// Package imageref splits container image references into repository, tag
// and digest.
package imageref

import (
	"regexp"
	"strings"
)

// Ref is an image reference split into its parts. Tag and Digest are empty
// when the reference has none.
type Ref struct {
	Repo   string
	Tag    string
	Digest string
}

// Parse splits ref into repository, tag and digest. A colon before the last
// "/" belongs to a registry host and port ("localhost:5000/foo"), not a tag.
func Parse(ref string) Ref {
	var r Ref
	if at := strings.Index(ref, "@"); at >= 0 {
		r.Digest = ref[at+1:]
		ref = ref[:at]
	}
	slash := strings.LastIndex(ref, "/")
	last := ref[slash+1:]
	if colon := strings.Index(last, ":"); colon >= 0 {
		r.Tag = last[colon+1:]
		ref = ref[:slash+1+colon]
	}
	r.Repo = ref
	return r
}

// IsRegistryHost reports whether the first path segment of a repository names
// a registry: it contains a "." or ":" or is "localhost".
func IsRegistryHost(segment string) bool {
	return strings.ContainsAny(segment, ".:") || segment == "localhost"
}

// String reassembles the reference as repo[:tag][@digest].
func (r Ref) String() string {
	s := r.Repo
	if r.Tag != "" {
		s += ":" + r.Tag
	}
	if r.Digest != "" {
		s += "@" + r.Digest
	}
	return s
}

var digestPattern = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)

// IsDigest reports whether d is a well-formed sha256 digest.
func IsDigest(d string) bool { return digestPattern.MatchString(d) }