# Source code for pex.resolver

    # Copyright 2014 Pants project contributors (see CONTRIBUTORS.md).
    # Licensed under the Apache License, Version 2.0 (see LICENSE).

    from __future__ import print_function

    import os
    import shutil
    import time
    from collections import namedtuple

    from pkg_resources import safe_name

    from .common import safe_mkdir
    from .fetcher import Fetcher
    from .interpreter import PythonInterpreter
    from .iterator import Iterator, IteratorInterface
    from .orderedset import OrderedSet
    from .package import Package, distribution_compatible
    from .platforms import Platform
    from .resolvable import ResolvableRequirement, resolvables_from_iterable
    from .resolver_options import ResolverOptionsBuilder
    from .tracer import TRACER
    from .util import DistributionHelper

    class Untranslateable(Exception):
      pass

    class Unsatisfiable(Exception):
      pass

    class StaticIterator(IteratorInterface):
      """An iterator that iterates over a static list of packages."""

      def __init__(self, packages):
        self._packages = packages

      def iter(self, req):
        for package in self._packages:
          if package.satisfies(req):
            yield package

    class _ResolvedPackages(namedtuple('_ResolvedPackages', 'resolvable packages parent')):
      @classmethod
      def empty(cls):
        return cls(None, OrderedSet(), None)

      def merge(self, other):
        if other.resolvable is None:
          return _ResolvedPackages(self.resolvable, self.packages, self.parent)
        return _ResolvedPackages(
            self.resolvable,
            self.packages & other.packages,
            self.parent)

    class _ResolvableSet(object):
      @classmethod
      def normalize(cls, name):
        return safe_name(name).lower()

      def __init__(self, tuples=None):
        # A list of _ResolvedPackages
        self.__tuples = tuples or []

      def _collapse(self):
        # Collapse all resolvables by name along with the intersection of all compatible packages.
        # If the set of compatible packages is the empty set, then we cannot satisfy all the
        # specifications for a particular name (e.g. "setuptools==2.2 setuptools>4".)
        #
        # We need to return the resolvable since it carries its own network context and configuration
        # regarding package precedence.  This is arbitrary -- we could just as easily say "last
        # resolvable wins" but it seems highly unlikely this will materially affect anybody
        # adversely but could be the source of subtle resolution quirks.
        resolvables = {}
        for resolved_packages in self.__tuples:
          key = self.normalize(resolved_packages.resolvable.name)
          previous = resolvables.get(key, _ResolvedPackages.empty())
          if previous.resolvable is None:
            resolvables[key] = resolved_packages
          else:
            resolvables[key] = previous.merge(resolved_packages)
        return resolvables

      def _synthesize_parents(self, name):
        def render_resolvable(resolved_packages):
          return '%s%s' % (
              str(resolved_packages.resolvable),
              '(from: %s)' % resolved_packages.parent if resolved_packages.parent else '')
        return ', '.join(
            render_resolvable(resolved_packages) for resolved_packages in self.__tuples
            if self.normalize(resolved_packages.resolvable.name) == self.normalize(name))

      def _check(self):
        # Check whether or not the resolvables in this set are satisfiable, raise an exception if not.
        for name, resolved_packages in self._collapse().items():
          if not resolved_packages.packages:
            raise Unsatisfiable('Could not satisfy all requirements for %s:\n    %s' % (
                resolved_packages.resolvable, self._synthesize_parents(name)))

      def merge(self, resolvable, packages, parent=None):
        """Add a resolvable and its resolved packages."""
        self.__tuples.append(_ResolvedPackages(resolvable, OrderedSet(packages), parent))
        self._check()

      def get(self, name):
        """Get the set of compatible packages given a resolvable name."""
        resolvable, packages, parent = self._collapse().get(
            self.normalize(name), _ResolvedPackages.empty())
        return packages

      def packages(self):
        """Return a snapshot of resolvable => compatible packages set from the resolvable set."""
        return list(self._collapse().values())

      def extras(self, name):
        return set.union(
            *[set(tup.resolvable.extras()) for tup in self.__tuples
              if self.normalize(tup.resolvable.name) == self.normalize(name)])

      def replace_built(self, built_packages):
        """Return a copy of this resolvable set but with built packages.

        :param dict built_packages: A mapping from a resolved package to its locally built package.
        :returns: A new resolvable set with built package replacements made.
        """
        def map_packages(resolved_packages):
          packages = OrderedSet(built_packages.get(p, p) for p in resolved_packages.packages)
          return _ResolvedPackages(resolved_packages.resolvable, packages, resolved_packages.parent)

        return _ResolvableSet([map_packages(rp) for rp in self.__tuples])

    class Resolver(object):
      """Interface for resolving resolvable entities into python packages."""

      class Error(Exception): pass

      @classmethod
      def filter_packages_by_interpreter(cls, packages, interpreter, platform):
        return [package for package in packages
            if package.compatible(interpreter.identity, platform)]

      def __init__(self, interpreter=None, platform=None):
        self._interpreter = interpreter or PythonInterpreter.get()
        self._platform = platform or Platform.current()

      def package_iterator(self, resolvable, existing=None):
        if existing:
          existing = resolvable.compatible(StaticIterator(existing))
        else:
          existing = resolvable.packages()
        return self.filter_packages_by_interpreter(existing, self._interpreter, self._platform)

      def build(self, package, options):
        context = options.get_context()
        translator = options.get_translator(self._interpreter, self._platform)
        with TRACER.timed('Fetching %s' % package.url, V=2):
          local_package = Package.from_href(context.fetch(package))
        if local_package is None:
          raise Untranslateable('Could not fetch package %s' % package)
        with TRACER.timed('Translating %s into distribution' % local_package.local_path, V=2):
          dist = translator.translate(local_package)
        if dist is None:
          raise Untranslateable('Package %s is not translateable by %s' % (package, translator))
        if not distribution_compatible(dist, self._interpreter, self._platform):
          raise Untranslateable(
            'Could not get distribution for %s on platform %s.' % (package, self._platform))
        return dist

      def resolve(self, resolvables, resolvable_set=None):
        resolvables = [(resolvable, None) for resolvable in resolvables]
        resolvable_set = resolvable_set or _ResolvableSet()
        processed_resolvables = set()
        processed_packages = {}
        distributions = {}

        while resolvables:
          while resolvables:
            resolvable, parent = resolvables.pop(0)
            if resolvable in processed_resolvables:
              continue
            packages = self.package_iterator(resolvable, existing=resolvable_set.get(resolvable.name))
            resolvable_set.merge(resolvable, packages, parent)
            processed_resolvables.add(resolvable)

          built_packages = {}
          for resolvable, packages, parent in resolvable_set.packages():
            assert len(packages) > 0, 'ResolvableSet.packages(%s) should not be empty' % resolvable
            package = next(iter(packages))
            if resolvable.name in processed_packages:
              # TODO implement backtracking?
              if package != processed_packages[resolvable.name]:
                raise self.Error('Ambiguous resolvable: %s' % resolvable)
              continue
            if package not in distributions:
              dist = self.build(package, resolvable.options)
              built_package = Package.from_href(dist.location)
              built_packages[package] = built_package
              distributions[built_package] = dist
              package = built_package

            distribution = distributions[package]
            processed_packages[resolvable.name] = package
            new_parent = '%s->%s' % (parent, resolvable) if parent else str(resolvable)
            resolvables.extend(
                (ResolvableRequirement(req, resolvable.options), new_parent) for req in
                distribution.requires(extras=resolvable_set.extras(resolvable.name)))
          resolvable_set = resolvable_set.replace_built(built_packages)

        return list(distributions.values())

    class CachingResolver(Resolver):
      """A package resolver implementing a package cache."""

      @classmethod
      def filter_packages_by_ttl(cls, packages, ttl, now=None):
        now = now if now is not None else time.time()
        return [package for package in packages
            if package.remote or package.local and (now - os.path.getmtime(package.local_path)) < ttl]

      def __init__(self, cache, cache_ttl, *args, **kw):
        self.__cache = cache
        self.__cache_ttl = cache_ttl
        safe_mkdir(self.__cache)
        super(CachingResolver, self).__init__(*args, **kw)

      # Short-circuiting package iterator.
      def package_iterator(self, resolvable, existing=None):
        iterator = Iterator(fetchers=[Fetcher([self.__cache])])
        packages = self.filter_packages_by_interpreter(
            resolvable.compatible(iterator), self._interpreter, self._platform)

        if packages:
          if resolvable.exact:
            return packages

          if self.__cache_ttl:
            packages = self.filter_packages_by_ttl(packages, self.__cache_ttl)
            if packages:
              return packages

        return super(CachingResolver, self).package_iterator(resolvable, existing=existing)

      # Caching sandwich.
      def build(self, package, options):
        # cache package locally
        if package.remote:
          package = Package.from_href(options.get_context().fetch(package, into=self.__cache))
          os.utime(package.local_path, None)

        # build into distribution
        dist = super(CachingResolver, self).build(package, options)

        # if distribution is not in cache, copy
        target = os.path.join(self.__cache, os.path.basename(dist.location))
        if not os.path.exists(target):
          shutil.copyfile(dist.location, target + '~')
          os.rename(target + '~', target)
        os.utime(target, None)

        return DistributionHelper.distribution_from_path(target)

    def resolve(
        requirements,
        fetchers=None,
        interpreter=None,
        platform=None,
        context=None,
        precedence=None,
        cache=None,
        cache_ttl=None):

      """Produce all distributions needed to (recursively) meet `requirements`

      :param requirements: An iterator of Requirement-like things, either
        :class:`pkg_resources.Requirement` objects or requirement strings.
      :keyword fetchers: (optional) A list of :class:`Fetcher` objects for locating packages.  If
        unspecified, the default is to look for packages on PyPI.
      :keyword interpreter: (optional) A :class:`PythonInterpreter` object to use for building
        distributions and for testing distribution compatibility.
      :keyword platform: (optional) A PEP425-compatible platform string to use for filtering
        compatible distributions.  If unspecified, the current platform is used, as determined by
        `Platform.current()`.
      :keyword context: (optional) A :class:`Context` object to use for network access.  If
        unspecified, the resolver will attempt to use the best available network context.
      :type threads: int
      :keyword precedence: (optional) An ordered list of allowable :class:`Package` classes
        to be used for producing distributions.  For example, if precedence is supplied as
        ``(WheelPackage, SourcePackage)``, wheels will be preferred over building from source, and
        eggs will not be used at all.  If ``(WheelPackage, EggPackage)`` is suppplied, both wheels and
        eggs will be used, but the resolver will not resort to building anything from source.
      :keyword cache: (optional) A directory to use to cache distributions locally.
      :keyword cache_ttl: (optional integer in seconds) If specified, consider non-exact matches when
        resolving requirements.  For example, if ``setuptools==2.2`` is specified and setuptools 2.2 is
        available in the cache, it will always be used.  However, if a non-exact requirement such as
        ``setuptools>=2,<3`` is specified and there exists a setuptools distribution newer than
        cache_ttl seconds that satisfies the requirement, then it will be used.  If the distribution
        is older than cache_ttl seconds, it will be ignored.  If ``cache_ttl`` is not specified,
        resolving inexact requirements will always result in making network calls through the
        ``context``.
      :returns: List of :class:`pkg_resources.Distribution` instances meeting ``requirements``.
      :raises Unsatisfiable: If ``requirements`` is not transitively satisfiable.
      :raises Untranslateable: If no compatible distributions could be acquired for
        a particular requirement.

      This method improves upon the setuptools dependency resolution algorithm by maintaining sets of
      all compatible distributions encountered for each requirement rather than the single best
      distribution encountered for each requirement.  This prevents situations where ``tornado`` and
      ``tornado==2.0`` could be treated as incompatible with each other because the "best
      distribution" when encountering ``tornado`` was tornado 3.0.  Instead, ``resolve`` maintains the
      set of compatible distributions for each requirement as it is encountered, and iteratively filters
      the set.  If the set of distributions ever becomes empty, then ``Unsatisfiable`` is raised.

      .. versionchanged:: 0.8
        A number of keywords were added to make requirement resolution slightly easier to configure.
        The optional ``obtainer`` keyword was replaced by ``fetchers``, ``translator``, ``context``,
        ``threads``, ``precedence``, ``cache`` and ``cache_ttl``, also all optional keywords.

      .. versionchanged:: 1.0
        The ``translator`` and ``threads`` keywords have been removed.  The choice of threading
        policy is now implicit.  The choice of translation policy is dictated by ``precedence``
        directly.

      .. versionchanged:: 1.0
        ``resolver`` is now just a wrapper around the :class:`Resolver` and :class:`CachingResolver`
        classes.
      """

      builder = ResolverOptionsBuilder(
          fetchers=fetchers,
          precedence=precedence,
          context=context,
      )

      if cache:
        resolver = CachingResolver(cache, cache_ttl, interpreter=interpreter, platform=platform)
      else:
        resolver = Resolver(interpreter=interpreter, platform=platform)

      return resolver.resolve(resolvables_from_iterable(requirements, builder))