package moves

import (
	"fmt"
	"strconv"
	"strings"

	"github.com/carlosframework/platform/internal/hostclaim"
	"github.com/superfly/ltx"
)

// ReplicaSource is where a move's source copy reads from (§7.3, round-3
// finding 5): the claim holder's location and generation, never the
// legacy HibernatePrefix guess. keep admits, relative to prefix, only the
// generation's own LTX files, `<level>/<min>-<max>.ltx` with a level from
// 0000 to 0009, so the staging lane holds the generation's files flat
// under replica/<level>/ and nothing else: no other generation (g-*/), no
// child incarnation, no generation.json, lock.json or closed/.
//
// The holder's location never carries a trailing slash (Claim.Validate
// accepts only instances/<host> or instances/<host>/<incarnation>), so the
// separator is added here, as genselect.requestLocation does (round-4
// finding 4). A generation of "" or hostclaim.RootGeneration is the root
// layout: the level directories sit directly under the location.
//
// The generation prefix rule has twins: hostbox.GenerationPrefix (which
// refuses the root generation and a holder with no session, so a source
// copy cannot use it) and genselect's unexported prefix and coordinates.
// The three change together.
func ReplicaSource(h hostclaim.Holder) (prefix string, keep func(rel string) bool) {
	base := strings.TrimSuffix(h.Location, "/") + "/"
	prefix = base
	if g := h.Generation; g != "" && g != hostclaim.RootGeneration {
		prefix = base + "g-" + g + "/"
	}
	return prefix, levelFile
}

// levelFile is ReplicaSource's keep: exactly two path parts, a level
// directory of four lowercase hex digits from 0000 to 0009, and an LTX
// file name in its canonical form with 0 < min <= max.
func levelFile(rel string) bool {
	parts := strings.Split(rel, "/")
	if len(parts) != 2 || len(parts[0]) != 4 {
		return false
	}
	level, err := strconv.ParseUint(parts[0], 16, 16)
	if err != nil || level > 9 || fmt.Sprintf("%04x", level) != parts[0] {
		return false
	}
	min, max, err := ltx.ParseFilename(parts[1])
	return err == nil && min != 0 && min <= max && ltx.FormatFilename(min, max) == parts[1]
}