package cli

import (
	"context"
	"net/http"
	"net/http/pprof"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/alecthomas/kingpin/v2"
	"github.com/gorilla/mux"
	"github.com/pkg/errors"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/push"
	"github.com/prometheus/common/expfmt"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/sdk/resource"
	"go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
	oteltrace "go.opentelemetry.io/otel/trace"

	"github.com/kopia/kopia/internal/clock"
	"github.com/kopia/kopia/internal/gather"
	"github.com/kopia/kopia/repo"
)

// DirMode is the directory mode for output directories.
const DirMode = 0o700

//nolint:gochecknoglobals
var metricsPushFormats = map[string]expfmt.Format{
	"text":               expfmt.NewFormat(expfmt.TypeTextPlain),
	"proto-text":         expfmt.NewFormat(expfmt.TypeProtoText),
	"proto-delim":        expfmt.NewFormat(expfmt.TypeProtoDelim),
	"proto-compact":      expfmt.NewFormat(expfmt.TypeProtoCompact),
	"open-metrics":       expfmt.NewFormat(expfmt.TypeOpenMetrics),
	"open-metrics-0.0.1": "application/openmetrics-text; version=0.0.1; charset=utf-8",
}

type observabilityFlags struct {
	outputDirectory string

	dumpAllocatorStats  bool
	enablePProfEndpoint bool
	metricsListenAddr   string
	metricsPushAddr     string
	metricsJob          string
	metricsPushInterval time.Duration
	metricsGroupings    []string
	metricsPushUsername string
	metricsPushPassword string
	metricsPushFormat   string
	otlpTrace           bool
	saveMetrics         bool
	pf                  profileFlags

	outputSubdirectoryName string

	stopPusher chan struct{}
	pusherWG   sync.WaitGroup

	traceProvider *trace.TracerProvider
}

func (c *observabilityFlags) setup(svc appServices, app *kingpin.Application) {
	app.Flag("dump-allocator-stats", "Dump allocator stats at the end of execution.").Hidden().Envar(svc.EnvName("KOPIA_DUMP_ALLOCATOR_STATS")).BoolVar(&c.dumpAllocatorStats)
	app.Flag("metrics-listen-addr", "Expose Prometheus metrics on a given host:port").Hidden().StringVar(&c.metricsListenAddr)
	app.Flag("enable-pprof", "Expose pprof handlers").Hidden().BoolVar(&c.enablePProfEndpoint)

	// push gateway parameters
	app.Flag("metrics-push-addr", "Address of push gateway").Envar(svc.EnvName("KOPIA_METRICS_PUSH_ADDR")).Hidden().StringVar(&c.metricsPushAddr)
	app.Flag("metrics-push-interval", "Frequency of metrics push").Envar(svc.EnvName("KOPIA_METRICS_PUSH_INTERVAL")).Hidden().Default("5s").DurationVar(&c.metricsPushInterval)
	app.Flag("metrics-push-job", "Job ID for to push gateway").Envar(svc.EnvName("KOPIA_METRICS_JOB")).Hidden().Default("kopia").StringVar(&c.metricsJob)
	app.Flag("metrics-push-grouping", "Grouping for push gateway").Envar(svc.EnvName("KOPIA_METRICS_PUSH_GROUPING")).Hidden().StringsVar(&c.metricsGroupings)
	app.Flag("metrics-push-username", "Username for push gateway").Envar(svc.EnvName("KOPIA_METRICS_PUSH_USERNAME")).Hidden().StringVar(&c.metricsPushUsername)
	app.Flag("metrics-push-password", "Password for push gateway").Envar(svc.EnvName("KOPIA_METRICS_PUSH_PASSWORD")).Hidden().StringVar(&c.metricsPushPassword)

	// tracing (OTLP) parameters
	app.Flag("otlp-trace", "Send OpenTelemetry traces to OTLP collector using gRPC").Hidden().Envar(svc.EnvName("KOPIA_ENABLE_OTLP_TRACE")).BoolVar(&c.otlpTrace)

	var formats []string

	for k := range metricsPushFormats {
		formats = append(formats, k)
	}

	sort.Strings(formats)

	app.Flag("metrics-push-format", "Format to use for push gateway").Envar(svc.EnvName("KOPIA_METRICS_FORMAT")).Hidden().EnumVar(&c.metricsPushFormat, formats...)

	//nolint:lll
	app.Flag("diagnostics-output-directory", "Directory where the diagnostics output should be stored saved when kopia exits. Diagnostics data includes among others: metrics, traces, profiles. The output files are stored in a sub-directory for each kopia (process) execution").Hidden().Default(filepath.Join(os.TempDir(), "kopia-diagnostics")).StringVar(&c.outputDirectory)

	app.Flag("metrics-store-on-exit", "Writes metrics to a file in a sub-directory of the directory specified with the --diagnostics-output-directory").Hidden().BoolVar(&c.saveMetrics)

	c.pf.setup(app)

	app.PreAction(c.initialize)
}

func (c *observabilityFlags) initialize(ctx *kingpin.ParseContext) error {
	// write to a separate file per command and process execution to avoid
	// conflicts with previously created files
	command := "unknown"
	if cmd := ctx.SelectedCommand; cmd != nil {
		command = strings.ReplaceAll(cmd.FullCommand(), " ", "-")
	}

	c.outputSubdirectoryName = clock.Now().Format("20060102-150405-") + command

	if (c.saveMetrics || c.pf.saveProfiles || c.pf.profileCPU) && c.outputDirectory == "" {
		return errors.New("writing diagnostics output requires a non-empty directory name (specified with the '--diagnostics-output-directory' flag)")
	}

	return nil
}

// spanName specifies the name of the span at the start of a trace. A tracer is
// started only when spanName is not empty.
func (c *observabilityFlags) run(ctx context.Context, spanName string, f func(context.Context) error) error {
	if err := c.start(ctx); err != nil {
		return errors.Wrap(err, "unable to start observability facilities")
	}

	defer c.stop(ctx)

	if err := c.pf.start(ctx, filepath.Join(c.outputDirectory, c.outputSubdirectoryName)); err != nil {
		return errors.Wrap(err, "failed to start profiling")
	}

	defer c.pf.stop(ctx)

	if spanName != "" {
		tctx, span := tracer.Start(ctx, spanName, oteltrace.WithSpanKind(oteltrace.SpanKindClient))
		ctx = tctx

		defer span.End()
	}

	return f(ctx)
}

func (c *observabilityFlags) start(ctx context.Context) error {
	c.maybeStartListener(ctx)

	if err := c.maybeStartMetricsPusher(ctx); err != nil {
		return err
	}

	if c.saveMetrics {
		// ensure the metrics output dir can be created
		if _, err := mkSubdirectories(c.outputDirectory, c.outputSubdirectoryName); err != nil {
			return err
		}
	}

	return c.maybeStartTraceExporter(ctx)
}

func mkSubdirectories(directoryNames ...string) (dirName string, err error) {
	dirName = filepath.Join(directoryNames...)

	if err := os.MkdirAll(dirName, DirMode); err != nil {
		return "", errors.Wrapf(err, "could not create '%q' subdirectory to save diagnostics output", dirName)
	}

	return dirName, nil
}

// Starts observability listener when a listener address is specified.
func (c *observabilityFlags) maybeStartListener(ctx context.Context) {
	if c.metricsListenAddr == "" {
		return
	}

	m := mux.NewRouter()
	initPrometheus(m)

	if c.enablePProfEndpoint {
		m.HandleFunc("/debug/pprof/", pprof.Index)
		m.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)
		m.HandleFunc("/debug/pprof/profile", pprof.Profile)
		m.HandleFunc("/debug/pprof/symbol", pprof.Symbol)
		m.HandleFunc("/debug/pprof/trace", pprof.Trace)
		m.HandleFunc("/debug/pprof/{cmd}", pprof.Index) // special handling for Gorilla mux, see https://stackoverflow.com/questions/30560859/cant-use-go-tool-pprof-with-an-existing-server/71032595#71032595
	}

	log(ctx).Infof("starting prometheus metrics on %v", c.metricsListenAddr)

	go http.ListenAndServe(c.metricsListenAddr, m) //nolint:errcheck,gosec
}

func (c *observabilityFlags) maybeStartMetricsPusher(ctx context.Context) error {
	if c.metricsPushAddr == "" {
		return nil
	}

	c.stopPusher = make(chan struct{})
	c.pusherWG.Add(1)

	pusher := push.New(c.metricsPushAddr, c.metricsJob)

	pusher.Gatherer(prometheus.DefaultGatherer)

	for _, g := range c.metricsGroupings {
		const nParts = 2

		parts := strings.SplitN(g, ":", nParts)
		if len(parts) != nParts {
			return errors.New("grouping must be name:value")
		}

		name := parts[0]
		val := parts[1]

		pusher.Grouping(name, val)
	}

	if c.metricsPushUsername != "" {
		pusher.BasicAuth(c.metricsPushUsername, c.metricsPushPassword)
	}

	if c.metricsPushFormat != "" {
		pusher.Format(metricsPushFormats[c.metricsPushFormat])
	}

	log(ctx).Infof("starting prometheus pusher on %v every %v", c.metricsPushAddr, c.metricsPushInterval)
	c.pushOnce(ctx, "initial", pusher)

	go c.pushPeriodically(ctx, pusher)

	return nil
}

func (c *observabilityFlags) maybeStartTraceExporter(ctx context.Context) error {
	if !c.otlpTrace {
		return nil
	}

	// Create the OTLP exporter.
	se := otlptracegrpc.NewUnstarted()

	r := resource.NewWithAttributes(
		semconv.SchemaURL,
		semconv.ServiceNameKey.String("kopia"),
		semconv.ServiceVersionKey.String(repo.BuildVersion),
	)

	tp := trace.NewTracerProvider(
		trace.WithBatcher(se),
		trace.WithResource(r),
	)

	if err := se.Start(ctx); err != nil {
		return errors.Wrap(err, "unable to start OTLP exporter")
	}

	otel.SetTracerProvider(tp)

	c.traceProvider = tp

	return nil
}

func (c *observabilityFlags) stop(ctx context.Context) {
	if c.dumpAllocatorStats {
		gather.DumpStats(ctx)
	}

	if c.stopPusher != nil {
		close(c.stopPusher)

		c.pusherWG.Wait()
	}

	if c.traceProvider != nil {
		if err := c.traceProvider.Shutdown(ctx); err != nil {
			log(ctx).Warnf("unable to shutdown trace provicer: %v", err)
		}
	}

	if c.saveMetrics {
		if metricsDir, err := mkSubdirectories(c.outputDirectory, c.outputSubdirectoryName); err != nil {
			log(ctx).Warnf("unable to create metrics output directory '%s': %v", metricsDir, err)
		} else {
			if err := prometheus.WriteToTextfile(filepath.Join(metricsDir, "kopia-metrics.prom"), prometheus.DefaultGatherer); err != nil {
				log(ctx).Warnf("unable to write metrics to file: %v", err)
			}
		}
	}
}

func (c *observabilityFlags) pushPeriodically(ctx context.Context, p *push.Pusher) {
	defer c.pusherWG.Done()

	ticker := time.NewTicker(c.metricsPushInterval)

	for {
		select {
		case <-ticker.C:
			c.pushOnce(ctx, "periodic", p)

		case <-c.stopPusher:
			ticker.Stop()
			c.pushOnce(ctx, "final", p)

			return
		}
	}
}

func (c *observabilityFlags) pushOnce(ctx context.Context, kind string, p *push.Pusher) {
	log(ctx).Debugw("pushing prometheus metrics", "kind", kind)

	if err := p.Push(); err != nil {
		log(ctx).Debugw("error pushing prometheus metrics", "kind", kind, "err", err)
	}
}