go_version/version.go

package version

import (
	"encoding/xml"
	"errors"
	"fmt"
	"strconv"
	"strings"
)

// Version defines a structure describing the version of a program or module.
type Version struct {
	Major    uint `json:"major"`
	Minor    uint `json:"minor"`
	Revision uint `json:"revision"`
	Build    uint `json:"build"`
}

// String converts a Version into its generic string representation
func (version Version) String() string {
	return version.SpecificString(0)
}

// SpecificString converts a Version into its string representation with either the specified number of components ([1,4]) or its generic string representation
func (version Version) SpecificString(numberOfComponents int) string {
	switch numberOfComponents {
	case 4:
		return fmt.Sprintf("%d.%d.%d.%d", version.Major, version.Minor, version.Revision, version.Build)
	case 3:
		return fmt.Sprintf("%d.%d.%d", version.Major, version.Minor, version.Revision)
	case 2:
		return fmt.Sprintf("%d.%d", version.Major, version.Minor)
	case 1:
		return fmt.Sprintf("%d", version.Major)
	default:
		if 0 < version.Build {
			return fmt.Sprintf("%d.%d.%d.%d", version.Major, version.Minor, version.Revision, version.Build)
		} else if 0 < version.Revision {
			return fmt.Sprintf("%d.%d.%d", version.Major, version.Minor, version.Revision)
		} else if 0 < version.Minor {
			return fmt.Sprintf("%d.%d", version.Major, version.Minor)
		}
		return fmt.Sprintf("%d", version.Major)
	}
}

// Equal verifies, whether two Versions are the same
func (version Version) Equal(comparand Version) bool {
	return version.Major == comparand.Major && version.Minor == comparand.Minor && version.Revision == comparand.Revision && version.Build == comparand.Build
}

// Smaller verifies, whether the Version is smaller than the comparand
func (version Version) Smaller(comparand Version) bool {
	if version.Major < comparand.Major {
		return true
	}
	if version.Major == comparand.Major {
		if version.Minor < comparand.Minor {
			return true
		}
		if version.Minor == comparand.Minor {
			if version.Revision < comparand.Revision {
				return true
			}
			if version.Revision == comparand.Revision {
				if version.Build < comparand.Build {
					return true
				}
			}
		}
	}
	return false
}

// Larger verifies, whether the Version is larger than the comparand
func (version Version) Larger(comparand Version) bool {
	if version.Equal(comparand) {
		return false
	}
	return !version.Smaller(comparand)
}

func parseError(part, value string) error {
	return fmt.Errorf("the '%s' component of the version could not be parsed ('%s')", part, value)
}

// ParseVersion tries to read all available parts of a version string
func ParseVersion(text string) (Version, error) {
	result := Version{}
	err := result.Parse(text)
	return result, err
}

// Parse tries to read all available parts of a version string to the internal variables
func (version *Version) Parse(text string) error {
	if nil == version {
		return fmt.Errorf("cannot parse to nil")
	}
	parts := strings.Split(text, ".")
	if 0 < len(parts) {
		var err error
		major, err := strconv.Atoi(strings.Trim(parts[0], " \t\r\n"))
		if nil != err || major < 0 {
			return parseError("Major", parts[0])
		}
		version.Major = uint(major)
		if 1 < len(parts) {
			minor, err := strconv.Atoi(strings.Trim(parts[1], " \t\r\n"))
			if nil != err || minor < 0 {
				return parseError("Minor", parts[1])
			}
			version.Minor = uint(minor)
			if 2 < len(parts) {
				revision, err := strconv.Atoi(strings.Trim(parts[2], " \t\r\n"))
				if nil != err || revision < 0 {
					return parseError("Revision", parts[2])
				}
				version.Revision = uint(revision)
				if 3 < len(parts) {
					build, err := strconv.Atoi(strings.Trim(parts[3], " \t\r\n"))
					if nil != err || build < 0 {
						return parseError("Build", parts[3])
					}
					version.Build = uint(build)
				}
			}
		}
	}
	return nil
}

// MarshalXML satisfies the xml.Marshaler interface
func (version Version) MarshalXML(e *xml.Encoder, start xml.StartElement) (err error) {
	if err = e.EncodeToken(start); err == nil {
		stringValue := version.String()
		if err = e.EncodeToken(xml.CharData([]byte(stringValue))); err == nil {
			if err = e.EncodeToken(xml.EndElement{
				Name: start.Name,
			}); err == nil {
				return e.Flush()
			}
		}
	}
	return
}

// MarshalJSON satisfies the json.Marshaler interface
func (version Version) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf("\"%s\"", version.String())), nil
}

// UnmarshalXML satisfies the xml.Unmarshaler interface
func (version *Version) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	var (
		token xml.Token
		err   error
	)

	if nil == version {
		return fmt.Errorf("cannot unmarshal to nil")
	}

	versionAttributeFound := false
	if nil != start.Attr {
		for _, attribute := range start.Attr {
			switch attribute.Name.Local {
			case "Major":
				major, err := strconv.Atoi(strings.Trim(attribute.Value, " \t\r\n"))
				if nil != err || major < 0 {
					return parseError("Major", attribute.Value)
				}
				version.Major = uint(major)
				versionAttributeFound = true
			case "Minor":
				minor, err := strconv.Atoi(strings.Trim(attribute.Value, " \t\r\n"))
				if nil != err || minor < 0 {
					return parseError("Minor", attribute.Value)
				}
				version.Minor = uint(minor)
				versionAttributeFound = true
			case "Revision":
				revision, err := strconv.Atoi(strings.Trim(attribute.Value, " \t\r\n"))
				if nil != err || revision < 0 {
					return parseError("Revision", attribute.Value)
				}
				version.Revision = uint(revision)
				versionAttributeFound = true
			case "Build":
				build, err := strconv.Atoi(strings.Trim(attribute.Value, " \t\r\n"))
				if nil != err || build < 0 {
					return parseError("Build", attribute.Value)
				}
				version.Build = uint(build)
				versionAttributeFound = true
			}
		}
	}

Loop:
	for {
		if token, err = d.Token(); err != nil {
			return err
		}

		if token == nil {
			break
		}

		switch se := token.(type) {
		case xml.StartElement:
			return errors.New("expected version string (eg. '1.0.0.0')")
		case xml.CharData:
			if !versionAttributeFound {
				stringData := strings.Trim(string(se), " \t\r\n")
				if 0 < len(stringData) {
					version.Parse(stringData)
				}
			}
		case xml.EndElement:
			break Loop
		}
	}

	return nil
}

func unquoteBytes(s []byte) (t []byte, ok bool) {
	if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
		return
	}
	return s[1 : len(s)-1], true
}

// UnmarshalJSON satisfies the json.Unmarshaler interface
func (version *Version) UnmarshalJSON(data []byte) error {
	cleanData, ok := unquoteBytes(data)
	if ok {
		return version.Parse(string(cleanData))
	}
	return fmt.Errorf("'%s' cannot be unmarshalled from JSON", string(data))
}