/*
gohpenc -- Go high-performance encryption utility
Copyright (C) 2017-2019 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/rand"
	"encoding/binary"
	"flag"
	"fmt"
	"io"
	"os"
	"runtime"
	"sync"

	"golang.org/x/crypto/blake2b"
	"golang.org/x/crypto/chacha20poly1305"
)

const (
	LenSize  = 4
	SaltSize = 32
)

type WorkerTask struct {
	key []byte
	n   int
}

type Worker struct {
	wg      *sync.WaitGroup
	buf     []byte
	ready   chan struct{}
	task    chan WorkerTask
	done    chan []byte
	written chan struct{}
}

func (w *Worker) Thread(doDecrypt bool) {
	var task WorkerTask
	nonce := make([]byte, chacha20poly1305.NonceSize)
	var done []byte
	for {
		w.ready <- struct{}{}
		task = <-w.task
		aead, err := chacha20poly1305.New(task.key)
		if err != nil {
			panic(err)
		}
		if doDecrypt {
			done, err = aead.Open(w.buf[:0], nonce, w.buf[LenSize:LenSize+task.n], w.buf[:LenSize])
			if err != nil {
				panic(err)
			}
		} else {
			binary.BigEndian.PutUint32(w.buf, uint32(task.n))
			done = aead.Seal(w.buf[:LenSize], nonce, w.buf[LenSize:LenSize+task.n], w.buf[:LenSize])
		}
		w.done <- done
		<-w.written
		w.wg.Done()
	}
}

func main() {
	var (
		doPSK     = flag.Bool("psk", false, "Generate PSK")
		key       = flag.String("k", "", "Encryption key")
		doDecrypt = 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")
	)
	flag.Parse()
	bs := *blockSize * 1 << 10

	if *doPSK {
		key := make([]byte, 32)
		if _, err := rand.Read(key); err != nil {
			panic(err)
		}
		fmt.Println(ToBase32(key))
		return
	}

	if len(*key) != 52 {
		panic("Invalid key size")
	}
	keyDecoded, err := FromBase32(*key)
	if err != nil {
		panic(err)
	}
	tmpAEAD, err := chacha20poly1305.New(make([]byte, chacha20poly1305.KeySize))
	if err != nil {
		panic(err)
	}
	keys, err := blake2b.NewXOF(blake2b.OutputLengthUnknown, keyDecoded)
	if err != nil {
		panic(err)
	}

	var wg sync.WaitGroup
	workers := make([]*Worker, 0, *threads)
	for i := 0; i < *threads; i++ {
		w := Worker{
			wg:      &wg,
			buf:     make([]byte, LenSize+bs+tmpAEAD.Overhead()),
			ready:   make(chan struct{}),
			task:    make(chan WorkerTask),
			done:    make(chan []byte),
			written: make(chan struct{}),
		}
		go w.Thread(*doDecrypt)
		workers = append(workers, &w)
	}
	go func() {
		i := 0
		var w *Worker
		for {
			w = workers[i%len(workers)]
			if _, err = os.Stdout.Write(<-w.done); err != nil {
				panic(err)
			}
			w.written <- struct{}{}
			i++
		}
	}()

	stdin := bufio.NewReaderSize(os.Stdin, LenSize+bs)
	if *doDecrypt {
		if _, err = io.CopyN(keys, stdin, SaltSize); err != nil {
			panic(err)
		}
	} else {
		salt := make([]byte, SaltSize)
		if _, err = rand.Read(salt); err != nil {
			panic(err)
		}
		if _, err = keys.Write(salt); err != nil {
			panic(err)
		}
		if _, err = os.Stdout.Write(salt); err != nil {
			panic(err)
		}
	}

	i := 0
	var n int
	var w *Worker
	for {
		key := make([]byte, chacha20poly1305.KeySize)
		if _, err = io.ReadFull(keys, key); err != nil {
			panic(err)
		}
		w = workers[i%len(workers)]
		<-w.ready
		if *doDecrypt {
			_, err = io.ReadFull(stdin, w.buf[:LenSize])
			if err != nil {
				if err == io.EOF {
					break
				}
				panic(err)
			}
			n = int(binary.BigEndian.Uint32(w.buf[:LenSize]))
			if n, err = io.ReadFull(stdin, w.buf[LenSize:LenSize+n+tmpAEAD.Overhead()]); err != nil {
				panic(err)
			}
		} else {
			n, err = stdin.Read(w.buf[LenSize : LenSize+bs])
			if err != nil {
				if err == io.EOF {
					break
				}
				panic(err)
			}
		}
		wg.Add(1)
		w.task <- WorkerTask{key, n}
		i++
	}
	wg.Wait()
}