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

from __future__ import print_function

import itertools
import os
import shutil
import time
from collections import namedtuple
from contextlib import contextmanager

import pkg_resources
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


@contextmanager
def patched_packing_env(env):
  """Monkey patch packaging.markers.default_environment"""
  old_env = pkg_resources.packaging.markers.default_environment
  new_env = lambda: env
  pkg_resources._vendor.packaging.markers.default_environment = new_env
  try:
    yield
  finally:
    pkg_resources._vendor.packaging.markers.default_environment = old_env


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, allow_prereleases=None):
    self._packages = packages
    self._allow_prereleases = allow_prereleases

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


class _ResolvedPackages(namedtuple('_ResolvedPackages',
                                   'resolvable packages parent constraint_only')):

  @classmethod
  def empty(cls):
    return cls(None, OrderedSet(), None, False)

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


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, resolvable.is_constraint))
    self._check()

  def get(self, name):
    """Get the set of compatible packages given a resolvable name."""
    resolvable, packages, parent, constraint_only = 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, resolved_packages.constraint_only)

    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

  def __init__(self, allow_prereleases=None, interpreter=None, platform=None,
               pkg_blacklist=None, use_manylinux=None):
    self._interpreter = interpreter or PythonInterpreter.get()
    self._platform = Platform.create(platform) if platform else Platform.current()
    self._allow_prereleases = allow_prereleases
    self._blacklist = pkg_blacklist.copy() if pkg_blacklist else {}
    self._supported_tags = self._platform.supported_tags(
      self._interpreter,
      use_manylinux
    )
    TRACER.log(
      'R: tags for %r x %r -> %s' % (self._platform, self._interpreter, self._supported_tags),
      V=9
    )

  def filter_packages_by_supported_tags(self, packages, supported_tags=None):
    return [
      package for package in packages
      if package.compatible(supported_tags or self._supported_tags)
    ]

  def package_iterator(self, resolvable, existing=None):
    if existing:
      existing = resolvable.compatible(
        StaticIterator(existing, allow_prereleases=self._allow_prereleases))
    else:
      existing = resolvable.packages()
    return self.filter_packages_by_supported_tags(existing)

  def build(self, package, options):
    context = options.get_context()
    translator = options.get_translator(self._interpreter, self._supported_tags)
    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._supported_tags):
      raise Untranslateable(
        'Could not get distribution for %s on platform %s.' % (package, self._platform))
    return dist

  def _resolvable_is_blacklisted(self, resolvable_name):
    return (
      resolvable_name in self._blacklist and
      self._interpreter.identity.matches(self._blacklist[resolvable_name])
    )

  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))

        # TODO: Remove blacklist strategy in favor of smart requirement handling
        # https://github.com/pantsbuild/pex/issues/456
        if not self._resolvable_is_blacklisted(resolvable.name):
          resolvable_set.merge(resolvable, packages, parent)
        processed_resolvables.add(resolvable)

      built_packages = {}
      for resolvable, packages, parent, constraint_only in resolvable_set.packages():
        if constraint_only:
          continue
        assert len(packages) > 0, 'ResolvableSet.packages(%s) should not be empty' % resolvable
        package = next(iter(packages))
        if resolvable.name in processed_packages:
          if package == processed_packages[resolvable.name]:
            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)
        # We patch packaging.markers.default_environment here so we find optional reqs for the
        # platform we're building the PEX for, rather than the one we're on.
        with patched_packing_env(self._interpreter.identity.pkg_resources_env(self._platform)):
          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)

    # We may have built multiple distributions depending upon if we found transitive dependencies
    # for the same package. But ultimately, resolvable_set.packages() contains the correct version
    # for all packages. So loop through it and only return the package version in
    # resolvable_set.packages() that is found in distributions.
    dists = []
    # No point in proceeding if distributions is empty
    if not distributions:
      return dists

    for resolvable, packages, parent, constraint_only in resolvable_set.packages():
      if constraint_only:
        continue
      assert len(packages) > 0, 'ResolvableSet.packages(%s) should not be empty' % resolvable
      package = next(iter(packages))
      dists.append(distributions[package])
    return dists


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])],
                        allow_prereleases=self._allow_prereleases)
    packages = self.filter_packages_by_supported_tags(resolvable.compatible(iterator))

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

    return itertools.chain(
      packages,
      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 platform_to_tags(platform, interpreter):
  """Splits a "platform" like linux_x86_64-36-cp-cp36m into its components.

  If a simple platform without hyphens is specified, we will fall back to using
  the current interpreter's tags.
  """
  if platform.count('-') >= 3:
    tags = platform.rsplit('-', 3)
  else:
    tags = [platform, interpreter.identity.impl_ver,
            interpreter.identity.abbr_impl, interpreter.identity.abi_tag]
  tags[0] = tags[0].replace('.', '_').replace('-', '_')
  return tags


def resolve(requirements,
            fetchers=None,
            interpreter=None,
            platform=None,
            context=None,
            precedence=None,
            cache=None,
            cache_ttl=None,
            allow_prereleases=None,
            pkg_blacklist=None,
            use_manylinux=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 versions: (optional) a list of string versions, of the form ["33", "32"],
    or None. The first version will be assumed to support our ABI.
  :keyword platform: (optional) specify the exact platform you want valid
    tags for, or None. If None, use the local system platform.
  :keyword impl: (optional) specify the exact implementation you want valid
    tags for, or None. If None, use the local interpreter impl.
  :keyword abi: (optional) specify the exact abi you want valid
    tags for, or None. If None, use the local interpreter abi.
  :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.
  :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``.
  :keyword allow_prereleases: (optional) Include pre-release and development versions.  If
    unspecified only stable versions will be resolved, unless explicitly included.
  :keyword pkg_blacklist: (optional) A blacklist dict (str->str) that maps package name to
    an interpreter constraint. If a package name is in the blacklist and its interpreter
    constraint matches the target interpreter, skip the requirement. This is needed to ensure
    that universal requirement resolves for a target interpreter version do not error out on
    interpreter specific requirements such as backport libs like `functools32`.
    For example, a valid blacklist is {'functools32': 'CPython>3'}.
    NOTE: this keyword is a temporary fix and will be reverted in favor of a long term solution
    tracked by: https://github.com/pantsbuild/pex/issues/456
  :keyword use_manylinux: (optional) Whether or not to use manylinux for linux resolves.
  :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,
                                   allow_prereleases=allow_prereleases,
                                   use_manylinux=use_manylinux,
                                   precedence=precedence,
                                   context=context)

  if cache:
    resolver = CachingResolver(cache,
                               cache_ttl,
                               allow_prereleases=allow_prereleases,
                               use_manylinux=use_manylinux,