// 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 types

import (
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"strings"

	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/tidwall/gjson"
)

var (
	// ErrInvalidPaginationTokenType is returned when an attempt at creating a
	// new instance of PaginationToken with an invalid type (i.e. neither "s"
	// nor "t").
	ErrInvalidPaginationTokenType = fmt.Errorf("Pagination token has an unknown prefix (should be either s or t)")
	// ErrInvalidPaginationTokenLen is returned when the pagination token is an
	// invalid length
	ErrInvalidPaginationTokenLen = fmt.Errorf("Pagination token has an invalid length")
)

// StreamPosition represents the offset in the sync stream a client is at.
type StreamPosition int64

// Same as gomatrixserverlib.Event but also has the PDU stream position for this event.
type StreamEvent struct {
	gomatrixserverlib.HeaderedEvent
	StreamPosition  StreamPosition
	TransactionID   *api.TransactionID
	ExcludeFromSync bool
}

// PaginationTokenType represents the type of a pagination token.
// It can be either "s" (representing a position in the whole stream of events)
// or "t" (representing a position in a room's topology/depth).
type PaginationTokenType string

const (
	// PaginationTokenTypeStream represents a position in the server's whole
	// stream of events
	PaginationTokenTypeStream PaginationTokenType = "s"
	// PaginationTokenTypeTopology represents a position in a room's topology.
	PaginationTokenTypeTopology PaginationTokenType = "t"
)

// PaginationToken represents a pagination token, used for interactions with
// /sync or /messages, for example.
type PaginationToken struct {
	//Position StreamPosition
	Type              PaginationTokenType
	PDUPosition       StreamPosition
	EDUTypingPosition StreamPosition
}

// NewPaginationTokenFromString takes a string of the form "xyyyy..." where "x"
// represents the type of a pagination token and "yyyy..." the token itself, and
// parses it in order to create a new instance of PaginationToken. Returns an
// error if the token couldn't be parsed into an int64, or if the token type
// isn't a known type (returns ErrInvalidPaginationTokenType in the latter
// case).
func NewPaginationTokenFromString(s string) (token *PaginationToken, err error) {
	if len(s) == 0 {
		return nil, ErrInvalidPaginationTokenLen
	}

	token = new(PaginationToken)
	var positions []string

	switch t := PaginationTokenType(s[:1]); t {
	case PaginationTokenTypeStream, PaginationTokenTypeTopology:
		token.Type = t
		positions = strings.Split(s[1:], "_")
	default:
		token.Type = PaginationTokenTypeStream
		positions = strings.Split(s, "_")
	}

	// Try to get the PDU position.
	if len(positions) >= 1 {
		if pduPos, err := strconv.ParseInt(positions[0], 10, 64); err != nil {
			return nil, err
		} else if pduPos < 0 {
			return nil, errors.New("negative PDU position not allowed")
		} else {
			token.PDUPosition = StreamPosition(pduPos)
		}
	}

	// Try to get the typing position.
	if len(positions) >= 2 {
		if typPos, err := strconv.ParseInt(positions[1], 10, 64); err != nil {
			return nil, err
		} else if typPos < 0 {
			return nil, errors.New("negative EDU typing position not allowed")
		} else {
			token.EDUTypingPosition = StreamPosition(typPos)
		}
	}

	return
}

// NewPaginationTokenFromTypeAndPosition takes a PaginationTokenType and a
// StreamPosition and returns an instance of PaginationToken.
func NewPaginationTokenFromTypeAndPosition(
	t PaginationTokenType, pdupos StreamPosition, typpos StreamPosition,
) (p *PaginationToken) {
	return &PaginationToken{
		Type:              t,
		PDUPosition:       pdupos,
		EDUTypingPosition: typpos,
	}
}

// String translates a PaginationToken to a string of the "xyyyy..." (see
// NewPaginationToken to know what it represents).
func (p *PaginationToken) String() string {
	return fmt.Sprintf("%s%d_%d", p.Type, p.PDUPosition, p.EDUTypingPosition)
}

// WithUpdates returns a copy of the PaginationToken with updates applied from another PaginationToken.
// If the latter PaginationToken contains a field that is not 0, it is considered an update,
// and its value will replace the corresponding value in the PaginationToken on which WithUpdates is called.
func (pt *PaginationToken) WithUpdates(other PaginationToken) PaginationToken {
	ret := *pt
	if other.PDUPosition != 0 {
		ret.PDUPosition = other.PDUPosition
	}
	if other.EDUTypingPosition != 0 {
		ret.EDUTypingPosition = other.EDUTypingPosition
	}
	return ret
}

// IsAfter returns whether one PaginationToken refers to states newer than another PaginationToken.
func (sp *PaginationToken) IsAfter(other PaginationToken) bool {
	return sp.PDUPosition > other.PDUPosition ||
		sp.EDUTypingPosition > other.EDUTypingPosition
}

// PrevEventRef represents a reference to a previous event in a state event upgrade
type PrevEventRef struct {
	PrevContent   json.RawMessage `json:"prev_content"`
	ReplacesState string          `json:"replaces_state"`
	PrevSender    string          `json:"prev_sender"`
}

// Response represents a /sync API response. See https://matrix.org/docs/spec/client_server/r0.2.0.html#get-matrix-client-r0-sync
type Response struct {
	NextBatch   string `json:"next_batch"`
	AccountData struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"account_data"`
	Presence struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"presence"`
	Rooms struct {
		Join   map[string]JoinResponse   `json:"join"`
		Invite map[string]InviteResponse `json:"invite"`
		Leave  map[string]LeaveResponse  `json:"leave"`
	} `json:"rooms"`
}

// NewResponse creates an empty response with initialised maps.
func NewResponse(token PaginationToken) *Response {
	res := Response{
		NextBatch: token.String(),
	}
	// Pre-initialise the maps. Synapse will return {} even if there are no rooms under a specific section,
	// so let's do the same thing. Bonus: this means we can't get dreaded 'assignment to entry in nil map' errors.
	res.Rooms.Join = make(map[string]JoinResponse)
	res.Rooms.Invite = make(map[string]InviteResponse)
	res.Rooms.Leave = make(map[string]LeaveResponse)

	// Also pre-intialise empty slices or else we'll insert 'null' instead of '[]' for the value.
	// TODO: We really shouldn't have to do all this to coerce encoding/json to Do The Right Thing. We should
	//       really be using our own Marshal/Unmarshal implementations otherwise this may prove to be a CPU bottleneck.
	//       This also applies to NewJoinResponse, NewInviteResponse and NewLeaveResponse.
	res.AccountData.Events = make([]gomatrixserverlib.ClientEvent, 0)
	res.Presence.Events = make([]gomatrixserverlib.ClientEvent, 0)

	// Fill next_batch with a pagination token. Since this is a response to a sync request, we can assume
	// we'll always return a stream token.
	res.NextBatch = NewPaginationTokenFromTypeAndPosition(
		PaginationTokenTypeStream,
		StreamPosition(token.PDUPosition),
		StreamPosition(token.EDUTypingPosition),
	).String()

	return &res
}

// IsEmpty returns true if the response is empty, i.e. used to decided whether
// to return the response immediately to the client or to wait for more data.
func (r *Response) IsEmpty() bool {
	return len(r.Rooms.Join) == 0 &&
		len(r.Rooms.Invite) == 0 &&
		len(r.Rooms.Leave) == 0 &&
		len(r.AccountData.Events) == 0 &&
		len(r.Presence.Events) == 0
}

// JoinResponse represents a /sync response for a room which is under the 'join' key.
type JoinResponse struct {
	State struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"state"`
	Timeline struct {
		Events    []gomatrixserverlib.ClientEvent `json:"events"`
		Limited   bool                            `json:"limited"`
		PrevBatch string                          `json:"prev_batch"`
	} `json:"timeline"`
	Ephemeral struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"ephemeral"`
	AccountData struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"account_data"`
}

// NewJoinResponse creates an empty response with initialised arrays.
func NewJoinResponse() *JoinResponse {
	res := JoinResponse{}
	res.State.Events = make([]gomatrixserverlib.ClientEvent, 0)
	res.Timeline.Events = make([]gomatrixserverlib.ClientEvent, 0)
	res.Ephemeral.Events = make([]gomatrixserverlib.ClientEvent, 0)
	res.AccountData.Events = make([]gomatrixserverlib.ClientEvent, 0)
	return &res
}

// InviteResponse represents a /sync response for a room which is under the 'invite' key.
type InviteResponse struct {
	InviteState struct {
		Events json.RawMessage `json:"events"`
	} `json:"invite_state"`
}

// NewInviteResponse creates an empty response with initialised arrays.
func NewInviteResponse(event gomatrixserverlib.HeaderedEvent) *InviteResponse {
	res := InviteResponse{}
	res.InviteState.Events = json.RawMessage{'[', ']'}
	if inviteRoomState := gjson.GetBytes(event.Unsigned(), "invite_room_state"); inviteRoomState.Exists() {
		res.InviteState.Events = json.RawMessage(inviteRoomState.Raw)
	}
	return &res
}

// LeaveResponse represents a /sync response for a room which is under the 'leave' key.
type LeaveResponse struct {
	State struct {
		Events []gomatrixserverlib.ClientEvent `json:"events"`
	} `json:"state"`
	Timeline struct {
		Events    []gomatrixserverlib.ClientEvent `json:"events"`
		Limited   bool                            `json:"limited"`
		PrevBatch string                          `json:"prev_batch"`
	} `json:"timeline"`
}

// NewLeaveResponse creates an empty response with initialised arrays.
func NewLeaveResponse() *LeaveResponse {
	res := LeaveResponse{}
	res.State.Events = make([]gomatrixserverlib.ClientEvent, 0)
	res.Timeline.Events = make([]gomatrixserverlib.ClientEvent, 0)
	return &res
}