// Package semver provides utilities for working with semantic
// versioning based on https://semver.org
package semver

import (
	"log"
	"regexp"

	"errors"
)

const (
	// SemverRegexpString is the officially recommended regular expression for
	// validating SemVer: https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
	SemverRegexpString = `^(?P<major>0|[1-9]\d*)\.(?P<minor>0|[1-9]\d*)\.(?P<patch>0|[1-9]\d*)(?:-(?P<prerelease>(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+(?P<buildmetadata>[0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$`
)

func init() {
	_, err := regexp.Compile(SemverRegexpString)
	if err != nil {
		log.Fatal("semver.init: failed to compile the SemVer regular expression")
	}
}

// IsValidSemver checks the input string against the recommended SemVer
// regular expression.
func IsValidSemver(ver string) error {
	// We can drop the error because we have a test that confirms the Regexp string
	// compiles, which is the only type of error regexp.MatchString can return
	ok, _ := regexp.MatchString(SemverRegexpString, ver)
	// if its not valid, return our custom error
	if !ok {
		return ErrInvalidSemVer
	}
	return nil
}

// ErrInvalidSemVer when the SemVer string simply don't follow that SemVer.org
// specification.
var ErrInvalidSemVer = errors.New("invalid semver provided")