// +build !solaris

package tail

import (
	"fmt"
	"log"
	"strings"
	"sync"

	"github.com/influxdata/tail"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/internal/globpath"
	"github.com/influxdata/telegraf/plugins/inputs"
	"github.com/influxdata/telegraf/plugins/parsers"
)

const (
	defaultWatchMethod = "inotify"
)

var (
	offsets      = make(map[string]int64)
	offsetsMutex = new(sync.Mutex)
)

type Tail struct {
	Files         []string
	FromBeginning bool
	Pipe          bool
	WatchMethod   string

	tailers    map[string]*tail.Tail
	offsets    map[string]int64
	parserFunc parsers.ParserFunc
	wg         sync.WaitGroup
	acc        telegraf.Accumulator

	sync.Mutex
}

func NewTail() *Tail {
	offsetsMutex.Lock()
	offsetsCopy := make(map[string]int64, len(offsets))
	for k, v := range offsets {
		offsetsCopy[k] = v
	}
	offsetsMutex.Unlock()

	return &Tail{
		FromBeginning: false,
		offsets:       offsetsCopy,
	}
}

const sampleConfig = `
  ## files to tail.
  ## These accept standard unix glob matching rules, but with the addition of
  ## ** as a "super asterisk". ie:
  ##   "/var/log/**.log"  -> recursively find all .log files in /var/log
  ##   "/var/log/*/*.log" -> find all .log files with a parent dir in /var/log
  ##   "/var/log/apache.log" -> just tail the apache log file
  ##
  ## See https://github.com/gobwas/glob for more examples
  ##
  files = ["/var/mymetrics.out"]
  ## Read file from beginning.
  from_beginning = false
  ## Whether file is a named pipe
  pipe = false

  ## Method used to watch for file updates.  Can be either "inotify" or "poll".
  # watch_method = "inotify"

  ## Data format to consume.
  ## Each data format has its own unique set of configuration options, read
  ## more about them here:
  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
  data_format = "influx"
`

func (t *Tail) SampleConfig() string {
	return sampleConfig
}

func (t *Tail) Description() string {
	return "Stream a log file, like the tail -f command"
}

func (t *Tail) Gather(acc telegraf.Accumulator) error {
	t.Lock()
	defer t.Unlock()

	return t.tailNewFiles(true)
}

func (t *Tail) Start(acc telegraf.Accumulator) error {
	t.Lock()
	defer t.Unlock()

	t.acc = acc
	t.tailers = make(map[string]*tail.Tail)

	err := t.tailNewFiles(t.FromBeginning)

	// clear offsets
	t.offsets = make(map[string]int64)
	// assumption that once Start is called, all parallel plugins have already been initialized
	offsetsMutex.Lock()
	offsets = make(map[string]int64)
	offsetsMutex.Unlock()

	return err
}

func (t *Tail) tailNewFiles(fromBeginning bool) error {
	var poll bool
	if t.WatchMethod == "poll" {
		poll = true
	}

	// Create a "tailer" for each file
	for _, filepath := range t.Files {
		g, err := globpath.Compile(filepath)
		if err != nil {
			t.acc.AddError(fmt.Errorf("glob %s failed to compile, %s", filepath, err))
		}
		for _, file := range g.Match() {
			if _, ok := t.tailers[file]; ok {
				// we're already tailing this file
				continue
			}

			var seek *tail.SeekInfo
			if !t.Pipe && !fromBeginning {
				if offset, ok := t.offsets[file]; ok {
					log.Printf("D! [inputs.tail] using offset %d for file: %v", offset, file)
					seek = &tail.SeekInfo{
						Whence: 0,
						Offset: offset,
					}
				} else {
					seek = &tail.SeekInfo{
						Whence: 2,
						Offset: 0,
					}
				}
			}

			tailer, err := tail.TailFile(file,
				tail.Config{
					ReOpen:    true,
					Follow:    true,
					Location:  seek,
					MustExist: true,
					Poll:      poll,
					Pipe:      t.Pipe,
					Logger:    tail.DiscardingLogger,
				})
			if err != nil {
				t.acc.AddError(err)
				continue
			}

			log.Printf("D! [inputs.tail] tail added for file: %v", file)

			parser, err := t.parserFunc()
			if err != nil {
				t.acc.AddError(fmt.Errorf("error creating parser: %v", err))
			}

			// create a goroutine for each "tailer"
			t.wg.Add(1)
			go t.receiver(parser, tailer)
			t.tailers[tailer.Filename] = tailer
		}
	}
	return nil
}

// this is launched as a goroutine to continuously watch a tailed logfile
// for changes, parse any incoming msgs, and add to the accumulator.
func (t *Tail) receiver(parser parsers.Parser, tailer *tail.Tail) {
	defer t.wg.Done()

	var firstLine = true
	var metrics []telegraf.Metric
	var m telegraf.Metric
	var err error
	var line *tail.Line
	for line = range tailer.Lines {
		if line.Err != nil {
			t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, err))
			continue
		}
		// Fix up files with Windows line endings.
		text := strings.TrimRight(line.Text, "\r")

		if firstLine {
			metrics, err = parser.Parse([]byte(text))
			if err == nil {
				if len(metrics) == 0 {
					firstLine = false
					continue
				} else {
					m = metrics[0]
				}
			}
			firstLine = false
		} else {
			m, err = parser.ParseLine(text)
		}

		if err == nil {
			if m != nil {
				tags := m.Tags()
				tags["path"] = tailer.Filename
				t.acc.AddFields(m.Name(), m.Fields(), tags, m.Time())
			}
		} else {
			t.acc.AddError(fmt.Errorf("malformed log line in %s: [%s], Error: %s",
				tailer.Filename, line.Text, err))
		}
	}

	log.Printf("D! [inputs.tail] tail removed for file: %v", tailer.Filename)

	if err := tailer.Err(); err != nil {
		t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, err))
	}
}

func (t *Tail) Stop() {
	t.Lock()
	defer t.Unlock()

	for _, tailer := range t.tailers {
		if !t.Pipe && !t.FromBeginning {
			// store offset for resume
			offset, err := tailer.Tell()
			if err == nil {
				log.Printf("D! [inputs.tail] recording offset %d for file: %v", offset, tailer.Filename)
			} else {
				t.acc.AddError(fmt.Errorf("error recording offset for file %s", tailer.Filename))
			}
		}
		err := tailer.Stop()
		if err != nil {
			t.acc.AddError(fmt.Errorf("error stopping tail on file %s", tailer.Filename))
		}
	}

	t.wg.Wait()

	// persist offsets
	offsetsMutex.Lock()
	for k, v := range t.offsets {
		offsets[k] = v
	}
	offsetsMutex.Unlock()
}

func (t *Tail) SetParserFunc(fn parsers.ParserFunc) {
	t.parserFunc = fn
}

func init() {
	inputs.Add("tail", func() telegraf.Input {
		return NewTail()
	})
}
