package papod

import (
	"bufio"
	"bytes"
	"database/sql"
	"errors"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log/slog"
	"net"
	"os"
	"regexp"
	"runtime/debug"
	"sort"
	"strings"
	"sync"
	"time"

	g "euandre.org/gobang/src"

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


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

var EmitActiveConnection   = g.MakeGauge("active-connections")
var EmitNicksInChannel     = g.MakeGauge("nicks-in-channel")
var EmitReceivedMessage    = g.MakeCounter("received-message")
var EmitWriteToClientError = g.MakeCounter("write-to-client")

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



type Channel struct {
}

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

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

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) {
	g.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(g.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) {
	msg, err := ParseMessage(rawMessage)
	if err != nil {
		g.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 {
			g.Error(
				"Failed to send data to user",
				"user-reply-error",
				"err", err,
			)
			EmitWriteToClientError()
			continue
		}
	}

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

func PingLoop(ctx *Context, connection *Connection) {
	// fmt.Println("PingLoop")
}

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

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

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

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

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

		// TODO: handle commands
	}
}

func TransactorLoop(ctx *Context) {
	g.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()
	g.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
		);
	`)
	g.FatalIf(err)
}

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

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

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

	for rows.Next() {
		var filename string
		err := rows.Scan(&filename)
		g.FatalIf(err)
		delete(set, filename)
	}
	g.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 (?);`)
	g.FatalIf(err)
	defer stmt.Close()

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

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

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

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

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

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

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

func Init() {
	g.Init()
	SetHostname()
	SetEnvironmentVariables()
}

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

	g.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)
}