// Copyright 2017 CoreOS, Inc.
//
// 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 dbtester

import (
	"crypto/rand"
	"fmt"
	mrand "math/rand"
	"os"
	"strings"
	"time"
)

// sequentialKey returns '00012' when size is 5 and num is 12.
func sequentialKey(size, num int64) string {
	txt := fmt.Sprintf("%d", num)
	if len(txt) > int(size) {
		return txt
	}
	delta := int(size) - len(txt)
	return strings.Repeat("0", delta) + txt
}

func sameKey(size int64) string {
	return strings.Repeat("a", int(size))
}

func randBytes(bytesN int64) []byte {
	const (
		letterBytes   = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
		letterIdxBits = 6                    // 6 bits to represent a letter index
		letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
		letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
	)
	src := mrand.NewSource(time.Now().UnixNano())
	b := make([]byte, bytesN)
	for i, cache, remain := bytesN-1, src.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = src.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			b[i] = letterBytes[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}
	return b
}

func mustRandBytes(n int) []byte {
	rb := make([]byte, n)
	_, err := rand.Read(rb)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to generate value: %v\n", err)
		os.Exit(1)
	}
	return rb
}

func multiRandStrings(keyN, sliceN int64) []string {
	m := make(map[string]struct{})
	for int64(len(m)) != sliceN {
		m[string(randBytes(keyN))] = struct{}{}
	}
	rs := make([]string, sliceN)
	idx := 0
	for k := range m {
		rs[idx] = k
		idx++
	}
	return rs
}