package host

import (
	"errors"
	"github.com/carlosframework/platform/internal/moves"
)

var errRootFloorHistory = errors.New("root floor history unavailable")

// This is a reconstruction decision, not an authority source. history is a
// complete root-authorized reconstruction; legacy supplies only extra denies.
// A nil history cannot be upgraded into authority by today's remote object.
func reconstructRootFloor(history, remote *moves.Floor, legacy []*moves.Floor) (*moves.Floor, error) {
	if history == nil {
		return nil, errRootFloorHistory
	}
	out := *history
	valid := func(f *moves.Floor) bool { return f != nil && f.Min > 0 && validFloorRelease(f.MinRelease) }
	if !valid(&out) {
		return nil, errRootFloorHistory
	}
	for _, f := range legacy {
		if !valid(f) {
			return nil, errRootFloorHistory
		}
		if err := floorRegression(&out, f); err == nil {
			out = *f
			continue
		}
		// Independent maxima: a larger protocol and a larger release can occur
		// in different files. Never choose just one file by its release string.
		if f.Min > out.Min {
			out.Min = f.Min
		}
		if ok, _ := moves.ReleaseAtOrAbove(f.MinRelease, out.MinRelease); ok {
			out.MinRelease = f.MinRelease
		}
	}
	if remote == nil {
		if out != *history {
			return &out, errRootFloorHistory
		}
		return &out, nil
	}
	if !valid(remote) {
		return &out, errRootFloorHistory
	}
	if err := floorRegression(&out, remote); err != nil {
		return &out, err
	}
	next := *remote
	return &next, nil
}