package room

import (
	"github.com/rs/xid"
	"go.uber.org/zap"
)

// internalClient is used by the room itself to track information about a client.
type internalClient struct {
	// id is the id that the client identifies itself with in all clientMessage instances it sends.
	id xid.ID
	// outgoingChannel is a channel that the room can send messages to the client on.
	outgoingChannel chan<- Message
	// privateChannel is true iff the room can close the outgoingChannel when the client and room have completed their
	// close handshake.
	privateChannel bool
	// broadcast is true iff the client requested to be included on broadcasts on creation.
	broadcast bool
}

type NewClientOptions struct {
	// IncomingChannel is the channel to use as the room's channel to send messages to - the new Client's IncomingChannel.
	// If this is non-nil, the room will not automatically close the IncomingChannel after a shutdown is negotiated.
	// If this is nil, a new channel will be allocated on join and closed on shutdown.
	IncomingChannel chan Message
	// If AcceptBroadcasts is true, the room will send all broadcasts originating from other clients to this client.
	AcceptBroadcasts bool
	// If RequestStartingState is true, the room will send a copy of the current state as of when the JoinRequest was
	// received in the JoinResponse that will be the first message the Client receives.
	RequestStartingState bool
	// If sets,
	Logger *zap.Logger
}

// Client is the structure used by clients external to the Room package to communicate with the Room.
// It is not expected to be parallel-safe; to run it in parallel, use the NewClient method and send the new client to
// the new goroutine.
type Client struct {
	// id is the ClientID used by the client for all communications.
	id xid.ID
	// roomId is the unique ID of the room (not its map).
	roomId xid.ID
	// incomingChannel is the channel that this client receives messages on.
	incomingChannel <-chan Message
	// outgoingChannel is the channel that this client sends messages on.
	// Becomes nil if the client has been completely shut down.
	outgoingChannel chan<- ClientMessage
	// Once Leave or AcknowledgeShutdown have been triggered, this flag is set, preventing use of other messages.
	shuttingDown bool
}

// ID is the ID used by this client to identify itself to the Room.
func (c *Client) ID() xid.ID {
	return c.id
}

// RoomID is the ID used by the room to differentiate itself from other rooms.
// It is not the map's internal ID.
func (c *Client) RoomID() xid.ID {
	return c.id
}

// IncomingChannel is the channel the client can listen on for messages from the room.
func (c *Client) IncomingChannel() <-chan Message {
	return c.incomingChannel
}

// OutgoingChannel is the channel the client can send messages to the room on.
func (c *Client) OutgoingChannel() chan<- ClientMessage {
	if c.outgoingChannel == nil {
		panic("Already finished shutting down; no new messages should be sent")
	}
	return c.outgoingChannel
}

// newClientForRoom uses the necessary parameters to create and join a Client for the given room.
func newClientForRoom(roomId xid.ID, outgoingChannel chan<- ClientMessage, opts NewClientOptions) *Client {
	var privateChannel bool
	var incomingChannel chan Message
	if opts.IncomingChannel != nil {
		incomingChannel = opts.IncomingChannel
		privateChannel = false
	} else {
		incomingChannel = make(chan Message, 1)
		privateChannel = true
	}
	result := Client{
		id:              xid.New(),
		roomId:          roomId,
		incomingChannel: incomingChannel,
		outgoingChannel: outgoingChannel,
		shuttingDown:    false,
	}
	result.outgoingChannel <- JoinRequest{
		id:               result.id,
		returnChannel:    incomingChannel,
		privateChannel:   privateChannel,
		broadcast:        opts.AcceptBroadcasts,
		wantCurrentState: opts.RequestStartingState,
	}
	return &result
}

// NewClient creates a new client belonging to the same room as this client with a random ID.
// The new client will be automatically joined to the channel.
func (c *Client) NewClient(opts NewClientOptions) *Client {
	if c.shuttingDown {
		panic("Already started shutting down; no new messages should be sent")
	}
	return newClientForRoom(c.roomId, c.outgoingChannel, opts)
}

// The message created by Refresh causes the client to request a fresh copy of the state.
func (c *Client) Refresh() RefreshRequest {
	if c.shuttingDown {
		panic("Already started shutting down; no new messages should be sent")
	}
	return RefreshRequest{
		id: c.id,
	}
}

// The message created by Leave causes the local client to signal that it is shutting down.
// It is important to Leave to avoid dangling clients having messages sent to nothing.
// After sending Leave, the client must confirm that it has been removed by waiting for a LeaveResponse, accompanied by
// the closing of the Client's IncomingChannel if it was a private channel.
// No further messages should be sent after Leave except AcknowledgeShutdown if Leave and requestShutdown crossed paths in midair.
func (c *Client) Leave() LeaveRequest {
	if c.shuttingDown {
		panic("Already started shutting down; no new messages should be sent")
	}
	c.shuttingDown = true
	return LeaveRequest{
		id: c.id,
	}
}

// The message created by Stop causes the local client to signal that it is shutting down.
// It is important to Stop when the room needs to be shut down.
// After sending Stop, the client must confirm that it has been removed by waiting for a ShutdownRequest, which should
// be handled normally.
// No further messages should be sent after Stop except AcknowledgeShutdown.
func (c *Client) Stop() StopRequest {
	if c.shuttingDown {
		panic("Already started shutting down; no new messages should be sent")
	}
	c.shuttingDown = true
	return StopRequest{
		id: c.id,
	}
}

// AcknowledgeShutdown causes the local client to signal that it has acknowledged that the room is shutting down.
// No further messages can be sent after AcknowledgeShutdown; attempting to do so will block forever, as the
// OutgoingChannel has become nil.
func (c *Client) AcknowledgeShutdown() ShutdownResponse {
	if c.outgoingChannel == nil {
		panic("Already finished shutting down; no new messages should be sent")
	}
	c.shuttingDown = true
	c.outgoingChannel = nil
	return ShutdownResponse{
		id: c.id,
	}
}