// Copyright 2018 The Kubeflow 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 util provides various helper routines.
package util

import (
        "encoding/json"
        "fmt"
        "math/rand"
        "time"

        log "github.com/sirupsen/logrus"
)

const (
        // Environment variable for namespace when deployed on kubernetes
        EnvKubeflowNamespace = "KUBEFLOW_NAMESPACE"
)

// Pformat returns a pretty format output of any value that can be marshalled to JSON.
func Pformat(value interface{}) string {
        if s, ok := value.(string); ok {
                return s
        }
        valueJSON, err := json.MarshalIndent(value, "", "  ")
        if err != nil {
                log.Warningf("Couldn't pretty format %v, error: %v", value, err)
                return fmt.Sprintf("%v", value)
        }
        return string(valueJSON)
}

var src = rand.NewSource(time.Now().UnixNano())

const letterBytes = "0123456789abcdefghijklmnopqrstuvwxyz"
const (
        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
)

// RandString generates a random string of the desired length.
//
// The string is DNS-1035 label compliant; i.e. its only alphanumeric lowercase.
// From: https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-golang
func RandString(n int) string {
        b := make([]byte, n)
        // A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
        for i, cache, remain := n-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 string(b)
}