package handler

import (
	"encoding/base64"
	"encoding/json"
	"net/http"
	"net/url"
	"strings"

	"github.com/prabhupadasays/spsays-bff/internal/middleware"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
	"github.com/prabhupadasays/spsays-bff/internal/service"
	"github.com/prabhupadasays/spsays-bff/pkg/response"
)

// Subscription limits. The endpoint length cap + host allow-list guard against
// junk/abusive rows and SSRF (the BFF POSTs to the endpoint when sending), and
// the per-user device cap bounds fan-out.
const (
	maxEndpointLen    = 2048
	maxKeyLen         = 256
	maxDevicesPerUser = 10

	// RFC 8291 fixes the key sizes: p256dh is an uncompressed P-256 point,
	// auth a 16-byte secret. Anything else is guaranteed to fail at send time.
	p256dhLen = 65
	authLen   = 16
)

// validatePushEndpoint requires an https URL belonging to a known browser push
// service — preventing the endpoint from pointing at internal/arbitrary hosts
// (SSRF) and keeping the table free of junk.
func validatePushEndpoint(endpoint string) bool {
	if l := len(endpoint); l == 0 || l > maxEndpointLen {
		return false
	}
	u, err := url.Parse(endpoint)
	if err != nil || u.Scheme != "https" || u.Host == "" {
		return false
	}
	host := strings.ToLower(u.Hostname())
	switch host {
	case "fcm.googleapis.com", "updates.push.services.mozilla.com":
		return true // Chrome/Brave/Edge (FCM), Firefox
	}
	// Safari/iOS (*.push.apple.com) and Windows/Edge WNS (*.notify.windows.com).
	for _, suffix := range []string{".push.apple.com", ".notify.windows.com", ".wns.windows.com"} {
		if strings.HasSuffix(host, suffix) {
			return true
		}
	}
	return false
}

// validateSubscriptionKey checks that a client key is base64(url)-decodable
// to exactly `want` bytes — the same decoding webpush-go applies at send
// time, so anything accepted here is actually deliverable.
func validateSubscriptionKey(key string, want int) bool {
	if l := len(key); l == 0 || l > maxKeyLen {
		return false
	}
	trimmed := strings.TrimRight(key, "=")
	b, err := base64.RawURLEncoding.DecodeString(trimmed)
	if err != nil {
		b, err = base64.RawStdEncoding.DecodeString(trimmed)
	}
	return err == nil && len(b) == want
}

// PushHandler serves Web Push subscription management. The VAPID public key
// is handed to the browser so it can subscribe; subscriptions are stored per
// user. All routes require auth.
type PushHandler struct {
	push *service.PushSender // optional — nil when VAPID isn't configured
	repo *repository.PushRepo
}

func NewPushHandler(push *service.PushSender, repo *repository.PushRepo) *PushHandler {
	return &PushHandler{push: push, repo: repo}
}

// Key — GET /push/key. Returns the VAPID public key + whether push is on.
func (h *PushHandler) Key(w http.ResponseWriter, r *http.Request) {
	response.JSON(w, http.StatusOK, struct {
		PublicKey string `json:"public_key"`
		Enabled   bool   `json:"enabled"`
	}{
		PublicKey: h.push.PublicKey(),
		Enabled:   h.push.Enabled(),
	})
}

type subscribeReq struct {
	Endpoint string `json:"endpoint"`
	Keys     struct {
		P256dh string `json:"p256dh"`
		Auth   string `json:"auth"`
	} `json:"keys"`
}

// Subscribe — POST /push/subscribe. Stores (or refreshes) the caller's push
// subscription. Body is the browser PushSubscription JSON.
func (h *PushHandler) Subscribe(w http.ResponseWriter, r *http.Request) {
	if h.repo == nil || !h.push.Enabled() {
		response.Error(w, http.StatusServiceUnavailable, "push not configured")
		return
	}
	uid := middleware.UserID(r.Context())
	var req subscribeReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		response.Error(w, http.StatusBadRequest, "invalid JSON body")
		return
	}
	if req.Endpoint == "" || req.Keys.P256dh == "" || req.Keys.Auth == "" {
		response.Error(w, http.StatusBadRequest, "missing subscription fields")
		return
	}
	if !validatePushEndpoint(req.Endpoint) {
		response.Error(w, http.StatusBadRequest, "invalid push endpoint")
		return
	}
	if !validateSubscriptionKey(req.Keys.P256dh, p256dhLen) ||
		!validateSubscriptionKey(req.Keys.Auth, authLen) {
		response.Error(w, http.StatusBadRequest, "invalid subscription keys")
		return
	}
	if err := h.repo.Upsert(r.Context(), uid, req.Endpoint, req.Keys.P256dh, req.Keys.Auth, r.UserAgent()); err != nil {
		response.Error(w, http.StatusInternalServerError, "could not save subscription")
		return
	}
	// Keep only the most-recent N devices per user (best-effort).
	_ = h.repo.PruneToMostRecent(r.Context(), uid, maxDevicesPerUser)
	response.NoContent(w)
}

type unsubscribeReq struct {
	Endpoint string `json:"endpoint"`
}

// Unsubscribe — POST /push/unsubscribe. Removes one of the caller's own
// subscriptions by endpoint (scoped to the user so nobody can delete another
// account's subscription by guessing/replaying an endpoint).
func (h *PushHandler) Unsubscribe(w http.ResponseWriter, r *http.Request) {
	if h.repo == nil {
		response.NoContent(w)
		return
	}
	uid := middleware.UserID(r.Context())
	var req unsubscribeReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil || strings.TrimSpace(req.Endpoint) == "" {
		response.Error(w, http.StatusBadRequest, "missing endpoint")
		return
	}
	if err := h.repo.DeleteByEndpointForUser(r.Context(), uid, req.Endpoint); err != nil {
		response.Error(w, http.StatusInternalServerError, "could not remove subscription")
		return
	}
	response.NoContent(w)
}