package main

import (
	"flag"
	"fmt"
	"os"
	"strconv"
	"strings"
)

type VERSION struct {
	Filename                                  string
	Major, Minor, Patch, Revision             uint64
	HasMajor, HasMinor, HasPatch, HasRevision bool
}

func (v *VERSION) Flush() error {
	return os.WriteFile(v.Filename, []byte(v.String()), 0664)
}

func (v VERSION) String() string {
	var buffer strings.Builder
	if v.HasMajor || v.HasMinor || v.HasPatch || v.HasRevision {
		buffer.WriteString(fmt.Sprintf("%d", v.Major))
	}
	if v.HasMinor || v.HasPatch || v.HasRevision {
		buffer.WriteString(fmt.Sprintf(".%d", v.Minor))
	}
	if v.HasPatch || v.HasRevision {
		buffer.WriteString(fmt.Sprintf(".%d", v.Patch))
	}
	if v.HasRevision {
		buffer.WriteString(fmt.Sprintf("-%d", v.Revision))
	}
	return buffer.String()
}

func NewVersion(filename string) (VERSION, error) {
	f, err := os.ReadFile(filename)
	if err != nil {
		return VERSION{}, fmt.Errorf("error reading %s: %w", filename, err)
	}
	fields := strings.FieldsFunc(string(f), func(r rune) bool { return r == '.' || r == '-' })
	if len(fields) > 4 {
		return VERSION{}, fmt.Errorf("invalid VERSION file format - %d fields (expected 0-4)", len(fields))
	}
	results := VERSION{
		Filename: filename,
	}
	if len(fields) > 0 {
		results.Major, err = strconv.ParseUint(fields[0], 10, 64)
		if err != nil {
			return VERSION{}, fmt.Errorf("error parsing major version: %w", err)
		}
		results.HasMajor = true
	}
	if len(fields) > 1 {
		results.Minor, err = strconv.ParseUint(fields[1], 10, 64)
		if err != nil {
			return VERSION{}, fmt.Errorf("error parsing minor version: %w", err)
		}
		results.HasMinor = true
	}
	if len(fields) > 2 {
		results.Patch, err = strconv.ParseUint(fields[2], 10, 64)
		if err != nil {
			return VERSION{}, fmt.Errorf("error parsing patch version: %w", err)
		}
		results.HasPatch = true
	}
	if len(fields) > 3 {
		results.Revision, err = strconv.ParseUint(fields[3], 10, 64)
		if err != nil {
			return VERSION{}, fmt.Errorf("error parsing revision: %w", err)
		}
		results.HasRevision = true
	}
	return results, nil
}

func IncrementVersion(version VERSION, major, minor, patch, revision bool) VERSION {
	if major {
		version.Major++
		version.HasMajor = true
	}
	if minor {
		version.Minor++
		version.HasMinor = true
	}
	if patch {
		version.Patch++
		version.HasPatch = true
	}
	if revision {
		version.Revision++
		version.HasRevision = true
	}
	return version
}

func main() {
	flag.Usage = func() {
		fmt.Println("usage: increment_version <path to VERSION file>")
		fmt.Println("       increment_version <optional flags> <path to VERSION file>")
		fmt.Println("increment_version increments the version of a given VERSION file.")
		fmt.Println("It accepts the following formats:")
		fmt.Println("\t<major>.<minor>.<patch>-<revision>")
		fmt.Println("\t<major>.<minor>.<patch>")
		fmt.Println("\t<major>.<minor>")
		fmt.Println("\t<major>")
		fmt.Println("the following flags are used to determine which fields to increment.")
		fmt.Println("using a flag without a corresponding value in the VERSION file will result")
		fmt.Println("in that field, along with all the necessary fields to the left being")
		fmt.Println("created inside that file.")
	}
	var major, minor, patch, revision, dry bool
	flag.BoolVar(&major, "major", false, "increment major version")
	flag.BoolVar(&minor, "minor", false, "increment minor version")
	flag.BoolVar(&patch, "patch", false, "increment patch version")
	flag.BoolVar(&revision, "revision", false, "increment revision")
	flag.BoolVar(&dry, "dry", true, "do not change the file (just print the new version)")
	flag.Parse()
	args := flag.Args()
	if len(args) == 0 {
		fmt.Println("requires path to VERSION file")
		flag.Usage()
		os.Exit(1)
	}
	filename := strings.Join(args, " ")
	oldversion, err := NewVersion(filename)
	if err != nil {
		fmt.Printf("error loading version file %s: %v\n", filename, err)
		os.Exit(1)
	}
	newversion := IncrementVersion(oldversion, major, minor, patch, revision)
	fmt.Printf("'%s' => '%s'\n", oldversion, newversion)
	if !dry {
		err = newversion.Flush()
		if err != nil {
			fmt.Printf("error writing updated VERSION to %s: %v\n", filename, err)
		}
	}
}