package patchruntime

import (
	"errors"
	"fmt"
	"strings"

	"github.com/distribution/reference"
	"golang.org/x/mod/semver"
)

// errImageRefNoTag reports that an image reference does not declare a
// tag. The patch service maps it to `image_ref_not_semver` because a
// digest-only or tagless reference cannot carry a semver-comparable
// version.
var errImageRefNoTag = errors.New("image reference is missing a tag")

// extractSemverTag returns the canonical semver string ("v1.4.7") for
// imageRef, ready to feed into golang.org/x/mod/semver. The leading "v"
// is added when the underlying tag omits it.
//
// Errors returned by this function are pre-formatted for inclusion in
// the patch service's `image_ref_not_semver` failure message.
func extractSemverTag(imageRef string) (string, error) {
	parsed, err := reference.ParseNormalizedNamed(imageRef)
	if err != nil {
		return "", fmt.Errorf("parse image reference %q: %w", imageRef, err)
	}
	tagged, ok := parsed.(reference.NamedTagged)
	if !ok {
		return "", fmt.Errorf("%w: %q", errImageRefNoTag, imageRef)
	}
	tag := strings.TrimSpace(tagged.Tag())
	if tag == "" {
		return "", fmt.Errorf("%w: %q", errImageRefNoTag, imageRef)
	}
	candidate := tag
	if !strings.HasPrefix(candidate, "v") {
		candidate = "v" + candidate
	}
	if !semver.IsValid(candidate) {
		return "", fmt.Errorf("tag %q on image reference %q is not a valid semver", tag, imageRef)
	}
	return candidate, nil
}

// samePatchSeries reports whether two canonical semver strings (with
// the leading "v") share their major and minor components. The third
// component (patch) and any pre-release / build metadata are ignored.
func samePatchSeries(currentSemver, newSemver string) bool {
	return semver.MajorMinor(currentSemver) == semver.MajorMinor(newSemver)
}