package sbproxy

import (
	"bytes"
	"context"
	"encoding/binary"
	"encoding/json"
	"io"
	"net"

	"github.com/sagernet/sing-box/adapter"
	N "github.com/sagernet/sing/common/network"
)

func (h *Inbound) handleJavaConnection(ctx context.Context, conn net.Conn, metadata adapter.InboundContext, onClose N.CloseHandlerFunc) {
	_, _, err := ReadVarInt(conn) // packet len
	if err != nil {
		conn.Close()
		return
	}
	packetID, _, err := ReadVarInt(conn)
	if err != nil || packetID != 0x00 {
		conn.Close()
		return
	}

	ReadVarInt(conn) // protocol version
	ReadString(conn) // server address
	binary.Read(conn, binary.BigEndian, new(uint16))
	nextState, _, _ := ReadVarInt(conn)

	switch nextState {
	case 1: // Status
		h.handleJavaStatus(conn)
	case 2: // Login
		h.handleJavaLogin(ctx, conn, metadata, onClose)
	default:
		conn.Close()
	}
}

func (h *Inbound) handleJavaStatus(conn net.Conn) {
	for {
		packetLen, _, err := ReadVarInt(conn)
		if err != nil {
			return
		}
		packetID, _, err := ReadVarInt(conn)
		if err != nil {
			return
		}

		if packetID == 0x00 { // Status Request
			motd := h.options.MOTD
			if motd == "" {
				motd = "A Minecraft Server"
			}
			ver := h.options.Version
			if ver == "" {
				ver = "1.20.1"
			}

			resp := map[string]any{
				"version":     map[string]any{"name": ver, "protocol": 763},
				"players":     map[string]any{"max": h.options.MaxPlayers, "online": 0, "sample": []any{}},
				"description": map[string]any{"text": motd},
			}
			data, _ := json.Marshal(resp)

			var body bytes.Buffer
			WriteVarInt(&body, 0x00) // Response ID
			WriteString(&body, string(data))

			WriteVarInt(conn, int32(body.Len()))
			conn.Write(body.Bytes())
		} else if packetID == 0x01 { // Ping
			var b [8]byte
			if _, err := io.ReadFull(conn, b[:]); err != nil {
				return
			}

			var body bytes.Buffer
			WriteVarInt(&body, 0x01)
			body.Write(b[:])

			WriteVarInt(conn, int32(body.Len()))
			conn.Write(body.Bytes())
			return
		} else {
			io.CopyN(io.Discard, conn, int64(packetLen)-1)
		}
	}
}

func (h *Inbound) handleJavaLogin(ctx context.Context, conn net.Conn, metadata adapter.InboundContext, onClose N.CloseHandlerFunc) {
	// Login Start
	_, _, err := ReadVarInt(conn)
	if err != nil {
		conn.Close()
		return
	}
	packetID, _, err := ReadVarInt(conn)
	if err != nil || packetID != 0x00 {
		conn.Close()
		return
	}
	user, _ := ReadString(conn)

	// Offline Mode: No encryption/auth sequence, just Login Success
	var loginSuccess bytes.Buffer
	WriteVarInt(&loginSuccess, 0x02) // Login Success ID
	// UUID (offline)
	loginSuccess.Write(make([]byte, 16))
	WriteString(&loginSuccess, user)
	WriteVarInt(&loginSuccess, 0) // No properties

	WriteVarInt(conn, int32(loginSuccess.Len()))
	conn.Write(loginSuccess.Bytes())

	h.handlePlay(ctx, conn, user, metadata, onClose)
}