package kubenat

import (
	"context"
	"fmt"
	"net"

	"github.com/golang/glog"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"

	"code.hackerspace.pl/hscloud/cluster/identd/cri"
)

// podInfoReq is a request passed to the podWorker.
type podInfoReq struct {
	local net.IP
	res   chan *podInfoResp
}

// podInfoResp is a response from a podWorker, sent over the res channel in a
// podInfoReq.
type podInfoResp struct {
	name      string
	namespace string
}

// reply sends a reply to the given podInfoReq based on a CRI PodSandboxStatus,
// sending nil if the status is nil.
func (r *podInfoReq) reply(s *cri.PodSandboxStatus) {
	if s == nil {
		r.res <- nil
		return
	}
	r.res <- &podInfoResp{
		name:      s.Metadata.Name,
		namespace: s.Metadata.Namespace,
	}
}

// getPodInfo performs a podInfoReq/podInfoResp exchange under a context that
// can be used to time out the query.
func (r *Resolver) getPodInfo(ctx context.Context, local net.IP) (*podInfoResp, error) {
	resC := make(chan *podInfoResp, 1)
	r.podInfoC <- &podInfoReq{
		local: local,
		res:   resC,
	}
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case res := <-resC:
		return res, nil
	}
}

// podStatus is a cache of data retrieved from CRI.
type podStatus struct {
	// info is a map from pod sandbox ID to PodSandboxStatus as retrieved from
	// CRI.
	info map[string]*cri.PodSandboxStatus
	// byIP is a map from pod IP (as string) to pod sandbox ID.
	byIP map[string]string
}

// update performs an update of the podStatus from CRI. It only retrieves
// information about pods that it doesn't yet have, and ensures that pods which
// do not exist in CRI are also removed from podStatus.
// TODO(q3k): make sure we don't cache PodSandboxStatus too early, eg. when
// it's not yet fully running?
func (p *podStatus) update(ctx context.Context, client cri.RuntimeServiceClient) error {
	res, err := client.ListPodSandbox(ctx, &cri.ListPodSandboxRequest{})
	if err != nil {
		return fmt.Errorf("ListPodSandbox: %w", err)
	}

	// set of all pod sandbox IDs in CRI.
	want := make(map[string]bool)
	// set of pod sandbox IDs in CRI that are not in podStatus.
	missing := make(map[string]bool)
	for _, item := range res.Items {
		want[item.Id] = true
		if _, ok := p.info[item.Id]; ok {
			continue
		}
		missing[item.Id] = true
	}

	// Get information about missing pod IDs into podStatus.
	for id, _ := range missing {
		res, err := client.PodSandboxStatus(ctx, &cri.PodSandboxStatusRequest{
			PodSandboxId: id,
		})
		if err != nil {
			if st, ok := status.FromError(err); ok && st.Code() == codes.NotFound {
				continue
			} else {
				return fmt.Errorf("while getting sandbox %s: %v", id, err)
			}
		}
		p.info[id] = res.Status
	}

	// byIP is fully repopulated on each update.
	p.byIP = make(map[string]string)

	// remove is the set of pods sandbox IDs that should be removed from podStatus.
	remove := make(map[string]bool)
	// Populate remove and p.byId in a single pass.
	for id, info := range p.info {
		if _, ok := want[id]; !ok {
			remove[id] = true
			continue
		}
		if info.Network == nil {
			continue
		}
		if info.Network.Ip == "" {
			continue
		}
		p.byIP[info.Network.Ip] = id
	}
	// Remove stale pod sandbox IDs from podStatus.
	for id, _ := range remove {
		delete(p.info, id)
	}
	return nil
}

// findByPodID returns a PodSandboxStatus for the pod running under a given pod
// IP address, or nil if not found.
func (p *podStatus) findByPodIP(ip net.IP) *cri.PodSandboxStatus {
	id, ok := p.byIP[ip.String()]
	if !ok {
		return nil
	}
	return p.info[id]
}

// runPodWorker runs the CRI cache 'pod worker'. It responds to requests over
// podInfoC until ctx is canceled.
func (r *Resolver) runPodWorker(ctx context.Context) error {
	conn, err := grpc.Dial(fmt.Sprintf("unix://%s", r.criPath), grpc.WithInsecure())
	if err != nil {
		return fmt.Errorf("Dial: %w", err)
	}
	defer conn.Close()
	client := cri.NewRuntimeServiceClient(conn)

	ps := &podStatus{
		info: make(map[string]*cri.PodSandboxStatus),
	}
	if err := ps.update(ctx, client); err != nil {
		return fmt.Errorf("initial pod update: %w", err)
	}

	for {
		select {
		case req := <-r.podInfoC:
			info := ps.findByPodIP(req.local)
			if info != nil {
				req.reply(info)
				continue
			}
			err := ps.update(ctx, client)
			if err != nil {
				glog.Errorf("Updating pods failed: %v", err)
				continue
			}
			req.reply(ps.findByPodIP(req.local))
		case <-ctx.Done():
			return ctx.Err()
		}
	}
}