#  Copyright 2022 The Matrix.org Foundation C.I.C.
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.
#

"""
This module exposes a single function which checks synapse's dependencies are present
and correctly versioned. It makes use of `importlib.metadata` to do so. The details
are a bit murky: there's no easy way to get a map from "extras" to the packages they
require. But this is probably just symptomatic of Python's package management.
"""

import logging
from typing import Iterable, NamedTuple, Optional

from packaging.requirements import Requirement

DISTRIBUTION_NAME = "matrix-synapse"

try:
    from importlib import metadata
except ImportError:
    import importlib_metadata as metadata  # type: ignore[no-redef]

__all__ = ["check_requirements"]


class DependencyException(Exception):
    @property
    def message(self) -> str:
        return "\n".join(
            [
                "Missing Requirements: %s" % (", ".join(self.dependencies),),
                "To install run:",
                "    pip install --upgrade --force %s" % (" ".join(self.dependencies),),
                "",
            ]
        )

    @property
    def dependencies(self) -> Iterable[str]:
        for i in self.args[0]:
            yield '"' + i + '"'


DEV_EXTRAS = {"lint", "mypy", "test", "dev"}
RUNTIME_EXTRAS = (
    set(metadata.metadata(DISTRIBUTION_NAME).get_all("Provides-Extra")) - DEV_EXTRAS
)
VERSION = metadata.version(DISTRIBUTION_NAME)


def _is_dev_dependency(req: Requirement) -> bool:
    return req.marker is not None and any(
        req.marker.evaluate({"extra": e}) for e in DEV_EXTRAS
    )


class Dependency(NamedTuple):
    requirement: Requirement
    must_be_installed: bool


def _generic_dependencies() -> Iterable[Dependency]:
    """Yield pairs (requirement, must_be_installed)."""
    requirements = metadata.requires(DISTRIBUTION_NAME)
    assert requirements is not None
    for raw_requirement in requirements:
        req = Requirement(raw_requirement)
        if _is_dev_dependency(req):
            continue

        # https://packaging.pypa.io/en/latest/markers.html#usage notes that
        #   > Evaluating an extra marker with no environment is an error
        # so we pass in a dummy empty extra value here.
        must_be_installed = req.marker is None or req.marker.evaluate({"extra": ""})
        yield Dependency(req, must_be_installed)


def _dependencies_for_extra(extra: str) -> Iterable[Dependency]:
    """Yield additional dependencies needed for a given `extra`."""
    requirements = metadata.requires(DISTRIBUTION_NAME)
    assert requirements is not None
    for raw_requirement in requirements:
        req = Requirement(raw_requirement)
        if _is_dev_dependency(req):
            continue
        # Exclude mandatory deps by only selecting deps needed with this extra.
        if (
            req.marker is not None
            and req.marker.evaluate({"extra": extra})
            and not req.marker.evaluate({"extra": ""})
        ):
            yield Dependency(req, True)


def _not_installed(requirement: Requirement, extra: Optional[str] = None) -> str:
    if extra:
        return (
            f"Synapse {VERSION} needs {requirement.name} for {extra}, "
            f"but it is not installed"
        )
    else:
        return f"Synapse {VERSION} needs {requirement.name}, but it is not installed"


def _incorrect_version(
    requirement: Requirement, got: str, extra: Optional[str] = None
) -> str:
    if extra:
        return (
            f"Synapse {VERSION} needs {requirement} for {extra}, "
            f"but got {requirement.name}=={got}"
        )
    else:
        return (
            f"Synapse {VERSION} needs {requirement}, but got {requirement.name}=={got}"
        )


def check_requirements(extra: Optional[str] = None) -> None:
    """Check Synapse's dependencies are present and correctly versioned.

    If provided, `extra` must be the name of an pacakging extra (e.g. "saml2" in
    `pip install matrix-synapse[saml2]`).

    If `extra` is None, this function checks that
    - all mandatory dependencies are installed and correctly versioned, and
    - each optional dependency that's installed is correctly versioned.

    If `extra` is not None, this function checks that
    - the dependencies needed for that extra are installed and correctly versioned.

    :raises DependencyException: if a dependency is missing or incorrectly versioned.
    :raises ValueError: if this extra does not exist.
    """
    # First work out which dependencies are required, and which are optional.
    if extra is None:
        dependencies = _generic_dependencies()
    elif extra in RUNTIME_EXTRAS:
        dependencies = _dependencies_for_extra(extra)
    else:
        raise ValueError(f"Synapse {VERSION} does not provide the feature '{extra}'")

    deps_unfulfilled = []
    errors = []

    for (requirement, must_be_installed) in dependencies:
        try:
            dist: metadata.Distribution = metadata.distribution(requirement.name)
        except metadata.PackageNotFoundError:
            if must_be_installed:
                deps_unfulfilled.append(requirement.name)
                errors.append(_not_installed(requirement, extra))
        else:
            if not requirement.specifier.contains(dist.version):
                deps_unfulfilled.append(requirement.name)
                errors.append(_incorrect_version(requirement, dist.version, extra))

    if deps_unfulfilled:
        for err in errors:
            logging.error(err)

        raise DependencyException(deps_unfulfilled)