package command

import (
	"context"
	"errors"
	"fmt"
	"gitea.illuad.fr/adrien/middleman"
	"gitea.illuad.fr/adrien/middleman/flag"
	"github.com/rs/zerolog/log"
	"github.com/urfave/cli/v3"
	"golang.org/x/sync/errgroup"
	"net"
	"net/http"
	"net/http/httputil"
	"net/netip"
	"net/url"
	"regexp"
	"strings"
	"time"
)

// serve is the structure representing the command described below.
type serve struct {
	group *errgroup.Group
}

// addrPorts holds netip.AddrPort of different HTTP servers.
type addrPorts struct {
	srvAddrPort, healthAddrPort netip.AddrPort
}

// methodRegex maps HTTP methods (GET, POST, DELETE...) to a compiled regular expression.
type methodRegex = map[string]*regexp.Regexp

// ProxyHandler takes an incoming request and sends it to another server, proxying the response back to the client.
type ProxyHandler struct {
	rp *httputil.ReverseProxy
}

// ErrHTTPMethodNotAllowed is returned if the request's HTTP method is not allowed for this container.
type ErrHTTPMethodNotAllowed struct {
	httpMethod string
}

// ErrNoMatch is returned if the request's URL path is not allowed for this container.
type ErrNoMatch struct {
	path, httpMethod string
}

func (e ErrHTTPMethodNotAllowed) Error() string {
	return fmt.Sprintf("%s is not in the list of HTTP methods allowed this container", e.httpMethod)
}

func (e ErrNoMatch) Error() string {
	return fmt.Sprintf("%s does not match any registered regular expression for this HTTP method (%s)", e.path, e.httpMethod)
}

// ServeCmd is the command name.
const ServeCmd = "serve"

const (
	// listenAddrFlagName is the flag name used to set the listen address and port.
	listenAddrFlagName = "listen-addr"
	// dockerSocketPathFlagName is the flag name used to set the Docker unix socket path.
	dockerSocketPathFlagName = "docker-socket-path"
	// shutdownTimeoutFlagName is the flag name used to set the server shutdown timeout.
	shutdownTimeoutFlagName = "shutdown-timeout"
	// noDockerSocketHealthcheckFlagName is the flag name used to disable the Docker unix socket healthcheck.
	noDockerSocketHealthcheckFlagName = "no-docker-socket-healthcheck"
	// noShutdownFlagName is the flag name used to disable the application shutdown in case of Docker unix socket healthcheck failure.
	noShutdownFlagName = "no-shutdown"
	// healthcheckRetryFlagName is the flag name used to set the number of dial attempts with the Docker unix socket before the application shutdown (if enabled).
	healthcheckRetryFlagName = "healthcheck-retry"
	// healthEndpointFlagName is the flag name used to set the health endpoint.
	healthEndpointFlagName = "health-endpoint"
	// healthListenAddrFlagName is the flag name used to set the health endpoint listen address and port.
	healthListenAddrFlagName = "health-listen-addr"
	// addRequestsFlagName is the flag name used to add allowed requests.
	addRequestsFlagName = "add-requests"
)

const (
	// defaultListenAddr is the proxy default listen address and port.
	defaultListenAddr = "0.0.0.0:2375"
	// defaultDockerSocketPath is the default Docker socket path.
	defaultDockerSocketPath = "/var/run/docker.sock"
	// defaultShutdownTimeout is the default server shutdown timeout.
	defaultShutdownTimeout = 5 * time.Second
	// defaultHealthcheckRetry is the default number of healthcheck retry
	defaultHealthcheckRetry uint64 = 3
	// defaultHealthEndpoint is the default health endpoint.
	defaultHealthEndpoint = "/healthz"
	// defaultHealthListenAddr is the proxy health endpoint default listen address and port.
	defaultHealthListenAddr = "127.0.0.1:5732"
	// defaultAllowedRequest is the proxy default allowed request.
	defaultAllowedRequest = "^/(version|containers/.*|events.*)$"
)

var s serve

var (
	containerMethodRegex = map[string]methodRegex{
		"*": {
			http.MethodGet: regexp.MustCompile(defaultAllowedRequest),
		},
	}
	applicatorURLRegex = regexp.MustCompile(`^([a-zA-Z0-9][a-zA-Z0-9_.-]+)\(((?:(?:GET|HEAD|POST|PUT|PATCH|DELETE|CONNECT|TRACE|OPTIONS)(?:,(?:GET|HEAD|POST|PUT|PATCH|DELETE|CONNECT|TRACE|OPTIONS))*)?)\):(.*)$`)
	validHTTPMethods   = map[string]struct{}{
		http.MethodGet:     {},
		http.MethodHead:    {},
		http.MethodPost:    {},
		http.MethodPut:     {},
		http.MethodPatch:   {},
		http.MethodDelete:  {},
		http.MethodConnect: {},
		http.MethodTrace:   {},
		http.MethodOptions: {},
	}
	containerNameRegex = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9_.-]+`)
	httpMethodsRegex   = regexp.MustCompile(`(?:GET|HEAD|POST|PUT|PATCH|DELETE|CONNECT|TRACE|OPTIONS)(?:GET|HEAD|POST|PUT|PATCH|DELETE|CONNECT|TRACE|OPTIONS)*`)
)

// Serve describes the serve command.
func Serve(group *errgroup.Group) *cli.Command {
	s.group = group
	return &cli.Command{
		Name:        ServeCmd,
		Aliases:     middleman.PluckAlias(ServeCmd, ServeCmd),
		Usage:       "Runs serve mode",
		Description: "Proxy requests to the Docker socket using defined access control",
		Flags: []cli.Flag{
			listenAddr(),
			dockerSocketPath(),
			shutdownTimeout(),
			noDockerSocketHealthcheck(),
			noShutdown(),
			healthcheckRetry(),
			healthEndpoint(),
			healthListenAddr(),
			addRequests(),
			flag.LogFormat(ServeCmd),
			flag.LogLevel(ServeCmd),
		},
		Before:                    before,
		Action:                    s.action,
		DisableSliceFlagSeparator: true,
	}
}

func (ph *ProxyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	log.Debug().Str("remote_addr", r.RemoteAddr).Str("method", r.Method).Str("path", r.URL.Path).Msg("incoming request")
	mr, ok := containerMethodRegex["*"]
	if ok {
		var req *regexp.Regexp
		req, ok = mr[r.Method]
		if !ok {
			log.Error().
				Str("remote_addr", r.RemoteAddr).
				Str("method", r.Method).
				Str("path", r.URL.Path).
				Str("decision", "denied").
				Msg("this HTTP method is not in the list of those authorized for this container")
			http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
			return
		}
		if !req.MatchString(r.URL.Path) {
			log.Error().
				Str("remote_addr", r.RemoteAddr).
				Str("method", r.Method).
				Str("path", r.URL.Path).
				Str("decision", "denied").
				Msg("this path does not match any regular expression for this HTTP method")
			http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
			return
		}
		log.Info().
			Str("remote_addr", r.RemoteAddr).
			Str("method", r.Method).
			Str("path", r.URL.Path).
			Str("decision", "authorized").
			Msg("incoming request matches a registered regular expression")
		return
		/*
			if err := checkMethodPath(r, mr); err != nil {
				handleError(w, err)
				log.Err(err).Send()
				return
			}
		*/
	} else {
		var (
			containerName string
			host, _, _    = net.SplitHostPort(r.RemoteAddr)
			ip            = net.ParseIP(host)
		)
		for containerName, mr = range containerMethodRegex {
			resolvedIPs, err := net.LookupIP(containerName)
			if err != nil {
				// log.Warn().Err(err).Msg("this error may be transient due to the unavailability of one of the services")
				continue
			}
			for _, resolvedIP := range resolvedIPs {
				if resolvedIP.Equal(ip) {
					var req *regexp.Regexp
					req, ok = mr[r.Method]
					if !ok {
						log.Error().
							Str("remote_addr", r.RemoteAddr).
							Str("method", r.Method).
							Str("path", r.URL.Path).
							Str("decision", "denied").
							Msg("this HTTP method is not in the list of those authorized for this container")
						http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
						return
					}
					if !req.MatchString(r.URL.Path) {
						log.Error().
							Str("remote_addr", r.RemoteAddr).
							Str("method", r.Method).
							Str("path", r.URL.Path).
							Str("decision", "denied").
							Msg("this path does not match any regular expression for this HTTP method")
						http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
						return
					}
					/*
						if err = checkMethodPath(r, mr); err != nil {
							handleError(w, err)
							log.Err(err).Send()
							return
						}
					*/
					log.Info().
						Str("remote_addr", r.RemoteAddr).
						Str("method", r.Method).
						Str("path", r.URL.Path).
						Str("decision", "authorized").
						Str("from", containerName).
						Msg("incoming request matches a registered regular expression")
					ph.rp.ServeHTTP(w, r)
					return
				}
			}
		}
	}
	log.Warn().
		Str("remote_addr", r.RemoteAddr).
		Str("method", r.Method).
		Str("path", r.URL.Path).
		Str("decision", "denied").
		Msg("this error may be transient due to the unavailability of one of the services")
	http.Error(w, http.StatusText(http.StatusServiceUnavailable), http.StatusServiceUnavailable)
	return
}

// checkMethodPath executes the regular expression on the path of the HTTP request if and only if
// the latter's HTTP method is actually present in the list of authorized HTTP methods.
func checkMethodPath(r *http.Request, mr methodRegex) error {
	req, ok := mr[r.Method]
	if !ok {
		return ErrHTTPMethodNotAllowed{httpMethod: r.Method}
	}
	if !req.MatchString(r.URL.Path) {
		return ErrNoMatch{path: r.URL.Path, httpMethod: r.Method}
	}
	return nil
}

// action is executed when the ServeCmd command is called.
func (s serve) action(ctx context.Context, command *cli.Command) error {
	if err := ctx.Err(); err != nil {
		return err
	}
	ap, err := parseAddrPorts(command.String(listenAddrFlagName), command.String(healthListenAddrFlagName))
	if err != nil {
		return err
	}
	var l net.Listener
	l, err = net.Listen("tcp", ap.srvAddrPort.String())
	if err != nil {
		return err
	}
	dummyURL, _ := url.Parse("http://dummy")
	rp := httputil.NewSingleHostReverseProxy(dummyURL)
	rp.Transport = &http.Transport{
		DialContext: func(_ context.Context, _ string, _ string) (net.Conn, error) {
			return net.Dial("unix", command.String(dockerSocketPathFlagName))
		},
	}
	srv := &http.Server{ // #nosec: G112
		Handler: &ProxyHandler{rp: rp},
	}
	s.group.Go(func() error {
		if err = srv.Serve(l); err != nil && !errors.Is(err, http.ErrServerClosed) {
			return err
		}
		return nil
	})
	retry := command.Uint(healthcheckRetryFlagName)
	if !command.Bool(noDockerSocketHealthcheckFlagName) {
		ticker := time.Tick(2 * time.Second)
		s.group.Go(func() error {
		loop:
			for {
				if err = unixDial(command.String(dockerSocketPathFlagName)); err != nil {
					if !command.Bool(noShutdownFlagName) {
						if retry == 0 {
							return err
						}
						log.Err(err).Uint64("retry_remaining", retry).Send()
						retry--
					}
				}
				select {
				case <-ticker:
					continue
				case <-ctx.Done():
					break loop
				}
			}
			return ctx.Err()
		})
	}
	mux := http.NewServeMux()
	mux.HandleFunc(command.String(healthEndpointFlagName), func(w http.ResponseWriter, r *http.Request) {
		log.Trace().Str("from", r.RemoteAddr).Msg("incoming healthcheck request")
		if r.Method != http.MethodHead {
			w.WriteHeader(http.StatusMethodNotAllowed)
			return
		}
		if err = unixDial(command.String(dockerSocketPathFlagName)); err != nil {
			w.WriteHeader(http.StatusServiceUnavailable)
		}
	})
	healthSrv := http.Server{
		Addr:              ap.healthAddrPort.String(),
		Handler:           mux,
		ReadTimeout:       3 * time.Second,
		ReadHeaderTimeout: 3 * time.Second,
		WriteTimeout:      3 * time.Second,
	}
	s.group.Go(func() error {
		if err = healthSrv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			return err
		}
		return nil
	})
	log.Info().
		Stringer("listen_addr", ap.srvAddrPort).
		Str("docker_socket_path", command.String(dockerSocketPathFlagName)).
		Stringer("shutdown_timeout", command.Duration(shutdownTimeoutFlagName)).
		Bool("docker_socket_healthcheck_disabled", command.Bool(noDockerSocketHealthcheckFlagName)).
		Bool("shutdown_on_failure_disabled", command.Bool(noShutdownFlagName)).
		Uint64("number_of_healthcheck_retry", command.Uint(healthcheckRetryFlagName)).
		Str("health_endpoint", command.String(healthEndpointFlagName)).
		Stringer("health_endpoint_listen_addr", ap.healthAddrPort).
		Strs("requests", command.StringSlice(addRequestsFlagName)).
		Str("log_format", command.String(flag.LogFormatFlagName)).
		Str("log_level", command.String(flag.LogLevelFlagName)).
		Msg("middleman started")
	<-ctx.Done()
	shutdownCtx, cancel := context.WithTimeout(context.Background(), command.Duration(shutdownTimeoutFlagName))
	defer cancel()
	if err = healthSrv.Close(); err != nil {
		log.Err(err).Send()
	}
	return srv.Shutdown(shutdownCtx)
}

func parseAddrPorts(srvAddrPort, healthAddrPort string) (addrPorts, error) {
	var ap addrPorts
	if err := parseAddrPort(srvAddrPort, &ap.srvAddrPort); err != nil {
		return ap, err
	}
	return ap, parseAddrPort(healthAddrPort, &ap.healthAddrPort)
}

func parseAddrPort(addrPortStr string, addrPort *netip.AddrPort) error {
	ap, err := netip.ParseAddrPort(addrPortStr)
	if err != nil {
		return err
	}
	*addrPort = ap
	return nil
}

func unixDial(socketPath string) error {
	conn, err := net.DialTimeout("unix", socketPath, 3*time.Second)
	if err != nil {
		return err
	}
	return conn.Close()
}

func listenAddr() cli.Flag {
	return &cli.StringFlag{
		Name:     listenAddrFlagName,
		Category: "network",
		Usage:    "proxy listen address",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, listenAddrFlagName),
		Value:    defaultListenAddr,
		Aliases:  middleman.PluckAlias(ServeCmd, listenAddrFlagName),
	}
}

func dockerSocketPath() cli.Flag {
	return &cli.StringFlag{
		Name:     dockerSocketPathFlagName,
		Category: "docker",
		Usage:    "Docker unix socket path",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, dockerSocketPathFlagName),
		Value:    defaultDockerSocketPath,
		Aliases:  middleman.PluckAlias(ServeCmd, dockerSocketPathFlagName),
	}
}

func shutdownTimeout() cli.Flag {
	return &cli.DurationFlag{
		Name:     shutdownTimeoutFlagName,
		Category: "network",
		Usage:    "server shutdown timeout",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, shutdownTimeoutFlagName),
		Value:    defaultShutdownTimeout,
		Aliases:  middleman.PluckAlias(ServeCmd, shutdownTimeoutFlagName),
	}
}

func noDockerSocketHealthcheck() cli.Flag {
	return &cli.BoolFlag{
		Name:        noDockerSocketHealthcheckFlagName,
		Category:    "docker",
		HideDefault: true,
		Usage:       "disable Docker unix socket healthcheck",
		Sources:     middleman.PluckEnvVar(EnvVarPrefix, noDockerSocketHealthcheckFlagName),
		Aliases:     middleman.PluckAlias(ServeCmd, noDockerSocketHealthcheckFlagName),
	}
}

func noShutdown() cli.Flag {
	return &cli.BoolFlag{
		Name:        noShutdownFlagName,
		Category:    "internal monitoring behavior",
		HideDefault: true,
		Usage:       "disable application shutdown in case of Docker unix socket healthcheck failure",
		Sources:     middleman.PluckEnvVar(EnvVarPrefix, noShutdownFlagName),
		Aliases:     middleman.PluckAlias(ServeCmd, noShutdownFlagName),
	}
}

func healthcheckRetry() cli.Flag {
	return &cli.UintFlag{
		Name:     healthcheckRetryFlagName,
		Category: "internal monitoring behavior",
		Usage:    "number of dial attempts with the Docker unix socket before the application shutdown (if enabled)",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, healthcheckRetryFlagName),
		Value:    defaultHealthcheckRetry,
		Aliases:  middleman.PluckAlias(ServeCmd, healthcheckRetryFlagName),
	}
}

func healthEndpoint() cli.Flag {
	return &cli.StringFlag{
		Name:     healthEndpointFlagName,
		Category: "monitoring",
		Usage:    "health endpoint",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, healthEndpointFlagName),
		Value:    defaultHealthEndpoint,
		Aliases:  middleman.PluckAlias(ServeCmd, healthEndpointFlagName),
	}
}

func healthListenAddr() cli.Flag {
	return &cli.StringFlag{
		Name:     healthListenAddrFlagName,
		Category: "monitoring",
		Usage:    "proxy health endpoint listen address",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, healthListenAddrFlagName),
		Value:    defaultHealthListenAddr,
		Aliases:  middleman.PluckAlias(ServeCmd, healthListenAddrFlagName),
	}
}

func addRequests() cli.Flag {
	return &cli.StringSliceFlag{
		Name:     addRequestsFlagName,
		Category: "network",
		Usage:    "add requests",
		Sources:  middleman.PluckEnvVar(EnvVarPrefix, addRequestsFlagName),
		// Local:    true, // Required to trigger the Action when this flag is set via the environment variable, see https://github.com/urfave/cli/issues/2041.
		Value:   []string{"*:" + defaultAllowedRequest},
		Aliases: middleman.PluckAlias(ServeCmd, addRequestsFlagName),
		Action: func(ctx context.Context, command *cli.Command, requests []string) error {
			clear(containerMethodRegex)
			for _, request := range requests {
				// An applicator is a container name/HTTP method pair e.g., nginx(GET).
				// The following regex extracts this applicator and the associated URL regex.
				aur := applicatorURLRegex.FindString(request)
				if aur == "" {
					// If we are here, it means that user set a wildcard (kinda) applicator e.g., GET,POST:URL_REGEX.
					// In its extended form, this applicator can be read as follows: *(GET,POST):URL_REGEX.
					methods, urlRegex, ok := strings.Cut(request, ":")
					if !ok { // || methods == ""?
						return errors.New("HTTP method(s) must be specified before ':'")
					}
					if err := registerMethodRegex("*", urlRegex, strings.Split(methods, ",")); err != nil {
						return err
					}
				}
				applicator, urlRegex, _ := strings.Cut(aur, ":")
				if err := registerMethodRegex(containerNameRegex.FindString(applicator), urlRegex, httpMethodsRegex.FindAllString(applicator, -1)); err != nil {
					return err
				}
			}
			return nil
		},
	}
}

func registerMethodRegex(containerName, urlRegex string, httpMethods []string) error {
	r, err := regexp.Compile(urlRegex)
	if err != nil {
		return err
	}
	for _, httpMethod := range httpMethods {
		if _, ok := validHTTPMethods[httpMethod]; !ok {
			return fmt.Errorf("%s is not a valid HTTP method", httpMethod)
		}
		if containerMethodRegex[containerName] == nil {
			containerMethodRegex[containerName] = make(methodRegex)
		}
		containerMethodRegex[containerName][httpMethod] = r
	}
	return nil
}

func handleError(w http.ResponseWriter, err error) {
	var methodNotAllowedErr ErrHTTPMethodNotAllowed
	var noMatchErr ErrNoMatch
	if errors.As(err, &methodNotAllowedErr) {
		http.Error(w, err.Error(), http.StatusMethodNotAllowed)
	} else if errors.As(err, &noMatchErr) {
		http.Error(w, err.Error(), http.StatusForbidden)
	} else {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}