package socks5

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net"

	"github.com/thinkgos/go-socks5/statute"
)

// GPool is used to implement custom goroutine pool default use goroutine
type GPool interface {
	Submit(f func()) error
}

// Server is reponsible for accepting connections and handling
// the details of the SOCKS5 protocol
type Server struct {
	authMethods map[uint8]Authenticator
	// AuthMethods can be provided to implement custom authentication
	// By default, "auth-less" mode is enabled.
	// For password-based auth use UserPassAuthenticator.
	authCustomMethods []Authenticator
	// If provided, username/password authentication is enabled,
	// by appending a UserPassAuthenticator to AuthMethods. If not provided,
	// and AUthMethods is nil, then "auth-less" mode is enabled.
	credentials CredentialStore
	// resolver can be provided to do custom name resolution.
	// Defaults to DNSResolver if not provided.
	resolver NameResolver
	// rules is provided to enable custom logic around permitting
	// various commands. If not provided, NewPermitAll is used.
	rules RuleSet
	// rewriter can be used to transparently rewrite addresses.
	// This is invoked before the RuleSet is invoked.
	// Defaults to NoRewrite.
	rewriter AddressRewriter
	// bindIP is used for bind or udp associate
	bindIP net.IP
	// logger can be used to provide a custom log target.
	// Defaults to ioutil.Discard.
	logger Logger
	// Optional function for dialing out
	dial func(ctx context.Context, network, addr string) (net.Conn, error)
	// buffer pool
	bufferPool BufferPool
	// goroutine pool
	gPool GPool
	// user's handle
	userConnectHandle   func(ctx context.Context, writer io.Writer, request *Request) error
	userBindHandle      func(ctx context.Context, writer io.Writer, request *Request) error
	userAssociateHandle func(ctx context.Context, writer io.Writer, request *Request) error
}

// NewServer creates a new Server and potentially returns an error
func NewServer(opts ...Option) *Server {
	server := &Server{
		authMethods:       make(map[uint8]Authenticator),
		authCustomMethods: []Authenticator{&NoAuthAuthenticator{}},
		bufferPool:        NewPool(32 * 1024),
		resolver:          DNSResolver{},
		rules:             NewPermitAll(),
		logger:            NewLogger(log.New(ioutil.Discard, "socks5: ", log.LstdFlags)),
		dial: func(ctx context.Context, net_, addr string) (net.Conn, error) {
			return net.Dial(net_, addr)
		},
	}

	for _, opt := range opts {
		opt(server)
	}

	// Ensure we have at least one authentication method enabled
	if len(server.authCustomMethods) == 0 && server.credentials != nil {
		server.authCustomMethods = []Authenticator{&UserPassAuthenticator{server.credentials}}
	}

	for _, v := range server.authCustomMethods {
		server.authMethods[v.GetCode()] = v
	}

	return server
}

// ListenAndServe is used to create a listener and serve on it
func (s *Server) ListenAndServe(network, addr string) error {
	l, err := net.Listen(network, addr)
	if err != nil {
		return err
	}
	return s.Serve(l)
}

// Serve is used to serve connections from a listener
func (s *Server) Serve(l net.Listener) error {
	for {
		conn, err := l.Accept()
		if err != nil {
			return err
		}
		s.submit(func() {
			if err := s.ServeConn(conn); err != nil {
				s.logger.Errorf("server conn %v", err)
			}
		})
	}
}

// ServeConn is used to serve a single connection.
func (s *Server) ServeConn(conn net.Conn) error {
	var authContext *AuthContext

	defer conn.Close()

	bufConn := bufio.NewReader(conn)

	mr, err := statute.ParseMethodRequest(bufConn)
	if err != nil {
		return err
	}
	if mr.Ver != statute.VersionSocks5 {
		return statute.ErrNotSupportVersion
	}

	// Authenticate the connection
	authContext, err = s.authenticate(conn, bufConn, conn.RemoteAddr().String(), mr.Methods)
	if err != nil {
		return fmt.Errorf("failed to authenticate: %w", err)
	}

	// The client request detail
	request, err := ParseRequest(bufConn)
	if err != nil {
		if errors.Is(err, statute.ErrUnrecognizedAddrType) {
			if err := SendReply(conn, statute.RepAddrTypeNotSupported, nil); err != nil {
				return fmt.Errorf("failed to send reply %w", err)
			}
		}
		return fmt.Errorf("failed to read destination address, %w", err)
	}

	if request.Request.Command != statute.CommandConnect &&
		request.Request.Command != statute.CommandBind &&
		request.Request.Command != statute.CommandAssociate {
		if err := SendReply(conn, statute.RepCommandNotSupported, nil); err != nil {
			return fmt.Errorf("failed to send reply, %v", err)
		}
		return fmt.Errorf("unrecognized command[%d]", request.Request.Command)
	}

	request.AuthContext = authContext
	request.LocalAddr = conn.LocalAddr()
	request.RemoteAddr = conn.RemoteAddr()
	// Process the client request
	return s.handleRequest(conn, request)
}

// authenticate is used to handle connection authentication
func (s *Server) authenticate(conn io.Writer, bufConn io.Reader, userAddr string, methods []byte) (*AuthContext, error) {
	// Select a usable method
	for _, method := range methods {
		if cator, found := s.authMethods[method]; found {
			return cator.Authenticate(bufConn, conn, userAddr)
		}
	}
	// No usable method found
	conn.Write([]byte{statute.VersionSocks5, statute.MethodNoAcceptable}) // nolint: errcheck
	return nil, statute.ErrNoSupportedAuth
}

func (s *Server) submit(f func()) {
	if s.gPool == nil || s.gPool.Submit(f) != nil {
		go f()
	}
}