package webservercodes

import (
	"net/http"
	"strconv"
	"sync"
	"time"
	"os"
	"io"
	"regexp"
	"errors"
	
	"github.com/rogpeppe/rog-go/reverse"
	"github.com/influxdb/telegraf/plugins"
)

type Vhost struct {
	Host string
	AccessLog string
	RegexParsestring string
	ParseInterval string
}

type Webservercodes struct {
	Vhosts []*Vhost
}

type HttpStats struct {
	codes map[int]int
}

type CombinedEntry struct {
	time time.Time
	code int
}

var sampleConfig = `
# List of virtualhosts for http codes collecting
# (each section for one virtualhost, none for disable collecting codes)
[[webservercodes.vhosts]]
# 'host' field should match hostname in appropriate status url
host = "defaulthost"

# Telegraf user must have read permissions to this log file
# (shell command 'sudo adduser telegraf adm' for apache on Ubuntu)
access_log = "/var/log/apache2/access.log"

# Regular expression for fetching codes from log file strings.
# You can adjust this pattern for your custom log format
# Example for apache "common" and "combined" log formats, nginx default log format ("combined"):
#	'\[(?P<time>[^\]]+)\] ".*?" (?P<code>\d{3})'
# This pattern matches for strings like (example):
# 127.0.0.1 - - [30/Aug/2015:05:59:36 +0000] "GET / HTTP/1.1" 404 379 "-" "-"
regex_parsestring = '\[(?P<time>[^\]]+)\] ".*?" (?P<code>\d{3})'

# Plugin will parse log for http codes from 'now' till 'now - parse_interval' moments.
# parse_interval must be in time.Duration format (see https://golang.org/pkg/time/#ParseDuration)
parse_interval = "10s"
`

func (n *Webservercodes) SampleConfig() string {
	return sampleConfig
}

func (n *Webservercodes) Description() string {
	return "Read webserver access log files and count http return codes found"
}

func (n *Webservercodes) Gather(acc plugins.Accumulator) error {
	var wg sync.WaitGroup
	
	hostStats := map[string]HttpStats{}
	errChan := make(chan error)
	successChan := make(chan bool)
	remainingItems := len(n.Vhosts)
	
	for _, vhost := range n.Vhosts {
		if duration, err := time.ParseDuration(vhost.ParseInterval); err == nil {
			wg.Add(1)
			go func(host string, logfile string, regex string, duration time.Duration, successChan chan bool, errChan chan error) {
				defer wg.Done()
				if stats, err := n.ParseHttpCodes(logfile, regex, duration); err == nil {
					hostStats[host] = *stats
					successChan <- true
				} else {
					errChan <- err
				}
			}(vhost.Host, vhost.AccessLog, vhost.RegexParsestring, duration, successChan, errChan)
		} else {
			return err
		}
	}
	for {
		select {
			case _ = <-successChan:
				remainingItems--
			case err := <-errChan:
				return err
		}
		if remainingItems == 0 {
			break;
		}
	}
	
	wg.Wait()
	
	for vhost, stats := range hostStats {
		n.gatherCodes(vhost, stats, acc)
	}
	
	return nil
}

func SearchStringInSlice(a string, list []string) bool {
	for _, b := range list {
		if b == a {
			return true
		}
	}
	return false
}

func (n Webservercodes) CombineKeysValues(keys []string, values []string) (*CombinedEntry, error) {
	
	if len(values) < len(keys) {
		return nil, errors.New("Not enough substrings")
	}
	
	items := map[string]string{}
	for k, v := range keys {
		items[v] = values[k]
	}
	
	combined := CombinedEntry{}
	if logDt, ok := items["time"]; ok {
		if time, err := time.Parse("02/Jan/2006:15:04:05 -0700", logDt); err == nil {
			combined.time = time
		} else {
			return nil, errors.New("Time must be in apache %t format. Example: '02/Jan/2006:15:04:05 -0700'")
		}
	} else {
		return nil, errors.New("Time is absent in log line")
	}
	
	if _, ok := items["code"]; ok {
		code, _ := strconv.Atoi(items["code"])
		combined.code = code
	} else {
		return nil, errors.New("Http code is absent in log line")
	}
	
	return &combined, nil
}

func (n Webservercodes) ValidateRegexp(regex string, f io.ReadSeeker) (*regexp.Regexp, []string, error) {
	
	keys := []string{}
	var rx *regexp.Regexp
	var err error
	
	if rx, err = regexp.Compile(regex); err != nil {
		// error in case of malformed regexp
		return nil, keys, err
	}
	
	keys = rx.SubexpNames();
	if !(SearchStringInSlice("time", keys) && SearchStringInSlice("code", keys)) {
		// error if fields 'time' or 'code' are defined
		return nil, keys, errors.New("Regexp must define 'time' and 'code' fields")
	}
	
	// we will check regexp validity by scan the last log line
	// and parse it, assuming that other lines will match as well
	reader := reverse.NewScanner(f)
	if (!reader.Scan()) {
		// if not Scanned, file is empty, so we don't need to return regex error
		return rx, keys, nil
	}
	
	strings := rx.FindStringSubmatch(reader.Text())
	if len(strings) == 0 {
		// error if regexp mismatch
		return nil, keys, errors.New("Log entries are not match regexp")
	}
	if _, err := n.CombineKeysValues(keys, strings); err != nil {
		// error if no values for 'time' or 'code' are found in parsed log line
		return nil, keys, err
	}
	
	return rx, keys, nil
}

func (n *Webservercodes) ParseHttpCodes(file string, regex string, duration time.Duration) (*HttpStats, error) {
	
	stats := HttpStats{codes: make(map[int]int)}
	
	if f, err := os.Open(file); err == nil {
		defer f.Close()
		
		if rx, keys, err := n.ValidateRegexp(regex, f); err == nil {
			curTime := time.Now()
			errorsCounter := 0
			errorsMax := 100 // there is something wrong if more than errorsMax parse errors
			var vastedLoop bool
			var strings []string
			
			reader := reverse.NewScanner(f)
			for reader.Scan() {
				vastedLoop = false
				strings = rx.FindStringSubmatch(reader.Text())
				if len(strings) > 0 {
					if parsedLine, err := n.CombineKeysValues(keys, strings); err == nil {
						if curTime.Sub(parsedLine.time) > duration {
							break
						}
						if _, ok := stats.codes[parsedLine.code]; ok {
							stats.codes[parsedLine.code]++
						} else {
							stats.codes[parsedLine.code] = 1
						}
					} else {
						vastedLoop = true
					}
				} else {
					vastedLoop = true
				}
				if vastedLoop {
					errorsCounter++
				}
				if errorsCounter >= errorsMax {
					break
				}
			}
			if errorsCounter >= errorsMax {
				return nil, errors.New("Too many entries with wrong format in log file. Check regex_parsestring")
			}
		} else {
			return nil, err
		}
	} else {
		return nil, err
	}
	
	return &stats, nil
}

func (n *Webservercodes) gatherCodes(vhost string, stats HttpStats, acc plugins.Accumulator) {
	
	tags := map[string]string{"virtualhost" : vhost}
	total := 0
	var num int
	
	for _, i := range []int{http.StatusContinue,
					http.StatusSwitchingProtocols,
					http.StatusOK,
					http.StatusCreated,
					http.StatusAccepted,
					http.StatusNonAuthoritativeInfo,
					http.StatusNoContent,
					http.StatusResetContent,
					http.StatusPartialContent,
					http.StatusMultipleChoices,
					http.StatusMovedPermanently,
					http.StatusFound,
					http.StatusSeeOther,
					http.StatusNotModified,
					http.StatusUseProxy,
					http.StatusTemporaryRedirect,
					http.StatusBadRequest,
					http.StatusUnauthorized,
					http.StatusPaymentRequired,
					http.StatusForbidden,
					http.StatusNotFound,
					http.StatusMethodNotAllowed,
					http.StatusNotAcceptable,
					http.StatusProxyAuthRequired,
					http.StatusRequestTimeout,
					http.StatusConflict,
					http.StatusGone,
					http.StatusLengthRequired,
					http.StatusPreconditionFailed,
					http.StatusRequestEntityTooLarge,
					http.StatusRequestURITooLong,
					http.StatusUnsupportedMediaType,
					http.StatusRequestedRangeNotSatisfiable,
					http.StatusExpectationFailed,
					http.StatusTeapot,
					http.StatusInternalServerError,
					http.StatusNotImplemented,
					http.StatusBadGateway,
					http.StatusServiceUnavailable,
					http.StatusGatewayTimeout,
					http.StatusHTTPVersionNotSupported} {
		if _, ok := stats.codes[i]; ok {
			num = stats.codes[i]
		} else {
			num = 0
		}
		total += num
		acc.Add(strconv.Itoa(i), num, tags);
	}
	acc.Add("total", total, tags);
}

func init() {
	plugins.Add("webservercodes", func() plugins.Plugin {
		return &Webservercodes{}
	})
}