#!/usr/bin/env python3.7
#
# Copyright (C) 2016,2017 The University of Sheffield, UK
#
# 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, either version 3 of the License, or
# (at your option) any later version.
#
# 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 <https://www.gnu.org/licenses/>.
#
"""Utility functions for working with Chrome extensionsx archives,
   i.e., *.crx files."""

import io
import os
import zipfile
import binascii
from Cryptodome.PublicKey import RSA
from Cryptodome.Hash import SHA
from Cryptodome.Signature import PKCS1_v1_5


class CrxFile:
    """Record class for storing crx files."""

    def __init__(self, filename, magic, version, public_key_len, sig_len,
                 public_key, sig, header_len, data):
        self.file = filename
        self.magic = magic
        self.version = version
        self.public_key_len = public_key_len
        self.sig_len = sig_len
        self.public_key = public_key
        self.sig = sig
        self.header_len = header_len
        self.data = data


def is_valid_magic(magic):
    """Check magic matches the magic bytes of the crx specificaton."""
    return magic == b'Cr24'


def is_crxfile(filename):
    """Check magic number: crx files should start with \"Cr24\"."""
    file = open(filename, 'rb')
    magic = file.read(4)
    file.close()
    return is_valid_magic(magic)


def check_signature(public_key, sig, data):
    """Check validity of signature contained in the crx file."""
    key = RSA.importKey(public_key)
    crxhash = SHA.new(data)
    return PKCS1_v1_5.new(key).verify(crxhash, sig)


def read_crx(filename):
    """Read header of an crx file (https://developer.chrome.com/extensions/crx)."""
    file = open(filename, 'rb')
    magic = file.read(4)
    version = int.from_bytes(file.read(4), byteorder='little')
    public_key_len = int.from_bytes(file.read(4), byteorder='little')
    sig_len = int.from_bytes(file.read(4), byteorder='little')
    public_key = file.read(public_key_len)
    sig = file.read(sig_len)
    header_len = 16 + public_key_len + sig_len
    data = file.read()
    file.close()
    return CrxFile(filename, magic, version, public_key_len, sig_len,
                   public_key, sig, header_len, data)


def print_crx_info(verbose, crx):
    """Print information extracted from a crx file."""
    if is_valid_magic(crx.magic):
        magic = "valid"
    else:
        magic = "invalid"
    if check_signature(crx.public_key, crx.sig, crx.data):
        sig = "valid"
    else:
        sig = "invalid"
    print("Filename:    " + crx.file)
    print("Header size: " + str(crx.header_len))
    print("Size:        " + str(crx.header_len + len(crx.data)))
    print("Magic byte:  " + str(crx.magic.decode("utf-8")) + " (" + magic +
          ")")
    print("Version:     " + str(crx.version))
    print("Signature:   " + sig)
    print("Public Key [" + str(crx.public_key_len) + "]:")
    key = RSA.importKey(crx.public_key)
    print(key.exportKey().decode("utf-8"))
    if verbose:
        print("Signature [" + str(crx.sig_len) + "]: " + str(
            binascii.hexlify(crx.sig)))
    out = io.BytesIO(crx.data)
    ziparchive = zipfile.ZipFile(out, 'r')
    print("Zip content:")
    for info in ziparchive.infolist():
        print('{:8d} {:8d}'.format(info.file_size, info.compress_size),
              info.filename)


def verify_crxfile(verbose, filename):
    """Verify integrity of a crx file."""
    if is_crxfile(filename):
        if verbose:
            print("Found correct magic bytes.")
        print_crx_info(verbose, read_crx(filename))
        return 0
    else:
        if verbose:
            print("No valid magic bytes found")
        return -1


def extract_crxfile(verbose, force, filename, destdir):
    """Extract crxfile into specified destdir."""
    crx = read_crx(filename)
    if is_valid_magic(crx.magic) | force:
        if (destdir == "") | (destdir is None):
            destdir = "."
        if filename.endswith(".crx"):
            extname = os.path.basename(filename)
            dirname = extname[0:len(os.path.basename(extname)) - 4]
        else:
            dirname = filename
        out = io.BytesIO(crx.data)
        ziparchive = zipfile.ZipFile(out, 'r')
        ziparchive.extractall(destdir + "/" + dirname)
        if verbose:
            print("Content extracted into: " + destdir + "/" + dirname)
        return 0
    else:
        print("Input file not valid.")
        return -1