# 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.

import optparse
import os.path
import subprocess
import sys

import fixtures

from openstack_requirements import requirement


def _parse_freeze(text):
    """Parse a freeze into structured data.

    :param text: The output from a pip freeze command.
    :return: A list of (package, version) tuples.
    """
    result = []
    for line in text.splitlines():
        line = line.strip()
        if line.startswith('-'):
            raise Exception("Irregular line: %s" % line)
        if line.startswith('#'):
            continue
        if not line:
            continue
        package, version = line.split('==')[:2]
        result.append((package, version))
    return result


def _freeze(requirements, python):
    """Generate a frozen install from requirements.

    A constraints file is the result of installing a set of requirements and
    then freezing the result. We currently special case pip and setuptools
    as pip does, excluding them from the set. We may however want to revisit
    this in future if releases of those things break our gate.

    In principle we should determine this by introspecting all the packages
    transitively, since we need to deal wit environment markers....
    but thats reimplementing a large chunk of pip (and since pip doesn't
    resolve yet, differently too). For now, we take a list of Python
    executables to test under, and then union the results. This is in fact the
    key difference between a constraints file and a requirements file: we're
    not triggering installation, so we can and will list packages that are
    not relevant to e.g. Python3.4 in the constraints output.

    :param requirements: The path to a requirements file to use when generating
        the constraints.
    :param python: A Python binary to use. E.g. /usr/bin/python3.4
    :return: A tuple (python_version, list of (package, version)'s)
    """
    output = []
    try:
        version_out = subprocess.check_output(
            [python, "--version"], stderr=subprocess.STDOUT)
        output.append(version_out)
        version_all = version_out.split()[1]
        version = '.'.join(version_all.split('.')[:2])
        with fixtures.TempDir() as temp:
            output.append(subprocess.check_output(
                ['virtualenv', '-p', python, temp.path]))
            pip_bin = os.path.join(temp.path, 'bin', 'pip')
            output.append(subprocess.check_output(
                [pip_bin, 'install', '-U', 'pip', 'setuptools', 'wheel']))
            output.append(subprocess.check_output(
                [pip_bin, 'install', '-r', requirements]))
            freeze = subprocess.check_output([pip_bin, 'freeze'])
            output.append(freeze)
            return (version, _parse_freeze(freeze))
    except Exception as exc:
        if isinstance(exc, subprocess.CalledProcessError):
            output.append(exc.output)
        raise Exception(
            "Failed to generate freeze: %s %s"
            % ('\n'.join(output), exc))


def _combine_freezes(freezes, blacklist=None):
    """Combine multiple freezes into a single structure.

    This deals with the variation between different python versions by
    generating environment markers when different pythons need different
    versions of a dependency.

    :param freezes: A list of (python_version, frozen_requirements) tuples.
    :param blacklist: An iterable of package names to exclude. These packages
        won't be included in the output.
    :return: A list of '\n' terminated lines for a requirements file.
    """
    packages = {}  # {package : {version : [py_version]}}
    excludes = frozenset((requirement.canonical_name(s)
                          for s in blacklist) if blacklist else ())
    reference_versions = []
    for py_version, freeze in freezes:
        if py_version in reference_versions:
            raise Exception("Duplicate python %s" % py_version)
        reference_versions.append(py_version)
        for package, version in freeze:
            packages.setdefault(
                package, {}).setdefault(version, []).append(py_version)

    for package, versions in sorted(packages.items()):
        if package.lower() in excludes:
            continue
        if len(versions) != 1 or versions.values()[0] != reference_versions:
            # markers
            for version, py_versions in sorted(versions.items()):
                # Once the ecosystem matures, we can consider using OR.
                for py_version in sorted(py_versions):
                    yield (
                        "%s===%s;python_version=='%s'\n" %
                        (package, version, py_version))
        else:
            # no markers
            yield '%s===%s\n' % (package, versions.keys()[0])


# -- untested UI glue from here down.

def _validate_options(options):
    """Check that options are valid.

    :param options: The optparse options for this program.
    """
    if not options.pythons:
        raise Exception("No Pythons given - see -p.")
    for python in options.pythons:
        if not os.path.exists(python):
            raise Exception(
                "Python %(python)s not found." % dict(python=python))
    if not options.requirements:
        raise Exception("No requirements file specified - see -r.")
    if not os.path.exists(options.requirements):
        raise Exception(
            "Requirements file %(req)s not found."
            % dict(req=options.requirements))
    if options.blacklist and not os.path.exists(options.blacklist):
        raise Exception(
            "Blacklist file %(path)s not found."
            % dict(path=options.blacklist))


def _parse_blacklist(path):
    """Return the strings from path if it is not None."""
    if path is None:
        return []
    with open(path, 'rt') as f:
        return [l.strip() for l in f]


def main(argv=None, stdout=None):
    parser = optparse.OptionParser()
    parser.add_option(
        "-p", dest="pythons", action="append",
        help="Specify Python versions to use when generating constraints."
             "e.g. -p /usr/bin/python3.4")
    parser.add_option(
        "-r", dest="requirements", help="Requirements file to process.")
    parser.add_option(
        "-b", dest="blacklist",
        help="Filename of a list of package names to exclude.")
    options, args = parser.parse_args(argv)
    if stdout is None:
        stdout = sys.stdout
    _validate_options(options)
    freezes = [
        _freeze(options.requirements, python) for python in options.pythons]
    blacklist = _parse_blacklist(options.blacklist)
    stdout.writelines(_combine_freezes(freezes, blacklist))
    stdout.flush()