package main

import (
	"fmt"
	"io"
	"os"
	"runtime/debug"
)

var (
	Name      string = ""
	Version   string = ""
	Commit    string = ""
	BuildTime string = ""
	OS        string = ""
	Arch      string = ""
	ShowDeps  bool   = false

	dependencies = []string{}
)

func main() {
	Print()
}

func Fprint(w io.Writer) {
	if OS == "" || Arch == "" || ShowDeps {
		fillDebugInfo()
	}

	if Name == "" {
		return
	}

	if Version != "" {
		fmt.Fprintf(w, "%s %s (built for %s/%s at %s)\n", Name, Version, OS, Arch, BuildTime)
	} else if Commit != "" {
		fmt.Fprintf(w, "%s (commit %s) (built at %s)\n", Name, Commit, BuildTime)
	}

	if ShowDeps {
		fmt.Println("\ndependencies:")
		for _, dep := range dependencies {
			fmt.Fprintf(w, "  %s\n", dep)
		}
	}
}

func Print() {
	Fprint(os.Stdout)
}

func overwriteValueIfEmpty(value *string, newValue string) {
	if *value == "" {
		*value = newValue
	}
}

func fillDebugInfo() {
	info, ok := debug.ReadBuildInfo()
	if !ok {
		return
	}

	for _, setting := range info.Settings {
		switch setting.Key {
		case "GOOS":
			overwriteValueIfEmpty(&OS, setting.Value)
		case "GOARCH":
			overwriteValueIfEmpty(&Arch, setting.Value)
		case "vcs.revision":
			overwriteValueIfEmpty(&Commit, setting.Value)
		}
	}

	for _, dep := range info.Deps {
		str := fmt.Sprintf("%s %s", dep.Path, dep.Version)
		dependencies = append(dependencies, str)
	}
}