// +build tools

package main

import (
	"bytes"
	"fmt"
	"go/format"
	"os"
	"os/exec"
	"regexp"
	"strconv"
	"strings"
	"text/template"
	"time"
)

var exactVer *regexp.Regexp
var gitVer *regexp.Regexp
var verFile = "generated-version.go"

func init() {
	// exactly vX.Y.Z (go-compatible semver)
	exactVer = regexp.MustCompile(`^v\d+\.\d+\.\d+$`)

	// vX.Y.Z-n-g0000000 git post-release, semver prerelease
	gitVer = regexp.MustCompile(`^(v\d+\.\d+)\.(\d+)-(\d+)-g`)
}

// Goal: Either use an exact version like v1.0.0
//       or translate the git version like v1.0.0-4-g0000000
//       to a semver like v1.0.1-pre4+g0000000
//       Don't fail when git repo isn't available.
func main() {
	desc := gitDesc()
	rev := gitRev()
	ver := semVer(desc)
	ts := time.Now().Format(time.RFC3339)

	v := struct {
		Timestamp string
		Version   string
		GitRev    string
	}{
		Timestamp: ts,
		Version:   ver,
		GitRev:    rev,
	}

	// Create or overwrite the go file from template
	var buf bytes.Buffer
	if err := versionTpl.Execute(&buf, v); nil != err {
		panic(err)
	}

	// Format
	src, err := format.Source(buf.Bytes())
	if nil != err {
		panic(err)
	}

	// Write to disk (in the Current Working Directory)
	f, err := os.Create(verFile)
	if nil != err {
		panic(err)
	}
	if _, err := f.Write(src); nil != err {
		panic(err)
	}
	if err := f.Close(); nil != err {
		panic(err)
	}
}

func gitDesc() string {
	args := strings.Split("git describe --tags --dirty --always", " ")
	cmd := exec.Command(args[0], args[1:]...)
	out, err := cmd.CombinedOutput()
	if nil != err {
		// Don't panic, just carry on
		out = []byte("v0.0.0-0-g0000000")
	}
	return strings.TrimSpace(string(out))
}

func gitRev() string {
	args := strings.Split("git rev-parse HEAD", " ")
	cmd := exec.Command(args[0], args[1:]...)
	out, err := cmd.CombinedOutput()
	if nil != err {
		// Don't panic, just carry on
		out = []byte("00000000000000000")
	}
	return strings.TrimSpace(string(out))
}

func semVer(desc string) string {
	var ver string
	if exactVer.MatchString(desc) {
		// v1.0.0
		ver = desc
	} else if gitVer.MatchString(desc) {
		// ((v1.0).(0)-(1))
		vers := gitVer.FindStringSubmatch(desc)
		patch, err := strconv.Atoi(vers[2])
		if nil != err {
			panic(err)
		}
		// v1.0.1-pre1
		ver = fmt.Sprintf("%s.%d-pre%s", vers[1], patch+1, vers[3])
	}
	return ver
}

var versionTpl = template.Must(template.New("").Parse(`// Code generated by go generate; DO NOT EDIT.
package main

func init() {
	Timestamp = "{{ .Timestamp }}"
	Version = "{{ .Version }}"
	GitRev = "{{ .GitRev }}"
}
`))