package imageparser

import "regexp"

/*
This code is directly lifted from the distribution codebase as they haven't been exported.

For reference: https://github.com/distribution/distribution/blob/9329f6a62b67d5e06d50dc93997c7705a075fcd9/reference/regexp.go
*/

var (
	// match compiles the string to a regular expression.
	match = regexp.MustCompile
	// TagRegexp matches valid tag names. From docker/docker:graph/tags.go.
	TagRegexp = match(`[\w][\w.-]{0,127}`)

	// anchoredTagRegexp matches valid tag names, anchored at the start and
	// end of the matched string.
	anchoredTagRegexp = anchored(TagRegexp)

	// DigestRegexp matches valid digests.
	DigestRegexp = match(`[A-Za-z][A-Za-z0-9]*(?:[-_+.][A-Za-z][A-Za-z0-9]*)*[:][[:xdigit:]]{32,}`)

	// anchoredDigestRegexp matches valid digests, anchored at the start and
	// end of the matched string.
	anchoredDigestRegexp = anchored(DigestRegexp)
)

// anchored anchors the regular expression by adding start and end delimiters.
func anchored(res ...*regexp.Regexp) *regexp.Regexp {
	return match(`^` + expression(res...).String() + `$`)
}

// expression defines a full expression, where each regular expression must
// follow the previous.
func expression(res ...*regexp.Regexp) *regexp.Regexp {
	var s string
	for _, re := range res {
		s += re.String()
	}

	return match(s)
}