// Package commenter contains an implementation of the code_review.ChangeListCommenter interface.
// It should be CRS-agnostic.
package commenter

import (
	"context"
	"fmt"
	"sync"
	"time"

	"go.skia.org/infra/go/metrics2"
	"go.skia.org/infra/go/skerr"
	"go.skia.org/infra/go/sklog"
	"go.skia.org/infra/go/util"
	"go.skia.org/infra/golden/go/clstore"
	"go.skia.org/infra/golden/go/code_review"
)

const (
	numRecentOpenCLsMetric = "gold_num_recent_open_cls"
	completedCommentCycle  = "gold_comment_monitoring"

	timePeriodOfCLsToCheck = 2 * time.Hour
)

type Impl struct {
	crs             code_review.Client
	store           clstore.Store
	instanceURL     string
	logCommentsOnly bool

	liveness metrics2.Liveness
}

func New(c code_review.Client, s clstore.Store, instanceURL string, logCommentsOnly bool) *Impl {
	return &Impl{
		crs:             c,
		store:           s,
		instanceURL:     instanceURL,
		logCommentsOnly: logCommentsOnly,
		liveness:        metrics2.NewLiveness(completedCommentCycle),
	}
}

// CommentOnChangeListsWithUntriagedDigests implements the code_review.ChangeListCommenter
// interface.
func (i *Impl) CommentOnChangeListsWithUntriagedDigests(ctx context.Context) error {
	total := 0
	// This pageSize was picked arbitrarily, could be larger, but hopefully we don't have to
	// deal with that many CLs at once.
	const pageSize = 10000
	// Due to the fact that cl.Updated gets set in ingestion when new data is seen, we only need
	// to look at CLs that were Updated "recently". We make the range of time that we search
	// much wider than we need to account for either glitches in ingestion or outages of the CRS.
	recent := time.Now().Add(-timePeriodOfCLsToCheck)
	xcl, _, err := i.store.GetChangeLists(ctx, clstore.SearchOptions{
		StartIdx:    0,
		Limit:       pageSize,
		OpenCLsOnly: true,
		After:       recent,
	})
	if err != nil {
		return skerr.Wrapf(err, "searching for open CLs")
	}

	// stillOpen maps id to ChangeList to avoid duplication
	// (this could happen due to paging trickiness)
	stillOpen := map[string]code_review.ChangeList{}
	var openMutex sync.Mutex
	// Number of shards was picked sort of arbitrarily. Updating CLs requires multiple network
	// requests, so we can run them in parallel basically for free.
	const shards = 4
	for len(xcl) > 0 {
		total += len(xcl)
		chunks := len(xcl) / shards
		if chunks < 1 {
			chunks = 1
		}
		beforeCount := len(stillOpen)
		err := util.ChunkIterParallel(ctx, len(xcl), chunks, func(ctx context.Context, startIdx int, endIdx int) error {
			for _, cl := range xcl[startIdx:endIdx] {
				if err := ctx.Err(); err != nil {
					return skerr.Wrap(err)
				}
				open, err := i.updateCLInStoreIfAbandoned(ctx, cl)
				if err != nil {
					return skerr.Wrap(err)
				}
				if open {
					openMutex.Lock()
					stillOpen[cl.SystemID] = cl
					openMutex.Unlock()
				}
			}
			return nil
		})
		if err != nil {
			return skerr.Wrap(err)
		}

		// We paged forward and didn't identify any new CLs, so we are done.
		if beforeCount == len(stillOpen) {
			break
		}

		// Page to the next ones using len(stillOpen) because the next iteration of this query
		// won't count the ones we just marked as Closed/Abandoned when computing the offset.
		xcl, _, err = i.store.GetChangeLists(ctx, clstore.SearchOptions{
			StartIdx:    len(stillOpen),
			Limit:       pageSize,
			OpenCLsOnly: true,
			After:       recent,
		})
		if err != nil {
			return skerr.Wrapf(err, "searching for open CLs total %d", total)
		}
	}
	metrics2.GetInt64Metric(numRecentOpenCLsMetric, nil).Update(int64(len(stillOpen)))
	sklog.Infof("There were originally %d recent open CLs; after checking with CRS there are %d still open", total, len(stillOpen))

	for _, cl := range stillOpen {
		xps, err := i.store.GetPatchSets(ctx, cl.SystemID)
		if err != nil {
			return skerr.Wrapf(err, "looking for patchsets on open CL %s", cl.SystemID)
		}
		// We only want to comment on the most recent PS and only if it has untriaged digests.
		// Earlier PS are probably obsolete.
		mostRecentPS := xps[len(xps)-1]
		if mostRecentPS.HasUntriagedDigests && !mostRecentPS.CommentedOnCL {
			if i.logCommentsOnly {
				sklog.Infof("Should comment on CL %s with message %s", cl.SystemID, i.untriagedMessage(cl, mostRecentPS))
			} else {
				err := i.crs.CommentOn(ctx, cl.SystemID, i.untriagedMessage(cl, mostRecentPS))
				if err != nil {
					return skerr.Wrapf(err, "commenting on %s CL %s", i.crs.System(), cl.SystemID)
				}
			}
			mostRecentPS.CommentedOnCL = true
			if err := i.store.PutPatchSet(ctx, mostRecentPS); err != nil {
				return skerr.Wrapf(err, "updating PS %#v that we commented on it", mostRecentPS)
			}
		}
	}
	i.liveness.Reset()
	return nil
}

const messageTemplate = `Gold has detected one or more untriaged digests on patchset %d.
Please triage them at %s/search?issue=%s.`

// untriagedMessage returns a message about untriaged images on the given CL/PS.
func (i *Impl) untriagedMessage(cl code_review.ChangeList, ps code_review.PatchSet) string {
	return fmt.Sprintf(messageTemplate, ps.Order, i.instanceURL, cl.SystemID)
}

// updateCLInStoreIfAbandoned checks with the CRS to see if the cl is still Open. If it is, it
// returns true. If it is Abandoned, it stores the updated CL in the store and returns false.
// If the CL is Landed, it returns false and *does not update anything* in the store.
func (i *Impl) updateCLInStoreIfAbandoned(ctx context.Context, cl code_review.ChangeList) (bool, error) {
	up, err := i.crs.GetChangeList(ctx, cl.SystemID)
	if err == code_review.ErrNotFound {
		sklog.Debugf("CL %s might have been deleted", cl.SystemID)
		return false, nil
	}
	if err != nil {
		return false, skerr.Wrapf(err, "querying crs %s for updated CL %s", i.crs.System(), cl.SystemID)
	}
	if up.Status == code_review.Open {
		return true, nil
	}
	// If the CRS is reporting a CL as Landed, but we think it to be Open, that means that
	// the code_review.ChangeListLandedUpdater hasn't had a chance to process it yet, which is
	// necessary to smoothly merge the Expectations from the CL into master.
	if up.Status == code_review.Landed {
		return false, nil
	}
	// Store the latest one from the CRS (with new timestamp) to the clstore so we
	// remember it is abandoned in the future. This also catches things like the cl Subject
	// changing since it was opened.
	up.Updated = time.Now()
	if err := i.store.PutChangeList(ctx, up); err != nil {
		return false, skerr.Wrapf(err, "storing CL %s", up.SystemID)
	}
	return false, nil
}

// Make sure Impl fulfills the code_review.ChangeListCommenter interface.
var _ code_review.ChangeListCommenter = (*Impl)(nil)