// Copyright 2018 Google LLC
//
// 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 main

import (
	"fmt"
	"math/rand"
	"time"
)

// seeded determines if the random number generator is ready.
var seeded bool = false

// CreateTrackingId generates a tracking ID.
func CreateTrackingId(salt string) string {
	if !seeded {
		rand.Seed(time.Now().UnixNano())
		seeded = true
	}

	return fmt.Sprintf("%c%c-%d%s-%d%s",
		getRandomLetterCode(),
		getRandomLetterCode(),
		len(salt),
		getRandomNumber(3),
		len(salt)/2,
		getRandomNumber(7),
	)
}

// getRandomLetterCode generates a code point value for a capital letter.
func getRandomLetterCode() uint32 {
	return 65 + uint32(rand.Intn(25))
}

// getRandomNumber generates a string representation of a number with the requested number of digits.
func getRandomNumber(digits int) string {
	str := ""
	for i := 0; i < digits; i++ {
		str = fmt.Sprintf("%s%d", str, rand.Intn(10))
	}

	return str
}