_FETCH", "FETCHING_NODEINFO"}, Dst: "EARLY_ERROR"},
			{Name: "TOOT_FETCH_ERROR", Src: []string{"FETCHING"}, Dst: "TOOT_FETCH_ERROR"},
			{Name: "TOOTS_FETCHED", Src: []string{"FETCHING"}, Dst: "READY_FOR_TOOTFETCH"},
			{Name: "DISABLEMENT", Src: []string{"WEIRD_NODE", "EARLY_ERROR", "TOOT_FETCH_ERROR"}, Dst: "DISABLED"},
		},
		fsm.Callbacks{
			"enter_state": func(e *fsm.Event) { i.fsmEnterState(e) },
		},
	)

	return i
}

// Status returns the instance's state in the FSM
func (i *Instance) Status() string {
	i.fsmLock.Lock()
	defer i.fsmLock.Unlock()
	return i.FSM.Current()
}

// SetTootDestination takes a channel from the manager that all toots
// fetched from this instance should be pushed into. The instance is not
// responsible for deduplication, it should shove all toots on every fetch
// into the channel.
func (i *Instance) SetTootDestination(d chan *toot.Toot) {
	i.tootDestination = d
}

// Event is the method that alters the FSM
func (i *Instance) Event(eventname string) {
	i.fsmLock.Lock()
	defer i.fsmLock.Unlock()
	i.FSM.Event(eventname)
}

func (i *Instance) fsmEnterState(e *fsm.Event) {
	log.Debug().
		Str("hostname", i.Hostname).
		Str("state", e.Dst).
		Msg("instance changed state")
}

// Lock locks the instance's mutex for reading/writing from the structure
func (i *Instance) Lock() {
	i.structLock.Lock()
}

// Unlock unlocks the instance's mutex for reading/writing from the structure
func (i *Instance) Unlock() {
	i.structLock.Unlock()
}

func (i *Instance) bumpFetchError() {
	i.Lock()
	probablyDead := i.ConsecutiveErrorCount > 3
	shouldDisable := i.ConsecutiveErrorCount > 6
	i.Unlock()

	if shouldDisable {
		// auf wiedersehen, felicia
		i.Lock()
		i.Disabled = true
		i.Unlock()
		i.Event("DISABLEMENT")
		return
	}

	if probablyDead {
		// if three consecutive fetch errors happen, only try once per day:
		i.setNextFetchAfter(instancePersistentErrorInterval)
	} else {
		// otherwise give them 1h
		i.setNextFetchAfter(instanceErrorInterval)
	}
}

func (i *Instance) bumpFetchSuccess() {
	i.setNextFetchAfter(instanceSpiderInterval)
}

func (i *Instance) scheduleFetchImmediate() {
	i.setNextFetchAfter(zeroInterval)
}

func (i *Instance) setNextFetchAfter(d time.Duration) {
	i.Lock()
	defer i.Unlock()
	i.NextFetch = time.Now().Add(d)
}

// Fetch prepares an instance for fetching.  Bad name, fix it.
// FIXME(sneak)
func (i *Instance) Fetch() {
	i.fetchingLock.Lock()
	defer i.fetchingLock.Unlock()

	i.bumpFetchError()
	err := i.DetectNodeTypeIfNecessary()
	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msg("unable to fetch instance metadata")
		return
	}
	i.scheduleFetchImmediate()
	log.Info().
		Str("hostname", i.Hostname).
		Msg("instance now ready for fetch")
}

// FIXME rename this function
func (i *Instance) dueForFetch() bool {
	// this just checks FSM state, the ticker must update it and do time
	// calcs
	if i.Status() == "READY_AND_DUE_FETCH" {
		return true
	}
	return false
}

func (i *Instance) isNowPastFetchTime() bool {
	return time.Now().After(i.NextFetch)
}

// Tick is responsible for pushing idle instance records between states.
// The instances will transition between states when doing stuff (e.g.
// investigating, fetching, et c) as well.
func (i *Instance) Tick() {
	if i.Status() == "READY_FOR_TOOTFETCH" {
		if i.isNowPastFetchTime() {
			i.Event("FETCH_TIME_REACHED")
		}
	} else if i.Status() == "STATUS_UNKNOWN" {
		i.Fetch()
	} else if i.Status() == "READY_AND_DUE_FETCH" {
		i.fetchRecentToots()
	}
}

func (i *Instance) nodeIdentified() bool {
	i.Lock()
	defer i.Unlock()
	if i.Implementation != "" {
		return true
	}
	return false
}

// DetectNodeTypeIfNecessary does some network requests if the node is as
// yet unidenfitied. No-op otherwise.
func (i *Instance) DetectNodeTypeIfNecessary() error {
	if !i.nodeIdentified() {
		return i.fetchNodeInfo()
	}
	return nil
}

func (i *Instance) registerError() {
	i.Lock()
	defer i.Unlock()
	i.ErrorCount++
	i.ConsecutiveErrorCount++
}

func (i *Instance) registerSuccess() {
	i.Lock()
	defer i.Unlock()
	i.SuccessCount++
	i.ConsecutiveErrorCount = 0
}

// Up returns true if the success count is >0
func (i *Instance) Up() bool {
	i.Lock()
	defer i.Unlock()
	return i.SuccessCount > 0
}

func (i *Instance) fetchNodeInfoURL() error {
	url := fmt.Sprintf("https://%s/.well-known/nodeinfo", i.Hostname)
	var c = &http.Client{
		Timeout: instanceNodeinfoTimeout,
	}

	log.Debug().
		Str("url", url).
		Str("hostname", i.Hostname).
		Msg("fetching nodeinfo reference URL")

	i.Event("BEGIN_NODEINFO_URL_FETCH")
	resp, err := c.Get(url)
	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msg("unable to fetch nodeinfo, node is down?")
		i.registerError()
		i.Event("EARLY_FETCH_ERROR")
		return err
	}

	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)

	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msg("unable to read nodeinfo")
		i.registerError()
		i.Event("EARLY_FETCH_ERROR")
		return err
	}

	nir := new(jsonapis.NodeInfoWellKnownResponse)
	err = json.Unmarshal(body, &nir)
	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msg("unable to parse nodeinfo, node is weird")
		i.registerError()
		i.Event("WEIRD_NODE_RESPONSE")
		return err
	}

	for _, item := range nir.Links {
		if item.Rel == nodeInfoSchemaVersionTwoName {
			log.Debug().
				Str("hostname", i.Hostname).
				Str("nodeinfourl", item.Href).
				Msg("success fetching url for nodeinfo")

			i.Lock()
			i.NodeInfoURL = item.Href
			i.Unlock()
			i.registerSuccess()
			i.Event("GOT_NODEINFO_URL")
			return nil
		}
		log.Debug().
			Str("hostname", i.Hostname).
			Str("item-rel", item.Rel).
			Str("item-href", item.Href).
			Msg("nodeinfo entry")
	}

	log.Error().
		Str("hostname", i.Hostname).
		Msg("incomplete nodeinfo")
	i.registerError()
	i.Event("WEIRD_NODE_RESPONSE")
	return errors.New("incomplete nodeinfo")
}

func (i *Instance) fetchNodeInfo() error {
	err := i.fetchNodeInfoURL()

	if err != nil {
		return err
	}

	var c = &http.Client{
		Timeout: instanceNodeinfoTimeout,
	}

	//FIXME make sure the nodeinfourl is on the same domain as the instance
	//hostname
	i.Lock()
	url := i.NodeInfoURL
	i.Unlock()

	i.Event("BEGIN_NODEINFO_FETCH")
	resp, err := c.Get(url)

	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to fetch nodeinfo data")
		i.registerError()
		i.Event("EARLY_FETCH_ERROR")
		return err
	}

	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)

	if err != nil {
		log.Error().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to read nodeinfo data")
		i.registerError()
		i.Event("EARLY_FETCH_ERROR")
		return err
	}

	ni := new(jsonapis.NodeInfoVersionTwoSchema)
	err = json.Unmarshal(body, &ni)
	if err != nil {
		log.Error().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to parse nodeinfo")
		i.registerError()
		i.Event("WEIRD_NODE_RESPONSE")
		return err
	}

	log.Debug().
		Str("serverVersion", ni.Software.Version).
		Str("software", ni.Software.Name).
		Str("hostname", i.Hostname).
		Str("nodeInfoURL", i.NodeInfoURL).
		Msg("received nodeinfo from instance")

	i.Lock()
	i.ServerVersionString = ni.Software.Version
	i.ServerImplementationString = ni.Software.Name
	ni.Software.Name = strings.ToLower(ni.Software.Name)

	if ni.Software.Name == "pleroma" {
		log.Debug().
			Str("hostname", i.Hostname).
			Str("software", ni.Software.Name).
			Msg("detected server software")
		i.Identified = true
		i.Implementation = "pleroma"
		i.Unlock()
		i.registerSuccess()
		i.Event("GOT_NODEINFO")
		return nil
	} else if ni.Software.Name == "mastodon" {
		log.Debug().
			Str("hostname", i.Hostname).
			Str("software", ni.Software.Name).
			Msg("detected server software")
		i.Identified = true
		i.Implementation = "mastodon"
		i.Unlock()
		i.registerSuccess()
		i.Event("GOT_NODEINFO")
		return nil
	} else {
		log.Error().
			Str("hostname", i.Hostname).
			Str("software", ni.Software.Name).
			Msg("FIXME unknown server implementation")
		i.Unlock()
		i.registerError()
		i.Event("WEIRD_NODE_RESPONSE")
		return errors.New("unknown server implementation")
	}
}

func (i *Instance) fetchRecentToots() error {
	// this would have been about a billion times shorter in python

	// it turns out pleroma supports the mastodon api so we'll just use that
	// for everything for now

	// FIXME would be nice to support non-https
	url := fmt.Sprintf("https://%s/api/v1/timelines/public?limit=40&local=true",
		i.Hostname)

	// FIXME support broken/expired certs
	var c = &http.Client{
		Timeout: instanceHTTPTimeout,
	}

	i.Event("BEGIN_TOOT_FETCH")
	// we set the interval now to the error interval regardless here as a
	// safety against bugs to avoid fetching too frequently by logic
	// bug. if the fetch is successful, we will conditionally re-update the
	// next fetch to now+successInterval.
	i.setNextFetchAfter(instanceErrorInterval)
	resp, err := c.Get(url)

	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to fetch recent toots")
		i.registerError()
		i.Event("TOOT_FETCH_ERROR")
		return err
	}

	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)

	if err != nil {
		log.Debug().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to read recent toots from response")
		i.registerError()
		i.Event("TOOT_FETCH_ERROR")
		return err
	}

	tc, err := toot.NewTootCollectionFromMastodonAPIResponse(body, i.Hostname)

	if err != nil {
		log.Error().
			Str("hostname", i.Hostname).
			Err(err).
			Msgf("unable to parse recent toot list")
		i.registerError()
		i.Event("TOOT_FETCH_ERROR")
		return err
	}

	log.Info().
		Str("hostname", i.Hostname).
		Int("tootCount", len(tc)).
		Msgf("got and parsed toots")
	i.registerSuccess()
	i.Event("TOOTS_FETCHED")
	i.bumpFetchSuccess()

	// this should go fast as either the channel is buffered bigly or the
	// ingester receives fast and does its own buffering, but run it in its
	// own goroutine anyway because why not
	go i.sendTootsToIngester(tc)
	return nil
}

func (i *Instance) sendTootsToIngester(tc []*toot.Toot) {
	for _, item := range tc {
		i.tootDestination <- item
	}
}