// Copyright 2017 Vector Creations Ltd
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
	"context"
	"fmt"

	"github.com/matrix-org/gomatrixserverlib"
)

// An OutputType is a type of roomserver output.
type OutputType string

const (
	// OutputTypeNewRoomEvent indicates that the event is an OutputNewRoomEvent
	OutputTypeNewRoomEvent OutputType = "new_room_event"
	// OutputTypeOldRoomEvent indicates that the event is an OutputOldRoomEvent
	OutputTypeOldRoomEvent OutputType = "old_room_event"
	// OutputTypeNewInviteEvent indicates that the event is an OutputNewInviteEvent
	OutputTypeNewInviteEvent OutputType = "new_invite_event"
	// OutputTypeRetireInviteEvent indicates that the event is an OutputRetireInviteEvent
	OutputTypeRetireInviteEvent OutputType = "retire_invite_event"
	// OutputTypeRedactedEvent indicates that the event is an OutputRedactedEvent
	//
	// This event is emitted when a redaction has been 'validated' (meaning both the redaction and the event to redact are known).
	// Redaction validation happens when the roomserver receives either:
	// - A redaction for which we have the event to redact.
	// - Any event for which we have a redaction.
	// When the roomserver receives an event, it will check against the redactions table to see if there is a matching redaction
	// for the event. If there is, it will mark the redaction as validated and emit this event. In the common case of a redaction
	// happening after receiving the event to redact, the roomserver will emit a OutputTypeNewRoomEvent of m.room.redaction
	// immediately followed by a OutputTypeRedactedEvent. In the uncommon case of receiving the redaction BEFORE the event to redact,
	// the roomserver will emit a OutputTypeNewRoomEvent of the event to redact immediately followed by a OutputTypeRedactedEvent.
	//
	// In order to honour redactions correctly, downstream components must ignore m.room.redaction events emitted via OutputTypeNewRoomEvent.
	// When downstream components receive an OutputTypeRedactedEvent they must:
	// - Pull out the event to redact from the database. They should have this because the redaction is validated.
	// - Redact the event and set the corresponding `unsigned` fields to indicate it as redacted.
	// - Replace the event in the database.
	OutputTypeRedactedEvent OutputType = "redacted_event"

	// OutputTypeNewPeek indicates that the kafka event is an OutputNewPeek
	OutputTypeNewPeek OutputType = "new_peek"
	// OutputTypeNewInboundPeek indicates that the kafka event is an OutputNewInboundPeek
	OutputTypeNewInboundPeek OutputType = "new_inbound_peek"
	// OutputTypeRetirePeek indicates that the kafka event is an OutputRetirePeek
	OutputTypeRetirePeek OutputType = "retire_peek"
)

// An OutputEvent is an entry in the roomserver output kafka log.
// Consumers should check the type field when consuming this event.
type OutputEvent struct {
	// What sort of event this is.
	Type OutputType `json:"type"`
	// The content of event with type OutputTypeNewRoomEvent
	NewRoomEvent *OutputNewRoomEvent `json:"new_room_event,omitempty"`
	// The content of event with type OutputTypeOldRoomEvent
	OldRoomEvent *OutputOldRoomEvent `json:"old_room_event,omitempty"`
	// The content of event with type OutputTypeNewInviteEvent
	NewInviteEvent *OutputNewInviteEvent `json:"new_invite_event,omitempty"`
	// The content of event with type OutputTypeRetireInviteEvent
	RetireInviteEvent *OutputRetireInviteEvent `json:"retire_invite_event,omitempty"`
	// The content of event with type OutputTypeRedactedEvent
	RedactedEvent *OutputRedactedEvent `json:"redacted_event,omitempty"`
	// The content of event with type OutputTypeNewPeek
	NewPeek *OutputNewPeek `json:"new_peek,omitempty"`
	// The content of event with type OutputTypeNewInboundPeek
	NewInboundPeek *OutputNewInboundPeek `json:"new_inbound_peek,omitempty"`
	// The content of event with type OutputTypeRetirePeek
	RetirePeek *OutputRetirePeek `json:"retire_peek,omitempty"`
}

// Type of the OutputNewRoomEvent.
type OutputRoomEventType int

const (
	// The event is a timeline event and likely just happened.
	OutputRoomTimeline OutputRoomEventType = iota

	// The event is a state event and quite possibly happened in the past.
	OutputRoomState
)

// An OutputNewRoomEvent is written when the roomserver receives a new event.
// It contains the full matrix room event and enough information for a
// consumer to construct the current state of the room and the state before the
// event.
//
// When we talk about state in a matrix room we are talking about the state
// after a list of events. The current state is the state after the latest
// event IDs in the room. The state before an event is the state after its
// prev_events.
type OutputNewRoomEvent struct {
	// The Event.
	Event *gomatrixserverlib.HeaderedEvent `json:"event"`
	// Does the event completely rewrite the room state? If so, then AddsStateEventIDs
	// will contain the entire room state.
	RewritesState bool `json:"rewrites_state,omitempty"`
	// The latest events in the room after this event.
	// This can be used to set the prev events for new events in the room.
	// This also can be used to get the full current state after this event.
	LatestEventIDs []string `json:"latest_event_ids"`
	// The state event IDs that were added to the state of the room by this event.
	// Together with RemovesStateEventIDs this allows the receiver to keep an up to date
	// view of the current state of the room.
	AddsStateEventIDs []string `json:"adds_state_event_ids,omitempty"`
	// The state event IDs that were removed from the state of the room by this event.
	RemovesStateEventIDs []string `json:"removes_state_event_ids,omitempty"`
	// The ID of the event that was output before this event.
	// Or the empty string if this is the first event output for this room.
	// This is used by consumers to check if they can safely update their
	// current state using the delta supplied in AddsStateEventIDs and
	// RemovesStateEventIDs.
	//
	// If the LastSentEventID doesn't match what they were expecting it to be
	// they can use the LatestEventIDs to request the full current state.
	LastSentEventID string `json:"last_sent_event_id"`
	// The state event IDs that are part of the state at the event, but not
	// part of the current state. Together with the StateBeforeRemovesEventIDs
	// this can be used to construct the state before the event from the
	// current state. The StateBeforeAddsEventIDs and StateBeforeRemovesEventIDs
	// delta is applied after the AddsStateEventIDs and RemovesStateEventIDs.
	//
	// Consumers need to know the state at each event in order to determine
	// which users and servers are allowed to see the event. This information
	// is needed to apply the history visibility rules and to tell which
	// servers we need to push events to over federation.
	//
	// The state is given as a delta against the current state because they are
	// usually either the same state, or differ by just a couple of events.
	StateBeforeAddsEventIDs []string `json:"state_before_adds_event_ids,omitempty"`
	// The state event IDs that are part of the current state, but not part
	// of the state at the event.
	StateBeforeRemovesEventIDs []string `json:"state_before_removes_event_ids,omitempty"`
	// The server name to use to push this event to other servers.
	// Or empty if this event shouldn't be pushed to other servers.
	//
	// This is used by the federation sender component. We need to tell it what
	// event it needs to send because it can't tell on its own. Normally if an
	// event was created on this server then we are responsible for sending it.
	// However there are a couple of exceptions. The first is that when the
	// server joins a remote room through another matrix server, it is the job
	// of the other matrix server to send the event over federation. The second
	// is the reverse of the first, that is when a remote server joins a room
	// that we are in over federation using our server it is our responsibility
	// to send the join event to other matrix servers.
	//
	// We encode the server name that the event should be sent using here to
	// future proof the API for virtual hosting.
	SendAsServer string `json:"send_as_server"`
	// The transaction ID of the send request if sent by a local user and one
	// was specified
	TransactionID *TransactionID `json:"transaction_id,omitempty"`
}

// AddsState asks the roomserver API for events specified in `adds_state_event_ids`.
// The slice returned contains the output room event itself in all cases.
func (o *OutputNewRoomEvent) AddsState(ctx context.Context, rsAPI RoomserverInternalAPI) ([]*gomatrixserverlib.HeaderedEvent, error) {
	events := make([]*gomatrixserverlib.HeaderedEvent, 0, len(o.AddsStateEventIDs))
	eventsReq := &QueryEventsByIDRequest{
		EventIDs: o.AddsStateEventIDs,
	}
	eventsRes := &QueryEventsByIDResponse{}
	if err := rsAPI.QueryEventsByID(ctx, eventsReq, eventsRes); err != nil {
		return nil, fmt.Errorf("s.rsAPI.QueryEventsByID: %w", err)
	}
	events = append(events, eventsRes.Events...)
	return events, nil
}

// An OutputOldRoomEvent is written when the roomserver receives an old event.
// This will typically happen as a result of getting either missing events
// or backfilling. Downstream components may wish to send these events to
// clients when it is advantageous to do so, but with the consideration that
// the event is likely a historic event.
//
// Old events do not update forward extremities or the current room state,
// therefore they must not be treated as if they do. Downstream components
// should build their current room state up from OutputNewRoomEvents only.
type OutputOldRoomEvent struct {
	// The Event.
	Event *gomatrixserverlib.HeaderedEvent `json:"event"`
}

// An OutputNewInviteEvent is written whenever an invite becomes active.
// Invite events can be received outside of an existing room so have to be
// tracked separately from the room events themselves.
type OutputNewInviteEvent struct {
	// The room version of the invited room.
	RoomVersion gomatrixserverlib.RoomVersion `json:"room_version"`
	// The "m.room.member" invite event.
	Event *gomatrixserverlib.HeaderedEvent `json:"event"`
}

// An OutputRetireInviteEvent is written whenever an existing invite is no longer
// active. An invite stops being active if the user joins the room or if the
// invite is rejected by the user.
type OutputRetireInviteEvent struct {
	// The ID of the "m.room.member" invite event.
	EventID string
	// The target user ID of the "m.room.member" invite event that was retired.
	TargetUserID string
	// Optional event ID of the event that replaced the invite.
	// This can be empty if the invite was rejected locally and we were unable
	// to reach the server that originally sent the invite.
	RetiredByEventID string
	// The "membership" of the user after retiring the invite. One of "join"
	// "leave" or "ban".
	Membership string
}

// An OutputRedactedEvent is written whenever a redaction has been /validated/.
// Downstream components MUST redact the given event ID if they have stored the
// event JSON. It is guaranteed that this event ID has been seen before.
type OutputRedactedEvent struct {
	// The event ID that was redacted
	RedactedEventID string
	// The value of `unsigned.redacted_because` - the redaction event itself
	RedactedBecause *gomatrixserverlib.HeaderedEvent
}

// An OutputNewPeek is written whenever a user starts peeking into a room
// using a given device.
type OutputNewPeek struct {
	RoomID   string
	UserID   string
	DeviceID string
}

// An OutputNewInboundPeek is written whenever a server starts peeking into a room
type OutputNewInboundPeek struct {
	RoomID string
	PeekID string
	// the event ID at which the peek begins (so we can avoid
	// a race between tracking the state returned by /peek and emitting subsequent
	// peeked events)
	LatestEventID string
	ServerName    gomatrixserverlib.ServerName
	// how often we told the peeking server to renew the peek
	RenewalInterval int64
}

// An OutputRetirePeek is written whenever a user stops peeking into a room.
type OutputRetirePeek struct {
	RoomID   string
	UserID   string
	DeviceID string
}