# -*- coding: utf-8 -*-
#
# This file is part of the qpageview package.
#
# Copyright (c) 2016 - 2019 by Wilbert Berendsen
#
# 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 2
# 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, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
# See http://www.gnu.org/licenses/ for more information.

"""
Cache logic.
"""

import weakref
import time


class ImageEntry:
    def __init__(self, image):
        self.image = image
        self.bcount = image.byteCount()
        self.time = time.time()


class ImageCache:
    """Cache generated images.

    Store and retrieve them under a key (see render.Renderer.key()).

    """
    maxsize = 209715200 # 200M
    currentsize = 0

    def __init__(self):
        self._cache = weakref.WeakKeyDictionary()

    def clear(self):
        """Remove all cached images."""
        self._cache.clear()
        self.currentsize = 0

    def invalidate(self, page):
        """Clear cache contents for the specified page."""
        try:
            del self._cache[page.group()][page.ident()]
        except KeyError:
            pass

    def tileset(self, key):
        """Return a dictionary with tile-entry pairs for the key.

        If no single tile is available, an empty dict is returned.

        """
        try:
            return self._cache[key.group][key.ident][key[2:]]
        except KeyError:
            return {}

    def addtile(self, key, tile, image):
        """Add image for the specified key and tile."""
        d = self._cache.setdefault(key.group, {}).setdefault(key.ident, {}).setdefault(key[2:], {})
        try:
            self.currentsize -= d[tile].bcount
        except KeyError:
            pass

        purgeneeded = self.currentsize > self.maxsize

        e = d[tile] = ImageEntry(image)
        self.currentsize += e.bcount

        if not purgeneeded:
            return

        # purge old images is needed,
        # cache groups may have disappeared so count all images

        entries = iter(sorted(
            ((entry.time, entry.bcount, group, ident, key, tile)
            for group, identd in self._cache.items()
                for ident, keyd in identd.items()
                    for key, tiled in keyd.items()
                        for tile, entry in tiled.items()),
            key=(lambda item: item[:2]), reverse=True))

        # now count the newest images until maxsize ...
        currentsize = 0
        for time, bcount, group, ident, key, tile in entries:
            currentsize += bcount
            if currentsize > self.maxsize:
                break
        self.currentsize = currentsize
        # ... and delete the remaining images, deleting empty dicts as well
        for time, bcount, group, ident, key, tile in entries:
            del self._cache[group][ident][key][tile]
            if not self._cache[group][ident][key]:
                del self._cache[group][ident][key]
                if not self._cache[group][ident]:
                    del self._cache[group][ident]
                    if not self._cache[group]:
                        del self._cache[group]

    def closest(self, key):
        """Iterate over suitable image tilesets but with a different size.

        Yields (width, height, tileset) tuples.

        This can be used for interim display while the real image is being
        rendered.

        """
        # group and ident must be there.
        try:
            keyd = self._cache[key.group][key.ident]
        except KeyError:
            return ()

        # prevent returning images that are too small
        minwidth = min(100, key.width / 2)

        suitable = [
            (k[1], k[2], tileset)
            for k, tileset in keyd.items()
                if k[0] == key.rotation and k[1] != key.width and k[1] > minwidth]
        return sorted(suitable, key=lambda s: abs(1 - s[0] / key.width))