/*
gohpenc -- Go high-performance encryption utility
Copyright (C) 2017-2020 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

// Go high-performance encryption utility
package main

import (
	"bufio"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base32"
	"encoding/binary"
	"flag"
	"fmt"
	"io"
	"os"
	"runtime"
	"sync"

	"golang.org/x/crypto/chacha20poly1305"
	"golang.org/x/crypto/poly1305"
)

const (
	LenSize  = 4
	SaltSize = 16
)

var (
	doPSK     = flag.Bool("psk", false, "Generate PSK")
	keyB32    = flag.String("k", "", "Encryption key")
	decrypt   = flag.Bool("d", false, "Decrypt, instead of encrypt")
	blockSize = flag.Int("b", 1<<10, "Blocksize, in KiB")
	threads   = flag.Int("c", runtime.NumCPU(), "Number of threads")

	Base32Codec *base32.Encoding = base32.StdEncoding.WithPadding(base32.NoPadding)

	key []byte
	bs  int
	wg  sync.WaitGroup
)

type Task struct {
	ctr  uint64
	size int
}

type Worker struct {
	aead    cipher.AEAD
	nonce   []byte
	input   []byte
	ready   chan struct{}
	task    chan Task
	output  chan []byte
	written chan struct{}
}

func NewWorker(key, salt []byte) *Worker {
	aead, err := chacha20poly1305.NewX(key)
	if err != nil {
		panic(err)
	}
	w := Worker{
		aead:    aead,
		nonce:   make([]byte, chacha20poly1305.NonceSizeX),
		input:   make([]byte, LenSize+bs+poly1305.TagSize),
		ready:   make(chan struct{}),
		task:    make(chan Task),
		output:  make(chan []byte),
		written: make(chan struct{}),
	}
	copy(w.nonce, salt)
	go w.Run()
	return &w
}

func (w *Worker) Run() {
	var output []byte
	var err error
	for {
		w.ready <- struct{}{}
		task := <-w.task
		binary.BigEndian.PutUint64(w.nonce[SaltSize:], task.ctr)
		if *decrypt {
			output, err = w.aead.Open(
				w.input[:LenSize],
				w.nonce,
				w.input[LenSize:LenSize+task.size+poly1305.TagSize],
				w.input[:LenSize],
			)
			if err != nil {
				panic(err)
			}
			output = output[LenSize:]
		} else {
			binary.BigEndian.PutUint32(w.input, uint32(task.size))
			output = w.aead.Seal(
				w.input[:LenSize],
				w.nonce,
				w.input[LenSize:LenSize+task.size],
				w.input[:LenSize],
			)
		}
		w.output <- output
		<-w.written
		wg.Done()
	}
}

func main() {
	flag.Parse()

	if *doPSK {
		key := make([]byte, chacha20poly1305.KeySize)
		if _, err := io.ReadFull(rand.Reader, key); err != nil {
			panic(err)
		}
		fmt.Println(Base32Codec.EncodeToString(key))
		return
	}

	var err error
	key, err = Base32Codec.DecodeString(*keyB32)
	if err != nil {
		panic(err)
	}
	if len(key) != chacha20poly1305.KeySize {
		panic("Invalid key size")
	}
	salt := make([]byte, SaltSize)

	if *decrypt {
		if _, err = io.ReadFull(os.Stdin, salt); err != nil {
			panic(err)
		}
	} else {
		if _, err = io.ReadFull(rand.Reader, salt); err != nil {
			panic(err)
		}
		if _, err = os.Stdout.Write(salt); err != nil {
			panic(err)
		}
	}

	bs = *blockSize * (1 << 10)
	stdin := bufio.NewReaderSize(os.Stdin, LenSize+bs+poly1305.TagSize)

	workers := make([]*Worker, *threads)
	for i := 0; i < *threads; i++ {
		workers[i] = NewWorker(key, salt)
	}
	go func() {
		var ctr uint64
		for {
			w := workers[ctr%uint64(len(workers))]
			if _, err := os.Stdout.Write(<-w.output); err != nil {
				panic(err)
			}
			w.written <- struct{}{}
			ctr++
		}
	}()

	var ctr uint64
	var size int
	for {
		w := workers[ctr%uint64(len(workers))]
		<-w.ready
		if *decrypt {
			_, err = io.ReadFull(stdin, w.input[:LenSize])
			if err != nil {
				if err == io.EOF {
					break
				}
				panic(err)
			}
			size = int(binary.BigEndian.Uint32(w.input[:LenSize]))
			if _, err = io.ReadFull(
				stdin,
				w.input[LenSize:LenSize+size+poly1305.TagSize],
			); err != nil {
				panic(err)
			}
		} else {
			size, err = stdin.Read(w.input[LenSize : LenSize+bs])
			if err != nil {
				if err == io.EOF {
					break
				}
				panic(err)
			}
		}
		wg.Add(1)
		w.task <- Task{ctr, size}
		ctr++
	}
	wg.Wait()
}