// Copyright (c) 2017 Cisco and/or its affiliates.
//
// 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 (
	"time"
)

// MessageType represents the type of a VPP message.
type MessageType int

const (
	// RequestMessage represents a VPP request message
	RequestMessage MessageType = iota
	// ReplyMessage represents a VPP reply message
	ReplyMessage
	// EventMessage represents a VPP notification event message
	EventMessage
	// OtherMessage represents other VPP message (e.g. counters)
	OtherMessage
)

// Message is an interface that is implemented by all VPP Binary API messages generated by the binapigenerator.
type Message interface {
	// GetMessageName returns the original VPP name of the message, as defined in the VPP API.
	GetMessageName() string

	// GetMessageType returns the type of the VPP message.
	GetMessageType() MessageType

	// GetCrcString returns the string with CRC checksum of the message definition (the string represents a hexadecimal number).
	GetCrcString() string
}

// DataType is an interface that is implemented by all VPP Binary API data types by the binapi_generator.
type DataType interface {
	// GetTypeName returns the original VPP name of the data type, as defined in the VPP API.
	GetTypeName() string

	// GetCrcString returns the string with CRC checksum of the data type definition (the string represents a hexadecimal number).
	GetCrcString() string
}

// ChannelProvider provides the communication channel with govpp core.
type ChannelProvider interface {
	// NewAPIChannel returns a new channel for communication with VPP via govpp core.
	// It uses default buffer sizes for the request and reply Go channels.
	NewAPIChannel() (Channel, error)

	// NewAPIChannelBuffered returns a new channel for communication with VPP via govpp core.
	// It allows to specify custom buffer sizes for the request and reply Go channels.
	NewAPIChannelBuffered(reqChanBufSize, replyChanBufSize int) (Channel, error)
}

// MessageDecoder provides functionality for decoding binary data to generated API messages.
type MessageDecoder interface {
	// DecodeMsg decodes binary-encoded data of a message into provided Message structure.
	DecodeMsg(data []byte, msg Message) error
}

// MessageIdentifier provides identification of generated API messages.
type MessageIdentifier interface {
	// GetMessageID returns message identifier of given API message.
	GetMessageID(msg Message) (uint16, error)
	// LookupByID looks up message name and crc by ID
	LookupByID(ID uint16) (string, error)
}

// Channel provides methods for direct communication with VPP channel.
type Channel interface {
	// SendRequest asynchronously sends a request to VPP. Returns a request context, that can be used to call ReceiveReply.
	// In case of any errors by sending, the error will be delivered to ReplyChan (and returned by ReceiveReply).
	SendRequest(msg Message) RequestCtx
	// SendMultiRequest asynchronously sends a multipart request (request to which multiple responses are expected) to VPP.
	// Returns a multipart request context, that can be used to call ReceiveReply.
	// In case of any errors by sending, the error will be delivered to ReplyChan (and returned by ReceiveReply).
	SendMultiRequest(msg Message) MultiRequestCtx
	// SubscribeNotification subscribes for receiving of the specified notification messages via provided Go channel.
	// Note that the caller is responsible for creating the Go channel with preferred buffer size. If the channel's
	// buffer is full, the notifications will not be delivered into it.
	SubscribeNotification(notifChan chan Message, msgFactory func() Message) (*NotifSubscription, error)
	// UnsubscribeNotification unsubscribes from receiving the notifications tied to the provided notification subscription.
	UnsubscribeNotification(subscription *NotifSubscription) error
	// CheckMessageCompatibility checks whether provided messages are compatible with the version of VPP
	// which the library is connected to.
	CheckMessageCompatibility(messages ...Message) error
	// SetReplyTimeout sets the timeout for replies from VPP. It represents the maximum time the API waits for a reply
	// from VPP before returning an error.
	SetReplyTimeout(timeout time.Duration)
	// GetRequestChannel returns request go channel of the VPP channel
	GetRequestChannel() chan<- *VppRequest
	// GetReplyChannel returns reply go channel of the VPP channel
	GetReplyChannel() <-chan *VppReply
	// GetNotificationChannel returns notification go channel of the VPP channel
	GetNotificationChannel() chan<- *NotifSubscribeRequest
	// GetNotificationReplyChannel returns notification reply go channel of the VPP channel
	GetNotificationReplyChannel() <-chan error
	// GetMessageDecoder returns message decoder instance
	GetMessageDecoder() MessageDecoder
	// GetID returns channel's ID
	GetID() uint16
	// Close closes the API channel and releases all API channel-related resources in the ChannelProvider.
	Close()
}

// RequestCtx is helper interface which allows to receive reply on request context data
type RequestCtx interface {
	// ReceiveReply receives a reply from VPP (blocks until a reply is delivered from VPP, or until an error occurs).
	// The reply will be decoded into the msg argument. Error will be returned if the response cannot be received or decoded.
	ReceiveReply(msg Message) error
}

// MultiRequestCtx is helper interface which allows to receive reply on multi-request context data
type MultiRequestCtx interface {
	// ReceiveReply receives a reply from VPP (blocks until a reply is delivered from VPP, or until an error occurs).
	// The reply will be decoded into the msg argument. If the last reply has been already consumed, lastReplyReceived is
	// set to true. Do not use the message itself if lastReplyReceived is true - it won't be filled with actual data.
	// Error will be returned if the response cannot be received or decoded.
	ReceiveReply(msg Message) (lastReplyReceived bool, err error)
}

// VppRequest is a request that will be sent to VPP.
type VppRequest struct {
	SeqNum    uint16  // sequence number
	Message   Message // binary API message to be send to VPP
	Multipart bool    // true if multipart response is expected, false otherwise
}

// VppReply is a reply received from VPP.
type VppReply struct {
	MessageID         uint16 // ID of the message
	SeqNum            uint16 // sequence number
	Data              []byte // encoded data with the message - MessageDecoder can be used for decoding
	LastReplyReceived bool   // in case of multipart replies, true if the last reply has been already received and this one should be ignored
	Error             error  // in case of error, data is nil and this member contains error description
}

// NotifSubscribeRequest is a request to subscribe for delivery of specific notification messages.
type NotifSubscribeRequest struct {
	Subscription *NotifSubscription // subscription details
	Subscribe    bool               // true if this is a request to subscribe, false if unsubscribe
}

// NotifSubscription represents a subscription for delivery of specific notification messages.
type NotifSubscription struct {
	NotifChan  chan Message   // channel where notification messages will be delivered to
	MsgFactory func() Message // function that returns a new instance of the specific message that is expected as a notification
}