package roomserver

import (
	"context"
	"fmt"

	"github.com/dariuszjaniak/warp/server/internal/matrix/event"
	"github.com/dariuszjaniak/warp/server/internal/matrix/signing"
)

// localVerifier checks an event's signature against this server's own key.
//
// One authorisation rule needs somebody else's signature verified: a join
// under the restricted join rule is authorised by a third party named in
// content.join_authorised_via_users_server, and the event must carry a
// signature from *that user's* server. While federation is off the only
// such server that can appear is this one, and its key is already in hand —
// so the rule can be applied in full, locally, without a key fetcher.
//
// Phase 5 replaces this with a verifier that can fetch and cache another
// server's keys. Until then a join authorised via a remote user is refused
// rather than waved through, which is the same answer the federation switch
// gives everywhere else.
type localVerifier struct {
	serverName string
	key        *signing.KeyPair
}

// verifier returns the Verifier the authorisation rules are given.
func (r *API) verifier() *localVerifier {
	return &localVerifier{serverName: r.serverName, key: r.signingKey}
}

// VerifyEventSignature implements auth.Verifier.
func (v *localVerifier) VerifyEventSignature(_ context.Context, serverName string, e *event.Event) error {
	if serverName != v.serverName {
		return fmt.Errorf("%w: cannot verify a signature from %s", ErrFederationDisabled, serverName)
	}
	return e.VerifySignature(v.serverName, v.key.KeyID(), v.key.Public)
}