"""
<p>This module implements the rather sophisticated F5 algorithm which was
invented by Andreas Westfeld.</p>

Unlike its vastly inferior predecessors, namely F3 and F4, it features matrix
encoding which makes it possible to embed a chunk of k bits within 2^k - 1
bits of the cover data and only change one bit (at most). A bit change is
done by subtracting the absolute value of the corresponding DCT coefficient.
When the embedding process begins, the parameter k is computed based on
the capacity of the cover image and the prospective embedding ratio.
With small amount of hidden data k becomes large which leads to a greater
embedding efficiency (embedded information per bit change).<br />

A permutation (initialized by a user-supplied seed) of the DCT coefficients
helps to scatter each chunk across the entire image.
F5 can be seen as meta-algorithm as it uses a coding scheme to change
as little data as possible and then applies a simpler algorithm (such as F3)
to actually embed data. That is why this module allows the user to specify
which embedding function (one of JSteg, F3, F4) should be used.
"""

import time
import math
import numpy as np
from stegotool.plugins.steganography.F4.F4 import F4
from stegotool.util.JPEGSteg import JPEGSteg
from stegotool.util.plugins import describe_annotate_convert
from stegotool.util.plugins import ident, ImagePath, FilePath, NewFilePath


class F5(JPEGSteg):
    """ This module has two methods: <i>embed_raw_data</i> to embed data
    with the F5 algorithm and <i>extract_raw_data</i> to extract data
    which was embedded previously. """

    def __init__(self, ui, core):
        """
        Constructor of the F5 class.
        """
        JPEGSteg.__init__(self, ui, core)
        self._embed_hook = self._embed_k
        self._extract_hook = self._extract_k
        self._embed_fun = None
        self.dct_p = None
        self.seed = None
        self.default_embedding = True
        self.steg_ind = -1
        self.excess_bits = None
        # needed because k is embedded separately
        self.cov_ind = -1
        self.k_coeff = -1

    @describe_annotate_convert((None, None, ident),
                               ("cover image", ImagePath, str),
                               ("hidden data", FilePath, str),
                               ("stego image", NewFilePath, str),
                               ("seed", int, int),
                               ("embedding behavior",
                                   ['Default', 'F3', 'JSteg'], str))
    def embed_raw_data(self, src_cover, src_hidden, tgt_stego, seed,
                       embed_fun):
        """<p>This method embeds arbitrary data into a cover image.
        The cover image must be a JPEG.</p>

        <p>Parameters:
        <ol>
        <li><pre>src_cover</pre>
        A valid pathname to an image file which serves as cover image
        (the image which the secret image is embedded into).</li>

        <li><pre>src_hidden</pre>
        A valid pathname to an arbitrary file that is supposed to be
        embedded into the cover image.</li>

        <li><pre>tgt_stego</pre>
        Target pathname of the resulting stego image. You should save to
        a PNG or another lossless format, because many LSBs don't survive
        lossy compression.</li>

        <li><pre>seed</pre>
        A seed for the random number generator that is responsible scattering
        the secret data within the cover image.</li>

        <li><pre>param embed_fun</pre>
        Specifies which embedding function should be used. Must be one of
        'Default', 'F3', 'Jsteg'. If 'Default' is selected, the algorithm uses
        the same behavior as Westfeld's implementation, i.e. decrementing
        absolute values for n > 1 (F3) and using F4 in the special case n = 1.
        Selecting F3 or JSteg results in using that scheme for all n.</li>
        </ol>
        </p>
        """
        self.t0 = time.time()
        self.seed = seed
        if embed_fun == 'F3':
            self._embed_fun = self._f3_embed
            self.default_embedding = False
        elif embed_fun == 'JSteg':
            self._embed_fun = self._jsteg_embed
            self.default_embedding = False
        elif embed_fun == 'Default':
            self._embed_fun = self._f3_embed
            self.default_embedding = True

        self.cov_ind = -1
        JPEGSteg._post_embed_actions(self, src_cover, src_hidden, tgt_stego)

    @describe_annotate_convert((None, None, ident),
                               ("stego image", ImagePath, str),
                               ("hidden data", NewFilePath, str),
                               ("seed", int, int),
                               ("embedding behavior", ['Default', 'F3/JSteg'],
                                str))
    def extract_raw_data(self, src_steg, tgt_hidden, seed, embed_fun):
        """<p>This method extracts secret data from a stego image. It is
        (obviously) the inverse operation of embed_raw_data.</p>

        <p>Parameters:
        <ol>
        <li><pre>src_stego</pre>
        A valid pathname to an image file which serves as stego image.</li>

        <li><pre>tgt_hidden</pre>
        A pathname denoting where the extracted data should be saved to.</li>

        <li><pre>param seed</pre>
        A seed for the random number generator that is responsible scattering
        the secret data within the cover image.</li>

        <li><pre>param embed_fun</pre>
        Specifies which embedding function should be used. Must be one of
        'Default', 'F3', 'JSteg'. If 'Default' is selected, the algorithm uses
        the same behavior as  Westfeld's implementation, i.e. decrementing
        absolute values for n > 1 (F3) and using F4 in the special case n = 1.
        Selecting F3 or JSteg results in using that scheme for all n.</li>
        </ol></pre>
        """

        self.t0 = time.time()
        self.seed = seed
        self.steg_ind = -1
        if embed_fun == 'F3/JSteg':
            self.default_embedding = False
        elif embed_fun == 'Default':
            self.default_embedding = True

        # excess bits occur when the size of extracted data is not a multiple
        # of k. if excess bits are available, they are prepended to hidden data
        self.excess_bits = None

        JPEGSteg._post_extract_actions(self, src_steg, tgt_hidden)

    def _embed_k(self, cov_data, hid_data):
        np.random.seed(self.seed)
        self.dct_p = np.random.permutation(cov_data.size)
        self.k_coeff = self._find_max_k(cov_data, hid_data)
        self.ui.display_status('setting k = %d' % self.k_coeff)
        k_split = self.lookup_tab.split_byte(self.k_coeff, 1)[-4:]
        # embed k in F3-like style
        for m in k_split:
            success = False
            while not success:
                self.cov_ind += 1
                while cov_data[self.dct_p[self.cov_ind]] == 0 or \
                          self.dct_p[self.cov_ind] % 64 == 0:
                    self.cov_ind += 1
                if m != cov_data[self.dct_p[self.cov_ind]] & 1:
                    cov_data[self.dct_p[self.cov_ind]] -= \
                        math.copysign(1, cov_data[self.dct_p[self.cov_ind]])
                success = cov_data[self.dct_p[self.cov_ind]] != 0

    def _extract_k(self, steg_data):
        # initializing the MT is done only once in order to retain the state
        self.dct_p = np.random.seed(self.seed)
        self.dct_p = np.random.permutation(self.steg_data.size)
        k_split = np.zeros(4, np.uint8)
        for i in xrange(k_split.size):
            self.steg_ind += 1
            while self.steg_data[self.dct_p[self.steg_ind]] == 0 or\
                      self.dct_p[self.steg_ind] % 64 == 0:
                self.steg_ind += 1
            k_split[i] = self.steg_data[self.dct_p[self.steg_ind]] & 1
        self.k_coeff = self.lookup_tab.merge_words(tuple([0, 0, 0, 0] +
                                                         list(k_split)), 1)

    def _find_max_k(self, cov_data, hid_data):
        cnt = 4  # information about k take up 4 bits
        # find number of DCT coefficients
        update_cnt = 10000
        for i, c in enumerate(cov_data):
            if update_cnt == 0:
                self._set_progress(
                        int(30 * (float(i) / float(cov_data.size))))
                update_cnt = 10000
            update_cnt -= 1
            # pessimistic, but accurate estimation of the capacity of the image
            ci = int(c)
            if (not (ci is 0)) and (not ((i % 64) is 0)) \
                    and (not (ci is 1)) and (not (ci is -1)):
                cnt += 1
        hid_size = hid_data.size
        cov_size = cnt
        if cov_size < hid_size:
            raise Exception("Cannot fit %d bits in %d DCT coefficients. \
                    Cover image is too small." % (hid_size, cov_size))
        self.ui.display_status('DCT embedding ratio = %f' \
                % (float(hid_size) / float(cov_size)))
        k = 1
        while True:
            k += 1
            n = (1 << k) - 1
            num_chunks = cov_size / n
            num_emb_bits = num_chunks * k
            if num_emb_bits < hid_size:
                return min(k - 1, 15)

    # low level embedding functions
    def _f3_embed(self, cov_data, ind):
        cov_data[ind] -= math.copysign(1, cov_data[ind])

    def _jsteg_embed(self, cov_data, ind):
        m = 1 ^ (cov_data[ind] & 1)
        cov_data[ind] = (cov_data[ind] & 0xffffe) | m

    def _raw_embed(self, cov_data, hid_data, status_begin=0):
        k = self.k_coeff
        n = (1 << k) - 1
        if n == 1 and self.default_embedding:
            # in case k = n = 1, Westfeld's implementation uses F4 for
            # embedding. Therefore, if 'default' embedding has been selected
            # we will do the same
            f4 = F4(self.ui, self.core)
            f4.seed = self.seed
            f4.dct_p = self.dct_p
            f4.cov_ind = self.cov_ind
            cov_data = f4._raw_embed(cov_data, hid_data, 30)
            return cov_data

        cov_ind = self.cov_ind  # preventing RSI by writing 'self' less often
        hid_ind = 0
        remaining_bits = hid_data.size
        hid_size = float(hid_data.size)
        dct_p = self.dct_p

        update_cnt = int(hid_size / (70.0 * k))
        while remaining_bits > 0:
            if update_cnt == 0:
                self._set_progress(30 + int(((
                    hid_size - remaining_bits) / hid_size) * 70))
                update_cnt = int(hid_size / (70.0 * k))
            update_cnt -= 1
            msg_chunk_size = min(remaining_bits, k)
            msg_chunk = np.zeros(k, np.int8)
            cov_chunk = np.zeros(n, np.int32)
            msg_chunk[0:msg_chunk_size] = hid_data[hid_ind:hid_ind +
                                                   msg_chunk_size]
            hid_ind += k

            # get n DCT coefficients
            for i in xrange(n):
                cov_ind += 1
                while cov_data[dct_p[cov_ind]] == 0 \
                        or dct_p[cov_ind] % 64 == 0:
                    cov_ind += 1
                cov_chunk[i] = dct_p[cov_ind]

            success = False
            while not success:  # loop necessary because of shrinkage
                h = 0
                for i in xrange(n):
                    h ^= ((cov_data[cov_chunk[i]] & 1) * (i + 1))
                scalar_x = 0
                for i in xrange(k):
                    scalar_x = (scalar_x << 1) + msg_chunk[i]
                s = scalar_x ^ h
                if s != 0:
                    self._embed_fun(cov_data, cov_chunk[s - 1])
                else:
                    break

                if cov_data[cov_chunk[s - 1]] == 0:  # test for shrinkage
                    cov_chunk[s - 1:-1] = cov_chunk[s:]  # adjusting
                    cov_ind += 1
                    while cov_data[dct_p[cov_ind]] == 0 or\
                              dct_p[cov_ind] % 64 == 0:
                        cov_ind += 1
                    cov_chunk[n - 1] = dct_p[cov_ind]
                else:
                    success = True

            remaining_bits -= k

        self.k_coeff = -1  # prevent k being read from this instance
        return cov_data

    def _raw_extract(self, num_bits):
        k = self.k_coeff
        n = (1 << k) - 1
        if self.is_header == None:
            self.is_header = True
        if n == 1 and self.default_embedding:
            f4 = F4(self.ui, self.core)
            f4.seed = self.seed
            f4.dct_p = self.dct_p
            f4.steg_data = self.steg_data
            f4.is_header = self.is_header
            f4.steg_ind = self.steg_ind
            hid_data = f4._raw_extract(num_bits)
            self.steg_ind = f4.steg_ind
            self.is_header = False
            return hid_data
        remaining_bits = num_bits
        hid_data = np.zeros(num_bits, np.uint8)
        hid_ind = 0

        dct_p = self.dct_p

        is_header = False  # signals whether or not extracting header

        if self.excess_bits != None:
            hid_data[hid_ind:hid_ind + self.excess_bits.size] = \
                    self.excess_bits
            hid_ind += self.excess_bits.size
            remaining_bits -= self.excess_bits.size

        curr_chunk = np.zeros(k, np.uint8)

        update_cnt = int(num_bits / (100.0 * k))

        while remaining_bits > 0:

            if update_cnt == 0 and not is_header:
                self._set_progress(int(((float(num_bits) \
                        - remaining_bits) / num_bits) * 100))
                update_cnt = int(num_bits / (100.0 * k))

            update_cnt -= 1

            steg_chunk = [0 for i in xrange(n)]
            for i in xrange(n):
                self.steg_ind += 1
                while self.steg_data[dct_p[self.steg_ind]] == 0 or\
                      dct_p[self.steg_ind] % 64 == 0:
                    self.steg_ind += 1
                steg_chunk[i] = self.steg_data[dct_p[self.steg_ind]]

            h = 0  # hash value
            for i in xrange(n):
                h ^= ((steg_chunk[i] & 1) * (i + 1))

            for i in xrange(k):
                curr_chunk[k - i - 1] = h % 2
                h /= 2

            l = min(k, remaining_bits)
            for i in xrange(l):
                hid_data[hid_ind] = curr_chunk[i]
                hid_ind += 1

            # save excess bits (for later calls)
            if k > remaining_bits:
                self.excess_bits = curr_chunk[remaining_bits:]
            else:
                self.excess_bits = None

            remaining_bits -= k

        self.is_header = False
        return hid_data

    def __str__(self):
        return 'F5'