# SPDX-License-Identifier: GPL-3.0-or-later

# Policies for resolving HTTP requests with local resources.
#
# This file is part of Hydrilla&Haketilo.
#
# Copyright (C) 2022 Wojtek Kosior
#
# 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 3 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, see <https://www.gnu.org/licenses/>.
#
#
# I, Wojtek Kosior, thereby promise not to sue for violation of this
# file's license. Although I request that you do not make use this code
# in a proprietary program, I am not going to enforce this in court.

"""
.....

We make file resources available to HTTP clients by mapping them
at:
    http(s)://<pattern-matching_origin>/<pattern_path>/<token>/
where <token> is a per-session secret unique for every mapping.
For example, a payload with pattern like the following:
    http*://***.example.com/a/b/**
Could cause resources to be mapped (among others) at each of:
    https://example.com/a/b/**/Da2uiF2UGfg/
    https://www.example.com/a/b/**/Da2uiF2UGfg/
    http://gnome.vs.kde.example.com/a/b/**/Da2uiF2UGfg/

Unauthorized web pages running in the user's browser are exected to be
unable to guess the secret. This way we stop them from spying on the
user and from interfering with Haketilo's normal operation.

This is only a soft prevention method. With some mechanisms
(e.g. service workers), under certain scenarios, it might be possible
to bypass it. Thus, to make the risk slightly smaller, we also block
the unauthorized accesses that we can detect.

Since a web page authorized to access the resources may only be served
when the corresponding mapping is enabled (or AUTO mode is on), we
consider accesses to non-enabled mappings' resources a security breach
and block them by responding with 403 Not Found.
"""

# Enable using with Python 3.7.
from __future__ import annotations

import dataclasses as dc
import typing as t

from ...translations import smart_gettext as _
from .. import state
from . import base
from .payload import PayloadAwarePolicy, PayloadAwarePolicyFactory


@dc.dataclass(frozen=True)
class PayloadResourcePolicy(PayloadAwarePolicy):
    """...."""
    process_request:  t.ClassVar[bool] = True

    priority: t.ClassVar[base.PolicyPriority] = base.PolicyPriority._THREE

    def _make_file_resource_response(self, path: tuple[str, ...]) \
        -> base.ProducedResponse:
        """...."""
        try:
            file_data = self.payload_data.payload_ref.get_file_data(
                self.haketilo_state,
                path
            )
        except state.MissingItemError:
            return resource_blocked_response

        if file_data is None:
            return base.ProducedResponse(
                404,
                [(b'Content-Type', b'text/plain; charset=utf-8')],
                _('api.file_not_found').encode()
            )

        return base.ProducedResponse(
            200,
            ((b'Content-Type', file_data.type.encode()),),
            file_data.contents
        )

    def consume_request(self, request_info: base.RequestInfo) \
        -> base.ProducedResponse:
        """...."""
        # Payload resource pattern has path of the form:
        #    "/some/arbitrary/segments/<per-session_token>/***"
        #
        # Corresponding requests shall have path of the form:
        #    "/some/arbitrary/segments/<per-session_token>/actual/resource/path"
        #
        # Here we need to extract the "/actual/resource/path" part.
        segments_to_drop = len(self.payload_data.pattern.path_segments) + 1
        resource_path = request_info.url.path_segments[segments_to_drop:]

        if resource_path == ():
            return resource_blocked_response
        elif resource_path[0] == 'static':
            return self._make_file_resource_response(resource_path[1:])
        elif resource_path[0] == 'api':
            # TODO: implement Haketilo APIs
            return resource_blocked_response
        else:
            return resource_blocked_response


resource_blocked_response = base.ProducedResponse(
    403,
    [(b'Content-Type', b'text/plain; charset=utf-8')],
    _('api.resource_not_enabled_for_access').encode()
)

@dc.dataclass(frozen=True)
class BlockedResponsePolicy(base.Policy):
    """...."""
    process_request: t.ClassVar[bool] = True

    priority: t.ClassVar[base.PolicyPriority] = base.PolicyPriority._THREE

    def consume_request(self, request_info: base.RequestInfo) \
        -> base.ProducedResponse:
        """...."""
        return resource_blocked_response


@dc.dataclass(frozen=True, unsafe_hash=True) # type: ignore[misc]
class PayloadResourcePolicyFactory(PayloadAwarePolicyFactory):
    """...."""
    def make_policy(self, haketilo_state: state.HaketiloState) \
        -> t.Union[PayloadResourcePolicy, BlockedResponsePolicy]:
        """...."""
        try:
            payload_data = self.payload_ref.get_data(haketilo_state)
        except state.MissingItemError:
            return BlockedResponsePolicy()

        if not payload_data.explicitly_enabled and \
           haketilo_state.get_settings().mapping_use_mode != \
               state.MappingUseMode.AUTO:
            return BlockedResponsePolicy()

        return PayloadResourcePolicy(haketilo_state, payload_data)