from __future__ import absolute_import, print_function, division
import time
import sys
import re

from netlib.http import request
from netlib.http import response
from netlib.http import headers
from netlib.http import url
from netlib import utils
from netlib import exceptions


def get_header_tokens(headers, key):
    """
        Retrieve all tokens for a header key. A number of different headers
        follow a pattern where each header line can containe comma-separated
        tokens, and headers can be set multiple times.
    """
    if key not in headers:
        return []
    tokens = headers[key].split(",")
    return [token.strip() for token in tokens]


def read_request(rfile, body_size_limit=None):
    request = read_request_head(rfile)
    expected_body_size = expected_http_body_size(request)
    request.data.content = b"".join(read_body(rfile, expected_body_size, limit=body_size_limit))
    request.timestamp_end = time.time()
    return request


def read_request_head(rfile):
    """
    Parse an HTTP request head (request line + headers) from an input stream

    Args:
        rfile: The input stream

    Returns:
        The HTTP request object (without body)

    Raises:
        exceptions.HttpReadDisconnect: No bytes can be read from rfile.
        exceptions.HttpSyntaxException: The input is malformed HTTP.
        exceptions.HttpException: Any other error occured.
    """
    timestamp_start = time.time()
    if hasattr(rfile, "reset_timestamps"):
        rfile.reset_timestamps()

    form, method, scheme, host, port, path, http_version = _read_request_line(rfile)
    headers = _read_headers(rfile)

    if hasattr(rfile, "first_byte_timestamp"):
        # more accurate timestamp_start
        timestamp_start = rfile.first_byte_timestamp

    return request.Request(
        form, method, scheme, host, port, path, http_version, headers, None, timestamp_start
    )


def read_response(rfile, request, body_size_limit=None):
    response = read_response_head(rfile)
    expected_body_size = expected_http_body_size(request, response)
    response.data.content = b"".join(read_body(rfile, expected_body_size, body_size_limit))
    response.timestamp_end = time.time()
    return response


def read_response_head(rfile):
    """
    Parse an HTTP response head (response line + headers) from an input stream

    Args:
        rfile: The input stream

    Returns:
        The HTTP request object (without body)

    Raises:
        exceptions.HttpReadDisconnect: No bytes can be read from rfile.
        exceptions.HttpSyntaxException: The input is malformed HTTP.
        exceptions.HttpException: Any other error occured.
    """

    timestamp_start = time.time()
    if hasattr(rfile, "reset_timestamps"):
        rfile.reset_timestamps()

    http_version, status_code, message = _read_response_line(rfile)
    headers = _read_headers(rfile)

    if hasattr(rfile, "first_byte_timestamp"):
        # more accurate timestamp_start
        timestamp_start = rfile.first_byte_timestamp

    return response.Response(http_version, status_code, message, headers, None, timestamp_start)


def read_body(rfile, expected_size, limit=None, max_chunk_size=4096):
    """
        Read an HTTP message body

        Args:
            rfile: The input stream
            expected_size: The expected body size (see :py:meth:`expected_body_size`)
            limit: Maximum body size
            max_chunk_size: Maximium chunk size that gets yielded

        Returns:
            A generator that yields byte chunks of the content.

        Raises:
            exceptions.HttpException, if an error occurs

        Caveats:
            max_chunk_size is not considered if the transfer encoding is chunked.
    """
    if not limit or limit < 0:
        limit = sys.maxsize
    if not max_chunk_size:
        max_chunk_size = limit

    if expected_size is None:
        for x in _read_chunked(rfile, limit):
            yield x
    elif expected_size >= 0:
        if limit is not None and expected_size > limit:
            raise exceptions.HttpException(
                "HTTP Body too large. "
                "Limit is {}, content length was advertised as {}".format(limit, expected_size)
            )
        bytes_left = expected_size
        while bytes_left:
            chunk_size = min(bytes_left, max_chunk_size)
            content = rfile.read(chunk_size)
            if len(content) < chunk_size:
                raise exceptions.HttpException("Unexpected EOF")
            yield content
            bytes_left -= chunk_size
    else:
        bytes_left = limit
        while bytes_left:
            chunk_size = min(bytes_left, max_chunk_size)
            content = rfile.read(chunk_size)
            if not content:
                return
            yield content
            bytes_left -= chunk_size
        not_done = rfile.read(1)
        if not_done:
            raise exceptions.HttpException("HTTP body too large. Limit is {}.".format(limit))


def connection_close(http_version, headers):
    """
        Checks the message to see if the client connection should be closed
        according to RFC 2616 Section 8.1.
    """
    # At first, check if we have an explicit Connection header.
    if "connection" in headers:
        tokens = get_header_tokens(headers, "connection")
        if "close" in tokens:
            return True
        elif "keep-alive" in tokens:
            return False

    # If we don't have a Connection header, HTTP 1.1 connections are assumed to
    # be persistent
    return http_version != "HTTP/1.1" and http_version != b"HTTP/1.1"  # FIXME: Remove one case.


def expected_http_body_size(request, response=None):
    """
        Returns:
            The expected body length:
            - a positive integer, if the size is known in advance
            - None, if the size in unknown in advance (chunked encoding)
            - -1, if all data should be read until end of stream.

        Raises:
            exceptions.HttpSyntaxException, if the content length header is invalid
    """
    # Determine response size according to
    # http://tools.ietf.org/html/rfc7230#section-3.3
    if not response:
        headers = request.headers
        response_code = None
        is_request = True
    else:
        headers = response.headers
        response_code = response.status_code
        is_request = False

    if is_request:
        if headers.get("expect", "").lower() == "100-continue":
            return 0
    else:
        if request.method.upper() == "HEAD":
            return 0
        if 100 <= response_code <= 199:
            return 0
        if response_code == 200 and request.method.upper() == "CONNECT":
            return 0
        if response_code in (204, 304):
            return 0

    if "chunked" in headers.get("transfer-encoding", "").lower():
        return None
    if "content-length" in headers:
        try:
            size = int(headers["content-length"])
            if size < 0:
                raise ValueError()
            return size
        except ValueError:
            raise exceptions.HttpSyntaxException("Unparseable Content Length")
    if is_request:
        return 0
    return -1


def _get_first_line(rfile):
    try:
        line = rfile.readline()
        if line == b"\r\n" or line == b"\n":
            # Possible leftover from previous message
            line = rfile.readline()
    except exceptions.TcpDisconnect:
        raise exceptions.HttpReadDisconnect("Remote disconnected")
    if not line:
        raise exceptions.HttpReadDisconnect("Remote disconnected")
    return line.strip()


def _read_request_line(rfile):
    try:
        line = _get_first_line(rfile)
    except exceptions.HttpReadDisconnect:
        # We want to provide a better error message.
        raise exceptions.HttpReadDisconnect("Client disconnected")

    try:
        method, path, http_version = line.split()

        if path == b"*" or path.startswith(b"/"):
            form = "relative"
            scheme, host, port = None, None, None
        elif method == b"CONNECT":
            form = "authority"
            host, port = _parse_authority_form(path)
            scheme, path = None, None
        else:
            form = "absolute"
            scheme, host, port, path = url.parse(path)

        _check_http_version(http_version)
    except ValueError:
        raise exceptions.HttpSyntaxException("Bad HTTP request line: {}".format(line))

    return form, method, scheme, host, port, path, http_version


def _parse_authority_form(hostport):
    """
        Returns (host, port) if hostport is a valid authority-form host specification.
        http://tools.ietf.org/html/draft-luotonen-web-proxy-tunneling-01 section 3.1

        Raises:
            ValueError, if the input is malformed
    """
    try:
        host, port = hostport.split(b":")
        port = int(port)
        if not utils.is_valid_host(host) or not utils.is_valid_port(port):
            raise ValueError()
    except ValueError:
        raise exceptions.HttpSyntaxException("Invalid host specification: {}".format(hostport))

    return host, port


def _read_response_line(rfile):
    try:
        line = _get_first_line(rfile)
    except exceptions.HttpReadDisconnect:
        # We want to provide a better error message.
        raise exceptions.HttpReadDisconnect("Server disconnected")

    try:
        parts = line.split(None, 2)
        if len(parts) == 2:  # handle missing message gracefully
            parts.append(b"")

        http_version, status_code, message = parts
        status_code = int(status_code)
        _check_http_version(http_version)

    except ValueError:
        raise exceptions.HttpSyntaxException("Bad HTTP response line: {}".format(line))

    return http_version, status_code, message


def _check_http_version(http_version):
    if not re.match(br"^HTTP/\d\.\d$", http_version):
        raise exceptions.HttpSyntaxException("Unknown HTTP version: {}".format(http_version))


def _read_headers(rfile):
    """
        Read a set of headers.
        Stop once a blank line is reached.

        Returns:
            A headers object

        Raises:
            exceptions.HttpSyntaxException
    """
    ret = []
    while True:
        line = rfile.readline()
        if not line or line == b"\r\n" or line == b"\n":
            break
        if line[0] in b" \t":
            if not ret:
                raise exceptions.HttpSyntaxException("Invalid headers")
            # continued header
            ret[-1] = (ret[-1][0], ret[-1][1] + b'\r\n ' + line.strip())
        else:
            try:
                name, value = line.split(b":", 1)
                value = value.strip()
                if not name:
                    raise ValueError()
                ret.append((name, value))
            except ValueError:
                raise exceptions.HttpSyntaxException(
                    "Invalid header line: %s" % repr(line)
                )
    return headers.Headers(ret)


def _read_chunked(rfile, limit=sys.maxsize):
    """
    Read a HTTP body with chunked transfer encoding.

    Args:
        rfile: the input file
        limit: A positive integer
    """
    total = 0
    while True:
        line = rfile.readline(128)
        if line == b"":
            raise exceptions.HttpException("Connection closed prematurely")
        if line != b"\r\n" and line != b"\n":
            try:
                length = int(line, 16)
            except ValueError:
                raise exceptions.HttpSyntaxException("Invalid chunked encoding length: {}".format(line))
            total += length
            if total > limit:
                raise exceptions.HttpException(
                    "HTTP Body too large. Limit is {}, "
                    "chunked content longer than {}".format(limit, total)
                )
            chunk = rfile.read(length)
            suffix = rfile.readline(5)
            if suffix != b"\r\n":
                raise exceptions.HttpSyntaxException("Malformed chunked body")
            if length == 0:
                return
            yield chunk