/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

// Package identifiers provides common validation for identifiers and keys
// across containerd.
//
// Identifiers in containerd must be a alphanumeric, allowing limited
// underscores, dashes and dots.
//
// While the character set may be expanded in the future, identifiers
// are guaranteed to be safely used as filesystem path components.
package identifiers

import (
	"regexp"

	"github.com/containerd/containerd/errdefs"
	"github.com/pkg/errors"
)

const (
	maxLength  = 76
	alphanum   = `[A-Za-z0-9]+`
	separators = `[._-]`
)

var (
	// identifierRe defines the pattern for valid identifiers.
	identifierRe = regexp.MustCompile(reAnchor(alphanum + reGroup(separators+reGroup(alphanum)) + "*"))
)

// Validate return nil if the string s is a valid identifier.
//
// identifiers must be valid domain names according to RFC 1035, section 2.3.1.  To
// enforce case insensitivity, all characters must be lower case.
//
// In general, identifiers that pass this validation, should be safe for use as
// a domain names or filesystem path component.
func Validate(s string) error {
	if len(s) == 0 {
		return errors.Wrapf(errdefs.ErrInvalidArgument, "identifier must not be empty")
	}

	if len(s) > maxLength {
		return errors.Wrapf(errdefs.ErrInvalidArgument, "identifier %q greater than maximum length (%d characters)", s, maxLength)
	}

	if !identifierRe.MatchString(s) {
		return errors.Wrapf(errdefs.ErrInvalidArgument, "identifier %q must match %v", s, identifierRe)
	}
	return nil
}

func reGroup(s string) string {
	return `(?:` + s + `)`
}

func reAnchor(s string) string {
	return `^` + s + `$`
}
