// Package e2ee is a backend-agnostic end-to-end encryption abstraction for
// telegabber's XMPP side. It knows nothing about stanza XML shape - a
// Backend deals only in opaque byte envelopes; wrapping/unwrapping those
// into <encrypted>/PEP XML is the caller's job (see e2ee/omemo for the
// first, and so far only, implementation, and its envelope.go for the
// XEP-0384 wire format specifically).
package e2ee

// PeerID identifies one bridging endpoint's cryptographic identity scope.
// For telegabber this is always a bare XMPP JID: either a bridged chat's
// pseudo-JID (whose keys the gateway owns and generates) or a real remote
// user's bare JID (whose keys the gateway only ever fetches).
type PeerID string

// DeviceID is an opaque per-backend device identifier, serialized as its
// natural string form (OMEMO: decimal uint32; a hypothetical single-key
// backend could always use "0" or the empty string).
type DeviceID string

// Envelope is an opaque, backend-defined encrypted payload, plus enough
// metadata for the xmpp layer to build the wire XML generically.
type Envelope struct {
	Backend string // e.g. "omemo" - which backend produced Raw, so the xmpp layer picks the right XML shape
	Raw     []byte // backend-specific serialized envelope
}

// Namespaces is what a Backend wants advertised/served.
type Namespaces struct {
	Disco []string // disco#info features to advertise, across every supported Variant (e.g. "...+notify" hints)
}

// Variant identifies one of a Backend's parallel wire-format generations
// (e.g. OMEMO's omemo0/omemo1/omemo2 - three simultaneously-supported
// namespaces sharing one identity/prekey set). It's an opaque string a
// Backend defines and interprets itself; other packages only ever pass a
// Variant back between Variants()/DefaultVariant()/NegotiatedVariant() and
// DeviceListNode()/BundleNode()/PublishedIdentity()/PublishedBundle() -
// never construct or compare one directly. A backend with only one
// generation can just always return/accept a single fixed value.
type Variant string

// DeviceListDoc is an opaque, backend-defined serialization of a peer's
// PEP device-list document (fetched from them, or published for a chat
// pseudo-JID we own).
type DeviceListDoc struct{ Raw []byte }

// BundleDoc is an opaque, backend-defined serialization of one device's
// PEP bundle document.
type BundleDoc struct{ Raw []byte }

// DeviceInfo describes one known device of a peer, for trust-listing
// ad-hoc commands. Trusted is false only if the device has been manually
// blocked (see Backend.BlockDevice) - TOFU itself always trusts a
// never-before-seen device automatically, so a session existing at all
// already implies TOFU accepted it; Trusted here reflects the manual
// override layered on top, not TOFU's own verdict.
type DeviceInfo struct {
	ID          DeviceID
	Trusted     bool
	Fingerprint string
}

// Backend is the minimal contract a pluggable E2EE scheme must implement.
type Backend interface {
	// Name identifies the backend for config/logging (e.g. "omemo").
	Name() string

	// Namespaces lists what this backend wants advertised/served.
	Namespaces() Namespaces

	// Variants lists every wire-format variant this backend can
	// simultaneously serve/negotiate right now (e.g. all three OMEMO
	// namespaces, or fewer if this build lacks support for some of them -
	// see libsignal.ProtocolV4Supported). All variants are always
	// servable/fetchable regardless of any given chat's negotiated state
	// (see NegotiatedVariant) - "supported" is a deploy-time/build-time
	// property, not a per-chat one.
	Variants() []Variant
	// DefaultVariant is what a brand new chat (no negotiation evidence
	// yet) starts out using for outgoing content - e.g. OMEMO's omemo0,
	// the most widely deployed variant.
	DefaultVariant() Variant
	// NegotiatedVariant is the wire-format variant currently in use for
	// owner's (an OwnedPeer) outgoing content: DefaultVariant until an
	// inbound message from owner's peer is decrypted, at which point it
	// tracks whatever variant that peer's own client is actually using
	// (see Decrypt). Implementations may only be able to fix this at
	// session establishment time, not change it later for an
	// already-established chat - see e2ee/omemo.Backend.NegotiatedVariant's
	// doc comment for a concrete example of why.
	NegotiatedVariant(owner PeerID) (Variant, error)

	// DeviceListNode and BundleNode name the PEP node one of this backend's
	// own device-list/bundle documents is published/fetched under, for the
	// given variant. Note BundleNode's return value may or may not depend
	// on device - some backends address every device's bundle under one
	// shared node (item id = device), others use a distinct node per
	// device; callers (e2ee/fetch.go, and the xmpp package's PEP-serving IQ
	// handlers) must not assume either shape.
	DeviceListNode(variant Variant) string
	BundleNode(variant Variant, device DeviceID) string

	// EnsureIdentity creates (idempotently) a local cryptographic identity
	// for a PeerID this gateway owns (a bridged chat pseudo-JID - built via
	// OwnedPeer, since a chat pseudo-JID alone isn't globally unique across
	// telegabber's multiple bridged Telegram logins), generating and
	// persisting whatever key material the backend needs. One identity
	// serves every Variant simultaneously. Every other method that touches
	// identity/prekey material calls this internally too (it's cheap and
	// idempotent), so callers never strictly need to call it themselves -
	// it's exposed mainly for a future eager-bootstrap use case (e.g.
	// pre-creating identities for every personal chat when an account's
	// OMEMO toggle is turned on, instead of lazily on first use).
	EnsureIdentity(peer PeerID) error

	// OwnDevice is this backend's own (and only) published device id for
	// any owned peer - telegabber only ever needs one device per bridged
	// chat identity (see EnsureIdentity's doc comment), so unlike Devices
	// (which lists a remote peer's possibly-many devices) this takes no
	// arguments and returns no error.
	OwnDevice() DeviceID

	// PublishedIdentity returns the material this gateway must SERVE to
	// pubsub GET requests for its own PeerID (an OwnedPeer - see
	// EnsureIdentity) device list under the given variant, pre-marshaled to
	// opaque bytes the xmpp layer wraps in <items>/<item>.
	PublishedIdentity(peer PeerID, variant Variant) (DeviceListDoc, error)
	// PublishedBundle is the same, for one specific device's bundle node.
	PublishedBundle(peer PeerID, device DeviceID, variant Variant) (BundleDoc, error)

	// IngestRemoteDeviceList / IngestRemoteBundle feed the results of an
	// outbound PEP fetch (device-list, then per-device bundle) for a real
	// remote peer (owner is an OwnedPeer identifying which of this
	// gateway's identities is doing the fetching; peer is the remote's
	// plain bare JID, no scoping needed) into the backend's store,
	// establishing/refreshing sessions as needed (trust decisions happen
	// inside here). IngestRemoteDeviceList returns the device ids it found,
	// so a caller like e2ee/fetch.go knows which bundles to fetch next
	// without needing to parse the backend-specific document itself.
	IngestRemoteDeviceList(owner PeerID, peer PeerID, doc DeviceListDoc) ([]DeviceID, error)
	IngestRemoteBundle(owner PeerID, peer PeerID, device DeviceID, doc BundleDoc) error

	// Encrypt produces an opaque envelope addressed to every known device
	// of every given recipient, ready to be embedded in a stanza by the
	// xmpp layer. from is the identity doing the encrypting (an OwnedPeer -
	// see EnsureIdentity); to are the real remote peers' plain bare JIDs.
	Encrypt(from PeerID, to []PeerID, plaintext []byte) (Envelope, error)

	// Decrypt consumes an inbound envelope addressed to "to" (an
	// OwnedPeer - see EnsureIdentity) from "from" (the real remote peer's
	// plain bare JID) and returns plaintext. A successful decrypt also
	// updates "to"'s NegotiatedVariant to whichever variant this envelope
	// actually used - see NegotiatedVariant's doc comment.
	Decrypt(from PeerID, to PeerID, env Envelope) ([]byte, error)

	// Devices lists peer's known devices, as seen from owner's (an
	// OwnedPeer) point of view - for trust-listing ad-hoc commands.
	Devices(owner PeerID, peer PeerID) ([]DeviceInfo, error)

	// Enabled and SetEnabled track the per-chat "OMEMO is active" sticky
	// flag (the auto-upgrade trigger: set the first time an inbound
	// message decrypts successfully for owner, read by the outbound
	// encrypt hook alongside the account-wide config toggle). owner is an
	// OwnedPeer; a chat that was never marked active reports false, not an
	// error.
	Enabled(owner PeerID) (bool, error)
	SetEnabled(owner PeerID, enabled bool) error

	// Override, SetOverride, and ClearOverride manage owner's (an
	// OwnedPeer) manual on/off override of the account-wide Mode (see
	// ShouldEncrypt) - a per-chat "/omemo on"/"/omemo off" that wins
	// regardless of the global setting, until cleared. isSet is false when
	// no override has been set (follow the account-wide mode instead).
	Override(owner PeerID) (on bool, isSet bool, err error)
	SetOverride(owner PeerID, on bool) error
	ClearOverride(owner PeerID) error

	// BlockDevice and UnblockDevice manually override one of peer's
	// devices' TOFU trust, as seen from owner's (an OwnedPeer) point of
	// view - TOFU itself always stays on (a device's first-seen key is
	// always trusted automatically), this only ever narrows it further. A
	// blocked device's messages are rejected by Decrypt and skipped by
	// Encrypt, regardless of any session already established with it - see
	// Devices' Trusted field for the resulting per-device state.
	BlockDevice(owner PeerID, peer PeerID, device DeviceID) error
	UnblockDevice(owner PeerID, peer PeerID, device DeviceID) error

	// Close flushes and releases whatever storage/resources this backend
	// holds (e.g. the underlying Badger DB), for a clean process shutdown -
	// mirrors gateway.IdsDB.Close()'s role for the id-mapping store.
	Close() error
}