package logmower

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sync"

	"github.com/jtagcat/util"
	prom "github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	mongoOpt "go.mongodb.org/mongo-driver/mongo/options"
	"go.uber.org/zap"
	"k8s.io/apimachinery/pkg/util/wait"
)

var (
	promCatchupDone = promauto.NewGaugeVec(prom.GaugeOpts{
		Subsystem: "file",
		Name:      "catchupped",
		Help:      "File count where backlog has been sent; <= watcher_file_count",
	}, []string{"filename"}) // TODO: rm filename?
	promFileErr = promauto.NewCounterVec(prom.CounterOpts{
		Subsystem: "file",
		Name:      "errors_count",
		Help:      "Error count for reading files",
	}, []string{"filename"})
)

type (
	submitter struct {
		l *zap.Logger

		hostInfo HostInfo
		db       *mongo.Collection

		sync.WaitGroup
	}
)

func (s *submitter) shipFile(ctx context.Context, name string) {
	baseName := filepath.Base(name)

	sigCatchupped := make(chan struct{}, 1)
	go func() {
		<-sigCatchupped
		close(sigCatchupped) // once

		promCatchupDone.WithLabelValues(baseName).Add(1)
	}()

	// TODO: restarting before mongo sendQueue finishes will result in duplicates
	wait.ManagedExponentialBackoffWithContext(ctx, defaultBackoff(), func() (done bool, _ error) {
		if err := s.shipFileRoutine(ctx, name, sigCatchupped); err != nil {
			promFileErr.WithLabelValues(baseName).Add(1)
			s.l.Error("shipping file", zap.String("filename", baseName), zap.Error(err))
			return false, nil // nil since we want it to loop and keep retrying indefinitely
		}
		return true, nil
	})
}

func (s *submitter) shipFileRoutine(ctx context.Context, name string, sigCatchupped chan<- struct{}) error {
	// Initialize in case of new file
	log := mLog{
		HostInfo: s.hostInfo,
		Filename: name,
	}

	// get files with offset
	offsetResult, err := mWithErr(s.db.FindOne(mongoTimeoutCtx(ctx),
		bson.D{{Key: "hostinfo.id", Value: s.hostInfo.id}, {Key: "filename", Value: name}},
		&mongoOpt.FindOneOptions{Sort: bson.D{{Key: "offset", Value: -1}}}, // sort descending (get largest)
	))
	if err != nil && !errors.Is(err, mongo.ErrNoDocuments) {
		return fmt.Errorf("retrieving mongo offset: %w", err)
	}

	// offsetResult.DecodeBytes() //TODO: check for extra fields

	if err := offsetResult.Decode(&log); err != nil && !errors.Is(err, mongo.ErrNoDocuments) {
		return fmt.Errorf("decoding mongo offset: %w", err)
	}

	fi, err := os.Stat(log.Filename)
	if err != nil {
		return fmt.Errorf("getting original file size")
	}
	startSize := fi.Size()

	// TODO: use inotify for file, and end with file deletion or replacement
	lineChan, errChan, err := util.TailFile(ctx, log.Filename, log.Offset, io.SeekStart)
	if err != nil {
		return fmt.Errorf("tailing file: %w", err)
	}
	for {
		select {
		case err := <-errChan:
			return fmt.Errorf("tailing file: %w", err)
		case line := <-lineChan:
			if line.EndOffset > startSize {
				select {
				case sigCatchupped <- struct{}{}:
				default:
				}
			}

			select {
			// TODO: use per-file batch senders for file deletion mongo synced, and better error handling; #3
			case s.sendQueue <- mLog{
				HostInfo: s.hostInfo,
				Filename: *line.Filename,
				Offset:   line.EndOffset,
				Content:  line.String,
			}:
			default:
				promShipperDropped.WithLabelValues(*line.Filename).Add(1)
			}
			// TODO:
			// default:
			// 	return nil
		}
	}
}

func mWithErr[t interface{ Err() error }](mongoWrap t) (t, error) {
	return mongoWrap, mongoWrap.Err()
}

// func JitterUntilCancelWithContext(pctx context.Context, f func(context.Context, context.CancelFunc), period time.Duration, jitterFactor float64, sliding bool) {
// 	ctx, cancel := context.WithCancel(pctx)
// 	wait.JitterUntil(func() { f(ctx, cancel) }, period, jitterFactor, sliding, ctx.Done())
// }