package parent

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/rootless-containers/rootlesskit/v3/pkg/api"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port/builtin/msg"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port/builtin/opaque"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port/builtin/parent/tcp"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port/builtin/parent/udp"
	"github.com/rootless-containers/rootlesskit/v3/pkg/port/portutil"
)

// NewDriver for builtin driver.
func NewDriver(logWriter io.Writer, stateDir string, sourceIPTransparent bool) (port.ParentDriver, error) {
	// TODO: consider using socketpair FD instead of socket file
	socketPath := filepath.Join(stateDir, ".bp.sock")
	childReadyPipePath := filepath.Join(stateDir, ".bp-ready.pipe")
	// remove the path just in case the previous rootlesskit instance crashed
	if err := os.RemoveAll(childReadyPipePath); err != nil {
		return nil, fmt.Errorf("cannot remove %s: %w", childReadyPipePath, err)
	}
	if err := syscall.Mkfifo(childReadyPipePath, 0600); err != nil {
		return nil, fmt.Errorf("cannot mkfifo %s: %w", childReadyPipePath, err)
	}
	d := driver{
		logWriter:           logWriter,
		socketPath:          socketPath,
		childReadyPipePath:  childReadyPipePath,
		sourceIPTransparent: sourceIPTransparent,
		ports:               make(map[int]*port.Status, 0),
		stoppers:            make(map[int]func(context.Context) error, 0),
		nextID:              1,
	}
	return &d, nil
}

type driver struct {
	logWriter           io.Writer
	socketPath          string
	childReadyPipePath  string
	sourceIPTransparent bool
	mu                  sync.Mutex
	ports               map[int]*port.Status
	stoppers            map[int]func(context.Context) error
	nextID              int
}

func (d *driver) Info(ctx context.Context) (*api.PortDriverInfo, error) {
	info := &api.PortDriverInfo{
		Driver:                  "builtin",
		Protos:                  []string{"tcp", "tcp4", "tcp6", "udp", "udp4", "udp6"},
		DisallowLoopbackChildIP: false,
	}
	return info, nil
}

func (d *driver) OpaqueForChild() map[string]string {
	m := map[string]string{
		opaque.SocketPath:         d.socketPath,
		opaque.ChildReadyPipePath: d.childReadyPipePath,
	}
	if d.sourceIPTransparent {
		m[opaque.SourceIPTransparent] = "true"
	}
	return m
}

func (d *driver) RunParentDriver(initComplete chan struct{}, quit <-chan struct{}, _ *port.ChildContext) error {
	childReadyPipeR, err := os.OpenFile(d.childReadyPipePath, os.O_RDONLY, os.ModeNamedPipe)
	if err != nil {
		return err
	}
	if _, err = io.ReadAll(childReadyPipeR); err != nil {
		return err
	}
	childReadyPipeR.Close()
	var dialer net.Dialer
	conn, err := dialer.Dial("unix", d.socketPath)
	if err != nil {
		return err
	}
	err = msg.Initiate(conn.(*net.UnixConn))
	conn.Close()
	if err != nil {
		return err
	}
	initComplete <- struct{}{}
	<-quit
	return nil
}

func isEPERM(err error) bool {
	k := "permission denied"
	// As of Go 1.14, errors.Is(err, syscall.EPERM) does not seem to work for
	// "listen tcp 0.0.0.0:80: bind: permission denied" error from net.ListenTCP().
	return errors.Is(err, syscall.EPERM) || strings.Contains(err.Error(), k)
}

// annotateEPERM annotates origErr for human-readability
func annotateEPERM(origErr error, spec port.Spec) error {
	// Read "net.ipv4.ip_unprivileged_port_start" value (typically 1024)
	// TODO: what for IPv6?
	// NOTE: sync.Once should not be used here
	b, e := os.ReadFile("/proc/sys/net/ipv4/ip_unprivileged_port_start")
	if e != nil {
		return origErr
	}
	start, e := strconv.Atoi(strings.TrimSpace(string(b)))
	if e != nil {
		return origErr
	}
	if spec.ParentPort >= start {
		// origErr is unrelated to ip_unprivileged_port_start
		return origErr
	}
	text := fmt.Sprintf("cannot expose privileged port %d, you can add 'net.ipv4.ip_unprivileged_port_start=%d' to /etc/sysctl.conf (currently %d)", spec.ParentPort, spec.ParentPort, start)
	if filepath.Base(os.Args[0]) == "rootlesskit" {
		// NOTE: The following sentence is appended only if Args[0] == "rootlesskit", because it does not apply to Podman (as of Podman v1.9).
		// Podman launches the parent driver in the child user namespace (but in the parent network namespace), which disables the file capability.
		text += ", or set CAP_NET_BIND_SERVICE on rootlesskit binary"
	}
	text += fmt.Sprintf(", or choose a larger port number (>= %d)", start)
	return fmt.Errorf(text+": %w", origErr)
}

func (d *driver) AddPort(ctx context.Context, spec port.Spec) (*port.Status, error) {
	d.mu.Lock()
	err := portutil.ValidatePortSpec(spec, d.ports)
	d.mu.Unlock()
	if err != nil {
		return nil, err
	}
	// NOTE: routineStopCh is close-only channel. Do not send any data.
	// See commit 4803f18fae1e39d200d98f09e445a97ccd6f5526 `Revert "port/builtin: RemovePort() block until conn is closed"`
	routineStopCh := make(chan struct{})
	routineStoppedCh := make(chan error)
	routineStop := func(ctx context.Context) error {
		close(routineStopCh)
		select {
		case stoppedResult, stoppedResultOk := <-routineStoppedCh:
			if stoppedResultOk {
				return stoppedResult
			}
			return errors.New("routineStoppedCh was closed without sending data?")
		case <-ctx.Done():
			return fmt.Errorf("timed out while waiting for routineStoppedCh after closing routineStopCh: %w", err)
		}
	}
	switch spec.Proto {
	case "tcp", "tcp4", "tcp6":
		err = tcp.Run(d.socketPath, spec, routineStopCh, routineStoppedCh, d.logWriter)
	case "udp", "udp4", "udp6":
		err = udp.Run(d.socketPath, spec, routineStopCh, routineStoppedCh, d.logWriter)
	default:
		return nil, fmt.Errorf("unsupported port protocol %s", spec.Proto)
	}
	if err != nil {
		if isEPERM(err) {
			err = annotateEPERM(err, spec)
		}
		return nil, err
	}
	d.mu.Lock()
	id := d.nextID
	st := port.Status{
		ID:   id,
		Spec: spec,
	}
	d.ports[id] = &st
	d.stoppers[id] = routineStop
	d.nextID++
	d.mu.Unlock()
	return &st, nil
}

func (d *driver) ListPorts(ctx context.Context) ([]port.Status, error) {
	var ports []port.Status
	d.mu.Lock()
	for _, p := range d.ports {
		ports = append(ports, *p)
	}
	d.mu.Unlock()
	return ports, nil
}

func (d *driver) RemovePort(ctx context.Context, id int) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	stop, ok := d.stoppers[id]
	if !ok {
		return fmt.Errorf("unknown id: %d", id)
	}
	if _, ok := ctx.Deadline(); !ok {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, 5*time.Second)
		defer cancel()
	}
	err := stop(ctx)
	delete(d.stoppers, id)
	delete(d.ports, id)
	return err
}
