package main

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

	"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/vishvananda/netlink"
	"github.com/vishvananda/netns"
)

const (
	PluginName        = "mycelium-cni"
	MyceliumInterface = "mycelium"
)

type NetConf struct {
	types.NetConf
	MyceliumInterface string `json:"myceliumInterface,omitempty"`
}

func main() {
	skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.All, "mycelium CNI plugin")
}

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

	// Get container network namespace
	containerNS, err := netns.GetFromPath(args.Netns)
	if err != nil {
		return fmt.Errorf("failed to open container netns %q: %v", args.Netns, err)
	}
	defer containerNS.Close()

	// Get Mycelium interface and its IPv6 prefix
	myceliumIP, err := getMyceliumIP(conf.MyceliumInterface)
	if err != nil {
		return fmt.Errorf("failed to get Mycelium IP: %v", err)
	}

	// Create veth pair
	hostVethName := fmt.Sprintf("veth-%s", args.ContainerID[:8])
	containerVethName := "eth0"

	hostVeth, containerVeth, err := createVethPair(hostVethName, containerVethName)
	if err != nil {
		return fmt.Errorf("failed to create veth pair: %v", err)
	}

	// Move container veth to container namespace
	if err := netlink.LinkSetNsFd(containerVeth, int(containerNS)); err != nil {
		return fmt.Errorf("failed to move veth to container netns: %v", err)
	}

	// Configure container interface
	containerIP := generateContainerIP(myceliumIP, args.ContainerID)
	if err := configureContainerInterface(containerNS, containerVethName, containerIP, hostVethName); err != nil {
		return fmt.Errorf("failed to configure container interface: %v", err)
	}

	// Configure host interface and routing
	if err := configureHostInterface(hostVeth, containerIP); err != nil {
		return fmt.Errorf("failed to configure host interface: %v", err)
	}

	// Build result
	result := &current.Result{
		CNIVersion: current.ImplementedSpecVersion,
		Interfaces: []*current.Interface{
			{
				Name: hostVethName,
			},
			{
				Name:    containerVethName,
				Sandbox: args.Netns,
			},
		},
		IPs: []*current.IPConfig{
			{
				Interface: current.Int(1), // container interface
				Address:   net.IPNet{IP: containerIP, Mask: net.CIDRMask(64, 128)},
			},
		},
	}

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

func cmdCheck(args *skel.CmdArgs) error {
	// Basic connectivity check could be implemented here
	return nil
}

func cmdDel(args *skel.CmdArgs) error {
	// Clean up veth pair (host side will be automatically removed)
	hostVethName := fmt.Sprintf("veth-%s", args.ContainerID[:8])

	link, err := netlink.LinkByName(hostVethName)
	if err != nil {
		// Interface might already be gone, which is fine
		return nil
	}

	return netlink.LinkDel(link)
}

func parseConfig(stdin []byte) (*NetConf, error) {
	conf := &NetConf{
		MyceliumInterface: MyceliumInterface,
	}

	if err := json.Unmarshal(stdin, conf); err != nil {
		return nil, fmt.Errorf("failed to parse network configuration: %v", err)
	}

	return conf, nil
}

func getMyceliumIP(interfaceName string) (net.IP, error) {
	link, err := netlink.LinkByName(interfaceName)
	if err != nil {
		return nil, fmt.Errorf("failed to find interface %s: %v", interfaceName, err)
	}

	addrs, err := netlink.AddrList(link, netlink.FAMILY_V6)
	if err != nil {
		return nil, fmt.Errorf("failed to get addresses for %s: %v", interfaceName, err)
	}

	for _, addr := range addrs {
		if addr.IP.IsGlobalUnicast() {
			// Return the /64 prefix
			return addr.IP.Mask(net.CIDRMask(64, 128)), nil
		}
	}

	return nil, fmt.Errorf("no global IPv6 address found on %s", interfaceName)
}

func generateContainerIP(myceliumPrefix net.IP, containerID string) net.IP {
	// Generate a container IP within the /64 prefix
	// Using simple approach: prefix + ::1 (could be made more sophisticated)
	containerIP := make(net.IP, len(myceliumPrefix))
	copy(containerIP, myceliumPrefix)
	containerIP[15] = 1 // Set last byte to 1
	return containerIP
}

func createVethPair(hostName, containerName string) (netlink.Link, netlink.Link, error) {
	veth := &netlink.Veth{
		LinkAttrs: netlink.LinkAttrs{Name: hostName},
		PeerName:  containerName,
	}

	if err := netlink.LinkAdd(veth); err != nil {
		return nil, nil, err
	}

	hostVeth, err := netlink.LinkByName(hostName)
	if err != nil {
		return nil, nil, err
	}

	containerVeth, err := netlink.LinkByName(containerName)
	if err != nil {
		return nil, nil, err
	}

	// Bring up host side
	if err := netlink.LinkSetUp(hostVeth); err != nil {
		return nil, nil, err
	}

	return hostVeth, containerVeth, nil
}

func configureContainerInterface(containerNS netns.NsHandle, ifName string, containerIP net.IP, hostVethName string) error {
	// Switch to container namespace
	originalNS, err := netns.Get()
	if err != nil {
		return err
	}
	defer originalNS.Close()
	defer netns.Set(originalNS)

	if err := netns.Set(containerNS); err != nil {
		return err
	}
	// Get the interface
	link, err := netlink.LinkByName(ifName)
	if err != nil {
		return err
	}

	// Bring interface up
	if err := netlink.LinkSetUp(link); err != nil {
		return err
	}

	// Add IP address
	addr := &netlink.Addr{
		IPNet: &net.IPNet{
			IP:   containerIP,
			Mask: net.CIDRMask(64, 128),
		},
	}
	if err := netlink.AddrAdd(link, addr); err != nil {
		return err
	}

	// Switch to main namespace to get host veth address
	if err := netns.Set(originalNS); err != nil {
		return err
	}

	// Get host veth link-local address
	hostVeth, err := netlink.LinkByName(hostVethName)
	if err != nil {
		return err
	}

	hostAddrs, err := netlink.AddrList(hostVeth, netlink.FAMILY_V6)
	if err != nil {
		return err
	}

	var hostLLAddr net.IP
	for _, addr := range hostAddrs {
		if addr.IP.IsLinkLocalUnicast() {
			hostLLAddr = addr.IP
			break
		}
	}

	// Switch back to container namespace to add route
	if err := netns.Set(containerNS); err != nil {
		return err
	}

	if hostLLAddr != nil {
		// Add route to Mycelium network via host veth
		route := &netlink.Route{
			Dst: &net.IPNet{
				IP:   net.ParseIP("400::"),
				Mask: net.CIDRMask(7, 128),
			},
			Gw:        hostLLAddr,
			LinkIndex: link.Attrs().Index,
		}
		if err := netlink.RouteAdd(route); err != nil {
			return err
		}
	}

	return nil
}

func configureHostInterface(hostVeth netlink.Link, containerIP net.IP) error {
	// Add route to container IP via host veth
	route := &netlink.Route{
		Dst: &net.IPNet{
			IP:   containerIP,
			Mask: net.CIDRMask(128, 128),
		},
		LinkIndex: hostVeth.Attrs().Index,
	}

	return netlink.RouteAdd(route)
}