// Copyright 2022 Arista Networks
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"net"

	"github.com/vishvananda/netlink"

	"github.com/containernetworking/cni/pkg/skel"
	"github.com/containernetworking/cni/pkg/types"
	current "github.com/containernetworking/cni/pkg/types/100"
	"github.com/containernetworking/cni/pkg/version"
	"github.com/containernetworking/plugins/pkg/ip"
	"github.com/containernetworking/plugins/pkg/ipam"
	"github.com/containernetworking/plugins/pkg/ns"
	bv "github.com/containernetworking/plugins/pkg/utils/buildversion"
)

func parseNetConf(bytes []byte) (*types.NetConf, error) {
	conf := &types.NetConf{}
	if err := json.Unmarshal(bytes, conf); err != nil {
		return nil, fmt.Errorf("failed to parse network config: %v", err)
	}
	return conf, nil
}

func createDummy(conf *types.NetConf, ifName string, netns ns.NetNS) (*current.Interface, error) {
	dummy := &current.Interface{}

	dm := &netlink.Dummy{
		LinkAttrs: netlink.LinkAttrs{
			Name:      ifName,
			Namespace: netlink.NsFd(int(netns.Fd())),
		},
	}

	if err := netlink.LinkAdd(dm); err != nil {
		return nil, fmt.Errorf("failed to create dummy: %v", err)
	}
	dummy.Name = ifName

	err := netns.Do(func(_ ns.NetNS) error {
		// Re-fetch interface to get all properties/attributes
		contDummy, err := netlink.LinkByName(ifName)
		if err != nil {
			return fmt.Errorf("failed to fetch dummy%q: %v", ifName, err)
		}

		dummy.Mac = contDummy.Attrs().HardwareAddr.String()
		dummy.Sandbox = netns.Path()

		return nil
	})
	if err != nil {
		return nil, err
	}

	return dummy, nil
}

func cmdAdd(args *skel.CmdArgs) error {
	conf, err := parseNetConf(args.StdinData)
	if err != nil {
		return err
	}

	if conf.IPAM.Type == "" {
		return errors.New("dummy interface requires an IPAM configuration")
	}

	netns, err := ns.GetNS(args.Netns)
	if err != nil {
		return fmt.Errorf("failed to open netns %q: %v", netns, err)
	}
	defer netns.Close()

	dummyInterface, err := createDummy(conf, args.IfName, netns)
	if err != nil {
		return err
	}

	// Delete link if err to avoid link leak in this ns
	defer func() {
		if err != nil {
			netns.Do(func(_ ns.NetNS) error {
				return ip.DelLinkByName(args.IfName)
			})
		}
	}()

	r, err := ipam.ExecAdd(conf.IPAM.Type, args.StdinData)
	if err != nil {
		return err
	}

	// defer ipam deletion to avoid ip leak
	defer func() {
		if err != nil {
			ipam.ExecDel(conf.IPAM.Type, args.StdinData)
		}
	}()

	// convert IPAMResult to current Result type
	result, err := current.NewResultFromResult(r)
	if err != nil {
		return err
	}

	if len(result.IPs) == 0 {
		return errors.New("IPAM plugin returned missing IP config")
	}

	for _, ipc := range result.IPs {
		// all addresses apply to the container dummy interface
		ipc.Interface = current.Int(0)
	}

	result.Interfaces = []*current.Interface{dummyInterface}

	err = netns.Do(func(_ ns.NetNS) error {
		if err := ipam.ConfigureIface(args.IfName, result); err != nil {
			return err
		}
		return nil
	})

	if err != nil {
		return err
	}

	return types.PrintResult(result, conf.CNIVersion)
}

func cmdDel(args *skel.CmdArgs) error {
	conf, err := parseNetConf(args.StdinData)
	if err != nil {
		return err
	}

	if err = ipam.ExecDel(conf.IPAM.Type, args.StdinData); err != nil {
		return err
	}

	if args.Netns == "" {
		return nil
	}

	err = ns.WithNetNSPath(args.Netns, func(ns.NetNS) error {
		err = ip.DelLinkByName(args.IfName)
		if err != nil && err == ip.ErrLinkNotFound {
			return nil
		}
		return err
	})

	if err != nil {
		//  if NetNs is passed down by the Cloud Orchestration Engine, or if it called multiple times
		// so don't return an error if the device is already removed.
		// https://github.com/kubernetes/kubernetes/issues/43014#issuecomment-287164444
		_, ok := err.(ns.NSPathNotExistErr)
		if ok {
			return nil
		}
		return err
	}

	return nil
}

func main() {
	skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.All, bv.BuildString("dummy"))
}

func cmdCheck(args *skel.CmdArgs) error {
	conf, err := parseNetConf(args.StdinData)
	if err != nil {
		return err
	}

	if conf.IPAM.Type == "" {
		return errors.New("dummy interface requires an IPAM configuration")
	}

	netns, err := ns.GetNS(args.Netns)
	if err != nil {
		return fmt.Errorf("failed to open netns %q: %v", args.Netns, err)
	}
	defer netns.Close()

	// run the IPAM plugin and get back the config to apply
	err = ipam.ExecCheck(conf.IPAM.Type, args.StdinData)
	if err != nil {
		return err
	}

	if conf.RawPrevResult == nil {
		return fmt.Errorf("dummy: Required prevResult missing")
	}

	if err := version.ParsePrevResult(conf); err != nil {
		return err
	}

	// Convert whatever the IPAM result was into the current Result type
	result, err := current.NewResultFromResult(conf.PrevResult)
	if err != nil {
		return err
	}

	var contMap current.Interface
	// Find interfaces for name whe know, that of dummy device inside container
	for _, intf := range result.Interfaces {
		if args.IfName == intf.Name {
			if args.Netns == intf.Sandbox {
				contMap = *intf
				continue
			}
		}
	}

	// The namespace must be the same as what was configured
	if args.Netns != contMap.Sandbox {
		return fmt.Errorf("Sandbox in prevResult %s doesn't match configured netns: %s",
			contMap.Sandbox, args.Netns)
	}

	//
	// Check prevResults for ips, routes and dns against values found in the container
	if err := netns.Do(func(_ ns.NetNS) error {
		// Check interface against values found in the container
		err := validateCniContainerInterface(contMap)
		if err != nil {
			return err
		}

		err = ip.ValidateExpectedInterfaceIPs(args.IfName, result.IPs)
		if err != nil {
			return err
		}
		return nil
	}); err != nil {
		return err
	}

	return nil
}

func validateCniContainerInterface(intf current.Interface) error {
	var link netlink.Link
	var err error

	if intf.Name == "" {
		return fmt.Errorf("Container interface name missing in prevResult: %v", intf.Name)
	}
	link, err = netlink.LinkByName(intf.Name)
	if err != nil {
		return fmt.Errorf("Container Interface name in prevResult: %s not found", intf.Name)
	}
	if intf.Sandbox == "" {
		return fmt.Errorf("Error: Container interface %s should not be in host namespace", link.Attrs().Name)
	}

	_, isDummy := link.(*netlink.Dummy)
	if !isDummy {
		return fmt.Errorf("Error: Container interface %s not of type dummy", link.Attrs().Name)
	}

	if intf.Mac != "" {
		if intf.Mac != link.Attrs().HardwareAddr.String() {
			return fmt.Errorf("Interface %s Mac %s doesn't match container Mac: %s", intf.Name, intf.Mac, link.Attrs().HardwareAddr)
		}
	}

	if link.Attrs().Flags&net.FlagUp != net.FlagUp {
		return fmt.Errorf("Interface %s is down", intf.Name)
	}

	return nil
}