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]


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 + '"'


EXTRAS = set(metadata.metadata(DISTRIBUTION_NAME).get_all("Provides-Extra"))


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)
        # 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)
        # 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"Need {requirement.name} for {extra}, but it is not installed"
    else:
        return f"Need {requirement.name}, but it is not installed"


def _incorrect_version(
    requirement: Requirement, got: str, extra: Optional[str] = None
) -> str:
    if extra:
        return f"Need {requirement} for {extra}, but got {requirement.name}=={got}"
    else:
        return f"Need {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 EXTRAS:
        dependencies = _dependencies_for_extra(extra)
    else:
        raise ValueError(f"Synapse 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)