cast-ghl-plugin/internal/ghl/webhook.go

package ghl

import (
	"context"
	"crypto/ecdsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"time"

	castclient "git.sds.dev/CAST/cast-ghl-plugin/internal/cast"
	"git.sds.dev/CAST/cast-ghl-plugin/internal/phone"
)

type WebhookHandler struct {
	webhookPubKey *ecdsa.PublicKey
	castClient    *castclient.Client
	ghlAPI        *APIClient
	oauthHandler  *OAuthHandler
}

func NewWebhookHandler(pubKeyPEM string, castClient *castclient.Client, ghlAPI *APIClient, oauth *OAuthHandler) (*WebhookHandler, error) {
	key, err := parseECDSAPublicKey(pubKeyPEM)
	if err != nil {
		return nil, fmt.Errorf("failed to parse webhook public key: %w", err)
	}
	return &WebhookHandler{
		webhookPubKey: key,
		castClient:    castClient,
		ghlAPI:        ghlAPI,
		oauthHandler:  oauth,
	}, nil
}

func (h *WebhookHandler) HandleWebhook(w http.ResponseWriter, r *http.Request) {
	sigHeader := r.Header.Get("x-wh-signature")

	body, err := io.ReadAll(r.Body)
	if err != nil {
		slog.Error("webhook: failed to read body", "err", err)
		http.Error(w, "failed to read request body", http.StatusInternalServerError)
		return
	}

	if !h.verifySignature(body, sigHeader) {
		slog.Warn("webhook: invalid signature")
		http.Error(w, "invalid webhook signature", http.StatusUnauthorized)
		return
	}

	var webhook OutboundMessageWebhook
	if err := json.Unmarshal(body, &webhook); err != nil {
		slog.Error("webhook: failed to parse payload", "err", err)
		http.Error(w, "invalid payload", http.StatusBadRequest)
		return
	}

	if webhook.Type != "SMS" {
		slog.Debug("webhook: ignoring non-SMS webhook", "type", webhook.Type)
		w.WriteHeader(http.StatusOK)
		return
	}

	slog.Info("webhook: received outbound SMS", "message_id", webhook.MessageID, "location_id", webhook.LocationID)
	w.WriteHeader(http.StatusOK)

	go h.processOutbound(webhook)
}

func (h *WebhookHandler) processOutbound(webhook OutboundMessageWebhook) {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	localPhone, err := phone.ToLocal(webhook.Phone)
	if err != nil {
		slog.Error("webhook: phone normalization failed", "phone", webhook.Phone, "err", err)
		h.updateStatus(ctx, webhook, "failed")
		return
	}

	_, err = h.castClient.SendSMS(ctx, localPhone, webhook.Message)
	if err != nil {
		slog.Error("webhook: cast send failed", "message_id", webhook.MessageID, "err", err)
		h.updateStatus(ctx, webhook, "failed")
		return
	}

	slog.Info("webhook: cast send success", "message_id", webhook.MessageID)
	h.updateStatus(ctx, webhook, "delivered")
}

func (h *WebhookHandler) updateStatus(ctx context.Context, webhook OutboundMessageWebhook, status string) {
	token, err := h.oauthHandler.GetValidToken(ctx, webhook.LocationID)
	if err != nil {
		slog.Error("webhook: failed to get valid token for status update", "location_id", webhook.LocationID, "err", err)
		return
	}

	if err := h.ghlAPI.UpdateMessageStatus(ctx, token, webhook.MessageID, status); err != nil {
		slog.Error("webhook: failed to update message status", "message_id", webhook.MessageID, "status", status, "err", err)
		return
	}
	slog.Info("webhook: message status updated", "message_id", webhook.MessageID, "status", status)
}

func (h *WebhookHandler) verifySignature(body []byte, signatureB64 string) bool {
	if signatureB64 == "" {
		return false
	}
	sigBytes, err := base64.StdEncoding.DecodeString(signatureB64)
	if err != nil {
		return false
	}
	hash := sha256.Sum256(body)
	return ecdsa.VerifyASN1(h.webhookPubKey, hash[:], sigBytes)
}

func parseECDSAPublicKey(pemStr string) (*ecdsa.PublicKey, error) {
	block, _ := pem.Decode([]byte(pemStr))
	if block == nil {
		return nil, fmt.Errorf("failed to decode PEM block")
	}
	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
		return nil, fmt.Errorf("failed to parse public key: %w", err)
	}
	ecdsaPub, ok := pub.(*ecdsa.PublicKey)
	if !ok {
		return nil, fmt.Errorf("key is not ECDSA")
	}
	return ecdsaPub, nil
}