// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: MIT

package logs

import (
	"context"
	"errors"
	"log"
	"time"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"

	"github.com/aws/amazon-cloudwatch-agent/plugins/inputs/logfile/tail"
)

var ErrOutputStopped = errors.New("Output plugin stopped")

// A LogCollection is a collection of LogSrc, a plugin which can provide many LogSrc
type LogCollection interface {
	FindLogSrc() []LogSrc
	Start(acc telegraf.Accumulator) error
}

type LogEvent interface {
	Message() string
	Time() time.Time
	Done()
}

// A LogSrc is a single source where log events are generated
// e.g. a single log file
type LogSrc interface {
	SetOutput(func(LogEvent))
	Group() string
	Stream() string
	Destination() string
	Description() string
	Retention() int
	Stop()
}

// A LogBackend is able to return a LogDest of a given name.
// The same name should always return the same LogDest.
type LogBackend interface {
	CreateDest(string, string, int) LogDest
}

// A LogDest represents a final endpoint where log events are published to.
// e.g. a particular log stream in cloudwatchlogs.
type LogDest interface {
	Publish(events []LogEvent) error
}

// LogAgent is the agent handles pure log pipelines
type LogAgent struct {
	Config                    *config.Config
	backends                  map[string]LogBackend
	destNames                 map[LogDest]string
	collections               []LogCollection
	retentionAlreadyAttempted map[string]bool
}

func NewLogAgent(c *config.Config) *LogAgent {
	return &LogAgent{
		Config:                    c,
		backends:                  make(map[string]LogBackend),
		destNames:                 make(map[LogDest]string),
		retentionAlreadyAttempted: make(map[string]bool),
	}
}

// Run LogAgent will scan all input and output plugins for LogCollection and LogBackend.
// And connect all the LogSrc from the LogCollection found to the respective LogDest
// based on the configured "destination", and "name"
func (l *LogAgent) Run(ctx context.Context) {
	log.Printf("I! [logagent] starting")
	for _, output := range l.Config.Outputs {
		backend, ok := output.Output.(LogBackend)
		if !ok {
			continue
		}
		log.Printf("I! [logagent] found plugin %v is a log backend", output.Config.Name)
		name := output.Config.Alias
		if name == "" {
			name = output.Config.Name
		}
		l.backends[name] = backend
	}

	for _, input := range l.Config.Inputs {
		if collection, ok := input.Input.(LogCollection); ok {
			log.Printf("I! [logagent] found plugin %v is a log collection", input.Config.Name)
			err := collection.Start(nil)
			if err != nil {
				log.Printf("E! could not start log collection %v err %v", input.Config.Name, err)
			}
			l.collections = append(l.collections, collection)
		}
	}

	t := time.NewTicker(time.Second)
	defer t.Stop()
	for {
		select {
		case <-t.C:
			log.Printf("D! [logagent] open file count, %v", tail.OpenFileCount.Load())
			for _, c := range l.collections {
				srcs := c.FindLogSrc()
				for _, src := range srcs {
					dname := src.Destination()
					logGroup := src.Group()
					logStream := src.Stream()
					description := src.Description()
					retention := src.Retention()
					backend, ok := l.backends[dname]
					if !ok {
						log.Printf("E! [logagent] Failed to find destination %s for log source %s/%s(%s) ", dname, logGroup, logStream, description)
						continue
					}
					retention = l.checkRetentionAlreadyAttempted(retention, logGroup)
					dest := backend.CreateDest(logGroup, logStream, retention)
					l.destNames[dest] = dname
					log.Printf("I! [logagent] piping log from %s/%s(%s) to %s with retention %d", logGroup, logStream, description, dname, retention)
					go l.runSrcToDest(src, dest)
				}
			}
		case <-ctx.Done():
			return
		}
	}
}

func (l *LogAgent) runSrcToDest(src LogSrc, dest LogDest) {
	eventsCh := make(chan LogEvent)
	defer src.Stop()

	src.SetOutput(func(e LogEvent) {
		if e == nil {
			close(eventsCh)
			log.Printf("I! [logagent] Log src has stopped for %v/%v(%v)", src.Group(), src.Stream(), src.Description())
			return
		}
		eventsCh <- e
	})

	for e := range eventsCh {
		err := dest.Publish([]LogEvent{e})
		if err == ErrOutputStopped {
			log.Printf("I! [logagent] Log destination %v has stopped, finalizing %v/%v", l.destNames[dest], src.Group(), src.Stream())
			return
		}
		if err != nil {
			log.Printf("E! [logagent] Failed to publish log to %v, error: %v", l.destNames[dest], err)
			return
		}
	}
}

func (l *LogAgent) checkRetentionAlreadyAttempted(retention int, logGroup string) int {
	if retention > 0 && l.retentionAlreadyAttempted[logGroup] {
		log.Printf("D! [logagent] Retention already set for log group %s, current retention %d", logGroup, retention)
		retention = -1
	} else if retention > 0 {
		log.Printf("I! First time setting retention for log group %s, update map to avoid setting twice", logGroup)
		l.retentionAlreadyAttempted[logGroup] = true
	}
	return retention
}