package pnet

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"io"
)

var (
	pathPSKv1  = []byte("/key/swarm/psk/1.0.0/")
	pathBin    = "/bin/"
	pathBase16 = "/base16/"
	pathBase64 = "/base64/"
)

func readHeader(r *bufio.Reader) ([]byte, error) {
	header, err := r.ReadBytes('\n')
	if err != nil {
		return nil, err
	}

	return bytes.TrimRight(header, "\r\n"), nil
}

func expectHeader(r *bufio.Reader, expected []byte) error {
	header, err := readHeader(r)
	if err != nil {
		return err
	}
	if !bytes.Equal(header, expected) {
		return fmt.Errorf("expected file header %s, got: %s", pathPSKv1, header)
	}
	return nil
}

// DecodeV1PSK reads a Multicodec encoded V1 PSK.
func DecodeV1PSK(in io.Reader) (PSK, error) {
	reader := bufio.NewReader(in)
	if err := expectHeader(reader, pathPSKv1); err != nil {
		return nil, err
	}
	header, err := readHeader(reader)
	if err != nil {
		return nil, err
	}

	var decoder io.Reader
	switch string(header) {
	case pathBase16:
		decoder = hex.NewDecoder(reader)
	case pathBase64:
		decoder = base64.NewDecoder(base64.StdEncoding, reader)
	case pathBin:
		decoder = reader
	default:
		return nil, fmt.Errorf("unknown encoding: %s", header)
	}
	out := make([]byte, 32)
	if _, err = io.ReadFull(decoder, out[:]); err != nil {
		return nil, err
	}
	return out, nil
}