// Copyright 2017, OpenCensus 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 prometheus

import (
	"strings"
	"unicode"
)

const labelKeySizeLimit = 100

// sanitize returns a string that is trunacated to 100 characters if it's too
// long, and replaces non-alphanumeric characters to underscores.
func sanitize(s string) string {
	if len(s) == 0 {
		return s
	}
	if len(s) > labelKeySizeLimit {
		s = s[:labelKeySizeLimit]
	}
	s = strings.Map(sanitizeRune, s)
	if unicode.IsDigit(rune(s[0])) {
		s = "key_" + s
	}
	if s[0] == '_' {
		s = "key" + s
	}
	return s
}

// converts anything that is not a letter or digit to an underscore
func sanitizeRune(r rune) rune {
	if unicode.IsLetter(r) || unicode.IsDigit(r) {
		return r
	}
	// Everything else turns into an underscore
	return '_'
}
