package logmower

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"runtime"
	"strings"
	"sync"
	"time"

	"github.com/fsnotify/fsnotify"
	prom "github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/urfave/cli/v2"
	"go.elastic.co/ecszap"
	"go.mongodb.org/mongo-driver/mongo"
	"go.uber.org/zap"
	"k8s.io/apimachinery/pkg/util/wait"
)

const (
	MachineId              = "/etc/machine-id"
	DatabaseCommandTimeout = 10 * time.Second
	PrometheusPrefix       = "logmower"
)

// wrapper to force copying before use
func defaultBackoff() wait.Backoff {
	return wait.Backoff{
		Duration: 2 * time.Second,
		Factor:   1.5,
		Jitter:   0.1,
		Cap:      30 * time.Second,
	}
}

func mongoTimeoutCtx(ctx context.Context) context.Context {
	ctx, _ = context.WithTimeout(ctx, DatabaseCommandTimeout) //nolint:lostcancel (cancelled by mongo, should be bug on them //TODO)
	return ctx
}

var App = &cli.App{
	Name:    "logmower-shipper",
	Version: "1.0.0",
	Authors: []*cli.Author{{Name: "jtagcat"}},

	Description: "Collect and ship kubernetes logs",
	// Usage:       "rubykana <input>",
	// TODO: #2: yaml
	Flags: []cli.Flag{
		&cli.BoolFlag{Name: "dry-run", Usage: "Do not write to database"}, // TODO:
		&cli.StringFlag{Name: "log-directory", Usage: "Directory to watch for logs", Value: "/var/log/containers"},
		&cli.IntFlag{Name: "max-record-size", Value: 128 * 1024, Usage: "Maximum record size in bytes"},            // TODO:
		&cli.BoolFlag{Name: "normalize-log-level", Usage: "Normalize log.level values to Syslog defined keywords"}, // TODO:
		// &cli.BoolFlag{Name: "parse-json"}, //TODO:
		&cli.StringFlag{Category: "k8s metadata", Name: "pod-namespace", EnvVars: []string{"KUBE_POD_NAMESPACE"}}, // TODO:
		&cli.StringFlag{Category: "k8s metadata", Name: "node-name", EnvVars: []string{"KUBE_NODE_NAME"}, Required: true},
		&cli.StringFlag{Category: "secrets", Name: "mongo-uri", EnvVars: []string{"MONGO_URI"}, Usage: "mongodb://foo:bar@host:27017/database", Required: true},
	},
	Before: func(ctx *cli.Context) error {
		if ctx.Int("max-record-size") < 1 {
			return fmt.Errorf("max-record-size must be postivie")
		}

		return nil
	},

	Action: func(ctx *cli.Context) error {
		ctx.Context, _ = signal.NotifyContext(ctx.Context, os.Interrupt) // TODO: test
		var wg sync.WaitGroup

		// init logger, ECS schema
		core := ecszap.NewCore(ecszap.NewDefaultEncoderConfig(),
			os.Stderr, zap.WarnLevel)
		l := zap.New(core, zap.AddCaller())

		l.Info("logmower starting", zap.String("version", ctx.App.Version))

		var (
			promWatcherOnline = promauto.NewGauge(prom.GaugeOpts{
				Namespace: PrometheusPrefix,
				Subsystem: "watcher",
				Name:      "online",
				Help:      "1 if initialized, and directory watcher has been engaged successfully",
			})
			promWatcherErr = promauto.NewCounter(prom.CounterOpts{
				Namespace: PrometheusPrefix,
				Subsystem: "watcher",
				Name:      "errors",
				Help:      "Error in logmower watching log files",
			})
			promWatcherFilesStarted = promauto.NewCounter(prom.CounterOpts{
				Namespace: PrometheusPrefix,
				// Subsystem: "watcher",
				Name: "log_file", // "discovered_logfiles",
				Help: "Number of tracked log files",
			})
			promWatcherFilesSkipped = promauto.NewCounter(prom.CounterOpts{
				Namespace: PrometheusPrefix,
				// Subsystem: "watcher",
				Name: "invalid_filename", // "skipped_files",
				Help: "Number of files in log directory skipped due to unexpected filename",
			})
			promWatcherEvents = promauto.NewCounter(prom.CounterOpts{
				Namespace: PrometheusPrefix,
				// Subsystem: "watcher",
				Name: "inotify_event", // "events",
				Help: "Number of events while watchng (includes initial create events for existing file discovery)",
			})
		)
		go func() {
			l.Info("/metrics starting", zap.Int("port", 2112))
			http.Handle("/metrics", promhttp.Handler())

			if err := http.ListenAndServe(":2112", nil); !errors.Is(err, http.ErrServerClosed) {
				l.Fatal("failed to serve /metrics", zap.Error(err))
			}
		}()

		state := submitter{l: l}

		dbOpt := mongoMonitoredClientOptions(l).ApplyURI(ctx.String("mongo-uri"))

		dbClient, err := mongo.Connect(mongoTimeoutCtx(ctx.Context))
		if err != nil {
			l.Fatal("connecting to database", zap.String("uri", dbOpt.GetURI()), zap.Error(err))
		}

		uriParsed, err := url.ParseRequestURI(ctx.String("mongo-uri"))
		if err != nil {
			l.Fatal("parsing URI for mongo database name", zap.Error(err))
		}

		uriParsed.Path = uriParsed.Path[1:] // remove leading slash
		if uriParsed.Path == "" {
			l.Fatal("mongo database name must be set in mongo URI")
		}

		state.db = dbClient.Database(uriParsed.Path).Collection("logs")

		err = initializeIndexes(ctx.Context, state.db)
		if err != nil {
			l.Fatal("initializing indexes", zap.Error(err))
		}

		state.hostInfo, err = getHostInfo(ctx.String("node-name"))
		if err != nil {
			l.Fatal("gathering host info", zap.Error(err))
		}

		watcher, err := fsnotify.NewWatcher()
		if err != nil {
			l.Fatal("setting up watcher", zap.Error(err))
		}

		logDir := ctx.String("log-directory")

		wg.Add(1)
		go func() {
			defer wg.Done()

			for {
				select {
				case <-ctx.Context.Done():
					return
				case event, ok := <-watcher.Events:
					if !ok {
						return
					}
					promWatcherEvents.Add(1)

					if event.Op != fsnotify.Create {
						continue
					}

					// TODO: #1: || if not in filterset
					_, ok = parseLogName(event.Name)
					if !ok {
						promWatcherFilesSkipped.Add(1)
						l.Warn("skipped file with unparsable name", zap.String("name", event.Name))
						continue
					}

					promWatcherFilesStarted.Add(1)

					wg.Add(1)
					go func() {
						state.shipFile(ctx.Context, event.Name, ctx.Int("max-record-size"))
						wg.Done()
					}()

				case err, ok := <-watcher.Errors:
					if !ok {
						return
					}
					promWatcherErr.Add(1)
					l.Error("while watching log dir events", zap.Error(err))
				}
			}
		}()

		// simulate create events to pick up files already created
		err = simulateInitialCreate(logDir, watcher.Events)
		if err != nil {
			promWatcherErr.Add(1)
			l.Fatal("listing initial log directory", zap.String("name", logDir), zap.Error(err))
		}

		err = watcher.Add(logDir)
		if err != nil {
			promWatcherErr.Add(1)
			l.Fatal("watching log directory", zap.String("name", logDir), zap.Error(err))
		}

		promWatcherOnline.Set(1)

		// waiting indefinitely for interrupt
		wg.Wait() // wait for watch and file processors to cleanup

		return errAppend(watcher.Close(), ctx.Err())
	},
}

type HostInfo struct {
	id   string
	name string
	arch string
}

func getHostInfo(nodeName string) (h HostInfo, err error) {
	if nodeName == "" {
		nodeName, err = os.Hostname()
		if err != nil {
			err = fmt.Errorf("name: hostname: %w", err) // don't exit early
		}
	}
	h.name = strings.TrimSpace(nodeName)

	id, errL := os.ReadFile(MachineId)
	if errL != nil {
		err = errAppend(err, fmt.Errorf("id: %w", errL))
	}

	h.id = strings.TrimSpace(string(id))

	h.arch = runtime.GOARCH

	return h, err
}

func errAppend(a, b error) error {
	if a == nil {
		return b
	}
	if b == nil {
		return a
	}
	return fmt.Errorf("%e; %e", a, b)
}

type logMeta struct {
	podName       string
	podNamespace  string
	containerName string
	containerId   string
}

func parseLogName(name string) (m logMeta, ok bool) {
	name = filepath.Base(name)

	// https://github.com/kubernetes/design-proposals-archive/blob/8da1442ea29adccea40693357d04727127e045ed/node/kubelet-cri-logging.md
	// <pod_name>_<pod_namespace>_<container_name>-<container_id>.log`

	m.podName, name, ok = strings.Cut(name, "_")
	if !ok {
		return
	}

	m.podNamespace, name, ok = strings.Cut(name, "_")
	if !ok {
		return
	}

	m.containerName, name, ok = strings.Cut(name, "-")
	if !ok {
		return
	}

	m.containerId = strings.TrimSuffix(name, ".log")
	if !strings.HasSuffix(name, ".log") {
		return
	}

	return m, true
}

func simulateInitialCreate(dirName string, eventChan chan<- fsnotify.Event) error {
	dir, err := os.ReadDir(dirName)
	if err != nil {
		return err
	}

	for _, file := range dir {
		eventChan <- fsnotify.Event{
			Name: filepath.Join(dirName, file.Name()),
			Op:   fsnotify.Create,
		}
	}

	return nil
}