# PyMod-Milter 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 3 of the License, or
# (at your option) any later version.
#
# PyMod-Milter 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 PyMod-Milter.  If not, see <http://www.gnu.org/licenses/>.
#

__all__ = [
    "AddHeader",
    "ModHeader",
    "DelHeader",
    "AddDisclaimer",
    "RewriteLinks"]

import logging
import re

from base64 import b64encode
from bs4 import BeautifulSoup
from collections import defaultdict
from copy import copy
from email.message import MIMEPart
from email.policy import SMTPUTF8

from pymodmilter import replace_illegal_chars


class AddHeader:
    """Add a mail header field."""
    def __init__(self, field, value):
        self.field = field
        self.value = value

    def execute(self, milter, pretend=False,
                logger=logging.getLogger(__name__)):
        header = f"{self.field}: {self.value}"
        if logger.getEffectiveLevel() == logging.DEBUG:
            logger.debug(f"add_header: {header}")
        else:
            logger.info(f"add_header: {header[0:70]}")

        milter.msg.add_header(self.field, self.value)

        if not pretend:
            milter.addheader(self.field, self.value)


class ModHeader:
    """Change the value of a mail header field."""
    def __init__(self, field, value, search=None):
        self.value = value

        try:
            self.field = re.compile(field, re.IGNORECASE)
            if search is not None:
                self.search = re.compile(
                    search, re.MULTILINE + re.DOTALL + re.IGNORECASE)
            else:
                self.search = search
        except re.error as e:
            raise RuntimeError(e)

    def execute(self, milter, pretend=False,
                logger=logging.getLogger(__name__)):
        idx = defaultdict(int)

        for i, (field, value) in enumerate(milter.msg.items()):
            field_lower = field.lower()
            idx[field_lower] += 1

            if not self.field.match(field):
                continue

            new_value = value
            if self.search is not None:
                new_value = self.search.sub(self.value, value).strip()
            else:
                new_value = self.value

            if not new_value:
                logger.warning(
                    "mod_header: resulting value is empty, "
                    "skip modification")
                continue

            if new_value == value:
                continue

            header = f"{field}: {value}"
            new_header = f"{field}: {new_value}"

            if logger.getEffectiveLevel() == logging.DEBUG:
                logger.debug(f"mod_header: {header}: {new_header}")
            else:
                logger.info(f"mod_header: {header[0:70]}: {new_header[0:70]}")

            milter.msg.replace_header(
                field, replace_illegal_chars(new_value), idx=idx[field_lower])

            if not pretend:
                milter.chgheader(field, new_value, idx=idx[field_lower])


class DelHeader:
    """Delete a mail header field."""
    def __init__(self, field, value=None):
        try:
            self.field = re.compile(field, re.IGNORECASE)
            if value is not None:
                self.value = re.compile(
                    value, re.MULTILINE + re.DOTALL + re.IGNORECASE)
            else:
                self.value = value
        except re.error as e:
            raise RuntimeError(e)

    def execute(self, milter, pretend=False,
                logger=logging.getLogger(__name__)):
        idx = defaultdict(int)

        for field, value in milter.msg.items():
            field_lower = field.lower()
            idx[field_lower] += 1

            if not self.field.match(field):
                continue

            if self.value is not None and not self.value.search(value):
                continue

            header = f"{field}: {value}"
            if logger.getEffectiveLevel() == logging.DEBUG:
                logger.debug(f"del_header: {header}")
            else:
                logger.info(f"del_header: {header[0:70]}")
            milter.msg.remove_header(field, idx=idx[field_lower])

            if not pretend:
                milter.chgheader(field, "", idx=idx[field_lower])

            idx[field_lower] -= 1


def _get_body_content(msg, pref):
    part = None
    content = None
    if not msg.is_multipart() and msg.get_content_type() == f"text/{pref}":
        part = msg
    else:
        part = msg.get_body(preferencelist=(pref))

    if part is not None:
        content = part.get_content()

    return (part, content)


def _has_content_before_body_tag(soup):
    s = copy(soup)
    for element in s.find_all("head") + s.find_all("body"):
        element.extract()

    if len(s.text.strip()) > 0:
        return True

    return False


def _inject_body(milter):
    if not milter.msg.is_multipart():
        milter.msg.make_mixed()

    attachments = []
    for attachment in milter.msg.iter_attachments():
        if "content-disposition" not in attachment:
            attachment["Content-Disposition"] = "attachment"
        attachments.append(attachment)

    milter.msg.clear_content()
    milter.msg.set_content("")
    milter.msg.add_alternative("", subtype="html")
    milter.msg.make_mixed()

    for attachment in attachments:
        milter.msg.attach(attachment)


def _wrap_message(milter):
    attachment = MIMEPart(policy=SMTPUTF8)
    attachment.set_content(milter.msg.as_bytes(),
                           maintype="plain", subtype="text",
                           disposition="attachment",
                           filename=f"{milter.qid}.eml",
                           params={"name": f"{milter.qid}.eml"})

    milter.msg.clear_content()
    milter.msg.set_content(
        "Please see the original email attached.")
    milter.msg.add_alternative(
        "<html><body>Please see the original email attached.</body></html>",
        subtype="html")
    milter.msg.make_mixed()
    milter.msg.attach(attachment)


class AddDisclaimer:
    """Append or prepend a disclaimer to the mail body."""
    def __init__(self, text_template, html_template, action, error_policy):
        try:
            with open(text_template, "r") as f:
                self.text_template = f.read()

            with open(html_template, "r") as f:
                html = BeautifulSoup(f.read(), "html.parser")

        except IOError as e:
            raise RuntimeError(e)

        body = html.find('body')
        self.html_template = body or html
        self.action = action
        self.error_policy = error_policy

    def patch_message_body(self, milter, logger):
        text_body, text_content = _get_body_content(milter.msg, "plain")
        html_body, html_content = _get_body_content(milter.msg, "html")

        if text_content is None and html_content is None:
            raise RuntimeError("message does not contain any body part")

        if text_content is not None:
            logger.info(f"{self.action} text disclaimer")

            if self.action == "prepend":
                content = f"{self.text_template}{text_content}"
            else:
                content = f"{text_content}{self.text_template}"

            text_body.set_content(
                content.encode(), maintype="text", subtype="plain")
            text_body.set_param("charset", "UTF-8", header="Content-Type")
            del text_body["MIME-Version"]

        if html_content is not None:
            logger.info(f"{self.action} html disclaimer")

            soup = BeautifulSoup(html_content, "html.parser")

            body = soup.find('body')
            if not body:
                body = soup
            elif _has_content_before_body_tag(soup):
                body = soup

            if self.action == "prepend":
                body.insert(0, copy(self.html_template))
            else:
                body.append(self.html_template)

            html_body.set_content(
                str(soup).encode(), maintype="text", subtype="html")
            html_body.set_param("charset", "UTF-8", header="Content-Type")
            del html_body["MIME-Version"]

    def execute(self, milter, pretend=False,
                logger=logging.getLogger(__name__)):
        old_headers = milter.msg.items()

        try:
            try:
                self.patch_message_body(milter, logger)
            except RuntimeError as e:
                logger.info(f"{e}, inject empty plain and html body")
                _inject_body(milter)
                self.patch_message_body(milter, logger)

        except Exception as e:
            logger.warning(e)
            if self.error_policy == "ignore":
                logger.info(
                    "unable to add disclaimer to message body, "
                    "ignore error according to policy")
                return
            elif self.error_policy == "reject":
                logger.info(
                    "unable to add disclaimer to message body, "
                    "reject message according to policy")
                return [
                    ("reject", "Message rejected due to error")]

            logger.info("wrap original message in a new message envelope")
            try:
                _wrap_message(milter)
                self.patch_message_body(milter, logger)
            except Exception as e:
                logger.error(e)
                raise Exception(
                    "unable to wrap message in a new message envelope, "
                    "give up ...")

        if not pretend:
            milter.update_headers(old_headers)
            milter.replacebody()


class RewriteLinks:
    """Rewrite link targets in the mail html body."""
    def __init__(self, repl):
        self.repl = repl

    def execute(self, milter, pretend=False,
                logger=logging.getLogger(__name__)):
        html_body, html_content = _get_body_content(milter.msg, "html")
        if html_content is not None:
            soup = BeautifulSoup(html_content, "html.parser")

            rewritten = 0
            for link in soup.find_all("a", href=True):
                if not link["href"]:
                    continue

                if "{URL_B64}" in self.repl:
                    url_b64 = b64encode(link["href"].encode()).decode()
                    target = self.repl.replace("{URL_B64}", url_b64)
                else:
                    target = self.repl

                link["href"] = target
                rewritten += 1

            if rewritten:
                logger.info(f"rewrote {rewritten} link(s) in html body")

                html_body.set_content(
                    str(soup).encode(), maintype="text", subtype="html")
                html_body.set_param("charset", "UTF-8", header="Content-Type")
                del html_body["MIME-Version"]

                if not pretend:
                    milter.replacebody()