// Package moves holds the move protocol's data shapes and arithmetic
// (move-any-app design rev 7.18). It imports no activator, registry
// writer or console: everything here is pure so the box, the console and
// the CLI agree on one definition.
package moves

import (
	"encoding/base32"
	"fmt"
	"io"
	"regexp"
)

// opIDShape is §3: a role prefix and 26 lowercase base32 characters (16
// random bytes, no padding).
//
// Twin of provision.moveIDShape and provision.rollbackIDShape: the copy is
// forced, because moves imports provision, so provision cannot import
// moves. TestOpIDShapeTwinsProvision holds the three together.
var opIDShape = regexp.MustCompile(`^(mv|rb)_[a-z2-7]{26}$`)

var lowerBase32 = base32.NewEncoding("abcdefghijklmnopqrstuvwxyz234567").WithPadding(base32.NoPadding)

func newID(prefix string, r io.Reader) (string, error) {
	var b [16]byte
	if _, err := io.ReadFull(r, b[:]); err != nil {
		return "", fmt.Errorf("moves: mint %s id: %w", prefix, err)
	}
	return prefix + "_" + lowerBase32.EncodeToString(b[:]), nil
}

// NewMoveID mints a move id. The console mints it at the request door and
// it names the operation in the claim, the record and every staging key.
func NewMoveID(r io.Reader) (string, error) { return newID("mv", r) }

// NewRollbackID mints a rollback id, minted by whichever actor wins the
// rollback CAS (§7.8).
func NewRollbackID(r io.Reader) (string, error) { return newID("rb", r) }

// ValidOpID reports whether id has §3's shape. Op ids are opaque beyond
// this: they are never compared for order (claim rev 6.1 Q1).
func ValidOpID(id string) bool { return opIDShape.MatchString(id) }

// OpIDKind is "move", "rollback" or "" for an id of neither shape.
func OpIDKind(id string) string {
	switch {
	case !ValidOpID(id):
		return ""
	case id[:3] == "mv_":
		return "move"
	default:
		return "rollback"
	}
}