package add_kubernetes_metadata

import (
	"fmt"
	"strings"

	"github.com/elastic/beats/libbeat/common"
	"github.com/elastic/beats/libbeat/logp"
	"github.com/elastic/beats/libbeat/processors/add_kubernetes_metadata"
)

func init() {
	add_kubernetes_metadata.Indexing.AddMatcher(LogPathMatcherName, newLogsPathMatcher)
	cfg := common.NewConfig()

	//Add a container indexer config by default.
	add_kubernetes_metadata.Indexing.AddDefaultIndexerConfig(add_kubernetes_metadata.ContainerIndexerName, *cfg)

	//Add a log path matcher which can extract container ID from the "source" field.
	add_kubernetes_metadata.Indexing.AddDefaultMatcherConfig(LogPathMatcherName, *cfg)
}

const LogPathMatcherName = "logs_path"

type LogPathMatcher struct {
	LogsPath string
}

func newLogsPathMatcher(cfg common.Config) (add_kubernetes_metadata.Matcher, error) {
	config := struct {
		LogsPath string `config:"logs_path"`
	}{
		LogsPath: "/var/lib/docker/containers/",
	}

	err := cfg.Unpack(&config)
	if err != nil || config.LogsPath == "" {
		return nil, fmt.Errorf("fail to unpack the `logs_path` configuration: %s", err)
	}

	logPath := config.LogsPath
	if logPath[len(logPath)-1:] != "/" {
		logPath = logPath + "/"
	}

	logp.Debug("kubernetes", "logs_path matcher log path: %s", logPath)

	return &LogPathMatcher{LogsPath: logPath}, nil
}

// Docker container ID is a 64-character-long hexadecimal string
const containerIdLen = 64

func (f *LogPathMatcher) MetadataIndex(event common.MapStr) string {
	if value, ok := event["source"]; ok {
		source := value.(string)
		logp.Debug("kubernetes", "Incoming source value: %s", source)

		if !strings.Contains(source, f.LogsPath) {
			logp.Debug("kubernetes", "Error extracting container id - source value does not contain matcher's logs_path '%s'.", f.LogsPath)
			return ""
		}

		sourceLen := len(source)
		logsPathLen := len(f.LogsPath)

		// In case of the Kubernetes log path "/var/log/containers/",
		// the container ID will be located right before the ".log" extension.
		if strings.HasPrefix(f.LogsPath, "/var/log/containers/") && strings.HasSuffix(source, ".log") && sourceLen >= containerIdLen+4 {
			containerIdEnd := sourceLen - 4
			cid := source[containerIdEnd-containerIdLen : containerIdEnd]
			logp.Debug("kubernetes", "Using container id: %s", cid)
			return cid
		}

		// In any other case, we assume the container ID will follow right after the log path.
		// However we need to check the length to prevent "slice bound out of range" runtime errors.
		if sourceLen >= logsPathLen+containerIdLen {
			cid := source[logsPathLen : logsPathLen+containerIdLen]
			logp.Debug("kubernetes", "Using container id: %s", cid)
			return cid
		}

		logp.Debug("kubernetes", "Error extracting container id - source value contains matcher's logs_path, however it is too short to contain a Docker container ID.")
	}

	return ""
}