// Copyright 2016 The Prometheus Authors
// 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 version

import (
	"bytes"
	"fmt"
	"runtime"
	"runtime/debug"
	"strings"
	"text/template"

	"github.com/prometheus/client_golang/prometheus"
)

// Build information. Populated at build-time.
var (
	Version   string
	Revision  string
	Branch    string
	BuildUser string
	BuildDate string
	GoVersion = runtime.Version()
	GoOS      = runtime.GOOS
	GoArch    = runtime.GOARCH
)

var (
	computedRevision string
	computedTags     string
)

func getRevision() string {
	if Revision != "" {
		return Revision
	}
	return computedRevision
}

func getTags() string {
	return computedTags
}

func init() {
	computedRevision, computedTags = computeRevision()
}

func computeRevision() (string, string) {
	var (
		rev      = "unknown"
		tags     = "unknown"
		modified bool
	)

	buildInfo, ok := debug.ReadBuildInfo()
	if !ok {
		return rev, tags
	}
	for _, v := range buildInfo.Settings {
		if v.Key == "vcs.revision" {
			rev = v.Value
		}
		if v.Key == "vcs.modified" {
			if v.Value == "true" {
				modified = true
			}
		}
		if v.Key == "-tags" {
			tags = v.Value
		}
	}
	if modified {
		return rev + "-modified", tags
	}
	return rev, tags
}

// NewCollector returns a collector that exports metrics about current version
// information.
func NewCollector(program string) prometheus.Collector {
	return prometheus.NewGaugeFunc(
		prometheus.GaugeOpts{
			Namespace: program,
			Name:      "build_info",
			Help: fmt.Sprintf(
				"A metric with a constant '1' value labeled by version, revision, branch, goversion from which %s was built, and the goos and goarch for the build.",
				program,
			),
			ConstLabels: prometheus.Labels{
				"version":   Version,
				"revision":  getRevision(),
				"branch":    Branch,
				"goversion": GoVersion,
				"goos":      GoOS,
				"goarch":    GoArch,
				"tags":      getTags(),
			},
		},
		func() float64 { return 1 },
	)
}

// versionInfoTmpl contains the template used by Info.
var versionInfoTmpl = `
{{.program}}, version {{.version}} (branch: {{.branch}}, revision: {{.revision}})
  build user:       {{.buildUser}}
  build date:       {{.buildDate}}
  go version:       {{.goVersion}}
  platform:         {{.platform}}
  tags:             {{.tags}}
`

// Print returns version information.
func Print(program string) string {
	m := map[string]string{
		"program":   program,
		"version":   Version,
		"revision":  getRevision(),
		"branch":    Branch,
		"buildUser": BuildUser,
		"buildDate": BuildDate,
		"goVersion": GoVersion,
		"platform":  GoOS + "/" + GoArch,
		"tags":      getTags(),
	}
	t := template.Must(template.New("version").Parse(versionInfoTmpl))

	var buf bytes.Buffer
	if err := t.ExecuteTemplate(&buf, "version", m); err != nil {
		panic(err)
	}
	return strings.TrimSpace(buf.String())
}

// Info returns version, branch and revision information.
func Info() string {
	return fmt.Sprintf("(version=%s, branch=%s, revision=%s)", Version, Branch, getRevision())
}

// BuildContext returns goVersion, platform, buildUser and buildDate information.
func BuildContext() string {
	return fmt.Sprintf("(go=%s, platform=%s, user=%s, date=%s, tags=%s)", GoVersion, GoOS+"/"+GoArch, BuildUser, BuildDate, getTags())
}