package main

import (
	"context"
	"log"
	"strconv"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/sqs"
	"github.com/aws/aws-sdk-go-v2/service/sqs/types"
	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/messages"
)

const (
	cleanupInterval  = time.Second * 30
	cleanupThreshold = -2 * time.Minute
)

type sqsHandler struct {
	SQSClient   *sqs.Client
	SQSQueueURL *string
	IPC         *IPC
}

func (r *sqsHandler) pollMessages(context context.Context, chn chan<- *types.Message) {
	for {
		res, err := r.SQSClient.ReceiveMessage(context, &sqs.ReceiveMessageInput{
			QueueUrl:            r.SQSQueueURL,
			MaxNumberOfMessages: 10,
			WaitTimeSeconds:     15,
			MessageAttributeNames: []string{
				string(types.QueueAttributeNameAll),
			},
		})

		if err != nil {
			log.Printf("SQSHandler: encountered error while polling for messages: %v\n", err)
		}

		for _, message := range res.Messages {
			chn <- &message
		}
	}
}

func (r *sqsHandler) cleanupClientQueues(context context.Context) {
	for range time.Tick(cleanupInterval) {
		// Runs at fixed intervals to clean up any client queues that were last changed more than 2 minutes ago
		queueURLsList := []string{}
		var nextToken *string
		for {
			res, err := r.SQSClient.ListQueues(context, &sqs.ListQueuesInput{
				QueueNamePrefix: aws.String("snowflake-client-"),
				MaxResults:      aws.Int32(1000),
				NextToken:       nextToken,
			})
			if err != nil {
				log.Printf("SQSHandler: encountered error while retrieving client queues to clean up: %v\n", err)
			}
			queueURLsList = append(queueURLsList, res.QueueUrls...)
			if res.NextToken == nil {
				break
			} else {
				nextToken = res.NextToken
			}
		}

		numDeleted := 0
		cleanupCutoff := time.Now().Add(cleanupThreshold)
		for _, queueURL := range queueURLsList {
			if !strings.Contains(queueURL, "snowflake-client-") {
				continue
			}
			res, err := r.SQSClient.GetQueueAttributes(context, &sqs.GetQueueAttributesInput{
				QueueUrl:       aws.String(queueURL),
				AttributeNames: []types.QueueAttributeName{types.QueueAttributeNameLastModifiedTimestamp},
			})
			if err != nil {
				// According to the AWS SQS docs, the deletion process for a queue can take up to 60 seconds. So the queue
				// can be in the process of being deleted, but will still be returned by the ListQueues operation, but
				// fail when we try to GetQueueAttributes for the queue
				log.Printf("SQSHandler: encountered error while getting attribute of client queue %s. queue may already be deleted.\n", queueURL)
				continue
			}
			lastModifiedInt64, err := strconv.ParseInt(res.Attributes[string(types.QueueAttributeNameLastModifiedTimestamp)], 10, 64)
			if err != nil {
				log.Printf("SQSHandler: encountered invalid lastModifiedTimetamp value from client queue %s: %v\n", queueURL, err)
				continue
			}
			lastModified := time.Unix(lastModifiedInt64, 0)
			if lastModified.Before(cleanupCutoff) {
				_, err := r.SQSClient.DeleteQueue(context, &sqs.DeleteQueueInput{
					QueueUrl: aws.String(queueURL),
				})
				if err != nil {
					log.Printf("SQSHandler: encountered error when deleting client queue %s: %v\n", queueURL, err)
					continue
				} else {
					numDeleted += 1
				}

			}
		}
		log.Printf("SQSHandler: finished running iteration of client queue cleanup. found and deleted %d client queues.\n", numDeleted)
	}
}

func (r *sqsHandler) handleMessage(context context.Context, message *types.Message) {
	var encPollReq []byte
	var response []byte
	var err error

	clientID := message.MessageAttributes["ClientID"].StringValue
	if clientID == nil {
		log.Println("SQSHandler: got SDP offer in SQS message with no client ID. ignoring this message.")
		return
	}

	res, err := r.SQSClient.CreateQueue(context, &sqs.CreateQueueInput{
		QueueName: aws.String("snowflake-client-" + *clientID),
	})
	answerSQSURL := res.QueueUrl
	if err != nil {
		log.Printf("SQSHandler: error encountered when creating answer queue for client %s: %v\n", *clientID, err)
	}

	encPollReq = []byte(*message.Body)
	arg := messages.Arg{
		Body:       encPollReq,
		RemoteAddr: "",
	}
	err = r.IPC.ClientOffers(arg, &response)

	if err != nil {
		log.Printf("SQSHandler: error encountered when handling message: %v\n", err)
		return
	}

	r.SQSClient.SendMessage(context, &sqs.SendMessageInput{
		QueueUrl:    answerSQSURL,
		MessageBody: aws.String(string(response)),
	})
}

func (r *sqsHandler) deleteMessage(context context.Context, message *types.Message) {
	r.SQSClient.DeleteMessage(context, &sqs.DeleteMessageInput{
		QueueUrl:      r.SQSQueueURL,
		ReceiptHandle: message.ReceiptHandle,
	})
}

func newSQSHandler(context context.Context, sqsQueueName string, region string, i *IPC) (*sqsHandler, error) {
	log.Printf("Loading SQSHandler using SQS Queue %s in region %s\n", sqsQueueName, region)
	cfg, err := config.LoadDefaultConfig(context, config.WithRegion(region))
	if err != nil {
		return nil, err
	}

	client := sqs.NewFromConfig(cfg)

	// Creates the queue if a queue with the same name doesn't exist. If a queue with the same name and attributes
	// already exists, then nothing will happen. If a queue with the same name, but different attributes exists, then
	// an error will be returned
	res, err := client.CreateQueue(context, &sqs.CreateQueueInput{
		QueueName: aws.String(sqsQueueName),
		Attributes: map[string]string{
			"MessageRetentionPeriod": strconv.FormatInt(int64((5 * time.Minute).Seconds()), 10),
		},
	})

	if err != nil {
		return nil, err
	}

	return &sqsHandler{
		SQSClient:   client,
		SQSQueueURL: res.QueueUrl,
		IPC:         i,
	}, nil
}

func (r *sqsHandler) PollAndHandleMessages(context context.Context) {
	log.Println("SQSHandler: Starting to poll for messages at: " + *r.SQSQueueURL)
	messagesChn := make(chan *types.Message, 2)
	go r.pollMessages(context, messagesChn)
	go r.cleanupClientQueues(context)

	for message := range messagesChn {
		r.handleMessage(context, message)
		r.deleteMessage(context, message)
	}
}