"""
Handlers for Content-Encoding.

See: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Encoding
"""
import codecs
import io
import typing
import zlib

from ._compat import brotli
from ._exceptions import DecodingError


class ContentDecoder:
    def decode(self, data: bytes) -> bytes:
        raise NotImplementedError()  # pragma: nocover

    def flush(self) -> bytes:
        raise NotImplementedError()  # pragma: nocover


class IdentityDecoder(ContentDecoder):
    """
    Handle unencoded data.
    """

    def decode(self, data: bytes) -> bytes:
        return data

    def flush(self) -> bytes:
        return b""


class DeflateDecoder(ContentDecoder):
    """
    Handle 'deflate' decoding.

    See: https://stackoverflow.com/questions/1838699
    """

    def __init__(self) -> None:
        self.first_attempt = True
        self.decompressor = zlib.decompressobj()

    def decode(self, data: bytes) -> bytes:
        was_first_attempt = self.first_attempt
        self.first_attempt = False
        try:
            return self.decompressor.decompress(data)
        except zlib.error as exc:
            if was_first_attempt:
                self.decompressor = zlib.decompressobj(-zlib.MAX_WBITS)
                return self.decode(data)
            raise DecodingError(str(exc)) from exc

    def flush(self) -> bytes:
        try:
            return self.decompressor.flush()
        except zlib.error as exc:  # pragma: nocover
            raise DecodingError(str(exc)) from exc


class GZipDecoder(ContentDecoder):
    """
    Handle 'gzip' decoding.

    See: https://stackoverflow.com/questions/1838699
    """

    def __init__(self) -> None:
        self.decompressor = zlib.decompressobj(zlib.MAX_WBITS | 16)

    def decode(self, data: bytes) -> bytes:
        try:
            return self.decompressor.decompress(data)
        except zlib.error as exc:
            raise DecodingError(str(exc)) from exc

    def flush(self) -> bytes:
        try:
            return self.decompressor.flush()
        except zlib.error as exc:  # pragma: nocover
            raise DecodingError(str(exc)) from exc


class BrotliDecoder(ContentDecoder):
    """
    Handle 'brotli' decoding.

    Requires `pip install brotlipy`. See: https://brotlipy.readthedocs.io/
        or   `pip install brotli`. See https://github.com/google/brotli
    Supports both 'brotlipy' and 'Brotli' packages since they share an import
    name. The top branches are for 'brotlipy' and bottom branches for 'Brotli'
    """

    def __init__(self) -> None:
        if brotli is None:  # pragma: nocover
            raise ImportError(
                "Using 'BrotliDecoder', but neither of the 'brotlicffi' or 'brotli' "
                "packages have been installed. "
                "Make sure to install httpx using `pip install httpx[brotli]`."
            ) from None

        self.decompressor = brotli.Decompressor()
        self.seen_data = False
        if hasattr(self.decompressor, "decompress"):
            # The 'brotlicffi' package.
            self._decompress = self.decompressor.decompress  # pragma: nocover
        else:
            # The 'brotli' package.
            self._decompress = self.decompressor.process  # pragma: nocover

    def decode(self, data: bytes) -> bytes:
        if not data:
            return b""
        self.seen_data = True
        try:
            return self._decompress(data)
        except brotli.error as exc:
            raise DecodingError(str(exc)) from exc

    def flush(self) -> bytes:
        if not self.seen_data:
            return b""
        try:
            if hasattr(self.decompressor, "finish"):
                # Only available in the 'brotlicffi' package.

                # As the decompressor decompresses eagerly, this
                # will never actually emit any data. However, it will potentially throw
                # errors if a truncated or damaged data stream has been used.
                self.decompressor.finish()  # pragma: nocover
            return b""
        except brotli.error as exc:  # pragma: nocover
            raise DecodingError(str(exc)) from exc


class MultiDecoder(ContentDecoder):
    """
    Handle the case where multiple encodings have been applied.
    """

    def __init__(self, children: typing.Sequence[ContentDecoder]) -> None:
        """
        'children' should be a sequence of decoders in the order in which
        each was applied.
        """
        # Note that we reverse the order for decoding.
        self.children = list(reversed(children))

    def decode(self, data: bytes) -> bytes:
        for child in self.children:
            data = child.decode(data)
        return data

    def flush(self) -> bytes:
        data = b""
        for child in self.children:
            data = child.decode(data) + child.flush()
        return data


class ByteChunker:
    """
    Handles returning byte content in fixed-size chunks.
    """

    def __init__(self, chunk_size: int = None) -> None:
        self._buffer = io.BytesIO()
        self._chunk_size = chunk_size

    def decode(self, content: bytes) -> typing.List[bytes]:
        if self._chunk_size is None:
            return [content]

        self._buffer.write(content)
        if self._buffer.tell() >= self._chunk_size:
            value = self._buffer.getvalue()
            chunks = [
                value[i : i + self._chunk_size]
                for i in range(0, len(value), self._chunk_size)
            ]
            if len(chunks[-1]) == self._chunk_size:
                self._buffer.seek(0)
                self._buffer.truncate()
                return chunks
            else:
                self._buffer.seek(0)
                self._buffer.write(chunks[-1])
                self._buffer.truncate()
                return chunks[:-1]
        else:
            return []

    def flush(self) -> typing.List[bytes]:
        value = self._buffer.getvalue()
        self._buffer.seek(0)
        self._buffer.truncate()
        return [value] if value else []


class TextChunker:
    """
    Handles returning text content in fixed-size chunks.
    """

    def __init__(self, chunk_size: int = None) -> None:
        self._buffer = io.StringIO()
        self._chunk_size = chunk_size

    def decode(self, content: str) -> typing.List[str]:
        if self._chunk_size is None:
            return [content]

        self._buffer.write(content)
        if self._buffer.tell() >= self._chunk_size:
            value = self._buffer.getvalue()
            chunks = [
                value[i : i + self._chunk_size]
                for i in range(0, len(value), self._chunk_size)
            ]
            if len(chunks[-1]) == self._chunk_size:
                self._buffer.seek(0)
                self._buffer.truncate()
                return chunks
            else:
                self._buffer.seek(0)
                self._buffer.write(chunks[-1])
                self._buffer.truncate()
                return chunks[:-1]
        else:
            return []

    def flush(self) -> typing.List[str]:
        value = self._buffer.getvalue()
        self._buffer.seek(0)
        self._buffer.truncate()
        return [value] if value else []


class TextDecoder:
    """
    Handles incrementally decoding bytes into text
    """

    def __init__(self, encoding: str = "utf-8"):
        self.decoder = codecs.getincrementaldecoder(encoding)(errors="replace")

    def decode(self, data: bytes) -> str:
        return self.decoder.decode(data)

    def flush(self) -> str:
        return self.decoder.decode(b"", True)


class LineDecoder:
    """
    Handles incrementally reading lines from text.

    Uses universal line decoding, supporting any of `\n`, `\r`, or `\r\n`
    as line endings, normalizing to `\n`.
    """

    def __init__(self) -> None:
        self.buffer = ""

    def decode(self, text: str) -> typing.List[str]:
        lines = []

        if text and self.buffer and self.buffer[-1] == "\r":
            if text.startswith("\n"):
                # Handle the case where we have an "\r\n" split across
                # our previous input, and our new chunk.
                lines.append(self.buffer[:-1] + "\n")
                self.buffer = ""
                text = text[1:]
            else:
                # Handle the case where we have "\r" at the end of our
                # previous input.
                lines.append(self.buffer[:-1] + "\n")
                self.buffer = ""

        while text:
            num_chars = len(text)
            for idx in range(num_chars):
                char = text[idx]
                next_char = None if idx + 1 == num_chars else text[idx + 1]
                if char == "\n":
                    lines.append(self.buffer + text[: idx + 1])
                    self.buffer = ""
                    text = text[idx + 1 :]
                    break
                elif char == "\r" and next_char == "\n":
                    lines.append(self.buffer + text[:idx] + "\n")
                    self.buffer = ""
                    text = text[idx + 2 :]
                    break
                elif char == "\r" and next_char is not None:
                    lines.append(self.buffer + text[:idx] + "\n")
                    self.buffer = ""
                    text = text[idx + 1 :]
                    break
                elif next_char is None:
                    self.buffer += text
                    text = ""
                    break

        return lines

    def flush(self) -> typing.List[str]:
        if self.buffer.endswith("\r"):
            # Handle the case where we had a trailing '\r', which could have
            # been a '\r\n' pair.
            lines = [self.buffer[:-1] + "\n"]
        elif self.buffer:
            lines = [self.buffer]
        else:
            lines = []
        self.buffer = ""
        return lines


SUPPORTED_DECODERS = {
    "identity": IdentityDecoder,
    "gzip": GZipDecoder,
    "deflate": DeflateDecoder,
    "br": BrotliDecoder,
}


if brotli is None:
    SUPPORTED_DECODERS.pop("br")  # pragma: nocover
