// Copyright 2019 Google LLC
//
// 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
//
//     https://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 lkml provides a controller which processes strings received
// containing mailing list patches, applies them to specified repo,
// and triggers ProwJobs.
package lkml

import (
	"errors"
	"fmt"
	"k8s.io/test-infra/prow/config"
	"k8s.io/test-infra/prow/kube"
	"k8s.io/test-infra/prow/pjutil"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"regexp"
	"strconv"
	"sync"
	"time"
)

const (
	QueueSize  = 10 // arbitrary queue size for processing msgs and series
	timeout    = time.Minute * 5
	jobTimeout = time.Hour * 1 // cleanup repo after job is done
	repoPath   = "/kunit/linux"

	// prowjob annotations used by reporter for sending reply
	SubjectAnnotation = "prowjobs.mail.subject"
	ReplyAnnotation   = "prowjobs.mail.reply"
)

var (
	// TODO: test regular expressions
	subjectRE   = regexp.MustCompile(`Subject:(\s*\[PATCH\s+[^\n\]\r]*?(?:([0-9]+)\/([0-9]+))?\][^\n\r]*)`)
	messageIdRE = regexp.MustCompile(`Message-I[Dd]:\s*<(.*)>`)
	inReplyToRE = regexp.MustCompile(`In-Reply-To:\s*<(.*)>`)
)

type patch struct {
	subject string
	body    string
	replyTo string
}

type patchSeries struct {
	branch   string
	patches  []patch
	num      int
	numAdded int
	ready    chan bool
}

// Lkml receives string email messages from msgQueue,
// converts them to patches / patchSeries,
// stores them in idToSeries by message id of the cover letter or patch in the
// case of a single patch.
// mutex guards access to map
// When entire series has been received, it will be send to the jobQueue for
// applying patches and triggering ProwJobs.
type Lkml struct {
	msgQueue     <-chan string
	seriesQueue  chan patchSeries
	idToSeries   map[string]*patchSeries
	mutex        sync.Mutex
	sourceRepo   string
	sourceBranch string
	jobURI       string
	cloneURI     url.URL
	ca           *config.Agent
	kc           *kube.Client
	pullNum      int
}

func New(msgQueue <-chan string, sourceRepo string, sourceBranch string, jobURI string, clusterIP string, ca *config.Agent, kc *kube.Client) Lkml {
	// TODO validate args

	l := Lkml{
		msgQueue:     msgQueue,
		seriesQueue:  make(chan patchSeries, QueueSize),
		idToSeries:   make(map[string]*patchSeries),
		sourceRepo:   sourceRepo,
		sourceBranch: sourceBranch,
		jobURI:       jobURI,
		cloneURI:     url.URL{},
		ca:           ca,
		kc:           kc,
	}

	return l
}

func (l *Lkml) Run() error {
	err := l.initStorage()
	if err != nil {
		log.Fatal("Failed to initialize git repo storage: %v", err)
	}

	done := make(chan error, 2)

	go func() {
		/*
		 * git daemon currently causes excessive memory usage
		 * using dumb http instead for now which works
		 * cmd := exec.Command("git", "daemon", "--verbose", "--reuseaddr", "--export-all", "--base-path=/kunit", "/kunit")
		 * TODO: fix git daemon memory issues, then need to change
		 * cloneURI to git://{IP}/linux instead of http://{IP}:8080/linux.git
		 */
		err := http.ListenAndServe(":8080", http.FileServer(http.Dir("/kunit")))
		done <- fmt.Errorf("GIT server died: %v", err)
	}()

	// handle messages and dispatch jobs once series received
	go func() {
		for msg := range l.msgQueue {
			if err := l.handleMessage(msg); err != nil {
				log.Printf("HandleMessageQueue: %v", err)
			}
		}
		done <- errors.New("Message queue closed.")
	}()

	// apply patch -> trigger in order
	go func() {
		for patch := range l.seriesQueue {
			if err := l.handleJob(patch); err != nil {
				log.Printf("HandleJobQueue: %v", err)
			}
		}
		done <- errors.New("Series queue closed.")
	}()

	// quit if git server dies or smtp server dies & queues empty
	return <-done
}

// run git command in repo dir
func runGitCommand(args ...string) error {
	allArgs := append([]string{"-C", repoPath}, args...)
	cmd := exec.Command("git", allArgs...)
	err := cmd.Run()
	return err
}

func (l *Lkml) initStorage() error {
	// set configs
	exec.Command("git", "config", "--global", "user.email", "prow@robot.com").Run()
	exec.Command("git", "config", "--global", "user.name", "Prow Robot").Run()
	exec.Command("git", "config", "--global", "pack.windowMemory", "100m").Run()
	exec.Command("git", "config", "--global", "pack.packSizeLimit", "100m").Run()
	exec.Command("git", "config", "--global", "pack.threads", "1").Run()

	// if existing, update and return
	if repoDir, err := os.Open(repoPath); err == nil {
		repoDir.Close()
		err1 := runGitCommand("checkout", l.sourceBranch)
		err2 := runGitCommand("pull")
		if err1 == nil || err2 == nil {
			return nil
		}
	}

	// otherwise reclone
	exec.Command("rm", "-rf", repoPath)
	exec.Command("git", "clone", l.sourceRepo, repoPath).Run()
	runGitCommand("checkout", l.sourceBranch)
	runGitCommand("update-server-info")
	exec.Command("mv", repoPath+"/.git/hooks/post-update.sample", repoPath+"/.git/hooks/post-update").Run()
	return nil
}

func (l *Lkml) newSeries(branchName string, numPatches int) (*patchSeries, error) {
	l.mutex.Lock()
	defer l.mutex.Unlock()

	_, exists := l.idToSeries[branchName]
	if exists == true {
		return nil, fmt.Errorf("Patch Series with id {%s} already existed", branchName)
	}

	// add series to map
	patch := patchSeries{
		branch:   branchName,
		patches:  make([]patch, numPatches),
		num:      numPatches,
		numAdded: 0,
		ready:    make(chan bool),
	}

	l.idToSeries[branchName] = &patch

	return &patch, nil
}

func (l *Lkml) addPatchToSeries(branchName string, patchInd int,
	subjectLine string, bodyString string, replyToString string) error {

	l.mutex.Lock()
	defer l.mutex.Unlock()

	series, exists := l.idToSeries[branchName]
	if exists == false {
		return fmt.Errorf("Patch Series with id {%s} doesn't existed", branchName)
	}

	if patch := series.patches[patchInd]; patch.subject != "" {
		return fmt.Errorf("Patch Series with id {%s} already has patch #%d/%d with subject line {%s}",
			branchName, patchInd, len(series.patches), patch.subject)
	}

	series.patches[patchInd] = patch{subject: subjectLine, body: bodyString, replyTo: replyToString}
	series.numAdded += 1

	if series.numAdded == series.num {
		defer func() { series.ready <- true }()
	}

	return nil
}

/*
 * Parse message body to identify one of 4 types of messages received:
 *
 *   Not a patch : ignore email
 *   Single patch : send to seriesQueue immediately
 *   Cover of multi patch : Create Series and wait until timeout for others to arrive.
 *    			    If patches arrive, copy to seriesQueue.
 *			    Series will be removed from map regardless by timeout.
 *   Member patch : Add patch to series by message id utilizing In-Reply-To header
 *		   which references the cover letter under shallow threading
 *
 * Note: All access to map and its series are managed by mutex to ensure synchronization.
 * This is the most flexible way to ensure proper ordering as emails may arrive
 * out of order.
 */
func (l *Lkml) handleMessage(body string) error {
	var err error

	// Get message id for replying in thread and mapping series
	idMatch := messageIdRE.FindStringSubmatch(body)
	if idMatch == nil || idMatch[1] == "" {
		err = errors.New("Message has no ID")
		return err
	}
	patchID := idMatch[1]

	// get subject line and patch information (x and n from "Patch x/n")
	subjectMatch := subjectRE.FindStringSubmatch(body)
	if subjectMatch == nil {
		err = errors.New("Message is not part of a patch")
		return err
	}
	subjectLine := subjectMatch[1]
	patchInd := 0
	if subjectMatch[2] != "" {
		patchInd, err = strconv.Atoi(subjectMatch[2])
	}
	patchNum := 0
	if subjectMatch[3] != "" {
		patchNum, err = strconv.Atoi(subjectMatch[3])
	}

	// check if single patch
	if patchNum == 0 {
		l.handleSinglePatch(body, patchID, subjectLine)
	}

	// cover letter
	if patchInd == 0 {
		l.handleCoverLetter(patchID, patchNum)
	}

	// patch in series
	replyMatch := inReplyToRE.FindStringSubmatch(body)
	if replyMatch == nil || replyMatch[1] == "" {
		err = fmt.Errorf("Patch in series has no reference to cover letter!")
		return err
	}
	seriesID := replyMatch[1]

	// add patch to series
	err = l.addPatchToSeries(seriesID, patchInd-1, subjectLine, body, patchID)
	if err != nil {
		return err
	}
	return nil
}

func (l *Lkml) handleCoverLetter(patchID string, patchNum int) error {
	series, err := l.newSeries(patchID, patchNum)
	if err != nil {
		return err
	}

	go l.handleSeries(series)
	return nil
}

func (l *Lkml) handleSinglePatch(body string, patchID string, subjectLine string) {
	patch := patchSeries{
		branch: patchID,
		patches: []patch{{
			subject: subjectLine,
			body:    body,
			replyTo: patchID,
		}},
		num:      1,
		numAdded: 1,
	}

	l.seriesQueue <- patch
}

/*
* Add to seriesQueue once all patches are in.
* Timeout specified as constant to delete outdated patches from map
 */
func (l *Lkml) handleSeries(series *patchSeries) error {
	shouldTrigger := false

	select {
	case <-series.ready:
		shouldTrigger = true
	case <-time.After(timeout):
		log.Print("TIMED OUT")
		break
	}

	if shouldTrigger {
		l.seriesQueue <- *series
	}

	// delete from map
	l.mutex.Lock()
	delete(l.idToSeries, series.branch)
	l.mutex.Unlock()

	return nil
}

func (l *Lkml) handleJob(series patchSeries) error {
	runGitCommand("pull") // update main branch

	// TODO : need to delete branches after use somehow, possibly launch a
	// goroutine after triggering for time to delete
	runGitCommand("checkout", l.sourceBranch)
	err := runGitCommand("checkout", "-b", series.branch)
	if err != nil {
		runGitCommand("checkout", l.sourceBranch)
		runGitCommand("branch", "-D", series.branch)
		runGitCommand("checkout", "-b", series.branch)
	}

	// TODO : handle multiple jobs mapped to the same uri
	// when we want to break jobs into multiple test suites, will need to
	// iterate over the the array of presubmits for specific job uri
	conf := l.ca.Config().Presubmits[l.jobURI][0]

	// need to also get tag as this git server doesn't let you fetch from sha
	// set tag of new commit to sha for fetching
	prevRef := series.branch + "base"
	err = runGitCommand("tag", prevRef)
	if err != nil {
		log.Printf("tag error %v", err)
	}

	baseURI := l.cloneURI.String()

	for i, p := range series.patches {
		// apply mail using git am
		err := runGitCommand("am")
		if err != nil {
			log.Printf("Patch cannot be applied: %v", err)
			runGitCommand("am", "--abort")
			break // abort remaining jobs
			// TODO possibly email if patch could not be applied
		}

		// set tag of new commit to message id for fetching (see above)
		ref := p.replyTo
		runGitCommand("tag", ref)

		log.Printf("\t Patch #%d has tag %s", i, ref)
		refs := kube.Refs{
			Org:      l.cloneURI.Host,
			Repo:     l.cloneURI.Path[1:],
			BaseRef:  prevRef,
			BaseSHA:  "",
			CloneURI: baseURI,
			Pulls: []kube.Pull{{
				// plank uses pull number to find duplicate jobs
				// need to monotonically increase
				// otherwise change job name, org, or repo
				Number: l.pullNum,
				Ref:    ref,
			}},
		}

		prevRef = ref

		annotations := map[string]string{
			SubjectAnnotation: p.subject,
			ReplyAnnotation:   p.replyTo,
		}

		runGitCommand("update-server-info") // update with new tag
		pr := pjutil.PresubmitSpec(conf, refs)
		pj := pjutil.NewProwJobWithAnnotation(pr, conf.Labels, annotations)
		_, err = l.kc.CreateProwJob(pj)
		if err != nil {
			log.Printf("Error in triggering prowjob : %v", err)
			return err
		}

		l.pullNum += 1 // increase pull number
	}

	runGitCommand("checkout", l.sourceBranch)

	// go cleanupBranch(series.branch) // enable after testing
	return nil
}

func (l *Lkml) cleanupBranch(branch string) {
	<-time.After(jobTimeout)
	runGitCommand("branch", "-D", branch)
	// need to delete created tags
	// git fetch --prune <remote> +refs/tags/*:refs/tags/*
}