package querylog

import (
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/AdguardTeam/AdGuardHome/dnsfilter"
	"github.com/AdguardTeam/golibs/log"
	"github.com/miekg/dns"
)

const (
	queryLogFileName = "querylog.json" // .gz added during compression
	getDataLimit     = 500             // GetData(): maximum log entries to return

	// maximum entries to parse when searching
	maxSearchEntries = 50000
)

// queryLog is a structure that writes and reads the DNS query log
type queryLog struct {
	conf    *Config
	lock    sync.Mutex
	logFile string // path to the log file

	bufferLock    sync.RWMutex
	buffer        []*logEntry
	fileFlushLock sync.Mutex // synchronize a file-flushing goroutine and main thread
	flushPending  bool       // don't start another goroutine while the previous one is still running
	fileWriteLock sync.Mutex
}

// create a new instance of the query log
func newQueryLog(conf Config) *queryLog {
	l := queryLog{}
	l.logFile = filepath.Join(conf.BaseDir, queryLogFileName)
	l.conf = &Config{}
	*l.conf = conf
	if !checkInterval(l.conf.Interval) {
		l.conf.Interval = 1
	}
	return &l
}

func (l *queryLog) Start() {
	if l.conf.HTTPRegister != nil {
		l.initWeb()
	}
	go l.periodicRotate()
}

func (l *queryLog) Close() {
	_ = l.flushLogBuffer(true)
}

func checkInterval(days uint32) bool {
	return days == 1 || days == 7 || days == 30 || days == 90
}

func (l *queryLog) WriteDiskConfig(dc *DiskConfig) {
	dc.Enabled = l.conf.Enabled
	dc.Interval = l.conf.Interval
}

// Clear memory buffer and remove log files
func (l *queryLog) clear() {
	l.fileFlushLock.Lock()
	defer l.fileFlushLock.Unlock()

	l.bufferLock.Lock()
	l.buffer = nil
	l.flushPending = false
	l.bufferLock.Unlock()

	err := os.Remove(l.logFile + ".1")
	if err != nil && !os.IsNotExist(err) {
		log.Error("file remove: %s: %s", l.logFile+".1", err)
	}

	err = os.Remove(l.logFile)
	if err != nil && !os.IsNotExist(err) {
		log.Error("file remove: %s: %s", l.logFile, err)
	}

	log.Debug("Query log: cleared")
}

type logEntry struct {
	IP   string    `json:"IP"`
	Time time.Time `json:"T"`

	QHost  string `json:"QH"`
	QType  string `json:"QT"`
	QClass string `json:"QC"`

	Answer     []byte `json:",omitempty"` // sometimes empty answers happen like binerdunt.top or rev2.globalrootservers.net
	OrigAnswer []byte `json:",omitempty"`

	Result   dnsfilter.Result
	Elapsed  time.Duration
	Upstream string `json:",omitempty"` // if empty, means it was cached
}

func (l *queryLog) Add(params AddParams) {
	if !l.conf.Enabled {
		return
	}

	if params.Question == nil || len(params.Question.Question) != 1 || len(params.Question.Question[0].Name) == 0 ||
		params.ClientIP == nil {
		return
	}

	if params.Result == nil {
		params.Result = &dnsfilter.Result{}
	}

	now := time.Now()
	entry := logEntry{
		IP:   params.ClientIP.String(),
		Time: now,

		Result:   *params.Result,
		Elapsed:  params.Elapsed,
		Upstream: params.Upstream,
	}
	q := params.Question.Question[0]
	entry.QHost = strings.ToLower(q.Name[:len(q.Name)-1]) // remove the last dot
	entry.QType = dns.Type(q.Qtype).String()
	entry.QClass = dns.Class(q.Qclass).String()

	if params.Answer != nil {
		a, err := params.Answer.Pack()
		if err != nil {
			log.Info("Querylog: Answer.Pack(): %s", err)
			return
		}
		entry.Answer = a
	}

	if params.OrigAnswer != nil {
		a, err := params.OrigAnswer.Pack()
		if err != nil {
			log.Info("Querylog: OrigAnswer.Pack(): %s", err)
			return
		}
		entry.OrigAnswer = a
	}

	l.bufferLock.Lock()
	l.buffer = append(l.buffer, &entry)
	needFlush := false
	if !l.flushPending {
		needFlush = len(l.buffer) >= int(l.conf.MemSize)
		if needFlush {
			l.flushPending = true
		}
	}
	l.bufferLock.Unlock()

	// if buffer needs to be flushed to disk, do it now
	if needFlush {
		// write to file
		// do it in separate goroutine -- we are stalling DNS response this whole time
		go l.flushLogBuffer(false) // nolint
	}
}

// Return TRUE if this entry is needed
func isNeeded(entry *logEntry, params getDataParams) bool {
	if params.ResponseStatus == responseStatusFiltered && !entry.Result.IsFiltered {
		return false
	}

	if len(params.QuestionType) != 0 {
		if entry.QType != params.QuestionType {
			return false
		}
	}

	if len(params.Domain) != 0 {
		if (params.StrictMatchDomain && entry.QHost != params.Domain) ||
			(!params.StrictMatchDomain && strings.Index(entry.QHost, params.Domain) == -1) {
			return false
		}
	}

	if len(params.Client) != 0 {
		if (params.StrictMatchClient && entry.IP != params.Client) ||
			(!params.StrictMatchClient && strings.Index(entry.IP, params.Client) == -1) {
			return false
		}
	}

	return true
}

func (l *queryLog) readFromFile(params getDataParams) ([]*logEntry, time.Time, int) {
	entries := []*logEntry{}
	oldest := time.Time{}

	r := l.OpenReader()
	if r == nil {
		return entries, time.Time{}, 0
	}
	r.BeginRead(params.OlderThan, getDataLimit, &params)
	total := uint64(0)
	for total <= maxSearchEntries {
		newEntries := []*logEntry{}
		for {
			entry := r.Next()
			if entry == nil {
				break
			}

			if !isNeeded(entry, params) {
				continue
			}
			if len(newEntries) == getDataLimit {
				newEntries = newEntries[1:]
			}
			newEntries = append(newEntries, entry)
		}

		log.Debug("entries: +%d (%d) [%d]", len(newEntries), len(entries), r.Total())

		entries = append(newEntries, entries...)
		if len(entries) > getDataLimit {
			toremove := len(entries) - getDataLimit
			entries = entries[toremove:]
			break
		}
		if r.Total() == 0 || len(entries) == getDataLimit {
			break
		}
		total += r.Total()
		oldest = r.Oldest()
		r.BeginReadPrev(getDataLimit)
	}

	r.Close()
	return entries, oldest, int(total)
}

// Parameters for getData()
type getDataParams struct {
	OlderThan         time.Time          // return entries that are older than this value
	Domain            string             // filter by domain name in question
	Client            string             // filter by client IP
	QuestionType      string             // filter by question type
	ResponseStatus    responseStatusType // filter by response status
	StrictMatchDomain bool               // if Domain value must be matched strictly
	StrictMatchClient bool               // if Client value must be matched strictly
}

// Response status
type responseStatusType int32

// Response status constants
const (
	responseStatusAll responseStatusType = iota + 1
	responseStatusFiltered
)

// Get log entries
func (l *queryLog) getData(params getDataParams) map[string]interface{} {
	var data = []map[string]interface{}{}

	var oldest time.Time
	now := time.Now()
	entries := []*logEntry{}
	total := 0

	// add from file
	entries, oldest, total = l.readFromFile(params)

	if params.OlderThan.IsZero() {
		params.OlderThan = now
	}

	// add from memory buffer
	l.bufferLock.Lock()
	total += len(l.buffer)
	for _, entry := range l.buffer {

		if !isNeeded(entry, params) {
			continue
		}

		if entry.Time.UnixNano() >= params.OlderThan.UnixNano() {
			break
		}

		if len(entries) == getDataLimit {
			entries = entries[1:]
		}
		entries = append(entries, entry)
	}
	l.bufferLock.Unlock()

	// process the elements from latest to oldest
	for i := len(entries) - 1; i >= 0; i-- {
		entry := entries[i]
		var a *dns.Msg

		if len(entry.Answer) > 0 {
			a = new(dns.Msg)
			if err := a.Unpack(entry.Answer); err != nil {
				log.Debug("Failed to unpack dns message answer: %s: %s", err, string(entry.Answer))
				a = nil
			}
		}

		jsonEntry := map[string]interface{}{
			"reason":    entry.Result.Reason.String(),
			"elapsedMs": strconv.FormatFloat(entry.Elapsed.Seconds()*1000, 'f', -1, 64),
			"time":      entry.Time.Format(time.RFC3339Nano),
			"client":    entry.IP,
		}
		jsonEntry["question"] = map[string]interface{}{
			"host":  entry.QHost,
			"type":  entry.QType,
			"class": entry.QClass,
		}

		if a != nil {
			jsonEntry["status"] = dns.RcodeToString[a.Rcode]
		}
		if len(entry.Result.Rule) > 0 {
			jsonEntry["rule"] = entry.Result.Rule
			jsonEntry["filterId"] = entry.Result.FilterID
		}

		if len(entry.Result.ServiceName) != 0 {
			jsonEntry["service_name"] = entry.Result.ServiceName
		}

		answers := answerToMap(a)
		if answers != nil {
			jsonEntry["answer"] = answers
		}

		if len(entry.OrigAnswer) != 0 {
			a := new(dns.Msg)
			err := a.Unpack(entry.OrigAnswer)
			if err == nil {
				answers = answerToMap(a)
				if answers != nil {
					jsonEntry["original_answer"] = answers
				}
			} else {
				log.Debug("Querylog: a.Unpack(entry.OrigAnswer): %s: %s", err, string(entry.OrigAnswer))
			}
		}

		data = append(data, jsonEntry)
	}

	log.Debug("QueryLog: prepared data (%d/%d) older than %s in %s",
		len(entries), total, params.OlderThan, time.Since(now))

	var result = map[string]interface{}{}
	if len(entries) == getDataLimit {
		oldest = entries[0].Time
	}
	result["oldest"] = ""
	if !oldest.IsZero() {
		result["oldest"] = oldest.Format(time.RFC3339Nano)
	}
	result["data"] = data
	return result
}

func answerToMap(a *dns.Msg) []map[string]interface{} {
	if a == nil || len(a.Answer) == 0 {
		return nil
	}

	var answers = []map[string]interface{}{}
	for _, k := range a.Answer {
		header := k.Header()
		answer := map[string]interface{}{
			"type": dns.TypeToString[header.Rrtype],
			"ttl":  header.Ttl,
		}
		// try most common record types
		switch v := k.(type) {
		case *dns.A:
			answer["value"] = v.A.String()
		case *dns.AAAA:
			answer["value"] = v.AAAA.String()
		case *dns.MX:
			answer["value"] = fmt.Sprintf("%v %v", v.Preference, v.Mx)
		case *dns.CNAME:
			answer["value"] = v.Target
		case *dns.NS:
			answer["value"] = v.Ns
		case *dns.SPF:
			answer["value"] = v.Txt
		case *dns.TXT:
			answer["value"] = v.Txt
		case *dns.PTR:
			answer["value"] = v.Ptr
		case *dns.SOA:
			answer["value"] = fmt.Sprintf("%v %v %v %v %v %v %v", v.Ns, v.Mbox, v.Serial, v.Refresh, v.Retry, v.Expire, v.Minttl)
		case *dns.CAA:
			answer["value"] = fmt.Sprintf("%v %v \"%v\"", v.Flag, v.Tag, v.Value)
		case *dns.HINFO:
			answer["value"] = fmt.Sprintf("\"%v\" \"%v\"", v.Cpu, v.Os)
		case *dns.RRSIG:
			answer["value"] = fmt.Sprintf("%v %v %v %v %v %v %v %v %v", dns.TypeToString[v.TypeCovered], v.Algorithm, v.Labels, v.OrigTtl, v.Expiration, v.Inception, v.KeyTag, v.SignerName, v.Signature)
		default:
			// type unknown, marshall it as-is
			answer["value"] = v
		}
		answers = append(answers, answer)
	}

	return answers
}