/*
Copyright 2017 The Kubernetes Authors All rights reserved.

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

    http://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 kmsg

import (
	"fmt"
	"strings"
	"time"

	"github.com/euank/go-kmsg-parser/kmsgparser"
	"k8s.io/klog/v2"

	"k8s.io/node-problem-detector/pkg/systemlogmonitor/logwatchers/types"
	logtypes "k8s.io/node-problem-detector/pkg/systemlogmonitor/types"
	"k8s.io/node-problem-detector/pkg/util"
	"k8s.io/node-problem-detector/pkg/util/tomb"
)

const (
	// retryDelay is the time to wait before attempting to restart the kmsg parser.
	retryDelay = 5 * time.Second
)

type kernelLogWatcher struct {
	cfg       types.WatcherConfig
	startTime time.Time
	logCh     chan *logtypes.Log
	tomb      *tomb.Tomb

	kmsgParser kmsgparser.Parser
}

// NewKmsgWatcher creates a watcher which will read messages from /dev/kmsg
func NewKmsgWatcher(cfg types.WatcherConfig) types.LogWatcher {
	uptime, err := util.GetUptimeDuration()
	if err != nil {
		klog.Fatalf("failed to get uptime: %v", err)
	}
	startTime, err := util.GetStartTime(time.Now(), uptime, cfg.Lookback, cfg.Delay)
	if err != nil {
		klog.Fatalf("failed to get start time: %v", err)
	}

	return &kernelLogWatcher{
		cfg:       cfg,
		startTime: startTime,
		tomb:      tomb.NewTomb(),
		// Arbitrary capacity
		logCh: make(chan *logtypes.Log, 100),
	}
}

var _ types.WatcherCreateFunc = NewKmsgWatcher

func (k *kernelLogWatcher) Watch() (<-chan *logtypes.Log, error) {
	if k.kmsgParser == nil {
		// nil-check to make mocking easier
		parser, err := kmsgparser.NewParser()
		if err != nil {
			return nil, fmt.Errorf("failed to create kmsg parser: %v", err)
		}
		k.kmsgParser = parser
	}

	go k.watchLoop()
	return k.logCh, nil
}

// Stop closes the kmsgparser
func (k *kernelLogWatcher) Stop() {
	if err := k.kmsgParser.Close(); err != nil {
		klog.Errorf("Failed to close kmsg parser: %v", err)
	}
	k.tomb.Stop()
}

// watchLoop is the main watch loop of kernel log watcher.
func (k *kernelLogWatcher) watchLoop() {
	kmsgs := k.kmsgParser.Parse()
	defer func() {
		if err := k.kmsgParser.Close(); err != nil {
			klog.Errorf("Failed to close kmsg parser: %v", err)
		}
		close(k.logCh)
		k.tomb.Done()
	}()

	for {
		select {
		case <-k.tomb.Stopping():
			klog.Infof("Stop watching kernel log")
			return
		case msg, ok := <-kmsgs:
			if !ok {
				klog.Error("Kmsg channel closed, attempting to restart kmsg parser")

				// Close the old parser
				if err := k.kmsgParser.Close(); err != nil {
					klog.Errorf("Failed to close kmsg parser: %v", err)
				}

				// Try to restart
				var restarted bool
				kmsgs, restarted = k.retryCreateParser()
				if !restarted {
					// Stopping was signaled
					return
				}
				continue
			}
			klog.V(5).Infof("got kernel message: %+v", msg)
			if msg.Message == "" {
				continue
			}

			// Discard messages before start time.
			if msg.Timestamp.Before(k.startTime) {
				klog.V(5).Infof("Throwing away msg %q before start time: %v < %v", msg.Message, msg.Timestamp, k.startTime)
				continue
			}

			k.logCh <- &logtypes.Log{
				Message:   strings.TrimSpace(msg.Message),
				Timestamp: msg.Timestamp,
			}
		}
	}
}

// retryCreateParser attempts to create a new kmsg parser.
// It tries immediately first, then waits retryDelay between subsequent failures.
// It returns the new message channel and true on success, or nil and false if stopping was signaled.
func (k *kernelLogWatcher) retryCreateParser() (<-chan kmsgparser.Message, bool) {
	for {
		parser, err := kmsgparser.NewParser()
		if err == nil {
			k.kmsgParser = parser
			klog.Infof("Successfully restarted kmsg parser")
			return parser.Parse(), true
		}

		klog.Errorf("Failed to create new kmsg parser, retrying in %v: %v", retryDelay, err)

		select {
		case <-k.tomb.Stopping():
			klog.Infof("Stop watching kernel log during restart attempt")
			return nil, false
		case <-time.After(retryDelay):
		}
	}
}