#
# The Python Imaging Library.
# $Id$
#
# PNG support code
#
# See "PNG (Portable Network Graphics) Specification, version 1.0;
# W3C Recommendation", 1996-10-01, Thomas Boutell (ed.).
#
# history:
# 1996-05-06 fl   Created (couldn't resist it)
# 1996-12-14 fl   Upgraded, added read and verify support (0.2)
# 1996-12-15 fl   Separate PNG stream parser
# 1996-12-29 fl   Added write support, added getchunks
# 1996-12-30 fl   Eliminated circular references in decoder (0.3)
# 1998-07-12 fl   Read/write 16-bit images as mode I (0.4)
# 2001-02-08 fl   Added transparency support (from Zircon) (0.5)
# 2001-04-16 fl   Don't close data source in "open" method (0.6)
# 2004-02-24 fl   Don't even pretend to support interlaced files (0.7)
# 2004-08-31 fl   Do basic sanity check on chunk identifiers (0.8)
# 2004-09-20 fl   Added PngInfo chunk container
# 2004-12-18 fl   Added DPI read support (based on code by Niki Spahiev)
# 2008-08-13 fl   Added tRNS support for RGB images
# 2009-03-06 fl   Support for preserving ICC profiles (by Florian Hoech)
# 2009-03-08 fl   Added zTXT support (from Lowell Alleman)
# 2009-03-29 fl   Read interlaced PNG files (from Conrado Porto Lopes Gouvua)
#
# Copyright (c) 1997-2009 by Secret Labs AB
# Copyright (c) 1996 by Fredrik Lundh
#
# See the README file for information on usage and redistribution.
#
from __future__ import annotations

import itertools
import logging
import re
import struct
import warnings
import zlib
from collections.abc import Callable
from enum import IntEnum
from typing import IO, Any, NamedTuple, NoReturn, cast

from . import Image, ImageChops, ImageFile, ImagePalette, ImageSequence
from ._binary import i16be as i16
from ._binary import i32be as i32
from ._binary import o8
from ._binary import o16be as o16
from ._binary import o32be as o32
from ._util import DeferredError

TYPE_CHECKING = False
if TYPE_CHECKING:
    from . import _imaging

logger = logging.getLogger(__name__)

is_cid = re.compile(rb"\w\w\w\w").match


_MAGIC = b"\211PNG\r\n\032\n"


_MODES = {
    # supported bits/color combinations, and corresponding modes/rawmodes
    # Grayscale
    (1, 0): ("1", "1"),
    (2, 0): ("L", "L;2"),
    (4, 0): ("L", "L;4"),
    (8, 0): ("L", "L"),
    (16, 0): ("I;16", "I;16B"),
    # Truecolour
    (8, 2): ("RGB", "RGB"),
    (16, 2): ("RGB", "RGB;16B"),
    # Indexed-colour
    (1, 3): ("P", "P;1"),
    (2, 3): ("P", "P;2"),
    (4, 3): ("P", "P;4"),
    (8, 3): ("P", "P"),
    # Grayscale with alpha
    (8, 4): ("LA", "LA"),
    (16, 4): ("RGBA", "LA;16B"),  # LA;16B->LA not yet available
    # Truecolour with alpha
    (8, 6): ("RGBA", "RGBA"),
    (16, 6): ("RGBA", "RGBA;16B"),
}


_simple_palette = re.compile(b"^\xff*\x00\xff*$")

MAX_TEXT_CHUNK = ImageFile.SAFEBLOCK
"""
Maximum decompressed size for a iTXt or zTXt chunk.
Eliminates decompression bombs where compressed chunks can expand 1000x.
See :ref:`Text in PNG File Format<png-text>`.
"""
MAX_TEXT_MEMORY = 64 * MAX_TEXT_CHUNK
"""
Set the maximum total text chunk size.
See :ref:`Text in PNG File Format<png-text>`.
"""


# APNG frame disposal modes
class Disposal(IntEnum):
    OP_NONE = 0
    """
    No disposal is done on this frame before rendering the next frame.
    See :ref:`Saving APNG sequences<apng-saving>`.
    """
    OP_BACKGROUND = 1
    """
    This frame’s modified region is cleared to fully transparent black before rendering
    the next frame.
    See :ref:`Saving APNG sequences<apng-saving>`.
    """
    OP_PREVIOUS = 2
    """
    This frame’s modified region is reverted to the previous frame’s contents before
    rendering the next frame.
    See :ref:`Saving APNG sequences<apng-saving>`.
    """


# APNG frame blend modes
class Blend(IntEnum):
    OP_SOURCE = 0
    """
    All color components of this frame, including alpha, overwrite the previous output
    image contents.
    See :ref:`Saving APNG sequences<apng-saving>`.
    """
    OP_OVER = 1
    """
    This frame should be alpha composited with the previous output image contents.
    See :ref:`Saving APNG sequences<apng-saving>`.
    """


def _safe_zlib_decompress(s: bytes) -> bytes:
    dobj = zlib.decompressobj()
    plaintext = dobj.decompress(s, MAX_TEXT_CHUNK)
    if dobj.unconsumed_tail:
        msg = "Decompressed data too large for PngImagePlugin.MAX_TEXT_CHUNK"
        raise ValueError(msg)
    return plaintext


def _crc32(data: bytes, seed: int = 0) -> int:
    return zlib.crc32(data, seed) & 0xFFFFFFFF


# --------------------------------------------------------------------
# Support classes.  Suitable for PNG and related formats like MNG etc.


class ChunkStream:
    def __init__(self, fp: IO[bytes]) -> None:
        self.fp: IO[bytes] | None = fp
        self.queue: list[tuple[bytes, int, int]] | None = []

    def read(self) -> tuple[bytes, int, int]:
        """Fetch a new chunk. Returns header information."""
        cid = None

        assert self.fp is not None
        if self.queue:
            cid, pos, length = self.queue.pop()
            self.fp.seek(pos)
        else:
            s = self.fp.read(8)
            cid = s[4:]
            pos = self.fp.tell()
            length = i32(s)

        if not is_cid(cid):
            if not ImageFile.LOAD_TRUNCATED_IMAGES:
                msg = f"broken PNG file (chunk {repr(cid)})"
                raise SyntaxError(msg)

        return cid, pos, length

    def __enter__(self) -> ChunkStream:
        return self

    def __exit__(self, *args: object) -> None:
        self.close()

    def close(self) -> None:
        self.queue = self.fp = None

    def push(self, cid: bytes, pos: int, length: int) -> None:
        assert self.queue is not None
        self.queue.append((cid, pos, length))

    def call(self, cid: bytes, pos: int, length: int) -> bytes:
        """Call the appropriate chunk handler"""

        logger.debug("STREAM %r %s %s", cid, pos, length)
        return getattr(self, f"chunk_{cid.decode('ascii')}")(pos, length)

    def crc(self, cid: bytes, data: bytes) -> None:
        """Read and verify checksum"""

        # Skip CRC checks for ancillary chunks if allowed to load truncated
        # images
        # 5th byte of first char is 1 [specs, section 5.4]
        if ImageFile.LOAD_TRUNCATED_IMAGES and (cid[0] >> 5 & 1):
            self.crc_skip(cid, data)
            return

        assert self.fp is not None
        try:
            crc1 = _crc32(data, _crc32(cid))
            crc2 = i32(self.fp.read(4))
            if crc1 != crc2:
                msg = f"broken PNG file (bad header checksum in {repr(cid)})"
                raise SyntaxError(msg)
        except struct.error as e:
            msg = f"broken PNG file (incomplete checksum in {repr(cid)})"
            raise SyntaxError(msg) from e

    def crc_skip(self, cid: bytes, data: bytes) -> None:
        """Read checksum"""

        assert self.fp is not None
        self.fp.read(4)

    def verify(self, endchunk: bytes = b"IEND") -> list[bytes]:
        # Simple approach; just calculate checksum for all remaining
        # blocks.  Must be called directly after open.

        cids = []

        assert self.fp is not None
        while True:
            try:
                cid, pos, length = self.read()
            except struct.error as e:
                msg = "truncated PNG file"
                raise OSError(msg) from e

            if cid == endchunk:
                break
            self.crc(cid, ImageFile._safe_read(self.fp, length))
            cids.append(cid)

        return cids


class iTXt(str):
    """
    Subclass of string to allow iTXt chunks to look like strings while
    keeping their extra information

    """

    lang: str | bytes | None
    tkey: str | bytes | None

    @staticmethod
    def __new__(
        cls, text: str, lang: str | None = None, tkey: str | None = None
    ) -> iTXt:
        """
        :param cls: the class to use when creating the instance
        :param text: value for this key
        :param lang: language code
        :param tkey: UTF-8 version of the key name
        """

        self = str.__new__(cls, text)
        self.lang = lang
        self.tkey = tkey
        return self


class PngInfo:
    """
    PNG chunk container (for use with save(pnginfo=))

    """

    def __init__(self) -> None:
        self.chunks: list[tuple[bytes, bytes, bool]] = []

    def add(self, cid: bytes, data: bytes, after_idat: bool = False) -> None:
        """Appends an arbitrary chunk. Use with caution.

        :param cid: a byte string, 4 bytes long.
        :param data: a byte string of the encoded data
        :param after_idat: for use with private chunks. Whether the chunk
                           should be written after IDAT

        """

        self.chunks.append((cid, data, after_idat))

    def add_itxt(
        self,
        key: str | bytes,
        value: str | bytes,
        lang: str | bytes = "",
        tkey: str | bytes = "",
        zip: bool = False,
    ) -> None:
        """Appends an iTXt chunk.

        :param key: latin-1 encodable text key name
        :param value: value for this key
        :param lang: language code
        :param tkey: UTF-8 version of the key name
        :param zip: compression flag

        """

        if not isinstance(key, bytes):
            key = key.encode("latin-1", "strict")
        if not isinstance(value, bytes):
            value = value.encode("utf-8", "strict")
        if not isinstance(lang, bytes):
            lang = lang.encode("utf-8", "strict")
        if not isinstance(tkey, bytes):
            tkey = tkey.encode("utf-8", "strict")

        if zip:
            self.add(
                b"iTXt",
                key + b"\0\x01\0" + lang + b"\0" + tkey + b"\0" + zlib.compress(value),
            )
        else:
            self.add(b"iTXt", key + b"\0\0\0" + lang + b"\0" + tkey + b"\0" + value)

    def add_text(
        self, key: str | bytes, value: str | bytes | iTXt, zip: bool = False
    ) -> None:
        """Appends a text chunk.

        :param key: latin-1 encodable text key name
        :param value: value for this key, text or an
           :py:class:`PIL.PngImagePlugin.iTXt` instance
        :param zip: compression flag

        """
        if isinstance(value, iTXt):
            return self.add_itxt(
                key,
                value,
                value.lang if value.lang is not None else b"",
                value.tkey if value.tkey is not None else b"",
                zip=zip,
            )

        # The tEXt chunk stores latin-1 text
        if not isinstance(value, bytes):
            try:
                value = value.encode("latin-1", "strict")
            except UnicodeError:
                return self.add_itxt(key, value, zip=zip)

        if not isinstance(key, bytes):
            key = key.encode("latin-1", "strict")

        if zip:
            self.add(b"zTXt", key + b"\0\0" + zlib.compress(value))
        else:
            self.add(b"tEXt", key + b"\0" + value)


# --------------------------------------------------------------------
# PNG image stream (IHDR/IEND)


class _RewindState(NamedTuple):
    info: dict[str | tuple[int, int], Any]
    tile: list[ImageFile._Tile]
    seq_num: int | None


class PngStream(ChunkStream):
    def __init__(self, fp: IO[bytes]) -> None:
        super().__init__(fp)

        # local copies of Image attributes
        self.im_info: dict[str | tuple[int, int], Any] = {}
        self.im_text: dict[str, str | iTXt] = {}
        self.im_size = (0, 0)
        self.im_mode = ""
        self.im_tile: list[ImageFile._Tile] = []
        self.im_palette: tuple[str, bytes] | None = None
        self.im_custom_mimetype: str | None = None
        self.im_n_frames: int | None = None
        self._seq_num: int | None = None
        self.rewind_state = _RewindState({}, [], None)

        self.text_memory = 0

    def check_text_memory(self, chunklen: int) -> None:
        self.text_memory += chunklen
        if self.text_memory > MAX_TEXT_MEMORY:
            msg = (
                "Too much memory used in text chunks: "
                f"{self.text_memory}>MAX_TEXT_MEMORY"
            )
            raise ValueError(msg)

    def save_rewind(self) -> None:
        self.rewind_state = _RewindState(
            self.im_info.copy(),
            self.im_tile,
            self._seq_num,
        )

    def rewind(self) -> None:
        self.im_info = self.rewind_state.info.copy()
        self.im_tile = self.rewind_state.tile
        self._seq_num = self.rewind_state.seq_num

    def chunk_iCCP(self, pos: int, length: int) -> bytes:
        # ICC profile
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        # according to PNG spec, the iCCP chunk contains:
        # Profile name  1-79 bytes (character string)
        # Null separator        1 byte (null character)
        # Compression method    1 byte (0)
        # Compressed profile    n bytes (zlib with deflate compression)
        i = s.find(b"\0")
        logger.debug("iCCP profile name %r", s[:i])
        comp_method = s[i + 1]
        logger.debug("Compression method %s", comp_method)
        if comp_method != 0:
            msg = f"Unknown compression method {comp_method} in iCCP chunk"
            raise SyntaxError(msg)
        try:
            icc_profile = _safe_zlib_decompress(s[i + 2 :])
        except ValueError:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                icc_profile = None
            else:
                raise
        except zlib.error:
            icc_profile = None  # FIXME
        self.im_info["icc_profile"] = icc_profile
        return s

    def chunk_IHDR(self, pos: int, length: int) -> bytes:
        # image header
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if length < 13:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                return s
            msg = "Truncated IHDR chunk"
            raise ValueError(msg)
        self.im_size = i32(s, 0), i32(s, 4)
        try:
            self.im_mode, self.im_rawmode = _MODES[(s[8], s[9])]
        except Exception:
            pass
        if s[12]:
            self.im_info["interlace"] = 1
        if s[11]:
            msg = "unknown filter category"
            raise SyntaxError(msg)
        return s

    def chunk_IDAT(self, pos: int, length: int) -> NoReturn:
        # image data
        if "bbox" in self.im_info:
            tile = [ImageFile._Tile("zip", self.im_info["bbox"], pos, self.im_rawmode)]
        else:
            if self.im_n_frames is not None:
                self.im_info["default_image"] = True
            tile = [ImageFile._Tile("zip", (0, 0) + self.im_size, pos, self.im_rawmode)]
        self.im_tile = tile
        self.im_idat = length
        msg = "image data found"
        raise EOFError(msg)

    def chunk_IEND(self, pos: int, length: int) -> NoReturn:
        msg = "end of PNG image"
        raise EOFError(msg)

    def chunk_PLTE(self, pos: int, length: int) -> bytes:
        # palette
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if self.im_mode == "P":
            self.im_palette = "RGB", s
        return s

    def chunk_tRNS(self, pos: int, length: int) -> bytes:
        # transparency
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if self.im_mode == "P":
            if _simple_palette.match(s):
                # tRNS contains only one full-transparent entry,
                # other entries are full opaque
                i = s.find(b"\0")
                if i >= 0:
                    self.im_info["transparency"] = i
            else:
                # otherwise, we have a byte string with one alpha value
                # for each palette entry
                self.im_info["transparency"] = s
        elif self.im_mode in ("1", "L", "I;16"):
            self.im_info["transparency"] = i16(s)
        elif self.im_mode == "RGB":
            self.im_info["transparency"] = i16(s), i16(s, 2), i16(s, 4)
        return s

    def chunk_gAMA(self, pos: int, length: int) -> bytes:
        # gamma setting
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        self.im_info["gamma"] = i32(s) / 100000.0
        return s

    def chunk_cHRM(self, pos: int, length: int) -> bytes:
        # chromaticity, 8 unsigned ints, actual value is scaled by 100,000
        # WP x,y, Red x,y, Green x,y Blue x,y

        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        raw_vals = struct.unpack(f">{len(s) // 4}I", s)
        self.im_info["chromaticity"] = tuple(elt / 100000.0 for elt in raw_vals)
        return s

    def chunk_sRGB(self, pos: int, length: int) -> bytes:
        # srgb rendering intent, 1 byte
        # 0 perceptual
        # 1 relative colorimetric
        # 2 saturation
        # 3 absolute colorimetric

        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if length < 1:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                return s
            msg = "Truncated sRGB chunk"
            raise ValueError(msg)
        self.im_info["srgb"] = s[0]
        return s

    def chunk_pHYs(self, pos: int, length: int) -> bytes:
        # pixels per unit
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if length < 9:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                return s
            msg = "Truncated pHYs chunk"
            raise ValueError(msg)
        px, py = i32(s, 0), i32(s, 4)
        unit = s[8]
        if unit == 1:  # meter
            dpi = px * 0.0254, py * 0.0254
            self.im_info["dpi"] = dpi
        elif unit == 0:
            self.im_info["aspect"] = px, py
        return s

    def chunk_tEXt(self, pos: int, length: int) -> bytes:
        # text
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        try:
            k, v = s.split(b"\0", 1)
        except ValueError:
            # fallback for broken tEXt tags
            k = s
            v = b""
        if k:
            k_str = k.decode("latin-1", "strict")
            v_str = v.decode("latin-1", "replace")

            self.im_info[k_str] = v if k == b"exif" else v_str
            self.im_text[k_str] = v_str
            self.check_text_memory(len(v_str))

        return s

    def chunk_zTXt(self, pos: int, length: int) -> bytes:
        # compressed text
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        try:
            k, v = s.split(b"\0", 1)
        except ValueError:
            k = s
            v = b""
        if v:
            comp_method = v[0]
        else:
            comp_method = 0
        if comp_method != 0:
            msg = f"Unknown compression method {comp_method} in zTXt chunk"
            raise SyntaxError(msg)
        try:
            v = _safe_zlib_decompress(v[1:])
        except ValueError:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                v = b""
            else:
                raise
        except zlib.error:
            v = b""

        if k:
            k_str = k.decode("latin-1", "strict")
            v_str = v.decode("latin-1", "replace")

            self.im_info[k_str] = self.im_text[k_str] = v_str
            self.check_text_memory(len(v_str))

        return s

    def chunk_iTXt(self, pos: int, length: int) -> bytes:
        # international text
        assert self.fp is not None
        r = s = ImageFile._safe_read(self.fp, length)
        try:
            k, r = r.split(b"\0", 1)
        except ValueError:
            return s
        if len(r) < 2:
            return s
        cf, cm, r = r[0], r[1], r[2:]
        try:
            lang, tk, v = r.split(b"\0", 2)
        except ValueError:
            return s
        if cf != 0:
            if cm == 0:
                try:
                    v = _safe_zlib_decompress(v)
                except ValueError:
                    if ImageFile.LOAD_TRUNCATED_IMAGES:
                        return s
                    else:
                        raise
                except zlib.error:
                    return s
            else:
                return s
        if k == b"XML:com.adobe.xmp":
            self.im_info["xmp"] = v
        try:
            k_str = k.decode("latin-1", "strict")
            lang_str = lang.decode("utf-8", "strict")
            tk_str = tk.decode("utf-8", "strict")
            v_str = v.decode("utf-8", "strict")
        except UnicodeError:
            return s

        self.im_info[k_str] = self.im_text[k_str] = iTXt(v_str, lang_str, tk_str)
        self.check_text_memory(len(v_str))

        return s

    def chunk_eXIf(self, pos: int, length: int) -> bytes:
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        self.im_info["exif"] = b"Exif\x00\x00" + s
        return s

    # APNG chunks
    def chunk_acTL(self, pos: int, length: int) -> bytes:
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if length < 8:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                return s
            msg = "APNG contains truncated acTL chunk"
            raise ValueError(msg)
        if self.im_n_frames is not None:
            self.im_n_frames = None
            warnings.warn("Invalid APNG, will use default PNG image if possible")
            return s
        n_frames = i32(s)
        if n_frames == 0 or n_frames > 0x80000000:
            warnings.warn("Invalid APNG, will use default PNG image if possible")
            return s
        self.im_n_frames = n_frames
        self.im_info["loop"] = i32(s, 4)
        self.im_custom_mimetype = "image/apng"
        return s

    def chunk_fcTL(self, pos: int, length: int) -> bytes:
        assert self.fp is not None
        s = ImageFile._safe_read(self.fp, length)
        if length < 26:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                return s
            msg = "APNG contains truncated fcTL chunk"
            raise ValueError(msg)
        seq = i32(s)
        if (self._seq_num is None and seq != 0) or (
            self._seq_num is not None and self._seq_num != seq - 1
        ):
            msg = "APNG contains frame sequence errors"
            raise SyntaxError(msg)
        self._seq_num = seq
        width, height = i32(s, 4), i32(s, 8)
        px, py = i32(s, 12), i32(s, 16)
        im_w, im_h = self.im_size
        if px + width > im_w or py + height > im_h:
            msg = "APNG contains invalid frames"
            raise SyntaxError(msg)
        self.im_info["bbox"] = (px, py, px + width, py + height)
        delay_num, delay_den = i16(s, 20), i16(s, 22)
        if delay_den == 0:
            delay_den = 100
        self.im_info["duration"] = float(delay_num) / float(delay_den) * 1000
        self.im_info["disposal"] = s[24]
        self.im_info["blend"] = s[25]
        return s

    def chunk_fdAT(self, pos: int, length: int) -> bytes:
        assert self.fp is not None
        if length < 4:
            if ImageFile.LOAD_TRUNCATED_IMAGES:
                s = ImageFile._safe_read(self.fp, length)
                return s
            msg = "APNG contains truncated fDAT chunk"
            raise ValueError(msg)
        s = ImageFile._safe_read(self.fp, 4)
        seq = i32(s)
        if self._seq_num != seq - 1:
            msg = "APNG contains frame sequence errors"
            raise SyntaxError(msg)
        self._seq_num = seq
        return self.chunk_IDAT(pos + 4, length - 4)


# --------------------------------------------------------------------
# PNG reader


def _accept(prefix: bytes) -> bool:
    return prefix.startswith(_MAGIC)


##
# Image plugin for PNG images.


class PngImageFile(ImageFile.ImageFile):
    format = "PNG"
    format_description = "Portable network graphics"

    def _open(self) -> None:
        if not _accept(self.fp.read(8)):
            msg = "not a PNG file"
            raise SyntaxError(msg)
        self._fp = self.fp
        self.__frame = 0

        #
        # Parse headers up to the first IDAT or fDAT chunk

        self.private_chunks: list[tuple[bytes, bytes] | tuple[bytes, bytes, bool]] = []
        self.png: PngStream | None = PngStream(self.fp)

        while True:
            #
            # get next chunk

            cid, pos, length = self.png.read()

            try:
                s = self.png.call(cid, pos, length)
            except EOFError:
                break
            except AttributeError:
                logger.debug("%r %s %s (unknown)", cid, pos, length)
                s = ImageFile._safe_read(self.fp, length)
                if cid[1:2].islower():
                    self.private_chunks.append((cid, s))

            self.png.crc(cid, s)

        #
        # Copy relevant attributes from the PngStream.  An alternative
        # would be to let the PngStream class modify these attributes
        # directly, but that introduces circular references which are
        # difficult to break if things go wrong in the decoder...
        # (believe me, I've tried ;-)

        self._mode = self.png.im_mode
        self._size = self.png.im_size
        self.info = self.png.im_info
        self._text: dict[str, str | iTXt] | None = None
        self.tile = self.png.im_tile
        self.custom_mimetype = self.png.im_custom_mimetype
        self.n_frames = self.png.im_n_frames or 1
        self.default_image = self.info.get("default_image", False)

        if self.png.im_palette:
            rawmode, data = self.png.im_palette
            self.palette = ImagePalette.raw(rawmode, data)

        if cid == b"fdAT":
            self.__prepare_idat = length - 4
        else:
            self.__prepare_idat = length  # used by load_prepare()

        if self.png.im_n_frames is not None:
            self._close_exclusive_fp_after_loading = False
            self.png.save_rewind()
            self.__rewind_idat = self.__prepare_idat
            self.__rewind = self._fp.tell()
            if self.default_image:
                # IDAT chunk contains default image and not first animation frame
                self.n_frames += 1
            self._seek(0)
        self.is_animated = self.n_frames > 1

    @property
    def text(self) -> dict[str, str | iTXt]:
        # experimental
        if self._text is None:
            # iTxt, tEXt and zTXt chunks may appear at the end of the file
            # So load the file to ensure that they are read
            if self.is_animated:
                frame = self.__frame
                # for APNG, seek to the final frame before loading
                self.seek(self.n_frames - 1)
            self.load()
            if self.is_animated:
                self.seek(frame)
        assert self._text is not None
        return self._text

    def verify(self) -> None:
        """Verify PNG file"""

        if self.fp is None:
            msg = "verify must be called directly after open"
            raise RuntimeError(msg)

        # back up to beginning of IDAT block
        self.fp.seek(self.tile[0][2] - 8)

        assert self.png is not None
        self.png.verify()
        self.png.close()

        if self._exclusive_fp:
            self.fp.close()
        self.fp = None

    def seek(self, frame: int) -> None:
        if not self._seek_check(frame):
            return
        if frame < self.__frame:
            self._seek(0, True)

        last_frame = self.__frame
        for f in range(self.__frame + 1, frame + 1):
            try:
                self._seek(f)
            except EOFError as e:
                self.seek(last_frame)
                msg = "no more images in APNG file"
                raise EOFError(msg) from e

    def _seek(self, frame: int, rewind: bool = False) -> None:
        assert self.png is not None
        if isinstance(self._fp, DeferredError):
            raise self._fp.ex

        self.dispose: _imaging.ImagingCore | None
        dispose_extent = None
        if frame == 0:
            if rewind:
                self._fp.seek(self.__rewind)
                self.png.rewind()
                self.__prepare_idat = self.__rewind_idat
                self._im = None
                self.info = self.png.im_info
                self.tile = self.png.im_tile
                self.fp = self._fp
            self._prev_im = None
            self.dispose = None
            self.default_image = self.info.get("default_image", False)
            self.dispose_op = self.info.get("disposal")
            self.blend_op = self.info.get("blend")
            dispose_extent = self.info.get("bbox")
            self.__frame = 0
        else:
            if frame != self.__frame + 1:
                msg = f"cannot seek to frame {frame}"
                raise ValueError(msg)

            # ensure previous frame was loaded
            self.load()

            if self.dispose:
                self.im.paste(self.dispose, self.dispose_extent)
            self._prev_im = self.im.copy()

            self.fp = self._fp

            # advance to the next frame
            if self.__prepare_idat:
                ImageFile._safe_read(self.fp, self.__prepare_idat)
                self.__prepare_idat = 0
            frame_start = False
            while True:
                self.fp.read(4)  # CRC

                try:
                    cid, pos, length = self.png.read()
                except (struct.error, SyntaxError):
                    break

                if cid == b"IEND":
                    msg = "No more images in APNG file"
                    raise EOFError(msg)
                if cid == b"fcTL":
                    if frame_start:
                        # there must be at least one fdAT chunk between fcTL chunks
                        msg = "APNG missing frame data"
                        raise SyntaxError(msg)
                    frame_start = True

                try:
                    self.png.call(cid, pos, length)
                except UnicodeDecodeError:
                    break
                except EOFError:
                    if cid == b"fdAT":
                        length -= 4
                        if frame_start:
                            self.__prepare_idat = length
                            break
                    ImageFile._safe_read(self.fp, length)
                except AttributeError:
                    logger.debug("%r %s %s (unknown)", cid, pos, length)
                    ImageFile._safe_read(self.fp, length)

            self.__frame = frame
            self.tile = self.png.im_tile
            self.dispose_op = self.info.get("disposal")
            self.blend_op = self.info.get("blend")
            dispose_extent = self.info.get("bbox")

            if not self.tile:
                msg = "image not found in APNG frame"
                raise EOFError(msg)
        if dispose_extent:
            self.dispose_extent: tuple[float, float, float, float] = dispose_extent

        # setup frame disposal (actual disposal done when needed in the next _seek())
        if self._prev_im is None and self.dispose_op == Disposal.OP_PREVIOUS:
            self.dispose_op = Disposal.OP_BACKGROUND

        self.dispose = None
        if self.dispose_op == Disposal.OP_PREVIOUS:
            if self._prev_im:
                self.dispose = self._prev_im.copy()
                self.dispose = self._crop(self.dispose, self.dispose_extent)
        elif self.dispose_op == Disposal.OP_BACKGROUND:
            self.dispose = Image.core.fill(self.mode, self.size)
            self.dispose = self._crop(self.dispose, self.dispose_extent)

    def tell(self) -> int:
        return self.__frame

    def load_prepare(self) -> None:
        """internal: prepare to read PNG file"""

        if self.info.get("interlace"):
            self.decoderconfig = self.decoderconfig + (1,)

        self.__idat = self.__prepare_idat  # used by load_read()
        ImageFile.ImageFile.load_prepare(self)

    def load_read(self, read_bytes: int) -> bytes:
        """internal: read more image data"""

        assert self.png is not None
        while self.__idat == 0:
            # end of chunk, skip forward to next one

            self.fp.read(4)  # CRC

            cid, pos, length = self.png.read()

            if cid not in [b"IDAT", b"DDAT", b"fdAT"]:
                self.png.push(cid, pos, length)
                return b""

            if cid == b"fdAT":
                try:
                    self.png.call(cid, pos, length)
                except EOFError:
                    pass
                self.__idat = length - 4  # sequence_num has already been read
            else:
                self.__idat = length  # empty chunks are allowed

        # read more data from this chunk
        if read_bytes <= 0:
            read_bytes = self.__idat
        else:
            read_bytes = min(read_bytes, self.__idat)

        self.__idat = self.__idat - read_bytes

        return self.fp.read(read_bytes)

    def load_end(self) -> None:
        """internal: finished reading image data"""
        assert self.png is not None
        if self.__idat != 0:
            self.fp.read(self.__idat)
        while True:
            self.fp.read(4)  # CRC

            try:
                cid, pos, length = self.png.read()
            except (struct.error, SyntaxError):
                break

            if cid == b"IEND":
                break
            elif cid == b"fcTL" and self.is_animated:
                # start of the next frame, stop reading
                self.__prepare_idat = 0
                self.png.push(cid, pos, length)
                break

            try:
                self.png.call(cid, pos, length)
            except UnicodeDecodeError:
                break
            except EOFError:
                if cid == b"fdAT":
                    length -= 4
                try:
                    ImageFile._safe_read(self.fp, length)
                except OSError as e:
                    if ImageFile.LOAD_TRUNCATED_IMAGES:
                        break
                    else:
                        raise e
            except AttributeError:
                logger.debug("%r %s %s (unknown)", cid, pos, length)
                s = ImageFile._safe_read(self.fp, length)
                if cid[1:2].islower():
                    self.private_chunks.append((cid, s, True))
        self._text = self.png.im_text
        if not self.is_animated:
            self.png.close()
            self.png = None
        else:
            if self._prev_im and self.blend_op == Blend.OP_OVER:
                updated = self._crop(self.im, self.dispose_extent)
                if self.im.mode == "RGB" and "transparency" in self.info:
                    mask = updated.convert_transparent(
                        "RGBA", self.info["transparency"]
                    )
                else:
                    if self.im.mode == "P" and "transparency" in self.info:
                        t = self.info["transparency"]
                        if isinstance(t, bytes):
                            updated.putpalettealphas(t)
                        elif isinstance(t, int):
                            updated.putpalettealpha(t)
                    mask = updated.convert("RGBA")
                self._prev_im.paste(updated, self.dispose_extent, mask)
                self.im = self._prev_im

    def _getexif(self) -> dict[int, Any] | None:
        if "exif" not in self.info:
            self.load()
        if "exif" not in self.info and "Raw profile type exif" not in self.info:
            return None
        return self.getexif()._get_merged_dict()

    def getexif(self) -> Image.Exif:
        if "exif" not in self.info:
            self.load()

        return super().getexif()


# --------------------------------------------------------------------
# PNG writer

_OUTMODES = {
    # supported PIL modes, and corresponding rawmode, bit depth and color type
    "1": ("1", b"\x01", b"\x00"),
    "L;1": ("L;1", b"\x01", b"\x00"),
    "L;2": ("L;2", b"\x02", b"\x00"),
    "L;4": ("L;4", b"\x04", b"\x00"),
    "L": ("L", b"\x08", b"\x00"),
    "LA": ("LA", b"\x08", b"\x04"),
    "I": ("I;16B", b"\x10", b"\x00"),
    "I;16": ("I;16B", b"\x10", b"\x00"),
    "I;16B": ("I;16B", b"\x10", b"\x00"),
    "P;1": ("P;1", b"\x01", b"\x03"),
    "P;2": ("P;2", b"\x02", b"\x03"),
    "P;4": ("P;4", b"\x04", b"\x03"),
    "P": ("P", b"\x08", b"\x03"),
    "RGB": ("RGB", b"\x08", b"\x02"),
    "RGBA": ("RGBA", b"\x08", b"\x06"),
}


def putchunk(fp: IO[bytes], cid: bytes, *data: bytes) -> None:
    """Write a PNG chunk (including CRC field)"""

    byte_data = b"".join(data)

    fp.write(o32(len(byte_data)) + cid)
    fp.write(byte_data)
    crc = _crc32(byte_data, _crc32(cid))
    fp.write(o32(crc))


class _idat:
    # wrap output from the encoder in IDAT chunks

    def __init__(self, fp: IO[bytes], chunk: Callable[..., None]) -> None:
        self.fp = fp
        self.chunk = chunk

    def write(self, data: bytes) -> None:
        self.chunk(self.fp, b"IDAT", data)


class _fdat:
    # wrap encoder output in fdAT chunks

    def __init__(self, fp: IO[bytes], chunk: Callable[..., None], seq_num: int) -> None:
        self.fp = fp
        self.chunk = chunk
        self.seq_num = seq_num

    def write(self, data: bytes) -> None:
        self.chunk(self.fp, b"fdAT", o32(self.seq_num), data)
        self.seq_num += 1


class _Frame(NamedTuple):
    im: Image.Image
    bbox: tuple[int, int, int, int] | None
    encoderinfo: dict[str, Any]


def _write_multiple_frames(
    im: Image.Image,
    fp: IO[bytes],
    chunk: Callable[..., None],
    mode: str,
    rawmode: str,
    default_image: Image.Image | None,
    append_images: list[Image.Image],
) -> Image.Image | None:
    duration = im.encoderinfo.get("duration")
    loop = im.encoderinfo.get("loop", im.info.get("loop", 0))
    disposal = im.encoderinfo.get("disposal", im.info.get("disposal", Disposal.OP_NONE))
    blend = im.encoderinfo.get("blend", im.info.get("blend", Blend.OP_SOURCE))

    if default_image:
        chain = itertools.chain(append_images)
    else:
        chain = itertools.chain([im], append_images)

    im_frames: list[_Frame] = []
    frame_count = 0
    for im_seq in chain:
        for im_frame in ImageSequence.Iterator(im_seq):
            if im_frame.mode == mode:
                im_frame = im_frame.copy()
            else:
                im_frame = im_frame.convert(mode)
            encoderinfo = im.encoderinfo.copy()
            if isinstance(duration, (list, tuple)):
                encoderinfo["duration"] = duration[frame_count]
            elif duration is None and "duration" in im_frame.info:
                encoderinfo["duration"] = im_frame.info["duration"]
            if isinstance(disposal, (list, tuple)):
                encoderinfo["disposal"] = disposal[frame_count]
            if isinstance(blend, (list, tuple)):
                encoderinfo["blend"] = blend[frame_count]
            frame_count += 1

            if im_frames:
                previous = im_frames[-1]
                prev_disposal = previous.encoderinfo.get("disposal")
                prev_blend = previous.encoderinfo.get("blend")
                if prev_disposal == Disposal.OP_PREVIOUS and len(im_frames) < 2:
                    prev_disposal = Disposal.OP_BACKGROUND

                if prev_disposal == Disposal.OP_BACKGROUND:
                    base_im = previous.im.copy()
                    dispose = Image.core.fill("RGBA", im.size, (0, 0, 0, 0))
                    bbox = previous.bbox
                    if bbox:
                        dispose = dispose.crop(bbox)
                    else:
                        bbox = (0, 0) + im.size
                    base_im.paste(dispose, bbox)
                elif prev_disposal == Disposal.OP_PREVIOUS:
                    base_im = im_frames[-2].im
                else:
                    base_im = previous.im
                delta = ImageChops.subtract_modulo(
                    im_frame.convert("RGBA"), base_im.convert("RGBA")
                )
                bbox = delta.getbbox(alpha_only=False)
                if (
                    not bbox
                    and prev_disposal == encoderinfo.get("disposal")
                    and prev_blend == encoderinfo.get("blend")
                    and "duration" in encoderinfo
                ):
                    previous.encoderinfo["duration"] += encoderinfo["duration"]
                    continue
            else:
                bbox = None
            im_frames.append(_Frame(im_frame, bbox, encoderinfo))

    if len(im_frames) == 1 and not default_image:
        return im_frames[0].im

    # animation control
    chunk(
        fp,
        b"acTL",
        o32(len(im_frames)),  # 0: num_frames
        o32(loop),  # 4: num_plays
    )

    # default image IDAT (if it exists)
    if default_image:
        if im.mode != mode:
            im = im.convert(mode)
        ImageFile._save(
            im,
            cast(IO[bytes], _idat(fp, chunk)),
            [ImageFile._Tile("zip", (0, 0) + im.size, 0, rawmode)],
        )

    seq_num = 0
    for frame, frame_data in enumerate(im_frames):
        im_frame = frame_data.im
        if not frame_data.bbox:
            bbox = (0, 0) + im_frame.size
        else:
            bbox = frame_data.bbox
            im_frame = im_frame.crop(bbox)
        size = im_frame.size
        encoderinfo = frame_data.encoderinfo
        frame_duration = int(round(encoderinfo.get("duration", 0)))
        frame_disposal = encoderinfo.get("disposal", disposal)
        frame_blend = encoderinfo.get("blend", blend)
        # frame control
        chunk(
            fp,
            b"fcTL",
            o32(seq_num),  # sequence_number
            o32(size[0]),  # width
            o32(size[1]),  # height
            o32(bbox[0]),  # x_offset
            o32(bbox[1]),  # y_offset
            o16(frame_duration),  # delay_numerator
            o16(1000),  # delay_denominator
            o8(frame_disposal),  # dispose_op
            o8(frame_blend),  # blend_op
        )
        seq_num += 1
        # frame data
        if frame == 0 and not default_image:
            # first frame must be in IDAT chunks for backwards compatibility
            ImageFile._save(
                im_frame,
                cast(IO[bytes], _idat(fp, chunk)),
                [ImageFile._Tile("zip", (0, 0) + im_frame.size, 0, rawmode)],
            )
        else:
            fdat_chunks = _fdat(fp, chunk, seq_num)
            ImageFile._save(
                im_frame,
                cast(IO[bytes], fdat_chunks),
                [ImageFile._Tile("zip", (0, 0) + im_frame.size, 0, rawmode)],
            )
            seq_num = fdat_chunks.seq_num
    return None


def _save_all(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
    _save(im, fp, filename, save_all=True)


def _save(
    im: Image.Image,
    fp: IO[bytes],
    filename: str | bytes,
    chunk: Callable[..., None] = putchunk,
    save_all: bool = False,
) -> None:
    # save an image to disk (called by the save method)

    if save_all:
        default_image = im.encoderinfo.get(
            "default_image", im.info.get("default_image")
        )
        modes = set()
        sizes = set()
        append_images = im.encoderinfo.get("append_images", [])
        for im_seq in itertools.chain([im], append_images):
            for im_frame in ImageSequence.Iterator(im_seq):
                modes.add(im_frame.mode)
                sizes.add(im_frame.size)
        for mode in ("RGBA", "RGB", "P"):
            if mode in modes:
                break
        else:
            mode = modes.pop()
        size = tuple(max(frame_size[i] for frame_size in sizes) for i in range(2))
    else:
        size = im.size
        mode = im.mode

    outmode = mode
    if mode == "P":
        #
        # attempt to minimize storage requirements for palette images
        if "bits" in im.encoderinfo:
            # number of bits specified by user
            colors = min(1 << im.encoderinfo["bits"], 256)
        else:
            # check palette contents
            if im.palette:
                colors = max(min(len(im.palette.getdata()[1]) // 3, 256), 1)
            else:
                colors = 256

        if colors <= 16:
            if colors <= 2:
                bits = 1
            elif colors <= 4:
                bits = 2
            else:
                bits = 4
            outmode += f";{bits}"

    # encoder options
    im.encoderconfig = (
        im.encoderinfo.get("optimize", False),
        im.encoderinfo.get("compress_level", -1),
        im.encoderinfo.get("compress_type", -1),
        im.encoderinfo.get("dictionary", b""),
    )

    # get the corresponding PNG mode
    try:
        rawmode, bit_depth, color_type = _OUTMODES[outmode]
    except KeyError as e:
        msg = f"cannot write mode {mode} as PNG"
        raise OSError(msg) from e

    #
    # write minimal PNG file

    fp.write(_MAGIC)

    chunk(
        fp,
        b"IHDR",
        o32(size[0]),  # 0: size
        o32(size[1]),
        bit_depth,
        color_type,
        b"\0",  # 10: compression
        b"\0",  # 11: filter category
        b"\0",  # 12: interlace flag
    )

    chunks = [b"cHRM", b"cICP", b"gAMA", b"sBIT", b"sRGB", b"tIME"]

    icc = im.encoderinfo.get("icc_profile", im.info.get("icc_profile"))
    if icc:
        # ICC profile
        # according to PNG spec, the iCCP chunk contains:
        # Profile name  1-79 bytes (character string)
        # Null separator        1 byte (null character)
        # Compression method    1 byte (0)
        # Compressed profile    n bytes (zlib with deflate compression)
        name = b"ICC Profile"
        data = name + b"\0\0" + zlib.compress(icc)
        chunk(fp, b"iCCP", data)

        # You must either have sRGB or iCCP.
        # Disallow sRGB chunks when an iCCP-chunk has been emitted.
        chunks.remove(b"sRGB")

    info = im.encoderinfo.get("pnginfo")
    if info:
        chunks_multiple_allowed = [b"sPLT", b"iTXt", b"tEXt", b"zTXt"]
        for info_chunk in info.chunks:
            cid, data = info_chunk[:2]
            if cid in chunks:
                chunks.remove(cid)
                chunk(fp, cid, data)
            elif cid in chunks_multiple_allowed:
                chunk(fp, cid, data)
            elif cid[1:2].islower():
                # Private chunk
                after_idat = len(info_chunk) == 3 and info_chunk[2]
                if not after_idat:
                    chunk(fp, cid, data)

    if im.mode == "P":
        palette_byte_number = colors * 3
        palette_bytes = im.im.getpalette("RGB")[:palette_byte_number]
        while len(palette_bytes) < palette_byte_number:
            palette_bytes += b"\0"
        chunk(fp, b"PLTE", palette_bytes)

    transparency = im.encoderinfo.get("transparency", im.info.get("transparency", None))

    if transparency or transparency == 0:
        if im.mode == "P":
            # limit to actual palette size
            alpha_bytes = colors
            if isinstance(transparency, bytes):
                chunk(fp, b"tRNS", transparency[:alpha_bytes])
            else:
                transparency = max(0, min(255, transparency))
                alpha = b"\xff" * transparency + b"\0"
                chunk(fp, b"tRNS", alpha[:alpha_bytes])
        elif im.mode in ("1", "L", "I", "I;16"):
            transparency = max(0, min(65535, transparency))
            chunk(fp, b"tRNS", o16(transparency))
        elif im.mode == "RGB":
            red, green, blue = transparency
            chunk(fp, b"tRNS", o16(red) + o16(green) + o16(blue))
        else:
            if "transparency" in im.encoderinfo:
                # don't bother with transparency if it's an RGBA
                # and it's in the info dict. It's probably just stale.
                msg = "cannot use transparency for this mode"
                raise OSError(msg)
    else:
        if im.mode == "P" and im.im.getpalettemode() == "RGBA":
            alpha = im.im.getpalette("RGBA", "A")
            alpha_bytes = colors
            chunk(fp, b"tRNS", alpha[:alpha_bytes])

    dpi = im.encoderinfo.get("dpi")
    if dpi:
        chunk(
            fp,
            b"pHYs",
            o32(int(dpi[0] / 0.0254 + 0.5)),
            o32(int(dpi[1] / 0.0254 + 0.5)),
            b"\x01",
        )

    if info:
        chunks = [b"bKGD", b"hIST"]
        for info_chunk in info.chunks:
            cid, data = info_chunk[:2]
            if cid in chunks:
                chunks.remove(cid)
                chunk(fp, cid, data)

    exif = im.encoderinfo.get("exif")
    if exif:
        if isinstance(exif, Image.Exif):
            exif = exif.tobytes(8)
        if exif.startswith(b"Exif\x00\x00"):
            exif = exif[6:]
        chunk(fp, b"eXIf", exif)

    single_im: Image.Image | None = im
    if save_all:
        single_im = _write_multiple_frames(
            im, fp, chunk, mode, rawmode, default_image, append_images
        )
    if single_im:
        ImageFile._save(
            single_im,
            cast(IO[bytes], _idat(fp, chunk)),
            [ImageFile._Tile("zip", (0, 0) + single_im.size, 0, rawmode)],
        )

    if info:
        for info_chunk in info.chunks:
            cid, data = info_chunk[:2]
            if cid[1:2].islower():
                # Private chunk
                after_idat = len(info_chunk) == 3 and info_chunk[2]
                if after_idat:
                    chunk(fp, cid, data)

    chunk(fp, b"IEND", b"")

    if hasattr(fp, "flush"):
        fp.flush()


# --------------------------------------------------------------------
# PNG chunk converter


def getchunks(im: Image.Image, **params: Any) -> list[tuple[bytes, bytes, bytes]]:
    """Return a list of PNG chunks representing this image."""
    from io import BytesIO

    chunks = []

    def append(fp: IO[bytes], cid: bytes, *data: bytes) -> None:
        byte_data = b"".join(data)
        crc = o32(_crc32(byte_data, _crc32(cid)))
        chunks.append((cid, byte_data, crc))

    fp = BytesIO()

    try:
        im.encoderinfo = params
        _save(im, fp, "", append)
    finally:
        del im.encoderinfo

    return chunks


# --------------------------------------------------------------------
# Registry

Image.register_open(PngImageFile.format, PngImageFile, _accept)
Image.register_save(PngImageFile.format, _save)
Image.register_save_all(PngImageFile.format, _save_all)

Image.register_extensions(PngImageFile.format, [".png", ".apng"])

Image.register_mime(PngImageFile.format, "image/png")
