package main
import (
  "github.com/hashicorp/consul/api"
  "errors"
  "log"
  "fmt"
  "os"
  "encoding/base64"
  /*"github.com/aws/aws-sdk-go/service/s3"*/
)

const consul_addr string = "KV2S3_CONSUL_ADDR"
const enc_key string = "KV2S3_ENC_KEY"

const key_exp_bits int = 256
const key_exp_bytes int = key_exp_bits / 8

func errIsPanic(err error, format string, a ...interface{}) {
  if err != nil {
    log.Panicf(format, a...)
  }
}

func absentIsErr(present bool) error {
  if !present {
    return errors.New("Environement variable is not set.")
  }
  return nil
}

func main() {
  log.Println("starting consul kv backup...")

  //--- Ask Consul to Snapshot our KV
  var present bool
  conf := api.DefaultConfig()
  conf.Address, present = os.LookupEnv(consul_addr)
  err := absentIsErr(present)
  errIsPanic(err, "%v env required. %v", consul_addr, err)
  //@FIXME add later support for HTTPS

  options := api.QueryOptions {
    // Prevent from backuping forever silently a desynchronized node
    AllowStale: false,
  }

  consul, err := api.NewClient(conf)
  errIsPanic(err, "Unable to build a new client. %v", err)

  reader, _, err := consul.Snapshot().Save(&options)
  defer reader.Close()
  errIsPanic(err, "Snapshot failed. %v", err)

  //--- Get encryption key and check it
  b64_key, present := os.LookupEnv(enc_key)
  err = absentIsErr(present)
  errIsPanic(err, "%v env required. %v", enc_key, err)
  raw_key, err := base64.StdEncoding.DecodeString(b64_key)
  errIsPanic(err, "Unable to decode base64 key. %v", err)

  err = nil
  key_size_bytes := len(raw_key)
  key_size_bits := key_size_bytes

  if key_size_bytes != key_exp_bytes {
    msg := fmt.Sprintf(
      "Key size is %d bits (%d bytes) instead of %d bits (%d bytes).",
      key_size_bits,
      key_size_bytes,
      key_exp_bits,
      key_exp_bytes)

    err = errors.New(msg)
  }
  errIsPanic(err, "We deliberately support only 256 bits (32 bytes) keys. %v", err)

  //--- Encryption
  // Not a simple thing to do it in a streaming manner - is it only a good idea?
  // https://neilmadden.blog/2019/12/30/a-few-comments-on-age/
  // https://moxie.org/2011/12/13/the-cryptographic-doom-principle.html


}