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

# Haketilo proxy payloads dependency resolution.
#
# 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.

"""
.....
"""

# Enable using with Python 3.7.
from __future__ import annotations

import dataclasses as dc
import typing as t

from ..exceptions import HaketiloException
from .. import item_infos
from .. import url_patterns


class ImpossibleSituation(HaketiloException):
    pass


@dc.dataclass(frozen=True)
class MappingRequirement:
    identifier: str

    def is_fulfilled_by(self, info: item_infos.MappingInfo) -> bool:
        return True

@dc.dataclass(frozen=True)
class MappingRepoRequirement(MappingRequirement):
    repo: str

    def is_fulfilled_by(self, info: item_infos.MappingInfo) -> bool:
        return info.repo == self.repo

@dc.dataclass(frozen=True)
class MappingVersionRequirement(MappingRequirement):
    version_info: item_infos.MappingInfo

    def __post_init__(self):
        assert self.version_info.identifier == self.identifier

    def is_fulfilled_by(self, info: item_infos.MappingInfo) -> bool:
        return info == self.version_info


@dc.dataclass
class ComputedPayload:
    resources: list[item_infos.ResourceInfo] = dc.field(default_factory=list)

    allows_eval:        bool = False
    allows_cors_bypass: bool = False

@dc.dataclass
class MappingChoice:
    info:     item_infos.MappingInfo
    required: bool = False
    payloads: dict[url_patterns.ParsedPattern, ComputedPayload] = \
        dc.field(default_factory=dict)


MappingsGraph = t.Union[
    t.Mapping[str, set[str]],
    t.Mapping[str, frozenset[str]]
]

def _mark_mappings(
        identifier:      str,
        mappings_graph:  MappingsGraph,
        marked_mappings: set[str]
) -> None:
    if identifier in marked_mappings:
        return

    marked_mappings.add(identifier)

    for next_mapping in mappings_graph.get(identifier, ()):
            _mark_mappings(next_mapping, mappings_graph, marked_mappings)


ComputedChoices = dict[str, MappingChoice]

@dc.dataclass(frozen=True)
class _ComputationData:
    resources: t.Mapping[str, item_infos.ResourceInfo]
    mappings:  t.Mapping[str, item_infos.MappingInfo]
    required:  frozenset[str]

    def _satisfy_payload_resource_rec(
            self,
            resource_identifier: str,
            processed_resources: set[str],
            computed_payload: ComputedPayload
    ) -> t.Optional[ComputedPayload]:
        if resource_identifier in processed_resources:
            # We forbid circular dependencies.
            return None

        resource_info = self.resources.get(resource_identifier)
        if resource_info is None:
            return None

        if resource_info in computed_payload.resources:
            return computed_payload

        processed_resources.add(resource_identifier)

        if resource_info.allows_eval:
            computed_payload.allows_eval = True

        if resource_info.allows_cors_bypass:
            computed_payload.allows_cors_bypass = True

        for dependency_spec in resource_info.dependencies:
            if self._satisfy_payload_resource_rec(
                    dependency_spec.identifier,
                    processed_resources,
                    computed_payload
            ) is None:
                return None

        processed_resources.remove(resource_identifier)

        computed_payload.resources.append(resource_info)

        return computed_payload

    def _satisfy_payload_resource(self, resource_identifier: str) \
        -> t.Optional[ComputedPayload]:
        return self._satisfy_payload_resource_rec(
            resource_identifier,
            set(),
            ComputedPayload()
        )

    def _compute_payloads_no_mapping_requirements(self) -> ComputedChoices:
        computed_result: ComputedChoices = ComputedChoices()

        for mapping_info in self.mappings.values():
            mapping_choice = MappingChoice(mapping_info)

            failure = False

            for pattern, resource_spec in mapping_info.payloads.items():
                computed_payload = self._satisfy_payload_resource(
                    resource_spec.identifier
                )
                if computed_payload is None:
                    failure = True
                    break

                if mapping_info.allows_eval:
                    computed_payload.allows_eval = True

                if mapping_info.allows_cors_bypass:
                    computed_payload.allows_cors_bypass = True

                mapping_choice.payloads[pattern] = computed_payload

            if not failure:
                computed_result[mapping_info.identifier] = mapping_choice

        return computed_result

    def _compute_inter_mapping_deps(self, choices: ComputedChoices) \
        -> dict[str, frozenset[str]]:
        mapping_deps: dict[str, frozenset[str]] = {}

        for mapping_choice in choices.values():
            specs_to_resolve = [*mapping_choice.info.required_mappings]

            for computed_payload in mapping_choice.payloads.values():
                for resource_info in computed_payload.resources:
                    specs_to_resolve.extend(resource_info.required_mappings)

            depended = frozenset(spec.identifier for spec in specs_to_resolve)
            mapping_deps[mapping_choice.info.identifier] = depended

        return mapping_deps

    def compute_payloads(self) -> ComputedChoices:
        choices = self._compute_payloads_no_mapping_requirements()

        mapping_deps = self._compute_inter_mapping_deps(choices)

        reverse_deps: dict[str, set[str]] = {}

        for depending, depended_set in mapping_deps.items():
            for depended in depended_set:
                reverse_deps.setdefault(depended, set()).add(depending)

        bad_mappings: set[str] = set()

        for depended_identifier in reverse_deps.keys():
            if self.mappings.get(depended_identifier) not in choices:
                _mark_mappings(depended_identifier, reverse_deps, bad_mappings)

        if any(identifier in self.required for identifier in bad_mappings):
            raise ImpossibleSituation()

        for identifier in bad_mappings:
            if identifier in self.required:
                raise ImpossibleSituation()

            if identifier in self.mappings:
                choices.pop(identifier, None)

        required_mappings: set[str] = set()

        for identifier in self.required:
            _mark_mappings(identifier, mapping_deps, required_mappings)

        for identifier in required_mappings:
            choices[identifier].required = True

        return choices


AnyInfoVar = t.TypeVar(
    'AnyInfoVar',
    item_infos.ResourceInfo,
    item_infos.MappingInfo
)

def _choose_newest(infos: t.Iterable[AnyInfoVar]) -> dict[str, AnyInfoVar]:
    best_versions: dict[str, AnyInfoVar] = {}

    for info in infos:
        other = best_versions.setdefault(info.identifier, info)

        if (other.version, other.repo, info.repo_iteration) < \
           (info.version, info.repo, other.repo_iteration):
            best_versions[info.identifier] = info

    return best_versions

def compute_payloads(
        resources:    t.Iterable[item_infos.ResourceInfo],
        mappings:     t.Iterable[item_infos.MappingInfo],
        requirements: t.Iterable[MappingRequirement]
) -> ComputedChoices:
    reqs_by_identifier = dict((req.identifier, req) for req in requirements)

    filtered_mappings = []

    for mapping_info in mappings:
        req = reqs_by_identifier.get(mapping_info.identifier)
        if req is not None and not req.is_fulfilled_by(mapping_info):
            continue

        filtered_mappings.append(mapping_info)

    best_resources = _choose_newest(resources)
    best_mappings  = _choose_newest(filtered_mappings)

    required = frozenset(reqs_by_identifier.keys())

    return _ComputationData(best_resources, best_mappings, required)\
        .compute_payloads()