// Copyright (C) 2026 Dcntrlized
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package realtime

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"net/http"
	"strings"

	"git.dcntrlized.org/Dcntrlized/Alarm/db"
	"git.dcntrlized.org/Dcntrlized/Alarm/internal/alarmtoken"
	"git.dcntrlized.org/Dcntrlized/Alarm/internal/apierr"
	"git.dcntrlized.org/Dcntrlized/Alarm/internal/deviceid"
	"git.dcntrlized.org/Dcntrlized/Alarm/logger"
	"git.dcntrlized.org/dcntrlized/dcntrlized-auth/authclient"
	"github.com/google/uuid"
)

// authenticateWS resolves a GET /ws/alarm upgrade request:
//
//	?alertId=<uuid>   required
//	&token=<secret>   required; the alert's admin token OR its subscribe token
//	&deviceId=<id>    optional; picks which device row is kept alive
//	&deviceToken=<t>  the subscriber credential (rev 10); replaces the access
//	                  token for a device that has no account
//
// The caller's identity always comes from a verified X-Access-Token header. The
// access token may also be supplied as ?accessToken= / ?access_token= for
// clients (and debugging tools) that cannot set headers on the upgrade; that is
// a convenience, not a second trust path — the token is verified identically.
//
// A subscribe token authorises only a user who actually has a subscription on
// the alert, so knowing the shared token is not enough on its own. The admin
// token is only honoured for the user the alert was created by.
func authenticateWS(r *http.Request) (*Identity, error) {
	// Device path first (rev 10): no access token, no account — the device token
	// names a subscription and `token` must still prove the caller was shown the
	// QR.
	if deviceTok := strings.TrimSpace(r.URL.Query().Get("deviceToken")); deviceTok != "" || strings.TrimSpace(r.Header.Get("X-Device-Token")) != "" {
		if deviceTok == "" {
			deviceTok = strings.TrimSpace(r.Header.Get("X-Device-Token"))
		}
		return authenticateWSDevice(r, deviceTok)
	}

	access := strings.TrimSpace(r.Header.Get("X-Access-Token"))
	if access == "" {
		access = strings.TrimSpace(r.URL.Query().Get("accessToken"))
	}
	if access == "" {
		access = strings.TrimSpace(r.URL.Query().Get("access_token"))
	}
	if access == "" {
		return nil, &AuthError{
			Status: http.StatusUnauthorized, Code: apierr.Unauthorized, Message: "missing access token",
		}
	}

	authReq := r.Clone(r.Context())
	authReq.Header.Set("X-Access-Token", access)
	p, err := authclient.Authorize(authReq)
	if err != nil {
		logger.Warn("ws: access token rejected: %v", err)
		return nil, &AuthError{
			Status: http.StatusUnauthorized, Code: apierr.Unauthorized, Message: "invalid access token",
		}
	}

	alertID, err := uuid.Parse(strings.TrimSpace(r.URL.Query().Get("alertId")))
	if err != nil {
		return nil, &AuthError{
			Status: http.StatusBadRequest, Code: apierr.Validation, Message: "alertId is required",
		}
	}
	token := strings.TrimSpace(r.URL.Query().Get("token"))
	if token == "" {
		return nil, &AuthError{
			Status: http.StatusForbidden, Code: apierr.AlertTokenInvalid, Message: "token is required",
		}
	}

	alert, err := db.GetAlert(r.Context(), alertID)
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil, &AuthError{
				Status: http.StatusNotFound, Code: apierr.AlertNotFound, Message: "alert not found",
			}
		}
		logger.Error("ws: alert lookup failed: %v", err)
		return nil, &AuthError{
			Status: http.StatusInternalServerError, Code: apierr.Internal, Message: "internal error",
		}
	}

	// Admin path: the alert's own admin token, presented by the alert's admin.
	if alarmtoken.EqualHash(alert.AdminTokenHash, token) {
		if alert.AdminUserID != p.ID {
			logger.Warn("ws: user=%s presented the admin token of alert=%s without owning it", p.ID, alert.ID)
			return nil, &AuthError{
				Status: http.StatusForbidden, Code: apierr.AlertNotAdmin, Message: "caller is not the alert admin",
			}
		}
		return &Identity{AlertID: alert.ID, UserID: p.ID, IsAdmin: true}, nil
	}

	// Subscriber path: the shared subscribe token plus a real subscription.
	if !alarmtoken.EqualToken(alert.SubscribeToken, token) {
		logger.Warn("ws: token mismatch alert=%s user=%s", alert.ID, p.ID)
		return nil, &AuthError{
			Status: http.StatusForbidden, Code: apierr.AlertTokenInvalid, Message: "invalid token",
		}
	}
	sub, err := resolveSubscription(r, alert.ID, p.ID)
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil, &AuthError{
				Status: http.StatusNotFound, Code: apierr.AlertNotSubscribed, Message: "no subscription for this user on the alert",
			}
		}
		logger.Error("ws: subscription lookup failed: %v", err)
		return nil, &AuthError{
			Status: http.StatusInternalServerError, Code: apierr.Internal, Message: "internal error",
		}
	}
	return &Identity{
		AlertID:        alert.ID,
		UserID:         p.ID,
		SubscriptionID: &sub.ID,
		DeviceID:       sub.DeviceID,
	}, nil
}

// resolveSubscription picks the device row a connection keeps alive: the one
// named by ?deviceId= when given, otherwise the user's oldest subscription on
// the alert.
func resolveSubscription(r *http.Request, alertID, userID uuid.UUID) (*db.Subscription, error) {
	if deviceID := strings.TrimSpace(r.URL.Query().Get("deviceId")); deviceID != "" {
		// The client sends the raw value; the row stores its digest.
		return db.GetSubscriptionByDevice(r.Context(), alertID, userID, deviceid.Hash(deviceID))
	}
	ids, err := db.UserSubscriptionIDs(r.Context(), alertID, userID)
	if err != nil {
		return nil, err
	}
	if len(ids) == 0 {
		return nil, db.ErrNotFound
	}
	return db.GetSubscription(r.Context(), alertID, ids[0])
}

// authenticateWSDevice upgrades a subscriber connection that has no account.
// The device token is looked up by hash; the shared subscribe token still has to
// match, so a leaked device token alone cannot attach to an alert's socket.
func authenticateWSDevice(r *http.Request, deviceToken string) (*Identity, error) {
	alertID, err := uuid.Parse(strings.TrimSpace(r.URL.Query().Get("alertId")))
	if err != nil {
		return nil, &AuthError{
			Status: http.StatusBadRequest, Code: apierr.Validation, Message: "alertId is required",
		}
	}
	sub, err := db.GetSubscriptionByToken(r.Context(), deviceTokenHash(deviceToken))
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil, &AuthError{
				Status: http.StatusUnauthorized, Code: apierr.Unauthorized, Message: "invalid device token",
			}
		}
		logger.Error("ws: device token lookup failed: %v", err)
		return nil, &AuthError{
			Status: http.StatusInternalServerError, Code: apierr.Internal, Message: "internal error",
		}
	}
	if sub.AlertID != alertID {
		return nil, &AuthError{
			Status: http.StatusNotFound, Code: apierr.AlertNotSubscribed, Message: "device is not subscribed to this alert",
		}
	}
	token := strings.TrimSpace(r.URL.Query().Get("token"))
	if token == "" {
		return nil, &AuthError{
			Status: http.StatusForbidden, Code: apierr.AlertTokenInvalid, Message: "token is required",
		}
	}
	alert, err := db.GetAlert(r.Context(), alertID)
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil, &AuthError{
				Status: http.StatusNotFound, Code: apierr.AlertNotFound, Message: "alert not found",
			}
		}
		logger.Error("ws: alert lookup failed: %v", err)
		return nil, &AuthError{
			Status: http.StatusInternalServerError, Code: apierr.Internal, Message: "internal error",
		}
	}
	if !alarmtoken.EqualToken(alert.SubscribeToken, token) {
		logger.Warn("ws: subscribe token mismatch alert=%s device-sub=%s", alert.ID, sub.ID)
		return nil, &AuthError{
			Status: http.StatusForbidden, Code: apierr.AlertTokenInvalid, Message: "invalid token",
		}
	}
	return &Identity{
		AlertID:        alert.ID,
		SubscriptionID: &sub.ID,
		DeviceID:       sub.DeviceID,
		IsDevice:       true,
	}, nil
}

// deviceTokenHash mirrors the service's device-token hash (plain SHA-256 hex):
// the WebSocket package verifies the same credential the actions accept, so the
// transform must be identical.
func deviceTokenHash(tok string) string {
	sum := sha256.Sum256([]byte(tok))
	return hex.EncodeToString(sum[:])
}