package regionname

import "regexp"

// HomeRegion is the engine region of the home placement (home-region parks,
// part 1, Paul 2026-10-11). The home's placement code is "", and "" already
// means unset to the engine and to the claim: an engine, view, chore or
// admission with region "" is refused or read as "holds nothing anywhere".
// So home is never "" here. It is this token, mapped once from the placement
// code by PlacementRegion where a box's or a record's code becomes an engine
// region.
//
// The "@" is outside the placement-code alphabet (provision.ValidRegion:
// lowercase a-z, 0-9 and hyphen), so no named region, one named "home"
// included, can ever equal it. It reaches the claim's obligation region, its
// "region:" owner, its quiet_after key and one control key, the home lane's
// staging lease (control/staging-leases/@home/<host>, keyed in the host's
// wiring). It never reaches an archive path: the archive is
// parked/<incarnation>/<host>/<retirement>/.
const HomeRegion = "@home"

// placementCode is a named placement code: provision.ValidRegion without the
// empty code. TestHomeRegionIsReserved holds the two together.
var placementCode = regexp.MustCompile(`^[a-z0-9-]{1,16}$`)

// PlacementRegion is the engine region of a placement code: HomeRegion for
// the home's "", a named code unchanged, and "" (unset, which every engine
// entry refuses) for anything that is not a placement code, HomeRegion
// itself included.
func PlacementRegion(code string) string {
	switch {
	case code == "":
		return HomeRegion
	case placementCode.MatchString(code):
		return code
	}
	return ""
}

func HomePlacementCode(home, region string) string {
	if home != "" && region == home {
		return ""
	}
	return region
}

// SameRegion preserves exact stored identities. The only alias is a verified
// home roster name and @home. Empty always means unset at this boundary.
func SameRegion(home, a, b string) bool {
	if a == "" || b == "" {
		return false
	}
	if a == b {
		return true
	}
	return home != "" && PlacementRegion(home) == home &&
		((a == home && b == HomeRegion) || (a == HomeRegion && b == home))
}