from typing import TYPE_CHECKING
from typing import Optional
from typing import Union

from poetry.core.semver.version import Version


if TYPE_CHECKING:
    from poetry.core.packages.package import Package
    from poetry.repositories import Pool


class VersionSelector:
    def __init__(self, pool: "Pool") -> None:
        self._pool = pool

    def find_best_candidate(
        self,
        package_name: str,
        target_package_version: Optional[str] = None,
        allow_prereleases: bool = False,
        source: Optional[str] = None,
    ) -> Union["Package", bool]:
        """
        Given a package name and optional version,
        returns the latest Package that matches
        """
        from poetry.factory import Factory

        dependency = Factory.create_dependency(
            package_name,
            {
                "version": target_package_version or "*",
                "allow_prereleases": allow_prereleases,
                "source": source,
            },
        )
        candidates = self._pool.find_packages(dependency)
        only_prereleases = all([c.version.is_unstable() for c in candidates])

        if not candidates:
            return False

        package = None
        for candidate in candidates:
            if (
                candidate.is_prerelease()
                and not dependency.allows_prereleases()
                and not only_prereleases
            ):
                continue

            # Select highest version of the two
            if package is None or package.version < candidate.version:
                package = candidate

        if package is None:
            return False
        return package

    def find_recommended_require_version(self, package: "Package") -> str:
        version = package.version

        return self._transform_version(version.text, package.pretty_version)

    def _transform_version(self, version: str, pretty_version: str) -> str:
        try:
            return f"^{Version.parse(version).to_string()}"
        except ValueError:
            return pretty_version
