package omemo

import (
	"fmt"

	"dev.narayana.im/narayana/telegabber/e2ee/omemo/libsignal"
)

// Version identifies which OMEMO wire-format generation a message, device
// list, or bundle uses - the full namespace+XML dialect, not just the
// underlying crypto-engine version (see libsignal.ProtocolVersionV3/V4,
// which is a strictly coarser, two-way distinction shared by two of the
// three versions below).
type Version int

const (
	// Omemo0 is the original "siacs" OMEMO (eu.siacs.conversations.axolotl,
	// XEP-0384 <= 0.3.0): libsignal.ProtocolVersionV3, AES-128-GCM directly
	// on the plaintext body, key||tag distributed per-device, <iv> element
	// present. Still the most widely deployed version as of this writing,
	// and the current implementation priority.
	Omemo0 Version = iota

	// Omemo1 is urn:xmpp:omemo:1 (XEP-0384 0.4.0-0.7.x, introduced
	// 2020-03-08): libsignal.ProtocolVersionV4, AES-256-CBC+HMAC-SHA256
	// (via HKDF) over an SCE envelope using the OLD (pre-0.4.0) XEP-0420
	// dialect: root element <content xmlns='urn:xmpp:sce:0'>, inner
	// wrapper <payload/>. Confirmed by reading the archived XEP-0420 0.3.2
	// spec directly (https://xmpp.org/extensions/attic/xep-0420-0.3.2.html),
	// not assumed - see sceEncodeV0/sceDecodeV0.
	Omemo1

	// Omemo2 is urn:xmpp:omemo:2 (XEP-0384 0.8.0+, current spec):
	// libsignal.ProtocolVersionV4, the same AES-256-CBC+HMAC-SHA256 scheme
	// as Omemo1, but over the NEW (XEP-0420 0.4.0+) dialect: root element
	// <envelope xmlns='urn:xmpp:sce:1'>, inner wrapper <content/>.
	Omemo2
)

func (v Version) String() string {
	switch v {
	case Omemo0:
		return "omemo0"
	case Omemo1:
		return "omemo1"
	case Omemo2:
		return "omemo2"
	default:
		return "omemo?"
	}
}

// ParseVersion maps an e2ee.Variant string (omemo0/omemo1/omemo2 - see
// Version.String()) back to a Version, at every point the generic
// e2ee.Backend interface hands one in (DeviceListNode, BundleNode,
// PublishedIdentity, PublishedBundle).
func ParseVersion(s string) (Version, error) {
	switch s {
	case "omemo0":
		return Omemo0, nil
	case "omemo1":
		return Omemo1, nil
	case "omemo2":
		return Omemo2, nil
	default:
		return 0, fmt.Errorf("omemo: unknown version %q (want omemo0, omemo1, or omemo2)", s)
	}
}

// libsignalVersion returns the underlying Signal-protocol wire version
// this OMEMO version uses. Omemo1 and Omemo2 share the same crypto-engine
// version - libomemo-c itself only branches on "message_version >= 4", not
// on which OMEMO namespace is in play (confirmed by reading protocol.c) -
// they differ only in the outer XML/SCE dialect (see envelope.go).
func (v Version) libsignalVersion() int {
	if v == Omemo0 {
		return libsignal.ProtocolVersionV3
	}
	return libsignal.ProtocolVersionV4
}