// Package tsigapi implements the companion TSIG API deployed by the operator.
// It exposes the HTTP contract consumed by vault-plugin-secrets-bind-tsig and
// fulfils it by managing BindTSIGKey custom resources, which the operator
// reconciles into key material.
package tsigapi

import (
	"crypto/subtle"
	"encoding/json"
	"net/http"
	"strings"
	"time"

	"github.com/go-logr/logr"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/types"
	"sigs.k8s.io/controller-runtime/pkg/client"
)

const rotationAnnotation = "bind.unkin.net/rotated-at"

// Server serves the TSIG key API.
type Server struct {
	Client    client.Client
	Namespace string
	Token     string
	Log       logr.Logger
	// WaitTimeout bounds how long a create/rotate waits for the operator to
	// reconcile the key material.
	WaitTimeout time.Duration
	// Now is injectable for tests; defaults to time.Now.
	Now func() time.Time
}

type keyResponse struct {
	Name       string `json:"name"`
	Algorithm  string `json:"algorithm"`
	Secret     string `json:"secret"`
	KeyName    string `json:"key_name"`
	ClusterRef string `json:"cluster_ref,omitempty"`
}

type createRequest struct {
	Name       string `json:"name"`
	Algorithm  string `json:"algorithm"`
	ClusterRef string `json:"cluster_ref"`
	Static     bool   `json:"static"`
}

// Handler returns the API's HTTP handler.
func (s *Server) Handler() http.Handler {
	if s.Now == nil {
		s.Now = time.Now
	}
	if s.WaitTimeout == 0 {
		s.WaitTimeout = 15 * time.Second
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) { _, _ = w.Write([]byte("ok")) })
	mux.HandleFunc("/v1/keys", s.auth(s.handleKeys))
	mux.HandleFunc("/v1/keys/", s.auth(s.handleKey))
	return mux
}

func (s *Server) auth(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if s.Token != "" {
			want := "Bearer " + s.Token
			got := r.Header.Get("Authorization")
			if subtle.ConstantTimeCompare([]byte(got), []byte(want)) != 1 {
				http.Error(w, "unauthorized", http.StatusUnauthorized)
				return
			}
		}
		next(w, r)
	}
}

// handleKeys serves POST /v1/keys (create).
func (s *Server) handleKeys(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	var req createRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "invalid body", http.StatusBadRequest)
		return
	}
	if req.Name == "" {
		http.Error(w, "name is required", http.StatusBadRequest)
		return
	}
	key, err := s.createKey(r.Context(), req)
	if err != nil {
		s.fail(w, "create", req.Name, err)
		return
	}
	writeJSON(w, http.StatusOK, key)
}

// handleKey serves GET/DELETE /v1/keys/{name} and POST /v1/keys/{name}/rotate.
func (s *Server) handleKey(w http.ResponseWriter, r *http.Request) {
	name := strings.Trim(strings.TrimPrefix(r.URL.Path, "/v1/keys/"), "/")
	rotate := strings.HasSuffix(name, "/rotate")
	name = strings.TrimSuffix(name, "/rotate")
	if name == "" {
		http.Error(w, "key name is required", http.StatusBadRequest)
		return
	}

	switch {
	case rotate && r.Method == http.MethodPost:
		key, err := s.rotateKey(r.Context(), name)
		if err != nil {
			s.fail(w, "rotate", name, err)
			return
		}
		writeJSON(w, http.StatusOK, key)
	case r.Method == http.MethodGet:
		key, err := s.readKey(r.Context(), name)
		if err != nil {
			s.fail(w, "read", name, err)
			return
		}
		writeJSON(w, http.StatusOK, key)
	case r.Method == http.MethodDelete:
		if err := s.deleteKey(r.Context(), name); err != nil {
			s.fail(w, "delete", name, err)
			return
		}
		w.WriteHeader(http.StatusNoContent)
	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

func (s *Server) fail(w http.ResponseWriter, op, name string, err error) {
	if apierrors.IsNotFound(err) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	s.Log.Error(err, "tsig api request failed", "op", op, "name", name)
	http.Error(w, err.Error(), http.StatusInternalServerError)
}

func writeJSON(w http.ResponseWriter, status int, v interface{}) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func (s *Server) key(name string) types.NamespacedName {
	return types.NamespacedName{Namespace: s.Namespace, Name: name}
}