// Copyright 2017 Google Inc.
//
// 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 apiGatewayConfDeploy

import (
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"path"
	"strings"
	"sync/atomic"
	"time"
)

const (
	blobStoreUri = "/blobs/{blobId}"
)

type bundleManagerInterface interface {
	initializeBundleDownloading()
	queueDownloadRequest(*DataDeployment)
	enqueueRequest(*DownloadRequest)
	makeDownloadRequest(string) *DownloadRequest
	deleteBundlesFromDeployments([]DataDeployment)
	deleteBundleById(string)
	Close()
}

type bundleManager struct {
	blobServerUrl             string
	dbMan                     dbManagerInterface
	apiMan                    apiManagerInterface
	concurrentDownloads       int
	markDeploymentFailedAfter time.Duration
	bundleDownloadConnTimeout time.Duration
	bundleRetryDelay          time.Duration
	bundleCleanupDelay        time.Duration
	downloadQueue             chan *DownloadRequest
	isClosed                  *int32
	workers                   []*BundleDownloader
}

type blobServerResponse struct {
	Id                       string `json:"id"`
	Kind                     string `json:"kind"`
	Self                     string `json:"self"`
	SignedUrl                string `json:"signedurl"`
	SignedUrlExpiryTimestamp string `json:"signedurlexpirytimestamp"`
}

func (bm *bundleManager) initializeBundleDownloading() {
	atomic.StoreInt32(bm.isClosed, 0)
	bm.workers = make([]*BundleDownloader, bm.concurrentDownloads)

	// create workers
	for i := 0; i < bm.concurrentDownloads; i++ {
		worker := BundleDownloader{
			id:       i + 1,
			workChan: make(chan *DownloadRequest),
			bm:       bm,
		}
		bm.workers[i] = &worker
		worker.Start()
	}
}

// download bundle blob and resource blob
// TODO do not download duplicate blobs
func (bm *bundleManager) queueDownloadRequest(dep *DataDeployment) {
	blobReq := bm.makeDownloadRequest(dep.BlobID)
	resourceReq := bm.makeDownloadRequest(dep.BlobResourceID)

	go func() {
		bm.enqueueRequest(blobReq)
		bm.enqueueRequest(resourceReq)
	}()
}

func (bm *bundleManager) makeDownloadRequest(id string) *DownloadRequest {
	markFailedAt := time.Now().Add(bm.markDeploymentFailedAfter)
	retryIn := bm.bundleRetryDelay
	maxBackOff := 5 * time.Minute

	return &DownloadRequest{
		blobServerURL: bm.blobServerUrl,
		bm:            bm,
		blobId:        id,
		backoffFunc:   createBackoff(retryIn, maxBackOff),
		markFailedAt:  markFailedAt,
		connTimeout:   bm.bundleDownloadConnTimeout,
	}
}

// a blocking method to enqueue download requests
func (bm *bundleManager) enqueueRequest(r *DownloadRequest) {
	if atomic.LoadInt32(bm.isClosed) == 1 {
		return
	}
	/*
		defer func() {
			if r := recover(); r != nil {
				log.Warn("trying to enque requests to closed bundleManager")
			}
		}()
	*/
	bm.downloadQueue <- r
}

func (bm *bundleManager) Close() {
	atomic.StoreInt32(bm.isClosed, 1)
	close(bm.downloadQueue)
}

func (bm *bundleManager) deleteBundlesFromDeployments(deletedDeployments []DataDeployment) {
	for _, dep := range deletedDeployments {
		go bm.deleteBundleById(dep.BlobID)
		go bm.deleteBundleById(dep.BlobResourceID)
	}

	/*
		log.Debugf("will delete %d old bundles", len(deletedDeployments))
		go func() {
			// give clients a minute to avoid conflicts
			time.Sleep(bm.bundleCleanupDelay)
			for _, dep := range deletedDeployments {
				bundleFile := getBlobFilePath(dep.BlobID)
				log.Debugf("removing old bundle: %v", bundleFile)
				// TODO Remove from the Database table apid_blob_available
				safeDelete(bundleFile)
			}
		}()
	*/
}

// TODO add delete support
func (bm *bundleManager) deleteBundleById(blobId string) {

}

type DownloadRequest struct {
	bm            *bundleManager
	blobId        string
	backoffFunc   func()
	markFailedAt  time.Time
	connTimeout   time.Duration
	blobServerURL string
}

func (r *DownloadRequest) downloadBundle() error {

	log.Debugf("starting bundle download attempt for blobId=%s", r.blobId)

	if r.checkTimeout() {
		return &timeoutError{
			markFailedAt: r.markFailedAt,
		}
	}

	downloadedFile, err := downloadFromURI(r.blobServerURL, r.blobId, r.connTimeout)

	if err != nil {
		log.Errorf("Unable to download blob file blobId=%s err:%v", r.blobId, err)
		return err
	}

	log.Debugf("blod downloaded. blobid=%s  filepath=%s", r.blobId, downloadedFile)

	err = r.bm.dbMan.updateLocalFsLocation(r.blobId, downloadedFile)
	if err != nil {
		log.Errorf("updateLocalFsLocation failed: blobId=%s", r.blobId)
		return err
	}

	log.Debugf("bundle downloaded: blobId=%s", r.blobId)

	// TODO send changed deployments to subscribers (API call with "block")
	//r.bm.apiMan.addChangedDeployment(dep.ID)

	return nil
}

func (r *DownloadRequest) checkTimeout() bool {

	if !r.markFailedAt.IsZero() && time.Now().After(r.markFailedAt) {
		r.markFailedAt = time.Time{}
		log.Debugf("bundle download timeout. blobId=", r.blobId)
		// TODO notify gateway of this failure
		return true
	}
	return false
}

func getBlobFilePath(blobId string) string {
	return path.Join(bundlePath, base64.StdEncoding.EncodeToString([]byte(blobId)))
}

func getSignedURL(blobServerURL string, blobId string, bundleDownloadConnTimeout time.Duration) (string, error) {

	blobUri, err := url.Parse(blobServerURL)
	if err != nil {
		log.Panicf("bad url value for config %s: %s", blobUri, err)
	}

	blobUri.Path += strings.Replace(blobStoreUri, "{blobId}", blobId, 1)
	parameters := url.Values{}
	parameters.Add("action", "GET")
	blobUri.RawQuery = parameters.Encode()

	uri := blobUri.String()

	surl, err := getURIReader(uri, bundleDownloadConnTimeout)
	if err != nil {
		log.Errorf("Unable to get signed URL from BlobServer %s: %v", uri, err)
		return "", err
	}
	defer surl.Close()

	body, err := ioutil.ReadAll(surl)
	if err != nil {
		log.Errorf("Invalid response from BlobServer for {%s} error: {%v}", uri, err)
		return "", err
	}
	res := blobServerResponse{}
	err = json.Unmarshal(body, &res)
	if err != nil {
		log.Errorf("Invalid response from BlobServer for {%s} error: {%v}", uri, err)
		return "", err
	}

	return res.SignedUrl, nil
}

// downloadFromURI involves retrieving the signed URL for the blob, and storing the resource locally
// after downloading the resource from GCS (via the signed URL)
func downloadFromURI(blobServerURL string, blobId string, bundleDownloadConnTimeout time.Duration) (tempFileName string, err error) {

	var tempFile *os.File
	log.Debugf("Downloading bundle: %s", blobId)

	uri, err := getSignedURL(blobServerURL, blobId, bundleDownloadConnTimeout)
	if err != nil {
		log.Errorf("Unable to get signed URL for blobId {%s}, error : {%v}", blobId, err)
		return
	}

	tempFile, err = ioutil.TempFile(bundlePath, "blob")
	if err != nil {
		log.Errorf("Unable to create temp file: %v", err)
		return
	}
	defer tempFile.Close()
	tempFileName = tempFile.Name()

	var confReader io.ReadCloser
	confReader, err = getURIReader(uri, bundleDownloadConnTimeout)
	if err != nil {
		log.Errorf("Unable to retrieve bundle %s: %v", uri, err)
		return
	}
	defer confReader.Close()

	_, err = io.Copy(tempFile, confReader)
	if err != nil {
		log.Errorf("Unable to write bundle %s: %v", tempFileName, err)
		return
	}

	log.Debugf("Bundle %s downloaded to: %s", uri, tempFileName)
	return
}

// retrieveBundle retrieves bundle data from a URI
func getURIReader(uriString string, bundleDownloadConnTimeout time.Duration) (io.ReadCloser, error) {

	client := http.Client{
		Timeout: bundleDownloadConnTimeout,
	}
	res, err := client.Get(uriString)
	if err != nil {
		return nil, err
	}
	if res.StatusCode != 200 {
		return nil, fmt.Errorf("GET uri %s failed with status %d", uriString, res.StatusCode)
	}
	return res.Body, nil
}

type BundleDownloader struct {
	id       int
	workChan chan *DownloadRequest
	bm       *bundleManager
}

func (w *BundleDownloader) Start() {
	go func() {
		log.Debugf("started bundle downloader %d", w.id)

		for req := range w.bm.downloadQueue {
			log.Debugf("starting download blobId=%s", req.blobId)
			err := req.downloadBundle()
			if err != nil {
				// timeout
				if _, ok := err.(*timeoutError); ok {
					continue
				}
				go func() {
					req.backoffFunc()
					w.bm.enqueueRequest(req)
				}()
			}
		}
		log.Debugf("bundle downloader %d stopped", w.id)
	}()
}

// simple doubling back-off
func createBackoff(retryIn, maxBackOff time.Duration) func() {
	return func() {
		log.Debugf("backoff called. will retry in %s.", retryIn)
		time.Sleep(retryIn)
		retryIn = retryIn * time.Duration(2)
		if retryIn > maxBackOff {
			retryIn = maxBackOff
		}
	}
}

type timeoutError struct {
	markFailedAt time.Time
}

func (e *timeoutError) Error() string {
	return fmt.Sprintf("Timeout. markFailedAt=%v", e.markFailedAt)
}