package server

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"github.com/docker/docker/api/types"
	"github.com/docker/docker/api/types/container"
	"github.com/docker/docker/api/types/mount"
	"github.com/docker/docker/client"
	"github.com/docker/docker/daemon/logger/jsonfilelog"
	"github.com/docker/go-connections/nat"
	"github.com/pkg/errors"
	"github.com/pterodactyl/wings/api"
	"go.uber.org/zap"
	"io"
	"os"
	"strconv"
	"strings"
	"time"
)

// Defines the base environment for Docker instances running through Wings.
type DockerEnvironment struct {
	Server *Server

	// The user ID that containers should be running as.
	User int

	// Defines the configuration for the Docker instance that will allow us to connect
	// and create and modify containers.
	TimezonePath string

	// The Docker client being used for this instance.
	Client *client.Client

	// Tracks if we are currently attached to the server container. This allows us to attach
	// once and then just use that attachment to stream logs out of the server and also stream
	// commands back into it without constantly attaching and detaching.
	attached bool

	// Controls the hijacked response stream which exists only when we're attached to
	// the running container instance.
	stream types.HijackedResponse

	// Holds the stats stream used by the polling commands so that we can easily close
	// it out.
	stats io.ReadCloser
}

// Creates a new base Docker environment. A server must still be attached to it.
func NewDockerEnvironment(opts ...func(*DockerEnvironment)) (*DockerEnvironment, error) {
	cli, err := client.NewClientWithOpts(client.FromEnv)
	if err != nil {
		return nil, err
	}

	env := &DockerEnvironment{
		User:   1000,
		Client: cli,
	}

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

	return env, nil
}

// Ensure that the Docker environment is always implementing all of the methods
// from the base environment interface.
var _ Environment = (*DockerEnvironment)(nil)

// Returns the name of the environment.
func (d *DockerEnvironment) Type() string {
	return "docker"
}

// Determines if the container exists in this environment.
func (d *DockerEnvironment) Exists() (bool, error) {
	_, err := d.Client.ContainerInspect(context.Background(), d.Server.Uuid)

	if err != nil {
		// If this error is because the container instance wasn't found via Docker we
		// can safely ignore the error and just return false.
		if client.IsErrNotFound(err) {
			return false, nil
		}

		return false, err
	}

	return true, nil
}

// Determines if the server's docker container is currently running. If there is no container
// present, an error will be raised (since this shouldn't be a case that ever happens under
// correctly developed circumstances).
//
// You can confirm if the instance wasn't found by using client.IsErrNotFound from the Docker
// API.
//
// @see docker/client/errors.go
func (d *DockerEnvironment) IsRunning() (bool, error) {
	ctx := context.Background()

	c, err := d.Client.ContainerInspect(ctx, d.Server.Uuid)
	if err != nil {
		return false, err
	}

	return c.State.Running, nil
}

// Performs an in-place update of the Docker container's resource limits without actually
// making any changes to the operational state of the container. This allows memory, cpu,
// and IO limitations to be adjusted on the fly for individual instances.
func (d *DockerEnvironment) InSituUpdate() error {
	if _, err := d.Client.ContainerInspect(context.Background(), d.Server.Uuid); err != nil {
		// If the container doesn't exist for some reason there really isn't anything
		// we can do to fix that in this process (it doesn't make sense at least). In those
		// cases just return without doing anything since we still want to save the configuration
		// to the disk.
		//
		// We'll let a boot process make modifications to the container if needed at this point.
		if client.IsErrNotFound(err) {
			return nil
		}

		return errors.WithStack(err)
	}

	u := container.UpdateConfig{
		Resources: d.getResourcesForServer(),
	}

	if _, err := d.Client.ContainerUpdate(context.Background(), d.Server.Uuid, u); err != nil {
		return errors.WithStack(err)
	}

	return nil
}

// Run before the container starts and get the process configuration from the Panel.
// This is important since we use this to check configuration files as well as ensure
// we always have the latest version of an egg available for server processes.
//
// This process will also confirm that the server environment exists and is in a bootable
// state. This ensures that unexpected container deletion while Wings is running does
// not result in the server becoming unbootable.
func (d *DockerEnvironment) OnBeforeStart() error {
	zap.S().Infow("syncing server configuration with Panel", zap.String("server", d.Server.Uuid))
	if err := d.Server.Sync(); err != nil {
		return err
	}

	// Always destroy and re-create the server container to ensure that synced data from
	// the Panel is used.
	if err := d.Client.ContainerRemove(context.Background(), d.Server.Uuid, types.ContainerRemoveOptions{RemoveVolumes: true}); err != nil {
		if !client.IsErrNotFound(err) {
			return err
		}
	}

	// The Create() function will check if the container exists in the first place, and if
	// so just silently return without an error. Otherwise, it will try to create the necessary
	// container and data storage directory.
	//
	// This won't actually run an installation process however, it is just here to ensure the
	// environment gets created properly if it is missing and the server is started. We're making
	// an assumption that all of the files will still exist at this point.
	if err := d.Create(); err != nil {
		return err
	}

	return nil
}

// Starts the server environment and begins piping output to the event listeners for the
// console. If a container does not exist, or needs to be rebuilt that will happen in the
// call to OnBeforeStart().
func (d *DockerEnvironment) Start() error {
	sawError := false
	// If sawError is set to true there was an error somewhere in the pipeline that
	// got passed up, but we also want to ensure we set the server to be offline at
	// that point.
	defer func() {
		if sawError {
			d.Server.SetState(ProcessOfflineState)
		}
	}()

	// If the server is suspended the user shouldn't be able to boot it, in those cases
	// return a suspension error and let the calling area handle the issue.
	//
	// Theoretically you'd have the Panel handle all of this logic, but we cannot do that
	// because we allow the websocket to control the server power state as well, so we'll
	// need to handle that action in here.
	if d.Server.Suspended {
		return &suspendedError{}
	}

	c, err := d.Client.ContainerInspect(context.Background(), d.Server.Uuid)
	if err != nil && !client.IsErrNotFound(err) {
		return errors.WithStack(err)
	}

	// No reason to try starting a container that is already running.
	if c.State.Running {
		d.Server.SetState(ProcessRunningState)
		if !d.attached {
			return d.Attach()
		}

		return nil
	}

	d.Server.SetState(ProcessStartingState)
	// Set this to true for now, we will set it to false once we reach the
	// end of this chain.
	sawError = true

	// Run the before start function and wait for it to finish. This will validate that the container
	// exists on the system, and rebuild the container if that is required for server booting to
	// occur.
	if err := d.OnBeforeStart(); err != nil {
		return errors.WithStack(err)
	}

	// Truncate the log file so we don't end up outputting a bunch of useless log information
	// to the websocket and whatnot. Check first that the path and file exist before trying
	// to truncate them.
	if _, err := os.Stat(c.LogPath); err == nil {
		if err := os.Truncate(c.LogPath, 0); err != nil {
			return errors.WithStack(err)
		}
	}

	// Update the configuration files defined for the server before beginning the boot process.
	// This process executes a bunch of parallel updates, so we just block until that process
	// is completed. Any errors as a result of this will just be bubbled out in the logger,
	// we don't need to actively do anything about it at this point, worst comes to worst the
	// server starts in a weird state and the user can manually adjust.
	d.Server.UpdateConfigurationFiles()

	// Reset the permissions on files for the server before actually trying
	// to start it.
	if err := d.Server.Filesystem.Chown("/"); err != nil {
		return errors.WithStack(err)
	}

	opts := types.ContainerStartOptions{}
	if err := d.Client.ContainerStart(context.Background(), d.Server.Uuid, opts); err != nil {
		return errors.WithStack(err)
	}

	// No errors, good to continue through.
	sawError = false

	return d.Attach()
}

// Stops the container that the server is running in. This will allow up to 10
// seconds to pass before a failure occurs.
func (d *DockerEnvironment) Stop() error {
	stop := d.Server.processConfiguration.Stop
	if stop.Type == api.ProcessStopSignal {
		return d.Terminate(os.Kill)
	}

	d.Server.SetState(ProcessStoppingState)
	if stop.Type == api.ProcessStopCommand {
		return d.SendCommand(stop.Value)
	}

	t := time.Second * 10

	return d.Client.ContainerStop(context.Background(), d.Server.Uuid, &t)
}

// Forcefully terminates the container using the signal passed through.
func (d *DockerEnvironment) Terminate(signal os.Signal) error {
	ctx := context.Background()

	c, err := d.Client.ContainerInspect(ctx, d.Server.Uuid)
	if err != nil {
		return errors.WithStack(err)
	}

	if !c.State.Running {
		return nil
	}

	d.Server.SetState(ProcessStoppingState)

	return d.Client.ContainerKill(
		ctx, d.Server.Uuid, strings.TrimSuffix(strings.TrimPrefix(signal.String(), "signal "), "ed"),
	)
}

// Remove the Docker container from the machine. If the container is currently running
// it will be forcibly stopped by Docker.
func (d *DockerEnvironment) Destroy() error {
	ctx := context.Background()

	return d.Client.ContainerRemove(ctx, d.Server.Uuid, types.ContainerRemoveOptions{
		RemoveVolumes: true,
		RemoveLinks:   false,
		Force:         true,
	})
}

// Determine the container exit state and return the exit code and wether or not
// the container was killed by the OOM killer.
func (d *DockerEnvironment) ExitState() (uint32, bool, error) {
	c, err := d.Client.ContainerInspect(context.Background(), d.Server.Uuid)
	if err != nil {
		return 0, false, errors.WithStack(err)
	}

	return uint32(c.State.ExitCode), c.State.OOMKilled, nil
}

// Attaches to the docker container itself and ensures that we can pipe data in and out
// of the process stream. This should not be used for reading console data as you *will*
// miss important output at the beginning because of the time delay with attaching to the
// output.
func (d *DockerEnvironment) Attach() error {
	if d.attached {
		return nil
	}

	if err := d.FollowConsoleOutput(); err != nil {
		return errors.WithStack(err)
	}

	ctx := context.Background()

	var err error
	d.stream, err = d.Client.ContainerAttach(ctx, d.Server.Uuid, types.ContainerAttachOptions{
		Stdin:  true,
		Stdout: true,
		Stderr: true,
		Stream: true,
	})

	if err != nil {
		return errors.WithStack(err)
	}

	console := Console{
		Server: d.Server,
	}

	d.EnableResourcePolling()
	d.attached = true

	go func() {
		defer d.stream.Close()
		defer func() {
			d.Server.SetState(ProcessOfflineState)
			d.attached = false
		}()

		io.Copy(console, d.stream.Reader)
	}()

	return nil
}

// Attaches to the log for the container. This avoids us missing cruicial output that
// happens in the split seconds before the code moves from 'Starting' to 'Attaching'
// on the process.
func (d *DockerEnvironment) FollowConsoleOutput() error {
	if exists, err := d.Exists(); !exists {
		if err != nil {
			return errors.WithStack(err)
		}

		return errors.New(fmt.Sprintf("no such container: %s", d.Server.Uuid))
	}

	ctx := context.Background()
	opts := types.ContainerLogsOptions{
		ShowStderr: true,
		ShowStdout: true,
		Follow:     true,
		Since:      time.Now().Format(time.RFC3339),
	}

	reader, err := d.Client.ContainerLogs(ctx, d.Server.Uuid, opts)

	go func(r io.ReadCloser) {
		defer r.Close()

		s := bufio.NewScanner(r)
		for s.Scan() {
			d.Server.Emit(ConsoleOutputEvent, s.Text())
		}

		if err := s.Err(); err != nil {
			zap.S().Warnw("error processing scanner line in console output", zap.String("server", d.Server.Uuid), zap.Error(err))
		}
	}(reader)

	return errors.WithStack(err)
}

// Enables resource polling on the docker instance. Except we aren't actually polling Docker for this
// information, instead just sit there with an async process that lets Docker stream all of this data
// to us automatically.
func (d *DockerEnvironment) EnableResourcePolling() error {
	if d.Server.State == ProcessOfflineState {
		return errors.New("cannot enable resource polling on a server that is not running")
	}

	ctx := context.Background()

	stats, err := d.Client.ContainerStats(ctx, d.Server.Uuid, true)
	if err != nil {
		return errors.WithStack(err)
	}
	d.stats = stats.Body

	dec := json.NewDecoder(d.stats)
	go func(s *Server) {
		for {
			var v *types.StatsJSON

			if err := dec.Decode(&v); err != nil {
				zap.S().Warnw("encountered error processing server stats; stopping collection", zap.Error(err))
				d.DisableResourcePolling()
				return
			}

			// Disable collection if the server is in an offline state and this process is
			// still running.
			if s.State == ProcessOfflineState {
				d.DisableResourcePolling()
				return
			}

			s.Resources.CpuAbsolute = s.Resources.CalculateAbsoluteCpu(&v.PreCPUStats, &v.CPUStats)
			s.Resources.Memory = v.MemoryStats.Usage
			s.Resources.MemoryLimit = v.MemoryStats.Limit

			// Why you ask? This already has the logic for caching disk space in use and then
			// also handles pushing that value to the resources object automatically.
			s.Filesystem.HasSpaceAvailable()

			for _, nw := range v.Networks {
				s.Resources.Network.RxBytes += nw.RxBytes
				s.Resources.Network.TxBytes += nw.TxBytes
			}

			b, _ := json.Marshal(s.Resources)
			s.Emit(StatsEvent, string(b))
		}
	}(d.Server)

	return nil
}

// Closes the stats stream for a server process.
func (d *DockerEnvironment) DisableResourcePolling() error {
	if d.stats == nil {
		return nil
	}

	err := d.stats.Close()

	d.Server.Resources.CpuAbsolute = 0
	d.Server.Resources.Memory = 0
	d.Server.Resources.Network.TxBytes = 0
	d.Server.Resources.Network.RxBytes = 0

	return errors.WithStack(err)
}

// Pulls the image from Docker.
//
// @todo handle authorization & local images
func (d *DockerEnvironment) ensureImageExists(c *client.Client) error {
	out, err := c.ImagePull(context.Background(), d.Server.Container.Image, types.ImagePullOptions{All: false})
	if err != nil {
		return err
	}
	defer out.Close()

	zap.S().Debugw("pulling docker image... this could take a bit of time", zap.String("image", d.Server.Container.Image))

	// I'm not sure what the best approach here is, but this will block execution until the image
	// is done being pulled, which is what we need.
	scanner := bufio.NewScanner(out)
	for scanner.Scan() {
		continue
	}

	if err := scanner.Err(); err != nil {
		return err
	}

	return nil
}

// Creates a new container for the server using all of the data that is currently
// available for it. If the container already exists it will be returned.
//
// @todo pull the image being requested if it doesn't exist currently.
func (d *DockerEnvironment) Create() error {
	ctx := context.Background()
	cli, err := client.NewClientWithOpts(client.FromEnv)
	if err != nil {
		return errors.WithStack(err)
	}

	// Ensure the data directory exists before getting too far through this process.
	if err := d.Server.Filesystem.EnsureDataDirectory(); err != nil {
		return errors.WithStack(err)
	}

	// If the container already exists don't hit the user with an error, just return
	// the current information about it which is what we would do when creating the
	// container anyways.
	if _, err := cli.ContainerInspect(ctx, d.Server.Uuid); err == nil {
		return nil
	} else if !client.IsErrNotFound(err) {
		return errors.WithStack(err)
	}

	// Try to pull the requested image before creating the container.
	if err := d.ensureImageExists(cli); err != nil {
		return errors.WithStack(err)
	}

	conf := &container.Config{
		Hostname:     "container",
		User:         strconv.Itoa(d.User),
		AttachStdin:  true,
		AttachStdout: true,
		AttachStderr: true,
		OpenStdin:    true,
		Tty:          true,

		ExposedPorts: d.exposedPorts(),

		Image: d.Server.Container.Image,
		Env:   d.environmentVariables(),

		Labels: map[string]string{
			"Service": "Pterodactyl",
		},
	}

	hostConf := &container.HostConfig{
		PortBindings: d.portBindings(),

		// Configure the mounts for this container. First mount the server data directory
		// into the container as a r/w bind. Additionally mount the host timezone data into
		// the container as a readonly bind so that software running in the container uses
		// the same time as the host system.
		Mounts: []mount.Mount{
			{
				Target:   "/home/container",
				Source:   d.Server.Filesystem.Path(),
				Type:     mount.TypeBind,
				ReadOnly: false,
			},
			{
				Target:   d.TimezonePath,
				Source:   d.TimezonePath,
				Type:     mount.TypeBind,
				ReadOnly: true,
			},
		},

		// Configure the /tmp folder mapping in containers. This is necessary for some
		// games that need to make use of it for downloads and other installation processes.
		Tmpfs: map[string]string{
			"/tmp": "rw,exec,nosuid,size=50M",
		},

		// Define resource limits for the container based on the data passed through
		// from the Panel.
		Resources: d.getResourcesForServer(),

		// @todo make this configurable again
		DNS: []string{"1.1.1.1", "8.8.8.8"},

		// Configure logging for the container to make it easier on the Daemon to grab
		// the server output. Ensure that we don't use too much space on the host machine
		// since we only need it for the last few hundred lines of output and don't care
		// about anything else in it.
		LogConfig: container.LogConfig{
			Type: jsonfilelog.Name,
			Config: map[string]string{
				"max-size": "5m",
				"max-file": "1",
			},
		},

		SecurityOpt:    []string{"no-new-privileges"},
		ReadonlyRootfs: true,
		CapDrop: []string{
			"setpcap", "mknod", "audit_write", "net_raw", "dac_override",
			"fowner", "fsetid", "net_bind_service", "sys_chroot", "setfcap",
		},
		NetworkMode: "pterodactyl_nw",
	}

	if _, err := cli.ContainerCreate(ctx, conf, hostConf, nil, d.Server.Uuid); err != nil {
		return errors.WithStack(err)
	}

	return nil
}

// Sends the specified command to the stdin of the running container instance. There is no
// confirmation that this data is sent successfully, only that it gets pushed into the stdin.
func (d *DockerEnvironment) SendCommand(c string) error {
	if !d.attached {
		return errors.New("attempting to send command to non-attached instance")
	}

	_, err := d.stream.Conn.Write([]byte(c + "\n"))

	return errors.WithStack(err)
}

// Reads the log file for the server. This does not care if the server is running or not, it will
// simply try to read the last X bytes of the file and return them.
func (d *DockerEnvironment) Readlog(len int64) ([]string, error) {
	ctx := context.Background()

	j, err := d.Client.ContainerInspect(ctx, d.Server.Uuid)
	if err != nil {
		return nil, err
	}

	if j.LogPath == "" {
		return nil, errors.New("empty log path defined for server")
	}

	f, err := os.Open(j.LogPath)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	// Check if the length of the file is smaller than the amount of data that was requested
	// for reading. If so, adjust the length to be the total length of the file. If this is not
	// done an error is thrown since we're reading backwards, and not forwards.
	if stat, err := os.Stat(j.LogPath); err != nil {
		return nil, err
	} else if stat.Size() < len {
		len = stat.Size()
	}

	// Seed to the end of the file and then move backwards until the length is met to avoid
	// reading the entirety of the file into memory.
	if _, err := f.Seek(-len, io.SeekEnd); err != nil {
		return nil, err
	}

	b := make([]byte, len)

	if _, err := f.Read(b); err != nil && err != io.EOF {
		return nil, err
	}

	return d.parseLogToStrings(b)
}

type dockerLogLine struct {
	Log string `json:"log"`
}

// Docker stores the logs for server output in a JSON format. This function will iterate over the JSON
// that was read from the log file and parse it into a more human readable format.
func (d *DockerEnvironment) parseLogToStrings(b []byte) ([]string, error) {
	var hasError = false
	var out []string

	scanner := bufio.NewScanner(bytes.NewReader(b))
	for scanner.Scan() {
		var l dockerLogLine
		// Unmarshal the contents and allow up to a single error before bailing out of the process. We
		// do this because if you're arbitrarily reading a length of the file you'll likely end up
		// with the first line in the output being improperly formatted JSON. In those cases we want to
		// just skip over it. However if we see another error we're going to bail out because that is an
		// abnormal situation.
		if err := json.Unmarshal([]byte(scanner.Text()), &l); err != nil {
			if hasError {
				return nil, err
			}

			hasError = true
			continue
		}

		out = append(out, l.Log)
	}

	return out, nil
}

// Returns the environment variables for a server in KEY="VALUE" form.
func (d *DockerEnvironment) environmentVariables() []string {
	var out = []string{
		fmt.Sprintf("STARTUP=%s", d.Server.Invocation),
		fmt.Sprintf("SERVER_MEMORY=%d", d.Server.Build.MemoryLimit),
		fmt.Sprintf("SERVER_IP=%s", d.Server.Allocations.DefaultMapping.Ip),
		fmt.Sprintf("SERVER_PORT=%d", d.Server.Allocations.DefaultMapping.Port),
	}

eloop:
	for k, v := range d.Server.EnvVars {
		for _, e := range out {
			if strings.HasPrefix(e, strings.ToUpper(k)) {
				continue eloop
			}
		}

		out = append(out, fmt.Sprintf("%s=\"%s\"", strings.ToUpper(k), v))
	}

	return out
}

func (d *DockerEnvironment) volumes() map[string]struct{} {
	return nil
}

// Converts the server allocation mappings into a format that can be understood
// by Docker.
func (d *DockerEnvironment) portBindings() nat.PortMap {
	var out = nat.PortMap{}

	for ip, ports := range d.Server.Allocations.Mappings {
		for _, port := range ports {
			// Skip over invalid ports.
			if port < 0 || port > 65535 {
				continue
			}

			binding := []nat.PortBinding{
				{
					HostIP:   ip,
					HostPort: strconv.Itoa(port),
				},
			}

			out[nat.Port(fmt.Sprintf("%d/tcp", port))] = binding
			out[nat.Port(fmt.Sprintf("%d/udp", port))] = binding
		}
	}

	return out
}

// Converts the server allocation mappings into a PortSet that can be understood
// by Docker. This formatting is slightly different than portBindings as it should
// return an empty struct rather than a binding.
//
// To accomplish this, we'll just get the values from portBindings and then set them
// to empty structs. Because why not.
func (d *DockerEnvironment) exposedPorts() nat.PortSet {
	var out = nat.PortSet{}

	for port := range d.portBindings() {
		out[port] = struct{}{}
	}

	return out
}

// Formats the resources available to a server instance in such as way that Docker will
// generate a matching environment in the container.
func (d *DockerEnvironment) getResourcesForServer() container.Resources {
	return container.Resources{
		// @todo memory limit should be slightly higher than the reservation
		Memory:            d.Server.Build.MemoryLimit * 1000000,
		MemoryReservation: d.Server.Build.MemoryLimit * 1000000,
		MemorySwap:        d.Server.Build.ConvertedSwap(),
		CPUQuota:          d.Server.Build.ConvertedCpuLimit(),
		CPUPeriod:         100000,
		CPUShares:         1024,
		BlkioWeight:       d.Server.Build.IoWeight,
		OomKillDisable:    &d.Server.Container.OomDisabled,
	}
}