package agent

import (
	"context"
	"fmt"
	"log/slog"
	"net"
	"strings"
	"time"

	flockcni "code.fritzlab.net/fritzlab/flock/pkg/cni"
	cnitypes "github.com/containernetworking/cni/pkg/types"
	current "github.com/containernetworking/cni/pkg/types/100"
	corev1 "k8s.io/api/core/v1"
)

// podTemplateHashLabel is the well-known label Kubernetes attaches to
// every Pod owned by a ReplicaSet so the ReplicaSet name can be
// reconstructed as "<deploy>-<hash>". We use it to peel the hash back off
// in deriveAppName.
const podTemplateHashLabel = "pod-template-hash"

// deriveAppName returns the stable workload identifier for a Pod — the
// name of the topmost stable controller, with the pod-template-hash
// stripped for ReplicaSet-owned pods.
//
// The rule maps to Kubernetes pod-name generation:
//
//	Deployment → ReplicaSet → Pod   pod owner is RS named "<deploy>-<hash>";
//	                                 strip the trailing "-<hash>" to recover
//	                                 the Deployment name.
//	StatefulSet → Pod                pod owner is the STS itself; use as-is.
//	DaemonSet  → Pod                 pod owner is the DS itself; use as-is.
//	Job        → Pod                 pod owner is the Job itself; use as-is.
//	(bare pod) → Pod                 no controller owner; fall back to pod name.
//
// All replicas of the same workload converge on the same return value,
// which is the property the ip-algo `app` field needs.
func deriveAppName(pod *corev1.Pod) string {
	owner := controllerOwner(pod)
	if owner == nil {
		return pod.Name
	}
	if owner.Kind == "ReplicaSet" {
		if hash, ok := pod.Labels[podTemplateHashLabel]; ok && hash != "" {
			suffix := "-" + hash
			if strings.HasSuffix(owner.Name, suffix) {
				return strings.TrimSuffix(owner.Name, suffix)
			}
		}
		// Custom controller named the RS something that doesn't match
		// the pod-template-hash convention. Falling back to the RS name
		// keeps replicas of the same RS aligned, which is the second-
		// best correctness we can offer.
		return owner.Name
	}
	return owner.Name
}

// controllerOwner returns the OwnerReference flagged with Controller=true,
// or nil if none. Kubernetes guarantees at most one controller per object.
func controllerOwner(pod *corev1.Pod) *metav1OwnerLite {
	for i := range pod.OwnerReferences {
		o := &pod.OwnerReferences[i]
		if o.Controller != nil && *o.Controller {
			return &metav1OwnerLite{Kind: o.Kind, Name: o.Name}
		}
	}
	return nil
}

// metav1OwnerLite is the slice of OwnerReference we actually consult,
// kept tiny so it can be returned by value-pointer cheaply.
type metav1OwnerLite struct {
	Kind string
	Name string
}

// podImageRef returns a deterministic image reference for the embed
// `image` field. We use the first container's spec'd image — this is
// stable across replicas of the same Deployment without requiring the
// runtime-resolved digest. Empty string if the pod has no containers,
// in which case the embed package falls back to FNV(containerID).
func podImageRef(pod *corev1.Pod) string {
	if len(pod.Spec.Containers) == 0 {
		return ""
	}
	return pod.Spec.Containers[0].Image
}

// PodHandler is the platform-agnostic ADD/DEL/CHECK implementation. It
// resolves the Pod from the informer cache, parses annotations, allocates
// from IPAM, programs netns (or skips on non-Linux build), and persists
// state. The netns ops are split into Setup/Teardown so platform stubs can
// keep the rest of the orchestration testable.
type PodHandler struct {
	Node       string
	Store      *Store
	IPAM       *IPAM
	Pods       *PodCache
	NodeConfig *NodeConfigCache
	Logger     *slog.Logger
	// SetupFunc and TeardownFunc are injected at startup; in production
	// they point at the Linux netlink ops, in tests they're fakes.
	SetupFunc    func(SetupRequest) error
	TeardownFunc func(containerID string, ip6, ip4 net.IP) error
	// AfterCommit is called after a successful ADD/DEL with the
	// post-mutation Snapshot — used to refresh BIRD config.
	AfterCommit func()
}

// Add implements the CNI ADD path.
func (h *PodHandler) Add(ctx context.Context, req flockcni.Request) (*current.Result, error) {
	args := ParseCNIArgs(req.Args)
	if args.PodName == "" || args.PodNamespace == "" {
		return nil, fmt.Errorf("CNI_ARGS missing K8S_POD_NAMESPACE/NAME")
	}

	// Idempotency: if we already committed this containerID, return the
	// existing IPs. kubelet retries ADD on the same sandbox.
	if existing, ok := h.Store.Get(req.ContainerID); ok && existing.State == StateCommitted {
		return resultFromAllocation(req.IfName, existing), nil
	}

	pod, err := h.Pods.WaitForPod(ctx, args.PodNamespace, args.PodName, 3*time.Second)
	if err != nil {
		return nil, fmt.Errorf("lookup pod: %w", err)
	}

	nc := h.NodeConfig.Load()
	defaults := FamilyDefaultsFromNodeConfig(nc)
	parsed, err := ParseAnnotations(pod.Annotations, defaults)
	if err != nil {
		return nil, fmt.Errorf("parse annotations: %w", err)
	}

	var nodeAnn map[string]string
	if nc != nil {
		nodeAnn = nc.GetAnnotations()
	}
	ipAlgo := ResolveIPAlgo(pod.Annotations, nodeAnn, h.Logger)

	allocReq := AllocRequest{
		ContainerID: req.ContainerID,
		Namespace:   args.PodNamespace,
		Pod:         args.PodName,
		App:         deriveAppName(pod),
		WantV6:      parsed.WantV6,
		WantV4:      parsed.WantV4,
		AnnCIDR6:    parsed.CIDR6,
		AnnCIDR4:    parsed.CIDR4,
		IPAlgo:      ipAlgo,
		Image:       podImageRef(pod),
	}
	res, err := h.IPAM.Allocate(allocReq)
	if err != nil {
		return nil, fmt.Errorf("ipam: %w", err)
	}

	// Persist pending entry before any netlink work so a crash mid-ADD
	// leaves recoverable state.
	pending := Allocation{
		ContainerID: req.ContainerID,
		Namespace:   args.PodNamespace,
		PodName:     args.PodName,
		OwnerUID:    string(pod.UID),
		IP6:         ipString(res.IP6),
		IP4:         ipString(res.IP4),
		Anycast:     anycastStrings(parsed.Anycast),
		Addresses:   anycastStrings(parsed.Addresses),
		State:       StatePending,
		AllocatedAt: time.Now().UTC(),
	}
	if err := h.Store.Upsert(pending); err != nil {
		h.IPAM.Release(res.IP6, res.IP4)
		return nil, fmt.Errorf("store pending: %w", err)
	}

	setup := SetupRequest{
		ContainerID: req.ContainerID,
		Netns:       req.Netns,
		IfName:      req.IfName,
		HostIface:   HostIfaceName(req.ContainerID),
		IP6:         res.IP6,
		IP4:         res.IP4,
		Anycast:     parsed.Anycast,
		Addresses:   parsed.Addresses,
	}
	if err := h.SetupFunc(setup); err != nil {
		// Roll forward: leave pending entry in place so startup GC can clean
		// up the partial netns; let kubelet retry ADD.
		return nil, fmt.Errorf("netns setup: %w", err)
	}

	committed := pending
	committed.State = StateCommitted
	if err := h.Store.Upsert(committed); err != nil {
		return nil, fmt.Errorf("store commit: %w", err)
	}

	if h.AfterCommit != nil {
		h.AfterCommit()
	}

	return resultFromAllocation(req.IfName, committed), nil
}

// Del implements CNI DEL. Idempotent.
func (h *PodHandler) Del(ctx context.Context, req flockcni.Request) error {
	entry, ok := h.Store.Get(req.ContainerID)
	if !ok {
		return nil
	}
	ip6 := net.ParseIP(entry.IP6)
	ip4 := net.ParseIP(entry.IP4)

	if err := h.TeardownFunc(req.ContainerID, ip6, ip4); err != nil {
		return fmt.Errorf("netns teardown: %w", err)
	}
	if err := h.Store.Delete(req.ContainerID); err != nil {
		return fmt.Errorf("store delete: %w", err)
	}
	h.IPAM.Release(ip6, ip4)
	if h.AfterCommit != nil {
		h.AfterCommit()
	}
	return nil
}

// Check verifies that the persisted state is consistent. M2 minimum: just
// look up the entry; full kernel-state comparison is M7.
func (h *PodHandler) Check(_ context.Context, req flockcni.Request) error {
	if _, ok := h.Store.Get(req.ContainerID); !ok {
		return cnitypes.NewError(cnitypes.ErrUnknownContainer, "flock-check",
			"container "+req.ContainerID+" has no allocation")
	}
	return nil
}

func resultFromAllocation(ifName string, a Allocation) *current.Result {
	r := &current.Result{CNIVersion: current.ImplementedSpecVersion}
	r.Interfaces = []*current.Interface{{Name: ifName, Sandbox: "pod"}}
	if a.IP6 != "" {
		ip6 := net.ParseIP(a.IP6)
		r.IPs = append(r.IPs, &current.IPConfig{
			Interface: intPtr(0),
			Address:   net.IPNet{IP: ip6, Mask: net.CIDRMask(128, 128)},
		})
	}
	if a.IP4 != "" {
		ip4 := net.ParseIP(a.IP4).To4()
		r.IPs = append(r.IPs, &current.IPConfig{
			Interface: intPtr(0),
			Address:   net.IPNet{IP: ip4, Mask: net.CIDRMask(32, 32)},
		})
	}
	// Addresses are assigned to eth0 and should appear in pod.status.podIPs
	// so Kubernetes and workloads that inspect pod metadata see them.
	for _, s := range a.Addresses {
		ip := net.ParseIP(s)
		if ip == nil {
			continue
		}
		if v4 := ip.To4(); v4 != nil {
			r.IPs = append(r.IPs, &current.IPConfig{
				Interface: intPtr(0),
				Address:   net.IPNet{IP: v4, Mask: net.CIDRMask(32, 32)},
			})
		} else {
			r.IPs = append(r.IPs, &current.IPConfig{
				Interface: intPtr(0),
				Address:   net.IPNet{IP: ip.To16(), Mask: net.CIDRMask(128, 128)},
			})
		}
	}
	return r
}

func intPtr(i int) *int { return &i }
func ipString(ip net.IP) string {
	if ip == nil {
		return ""
	}
	return canonical(ip)
}

func anycastStrings(ips []net.IP) []string {
	if len(ips) == 0 {
		return nil
	}
	out := make([]string, len(ips))
	for i, ip := range ips {
		out[i] = canonical(ip)
	}
	return out
}