package papod

import (
	"bufio"
	"bytes"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"flag"
	"fmt"
	"hash"
	"io"
	"io/ioutil"
	"log/slog"
	"math/big"
	"math/bits"
	"net"
	"os"
	"regexp"
	"runtime/debug"
	"sort"
	"strings"
	"sync"
	"syscall"
	"time"

	_ "github.com/mattn/go-sqlite3"
)


/* Global variables */
var (
	Hostname string
	Version  string
	Colour   string
)

// FIXME: reorder
var EmitActiveConnection   = MakeGauge("active-connections")
var EmitNicksInChannel     = MakeGauge("nicks-in-channel")
var EmitReceivedMessage    = MakeCounter("received-message")
var EmitWriteToClientError = MakeCounter("write-to-client")

const pingFrequency  = time.Duration(30) * time.Second
const pongMaxLatency = time.Duration(5)  * time.Second



// FIXME: finish rewriting
//
// lastV7time is the last time we returned stored as:
//
//   52 bits of time in milliseconds since epoch
//   12 bits of (fractional nanoseconds) >> 8
var lastV7Time int64
var timeMu sync.Mutex
// getV7Time returns the time in milliseconds and nanoseconds / 256.
// The returned (milli << (12 + seq)) is guaranteed to be greater than
// (milli << (12 + seq)) returned by any previous call to getV7Time.
// `seq` Sequence number is between 0 and 3906 (nanoPerMilli >> 8)
func getV7Time(nano int64) (int64, int64) {
	const nanoPerMilli = 1000 * 1000

	milli := nano / nanoPerMilli
	seq := (nano - (milli * nanoPerMilli)) >> 8
	now := milli << (12 + seq)

	timeMu.Lock()
	defer timeMu.Unlock()
	if now <= lastV7Time {
		now = lastV7Time + 1
		milli = now >> 12
		seq = now & 0xfff
	}
	lastV7Time = now
	return milli, seq
}

const lengthUUID = 16

type UUID struct {
	bytes [lengthUUID]byte
}

func NewUUID() UUID {
	var buf [lengthUUID]byte
	_, err := io.ReadFull(rand.Reader, buf[7:])
	if err != nil {
		panic(err)
	}

	buf[6] = (buf[6] & 0x0f) | 0x40 // Version 4
	buf[8] = (buf[8] & 0x3f) | 0x80 // Variant is 10

	t, s := getV7Time(time.Now().UnixNano())

	buf[0] = byte(t >> 40)
	buf[1] = byte(t >> 32)
	buf[2] = byte(t >> 24)
	buf[3] = byte(t >> 16)
	buf[4] = byte(t >> 8)
	buf[5] = byte(t >> 0)

	buf[6] = 0x70 | (0x0f & byte(s >> 8))
	buf[7] = byte(s)
	return UUID { bytes: buf }
}

func (uuid UUID) ToString() string {
	const dashCount = 4
	const encodedLength = (lengthUUID * 2) + dashCount
	dst := [encodedLength]byte {
		0, 0, 0, 0,
		0, 0, 0, 0,
		'-',
		0, 0, 0, 0,
		'-',
		0, 0, 0, 0,
		'-',
		0, 0, 0, 0,
		'-',
		0, 0, 0, 0,
		0, 0, 0, 0,
		0, 0, 0, 0,
	}

	hex.Encode(dst[ 0:8],  uuid.bytes[0:4])
	hex.Encode(dst[ 9:13], uuid.bytes[4:6])
	hex.Encode(dst[14:18], uuid.bytes[6:8])
	hex.Encode(dst[19:23], uuid.bytes[8:10])
	hex.Encode(dst[24:36], uuid.bytes[10:])

	return string(dst[:])
}

type LogLevel int8

const (
	 LevelNone    LogLevel = 0
	 LevelError   LogLevel = 1
	 LevelWarning LogLevel = 2
	 LevelInfo    LogLevel = 3
	 LevelDebug   LogLevel = 4
)

var Level LogLevel = LevelInfo

var EmitMetric bool = true


func Debug(message string, type_ string, args ...any) {
	if (Level < LevelDebug) {
		return
	}

	slog.Debug(
		message,
		append(
			[]any {
				"id",    NewUUID().ToString(),
				"kind",  "log",
				"type",  type_,
			},
			args...,
		)...,
	)
}

func Info(message string, type_ string, args ...any) {
	if (Level < LevelInfo) {
		return
	}

	slog.Info(
		message,
		append(
			[]any {
				"id",    NewUUID().ToString(),
				"kind",  "log",
				"type",  type_,
			},
			args...,
		)...,
	)
}

func Warning(message string, type_ string, args ...any) {
	if (Level < LevelWarning) {
		return
	}

	slog.Warn(
		message,
		append(
			[]any {
				"id",    NewUUID().ToString(),
				"kind",  "log",
				"type",  type_,
			},
			args...,
		)...,
	)
}

func Error(message string, type_ string, args ...any) {
	if (Level < LevelError) {
		return
	}

	slog.Error(
		message,
		append(
			[]any {
				"id",    NewUUID().ToString(),
				"kind",  "log",
				"type",  type_,
			},
			args...,
		)...,
	)
}

func Metric(type_ string, label string, args ...any) {
	if (!EmitMetric) {
		return
	}

	slog.Info(
		"_",
		append(
			[]any {
				"id",    NewUUID().ToString(),
				"kind",  "metric",
				"type",  type_,
				"label", label,
			},
			args...,
		)...,
	)
}

type Gauge struct {
	Inc func(...any)
	Dec func(...any)
}

var zero = big.NewInt(0)
var one  = big.NewInt(1)
func MakeGauge(label string, staticArgs ...any) Gauge {
	count := big.NewInt(0)
	emitGauge := func(dynamicArgs ...any) {
		if count.Cmp(zero) == -1 {
			Error(
				"Gauge went negative",
				"process-metric",
				append(
					[]any { "value", count },
					append(
						staticArgs,
						dynamicArgs...,
					)...,
				)...,
			)
			return  // avoid wrong metrics being emitted
		}
		Metric(
			"gauge", label,
			// TODO: we'll have slices.Concat on Go 1.22
			append(
				[]any { "value", count },
				append(
					staticArgs,
					dynamicArgs...,
				)...,
			)...,
		)
	}
	return Gauge {
		Inc: func(dynamicArgs ...any) {
			count.Add(count, one)
			emitGauge(dynamicArgs...)
		},
		Dec: func(dynamicArgs ...any) {
			count.Sub(count, one)
			emitGauge(dynamicArgs...)
		},
	}
}

func MakeCounter(label string) func(...any) {
	return func(args ...any) {
		Metric(
			"counter", label,
			append([]any { "value", 1 }, args...)...,
		)
	}
}

func SetLoggerOutput(w io.Writer) {
	slog.SetDefault(slog.New(slog.NewJSONHandler(w, &slog.HandlerOptions {
		AddSource: true,
	})).With(
		slog.Group(
			"info",
			"pid",   os.Getpid(),
			"ppid",  os.Getppid(),
			"puuid", NewUUID().ToString(),
		),
	))
}

func SetTraceback() {
	if os.Getenv("GOTRACEBACK") == "" {
		debug.SetTraceback("crash")
	}
}

func Fatal(err error) {
	Error(
		"Fatal error", "fatal-error",
		"error", err,
		"stack", string(debug.Stack()),
	)
	syscall.Kill(os.Getpid(), syscall.SIGABRT)
	os.Exit(3)
}

func FatalIf(err error) {
	if err != nil {
		Fatal(err)
	}
}


/*
Package pbkdf2 implements the key derivation function PBKDF2 as defined in RFC
2898 / PKCS #5 v2.0.

A key derivation function is useful when encrypting data based on a password
or any other not-fully-random data. It uses a pseudorandom function to derive
a secure encryption key based on the password.

While v2.0 of the standard defines only one pseudorandom function to use,
HMAC-SHA1, the drafted v2.1 specification allows use of all five FIPS Approved
Hash Functions SHA-1, SHA-224, SHA-256, SHA-384 and SHA-512 for HMAC. To
choose, you can pass the `New` functions from the different SHA packages to
pbkdf2.Key.
*/

// Key derives a key from the password, salt and iteration count, returning a
// []byte of length keylen that can be used as cryptographic key. The key is
// derived based on the method described as PBKDF2 with the HMAC variant using
// the supplied hash function.
//
// For example, to use a HMAC-SHA-1 based PBKDF2 key derivation function, you
// can get a derived key for e.g. AES-256 (which needs a 32-byte key) by
// doing:
//
//	dk := pbkdf2.Key([]byte("some password"), salt, 4096, 32, sha1.New)
//
// Remember to get a good random salt. At least 8 bytes is recommended by the
// RFC.
//
// Using a higher iteration count will increase the cost of an exhaustive
// search but will also make derivation proportionally slower.
func PBKDF2Key(
	password []byte,
	salt []byte,
	iter int,
	keyLen int,
	h func() hash.Hash,
) []byte {
	prf := hmac.New(h, password)
	hashLen := prf.Size()
	numBlocks := (keyLen + hashLen - 1) / hashLen

	var buf [4]byte
	dk := make([]byte, 0, numBlocks*hashLen)
	U := make([]byte, hashLen)
	for block := 1; block <= numBlocks; block++ {
		// N.B.: || means concatenation, ^ means XOR
		// for each block T_i = U_1 ^ U_2 ^ ... ^ U_iter
		// U_1 = PRF(password, salt || uint(i))
		prf.Reset()
		prf.Write(salt)
		buf[0] = byte(block >> 24)
		buf[1] = byte(block >> 16)
		buf[2] = byte(block >> 8)
		buf[3] = byte(block)
		prf.Write(buf[:4])
		dk = prf.Sum(dk)
		T := dk[len(dk)-hashLen:]
		copy(U, T)

		// U_n = PRF(password, U_(n-1))
		for n := 2; n <= iter; n++ {
			prf.Reset()
			prf.Write(U)
			U = U[:0]
			U = prf.Sum(U)
			for x := range U {
				T[x] ^= U[x]
			}
		}
	}
	return dk[:keyLen]
}

// Package scrypt implements the scrypt key derivation function as defined in
// Colin Percival's paper "Stronger Key Derivation via Sequential Memory-Hard
// Functions" (https://www.tarsnap.com/scrypt/scrypt.pdf).

const maxInt = int(^uint(0) >> 1)

// blockCopy copies n numbers from src into dst.
func blockCopy(dst []uint32, src []uint32, n int) {
	copy(dst, src[:n])
}

// blockXOR XORs numbers from dst with n numbers from src.
func blockXOR(dst []uint32, src []uint32, n int) {
	for i, v := range src[:n] {
		dst[i] ^= v
	}
}

// salsaXOR applies Salsa20/8 to the XOR of 16 numbers from tmp and in,
// and puts the result into both tmp and out.
func salsaXOR(tmp *[16]uint32, in []uint32, out []uint32) {
	w0  := tmp[0]  ^ in[0]
	w1  := tmp[1]  ^ in[1]
	w2  := tmp[2]  ^ in[2]
	w3  := tmp[3]  ^ in[3]
	w4  := tmp[4]  ^ in[4]
	w5  := tmp[5]  ^ in[5]
	w6  := tmp[6]  ^ in[6]
	w7  := tmp[7]  ^ in[7]
	w8  := tmp[8]  ^ in[8]
	w9  := tmp[9]  ^ in[9]
	w10 := tmp[10] ^ in[10]
	w11 := tmp[11] ^ in[11]
	w12 := tmp[12] ^ in[12]
	w13 := tmp[13] ^ in[13]
	w14 := tmp[14] ^ in[14]
	w15 := tmp[15] ^ in[15]

	x0  := w0
	x1  := w1
	x2  := w2
	x3  := w3
	x4  := w4
	x5  := w5
	x6  := w6
	x7  := w7
	x8  := w8
	x9  := w9
	x10 := w10
	x11 := w11
	x12 := w12
	x13 := w13
	x14 := w14
	x15 := w15

	for i := 0; i < 8; i += 2 {
		x4  ^= bits.RotateLeft32(x0  + x12, 7)
		x8  ^= bits.RotateLeft32(x4  + x0,  9)
		x12 ^= bits.RotateLeft32(x8  + x4,  13)
		x0  ^= bits.RotateLeft32(x12 + x8,  18)

		x9  ^= bits.RotateLeft32(x5  + x1,  7)
		x13 ^= bits.RotateLeft32(x9  + x5,  9)
		x1  ^= bits.RotateLeft32(x13 + x9,  13)
		x5  ^= bits.RotateLeft32(x1  + x13, 18)

		x14 ^= bits.RotateLeft32(x10 + x6,  7)
		x2  ^= bits.RotateLeft32(x14 + x10, 9)
		x6  ^= bits.RotateLeft32(x2  + x14, 13)
		x10 ^= bits.RotateLeft32(x6  + x2,  18)

		x3  ^= bits.RotateLeft32(x15 + x11, 7)
		x7  ^= bits.RotateLeft32(x3  + x15, 9)
		x11 ^= bits.RotateLeft32(x7  + x3,  13)
		x15 ^= bits.RotateLeft32(x11 + x7,  18)

		x1  ^= bits.RotateLeft32(x0  + x3,  7)
		x2  ^= bits.RotateLeft32(x1  + x0,  9)
		x3  ^= bits.RotateLeft32(x2  + x1,  13)
		x0  ^= bits.RotateLeft32(x3  + x2,  18)

		x6  ^= bits.RotateLeft32(x5  + x4,  7)
		x7  ^= bits.RotateLeft32(x6  + x5,  9)
		x4  ^= bits.RotateLeft32(x7  + x6,  13)
		x5  ^= bits.RotateLeft32(x4  + x7,  18)

		x11 ^= bits.RotateLeft32(x10 + x9,  7)
		x8  ^= bits.RotateLeft32(x11 + x10, 9)
		x9  ^= bits.RotateLeft32(x8  + x11, 13)
		x10 ^= bits.RotateLeft32(x9  + x8,  18)

		x12 ^= bits.RotateLeft32(x15 + x14, 7)
		x13 ^= bits.RotateLeft32(x12 + x15, 9)
		x14 ^= bits.RotateLeft32(x13 + x12, 13)
		x15 ^= bits.RotateLeft32(x14 + x13, 18)
	}

	x0  += w0
	x1  += w1
	x2  += w2
	x3  += w3
	x4  += w4
	x5  += w5
	x6  += w6
	x7  += w7
	x8  += w8
	x9  += w9
	x10 += w10
	x11 += w11
	x12 += w12
	x13 += w13
	x14 += w14
	x15 += w15

	out[0],  tmp[0]  = x0,  x0
	out[1],  tmp[1]  = x1,  x1
	out[2],  tmp[2]  = x2,  x2
	out[3],  tmp[3]  = x3,  x3
	out[4],  tmp[4]  = x4,  x4
	out[5],  tmp[5]  = x5,  x5
	out[6],  tmp[6]  = x6,  x6
	out[7],  tmp[7]  = x7,  x7
	out[8],  tmp[8]  = x8,  x8
	out[9],  tmp[9]  = x9,  x9
	out[10], tmp[10] = x10, x10
	out[11], tmp[11] = x11, x11
	out[12], tmp[12] = x12, x12
	out[13], tmp[13] = x13, x13
	out[14], tmp[14] = x14, x14
	out[15], tmp[15] = x15, x15
}

func blockMix(tmp *[16]uint32, in []uint32, out []uint32, r int) {
	blockCopy(tmp[:], in[(2*r-1)*16:], 16)
	for i := 0; i < 2*r; i += 2 {
		salsaXOR(tmp, in[i*16:], out[i*8:])
		salsaXOR(tmp, in[i*16+16:], out[i*8+r*16:])
	}
}

func integer(b []uint32, r int) uint64 {
	j := (2*r - 1) * 16
	return uint64(b[j]) | uint64(b[j+1])<<32
}

func smix(b []byte, r int, N int, v []uint32, xy []uint32) {
	var tmp [16]uint32
	R := 32 * r
	x := xy
	y := xy[R:]

	j := 0
	for i := 0; i < R; i++ {
		x[i] = binary.LittleEndian.Uint32(b[j:])
		j += 4
	}
	for i := 0; i < N; i += 2 {
		blockCopy(v[i*R:], x, R)
		blockMix(&tmp, x, y, r)

		blockCopy(v[(i+1)*R:], y, R)
		blockMix(&tmp, y, x, r)
	}
	for i := 0; i < N; i += 2 {
		j := int(integer(x, r) & uint64(N-1))
		blockXOR(x, v[j*R:], R)
		blockMix(&tmp, x, y, r)

		j = int(integer(y, r) & uint64(N-1))
		blockXOR(y, v[j*R:], R)
		blockMix(&tmp, y, x, r)
	}
	j = 0
	for _, v := range x[:R] {
		binary.LittleEndian.PutUint32(b[j:], v)
		j += 4
	}
}

// Key derives a key from the password, salt, and cost parameters, returning
// a byte slice of length keyLen that can be used as cryptographic key.
//
// N is a CPU/memory cost parameter, which must be a power of 2 greater than 1.
// r and p must satisfy r * p < 2³⁰. If the parameters do not satisfy the
// limits, the function returns a nil byte slice and an error.
//
// For example, you can get a derived key for e.g. AES-256 (which needs a
// 32-byte key) by doing:
//
//	dk, err := scrypt.Key([]byte("some password"), salt, 32768, 8, 1, 32)
//
// The recommended parameters for interactive logins as of 2017 are N=32768, r=8
// and p=1. The parameters N, r, and p should be increased as memory latency and
// CPU parallelism increases; consider setting N to the highest power of 2 you
// can derive within 100 milliseconds. Remember to get a good random salt.
func Scrypt(
	password []byte,
	salt []byte,
	N int,
	r int,
	p int,
	keyLen int,
) ([]byte, error) {
	if N <= 1 || N&(N-1) != 0 {
		return nil, errors.New("scrypt: N must be > 1 and a power of 2")
	}
	if uint64(r)*uint64(p) >= 1<<30 ||
			r > maxInt/128/p || r > maxInt/256 || N > maxInt/128/r {
		return nil, errors.New("scrypt: parameters are too large")
	}

	xy := make([]uint32, 64*r)
	v := make([]uint32, 32*N*r)
	b := PBKDF2Key(password, salt, 1, p*128*r, sha256.New)

	for i := 0; i < p; i++ {
		smix(b[i*128*r:], r, N, v, xy)
	}

	return PBKDF2Key(password, b, 1, keyLen, sha256.New), nil
}


// type UUID string
	
type Channel struct {
}

type Connection struct {
	conn            net.Conn
	replyChan       chan string
	lastReadFrom    time.Time
	lastWrittenTo   time.Time
	// id              *UUID
	id              string
	isAuthenticated bool
}

type User struct {
	connections []Connection
}

type State struct {
	users map[string]*User
}

type Context struct {
	db *sql.DB
	state State
	tx chan int
}

type MessageParams struct {
	Middle   []string
	Trailing string
}

type Message struct {
	Prefix  string
	Command string
	Params  MessageParams
	Raw     string
}

var (
	CmdUSER    = Message { Command: "USER"    }
	CmdPRIVMSG = Message { Command: "PRIVMSG" }
	CmdJOIN    = Message { Command: "JOIN"    }
)

func SplitOnCRLF(data []byte, _atEOF bool) (int, []byte, error) {
	idx := bytes.Index(data, []byte { '\r', '\n' })
	if idx == -1 {
		return 0, nil, nil
	}

	return idx + 2, data[0:idx], nil
}

func SplitOnRawMessage(data []byte, atEOF bool) (int, []byte, error) {
	advance, token, error := SplitOnCRLF(data, atEOF)

	if len(token) == 0 {
		return advance, nil, error
	}

	return advance, token, error
}

func SplitSpaces(r rune) bool {
	return r == ' '
}

func ParseMessageParams(params string) MessageParams {
	const sep = " :"

	var middle string
	var trailing string

	idx := strings.Index(params, sep)
	if idx == -1 {
		middle = params
		trailing = ""
	} else {
		middle = params[:idx]
		trailing = params[idx + len(sep):]
	}

	return MessageParams {
		Middle: strings.FieldsFunc(middle, SplitSpaces),
		Trailing: trailing,
	}
}

var MessageRegex = regexp.MustCompilePOSIX(
	//  <prefix>   <command>    <params>
	//1 2          3            4
	`^(:([^ ]+) +)?([a-zA-Z]+) *( .*)$`,
)
func ParseMessage(rawMessage string) (Message, error) {
	var msg Message

	components := MessageRegex.FindStringSubmatch(rawMessage)
	if components == nil {
		return msg, errors.New("Can't parse message")
	}

	msg = Message {
		Prefix:  components[2],
		Command: components[3],
		Params:  ParseMessageParams(components[4]),
		Raw:     rawMessage,
	}
	return msg, nil
}

func HandleUnknown(ctx *Context, msg Message) {
	Warning(
		"Unsupported command", "unsupported-command",
		"command", msg.Command,
	)
	var r Reply = ReplyUnknown
	r.Prefix = "dunno"
	// return []Action { r }
}

func HandleUSER(ctx *Context, msg Message) {
	fmt.Printf("USER: %#v\n", msg)
}

func HandlePRIVMSG(ctx *Context, msg Message) {
	// . assert no missing params
	// . write to DB: (after auth)
	//   . channel timeline: message from $USER
	// . reply to $USER
	// . broadcast new timeline event to members of the channel

	stmt, err := ctx.db.Prepare(`
		INSERT INTO messages
			(id, sender_id, body, timestamp)
		VALUES
			(?,  ?,         ?,    ?        );
	`)
	if err != nil {
		// FIXME: reply error
		fmt.Println("can't prepare: ", err)
		return
	}
	defer stmt.Close()

	ret, err := stmt.Exec(
		NewUUID().ToString(),
		"FIXME",
		"FIXME",
		time.Now(),
	)
	if err != nil {
		// FIXME: reply error
		fmt.Println("xablau can't prepare: ", err)
		return
	}

	fmt.Println("ret: ", ret)
}

func HandleJOIN(ctx *Context, msg Message) {
	fmt.Printf("JOIN: %#v\n", msg)

	// . write to DB: (after auth)
	//   . $USER now in channel
	//   . channel timeline: $USER joined
	// . reply to $USER
	// . broadcast new timeline event to members of the channel
}

func ReplyAnonymous() {
}

func PersistMessage(msg Message) {
}

type ActionType int
const (
	ActionReply = iota
)

type Action interface {
	Type() ActionType
}

type Reply struct {
	Prefix  string
	Command int
	Params  MessageParams
}

func (reply Reply) Type() ActionType {
	return ActionReply
}

var (
	ReplyUnknown = Reply {
		Command: 421,
		Params: MessageParams {
			Middle: []string { },
			Trailing: "Unknown command",
		},
	}
)

var Commands = map[string]func(*Context, Message) {
	   CmdUSER.Command: HandleUSER,
	CmdPRIVMSG.Command: HandlePRIVMSG,
	   CmdJOIN.Command: HandleJOIN,
}

func ActionFnFor(command string) func(*Context, Message) {
	fn := Commands[command]
	if fn != nil {
		return fn
	}

	return HandleUnknown
}

func ProcessMessage(ctx *Context, connection *Connection, rawMessage string) {
	connection.lastReadFrom = time.Now()

	msg, err := ParseMessage(rawMessage)
	if err != nil {
		Info(
			"Error processing message",
			"process-message",
			"err", err,
		)
		return
	}

	if msg.Command == CmdUSER.Command {
		args := msg.Params.Middle
		if len(args) == 0 {
			go ReplyAnonymous()
			return
		}
		connection.id = args[0]
		connection.isAuthenticated = true
	}

	if !connection.isAuthenticated {
		go ReplyAnonymous()
		return
	}

	ActionFnFor(msg.Command)(ctx, msg)
}

func ReadLoop(ctx *Context, connection *Connection) {
	scanner := bufio.NewScanner(connection.conn)
	scanner.Split(SplitOnRawMessage)
	for scanner.Scan() {
		ProcessMessage(ctx, connection, scanner.Text())
	}
}

func WriteLoop(ctx *Context, connection *Connection) {
	for message := range connection.replyChan {
		_, err := io.WriteString(connection.conn, message)
		if err != nil {
			Error(
				"Failed to send data to user",
				"user-reply-error",
				"err", err,
			)
			EmitWriteToClientError()
			continue
		}

		connection.lastWrittenTo = time.Now()
	}

	EmitActiveConnection.Dec()
	connection.conn.Close()
}

func Kill(ctx *Context, connection *Connection) {
	// lock?
	delete(ctx.state.users, connection.id)
	// unlock?
	close(connection.replyChan)
	connection.conn.Close() // Ignore errors?
}

const PingWindow = 30 * time.Second
func PingLoop(ctx *Context, connection *Connection) {
	for {
		time.Sleep(PingWindow)
		if (time.Since(connection.lastReadFrom) <= PingWindow) {
			continue
		}
		window := connection.lastWrittenTo.Sub(connection.lastReadFrom)
		if (window <= PingWindow) {
			connection.replyChan <- "PING"
			continue
		}

		Kill(ctx, connection)
		break
	}
}

func HandleConnection(ctx *Context, conn net.Conn) {
	EmitActiveConnection.Inc()
	// FIXME: WaitGroup here?
	now := time.Now()
	connection := Connection {
		conn: conn,
		isAuthenticated: false,
		lastReadFrom:  now,
		lastWrittenTo: now,
	}
	go  ReadLoop(ctx, &connection)
	go WriteLoop(ctx, &connection)
	go  PingLoop(ctx, &connection)
}

func IRCdLoop(ctx *Context, publicSocketPath string) {
	listener, err := net.Listen("unix", publicSocketPath)
	FatalIf(err)
	Info("IRCd started", "component-up", "component", "ircd")

	for {
		conn, err := listener.Accept()
		if err != nil {
			Warning(
				"Error accepting a public IRCd connection",
				"accept-connection",
				"err", err,
			)
			// conn.Close() // FIXME: is conn nil?
			continue
		}
		// FIXME: where does it get closed
		go HandleConnection(ctx, conn)
	}
}

func CommandListenerLoop(ctx *Context, commandSocketPath string) {
	listener, err := net.Listen("unix", commandSocketPath)
	FatalIf(err)
	Info(
		"command listener started",
		"component-up",
		"component", "command-listener",
	)

	for {
		conn, err := listener.Accept()
		if err != nil {
			Warning(
				"Error accepting a command connection",
				"accept-command",
				"err", err,
			)
			continue
		}
		defer conn.Close()

		// TODO: handle commands
	}
}

func TransactorLoop(ctx *Context) {
	Info("transactor started", "component-up", "component", "transactor")
	EmitActiveConnection.Inc()

	for tx := range ctx.tx {
		fmt.Println(tx)
	}
}

func SetHostname() {
	var err error
	Hostname, err = os.Hostname()
	FatalIf(err)
}

func SetEnvironmentVariables() {
	Version = os.Getenv("PAPOD_VERSION")
	if Version == "" {
		Version = "PAPOD-VERSION-UNKNOWN"
	}

	Colour = os.Getenv("PAPOD_COLOUR")
	if Colour == "" {
		Colour = "PAPOD-COLOUR-UNKNOWN"
	}
}

func InitMigrations(db *sql.DB) {
	_, err := db.Exec(`
		CREATE TABLE IF NOT EXISTS migrations (
			filename TEXT PRIMARY KEY
		);
	`)
	FatalIf(err)
}

const MIGRATIONS_DIR = "src/sql/migrations/"
func PendingMigrations(db *sql.DB) []string {
	files, err := ioutil.ReadDir(MIGRATIONS_DIR)
	FatalIf(err)

	set := make(map[string]bool)
	for _, file := range files {
		set[file.Name()] = true
	}

	rows, err := db.Query(`SELECT filename FROM migrations;`)
	FatalIf(err)
	defer rows.Close()

	for rows.Next() {
		var filename string
		err := rows.Scan(&filename)
		FatalIf(err)
		delete(set, filename)
	}
	FatalIf(rows.Err())

	difference := make([]string, 0)
	for filename := range set {
		difference = append(difference, filename)
	}

	sort.Sort(sort.StringSlice(difference))
	return difference
}

func RunMigrations(db *sql.DB) {
	InitMigrations(db)

	stmt, err := db.Prepare(`INSERT INTO migrations (filename) VALUES (?);`)
	FatalIf(err)
	defer stmt.Close()

	for _, filename := range PendingMigrations(db) {
		Info("Running migration file", "exec-migration-file",
			"filename", filename,
		)

		tx, err := db.Begin()
		FatalIf(err)

		sql, err := os.ReadFile(MIGRATIONS_DIR + filename)
		FatalIf(err)

		_, err = tx.Exec(string(sql))
		FatalIf(err)

		_, err = tx.Stmt(stmt).Exec(filename)
		FatalIf(err)

		err = tx.Commit()
		FatalIf(err)
	}
}

func InitDB(databasePath string) *sql.DB {
	db, err := sql.Open("sqlite3", databasePath)
	FatalIf(err)
	RunMigrations(db)
	return db
}

func Init() {
	SetLoggerOutput(os.Stdout)
	SetTraceback()
	SetHostname()
	SetEnvironmentVariables()
}

func Start(ctx *Context, publicSocketPath string, commandSocketPath string) {
	buildInfo, ok := debug.ReadBuildInfo()
	if !ok {
		Fatal(errors.New("error on debug.ReadBuildInfo()"))
	}

	Info("-", "lifecycle-event",
		"event", "starting-server",
		slog.Group(
			"go",
			"version", buildInfo.GoVersion,
			"settings", buildInfo.Settings,
			"deps", buildInfo.Deps,
		),
	)

	var wg sync.WaitGroup
	bgRun := func(f func()) {
		wg.Add(1)
		go func() {
			f()
			wg.Done()
		}()
	}
	bgRun(func() { IRCdLoop(ctx, publicSocketPath)             })
	bgRun(func() { CommandListenerLoop(ctx, commandSocketPath) })
	bgRun(func() { TransactorLoop(ctx)                         })
	wg.Wait()
}

func BuildContext(databasePath string) *Context {
	db := InitDB(databasePath)
	tx := make(chan int, 100)
	return &Context {
		db: db,
		tx: tx,
	}
}

var (
	databasePath = flag.String(
		"f",
		"papod.db",
		"The path to the database file",
	)
	publicSocketPath = flag.String(
		"s",
		"papod.public.socket",
		"The path to the socket that handles the public traffic",
	)
	commandSocketPath = flag.String(
		"S",
		"papod.command.socket",
		"The path to the private IPC commands socket",
	)
)


func Main() {
	Init()
	flag.Parse()
	ctx := BuildContext(*databasePath)
	Start(ctx, *publicSocketPath, *commandSocketPath)
}