# Copyright (C) 2012-2016  Codethink Limited
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.


import cliapp
import fs.osfs

import json
import logging
import os
import string
import sys
import tempfile
import urllib2
import urlparse
import urllib

import morphlib
from morphlib.util import word_join_list as _word_join_list


# urlparse.urljoin needs to know details of the URL scheme being used.
# It does not know about git:// by default, so we teach it here.
gitscheme = ['git']
urlparse.uses_relative.extend(gitscheme)
urlparse.uses_netloc.extend(gitscheme)
urlparse.uses_params.extend(gitscheme)
urlparse.uses_query.extend(gitscheme)
urlparse.uses_fragment.extend(gitscheme)


def quote_url(url):
    ''' Convert URIs to strings that only contain digits, letters, % and _.

    NOTE: When changing the code of this function, make sure to also apply
    the same to the quote_url() function of lorry. Otherwise the git tarballs
    generated by lorry may no longer be found by morph.

    '''
    valid_chars = string.digits + string.letters + '%_'
    transl = lambda x: x if x in valid_chars else '_'
    return ''.join([transl(x) for x in url])


class NoRemote(morphlib.Error):

    def __init__(self, reponame, errors):
        self.reponame = reponame
        self.errors = errors

    def __str__(self):
        return '\n\t'.join(['Cannot find remote git repository: %s' %
                            self.reponame] + self.errors)


class NotCached(morphlib.Error):
    def __init__(self, reponame):
        self.reponame = reponame

    def __str__(self):  # pragma: no cover
        return 'Repository %s is not cached yet' % self.reponame


class UpdateError(cliapp.AppException):  # pragma: no cover

    def __init__(self, repo):
        cliapp.AppException.__init__(
            self, 'Failed to update cached version of repo %s' % repo)


class CachedRepo(morphlib.gitdir.GitDirectory):
    '''A locally cached Git repository with an origin remote set up.

    On instance of this class represents a locally cached version of a
    remote Git repository. This remote repository is set up as the
    'origin' remote.

    Cached repositories are bare mirrors of the upstream.  Locally created
    branches will be lost the next time the repository updates.

    '''
    def __init__(self, path, original_name, url):
        self.original_name = original_name
        self.url = url
        self.is_mirror = not url.startswith('file://')
        self.already_updated = False

        super(CachedRepo, self).__init__(path)

    def __str__(self):  # pragma: no cover
        return self.url


class RepoCache(object):
    '''Manage a collection of Git repositories.

    When we build stuff, we need a local copy of the git repository.
    To avoid having to clone the repositories for every build, we
    maintain a local cache of the repositories: we first clone the
    remote repository to the cache, and then make a local clone from
    the cache to the build environment. This class manages the local
    cached repositories.

    Repositories may be specified either using a full URL, in a form
    understood by git(1), or as a repository name to which a base url
    is prepended. The base urls are given to the class when it is
    created.

    Instead of cloning via a normal 'git clone' directly from the
    git server, we first try to download a tarball from a url, and
    if that works, we unpack the tarball.

    Certain questions about a repo can be resolved without cloning the whole
    thing, if an instance of 'morph-cache-server' is available on the remote
    Git server. This makes calculating the build graph for the first time
    a whole lot faster, as we avoid cloning every repo locally. The
    git_resolve_cache_url parameter enables this feature. Baserock 'Trove'
    systems run 'morph-cache-server' by default.

    The 'custom_fs' parameter takes a PyFilesystem instance, which you can use
    to override where 'cachedir' is stored. This should probably only be used
    for testing.

    '''
    def __init__(self, cachedir, resolver, tarball_base_url=None,
                 git_resolve_cache_url=None,
                 update_gits=True,
                 runcmd_cb=cliapp.runcmd, status_cb=lambda **kwargs: None,
                 verbose=False, debug=False,
                 custom_fs=None):
        self.fs = custom_fs or fs.osfs.OSFS('/')

        self.fs.makedir(cachedir, recursive=True, allow_recreate=True)

        self.cachedir = cachedir
        self._resolver = resolver
        if tarball_base_url and not tarball_base_url.endswith('/'):
            tarball_base_url += '/'
        self._tarball_base_url = tarball_base_url
        self._cached_repo_objects = {}

        # Corresponds to the app 'no-git-update' setting
        self.update_gits = update_gits

        self.runcmd_cb = runcmd_cb
        self.status_cb = status_cb
        self.verbose = verbose
        self.debug = debug

        if git_resolve_cache_url:  # pragma: no cover
            self.remote_cache = RemoteRepoCache(git_resolve_cache_url,
                                                resolver)
        else:
            self.remote_cache = None

    def _git(self, args, **kwargs):  # pragma: no cover
        '''Execute git command.

        This is a method of its own so that unit tests can easily override
        all use of the external git command.

        '''

        morphlib.git.gitcmd(self.runcmd_cb, *args, **kwargs)

    def _fetch(self, url, path):  # pragma: no cover
        '''Fetch contents of url into a file.

        This method is meant to be overridden by unit tests.

        '''
        self.status_cb(msg="Trying to fetch %(tarball)s to seed the cache",
                       tarball=url, chatty=True)

        if self.verbose:
            verbosity_flags = []
            kwargs = dict(stderr=sys.stderr)
        else:
            verbosity_flags = ['--quiet']
            kwargs = dict()

        def wget_command():
            return ['wget'] + verbosity_flags + ['-O-', url]

        self.runcmd_cb(wget_command(),
                       ['tar', '--no-same-owner', '-xf', '-'],
                       cwd=path, **kwargs)

    def _mkdtemp(self, dirname):  # pragma: no cover
        '''Creates a temporary directory.

        This method is meant to be overridden by unit tests.

        '''
        return tempfile.mkdtemp(dir=self.fs.getsyspath(dirname))

    def _escape(self, url):
        '''Escape a URL so it can be used as a basename in a file.'''

        # FIXME: The following is a nicer way than to do this.
        # However, for compatibility, we need to use the same as the
        # tarball server (set up by Lorry) uses.
        # return urllib.quote(url, safe='')

        return quote_url(url)

    def _cache_name(self, url):
        scheme, netloc, path, query, fragment = urlparse.urlsplit(url)
        if scheme != 'file':
            path = os.path.join(self.cachedir, self._escape(url))
        return path

    def has_repo(self, reponame):
        '''Have we already got a cache of a given repo?'''
        url = self._resolver.pull_url(reponame)
        path = self._cache_name(url)
        return self.fs.exists(path)

    def _clone_with_tarball(self, repourl, path):
        tarball_url = urlparse.urljoin(self._tarball_base_url,
                                       self._escape(repourl)) + '.tar'
        try:
            self.fs.makedir(path)
            self._fetch(tarball_url, path)
            self._git(['config', 'remote.origin.url', repourl], cwd=path)
            self._git(['config', 'remote.origin.mirror', 'true'], cwd=path)
            self._git(['config', 'remote.origin.fetch', '+refs/*:refs/*'],
                      cwd=path)
        except BaseException as e:
            if self.fs.exists(path):
                self.fs.removedir(path, force=True)
            return False, 'Unable to extract tarball %s: %s' % (
                tarball_url, e)

        return True, None

    def _new_cached_repo_instance(self, path, reponame, repourl):
        return CachedRepo(path, reponame, repourl)

    def _cache_repo(self, reponame):
        '''Clone the given repo into the cache.

        If the repo is already cloned, do nothing.

        '''
        errors = []

        repourl = self._resolver.pull_url(reponame)
        path = self._cache_name(repourl)
        if self._tarball_base_url:
            ok, error = self._clone_with_tarball(repourl, path)
            if ok:
                repo = self._get_repo(reponame)
                self._update_repo(repo)
                return repo
            else:
                errors.append(error)
                self.status_cb(msg='Using git clone.')

        target = self._mkdtemp(self.cachedir)

        try:
            self._git(['clone', '--mirror', '-n', repourl, target],
                      echo_stderr=self.debug)
        except cliapp.AppException as e:
            errors.append('Unable to clone from %s to %s: %s' %
                          (repourl, target, e))
            if self.fs.exists(target):
                self.fs.removedir(target, force=True)
            raise NoRemote(reponame, errors)

        self.fs.rename(target, path)

        repo = self._new_cached_repo_instance(path, reponame, repourl)
        repo.already_updated = True
        return repo

    def _get_repo(self, reponame):
        '''Return an object representing a cached repository.'''

        if reponame in self._cached_repo_objects:
            return self._cached_repo_objects[reponame]
        else:
            repourl = self._resolver.pull_url(reponame)
            path = self._cache_name(repourl)
            if self.fs.exists(path):
                repo = self._new_cached_repo_instance(path, reponame, repourl)
                self._cached_repo_objects[reponame] = repo
                return repo
            elif self.update_gits:
                return self._cache_repo(reponame)
            else:
                raise NotCached(reponame)

    def _update_repo(self, cachedrepo):  # pragma: no cover
        try:
            cachedrepo.update_remotes(
                echo_stderr=self.verbose)
            cachedrepo.already_updated = True
        except cliapp.AppException:
            raise UpdateError(self)

    def get_updated_repo(self, repo_name,
                         ref=None, refs=None):
        '''Return object representing cached repository.

        If all the specified refs in 'ref' or 'refs' point to SHA1s that are
        already in the repository, or --no-git-update is set, then the
        repository won't be updated.

        '''

        if not self.update_gits:
            self.status_cb(msg='Not updating existing git repository '
                               '%(repo_name)s '
                               'because of no-git-update being set',
                           chatty=True,
                           repo_name=repo_name)
            return self._get_repo(repo_name)

        if ref is not None and refs is None:
            refs = (ref,)
        else:
            refs = list(refs)

        if self.has_repo(repo_name):
            repo = self._get_repo(repo_name)
            if refs:
                required_refs = set(refs)
                missing_refs = set()
                for required_ref in required_refs:  # pragma: no cover
                    if morphlib.git.is_valid_sha1(required_ref):
                        try:
                            repo.resolve_ref_to_commit(required_ref)
                            continue
                        except morphlib.gitdir.InvalidRefError:
                            pass
                    missing_refs.add(required_ref)

                if not missing_refs:  # pragma: no cover
                    self.status_cb(
                        msg='Not updating git repository %(repo_name)s '
                            'because it already contains %(sha1s)s',
                        chatty=True, repo_name=repo_name,
                        sha1s=_word_join_list(tuple(required_refs)))
                    return repo

            if ref:
                ref_str = 'ref %s' % ref
            else:
                ref_str = '%i refs' % len(refs)
            self.status_cb(msg='Updating %(repo_name)s for %(ref_str)s',
                           repo_name=repo_name, ref_str=ref_str)
            self._update_repo(repo)
            return repo
        else:
            self.status_cb(msg='Cloning %(repo_name)s', repo_name=repo_name)
            return self._get_repo(repo_name)

    def ensure_submodules(self, toplevel_repo,
                          toplevel_ref, submodules={}):  # pragma: no cover
        '''Ensure any submodules of a given repo are cached and up to date.'''

        def submodules_for_repo(repo_path, ref):
            try:
                submodules = morphlib.git.Submodules(repo_path, ref,
                                                     runcmd_cb=self.runcmd_cb)
                submodules.load()
                return [(submod.name, submod.url, submod.commit)
                            for submod in submodules]
            except morphlib.git.NoModulesFileError:
                return []

        done = set()
        subs_to_process = submodules_for_repo(toplevel_repo.dirname,
                                              toplevel_ref)
        while subs_to_process:
            name, url, ref = subs_to_process.pop()
            done.add((url, ref))
            if name in submodules:
                url = submodules[name]['url']

            cached_repo = self.get_updated_repo(url, ref=ref)

            for submod in submodules_for_repo(cached_repo.dirname, ref):
                if submod not in done:
                    subs_to_process.append(submod)

    def resolve_ref_to_commit_and_tree(self, repo_name,
            ref):  # pragma: no cover
        '''Given the name of a ref, returns the commit and tree SHA1.

        If a remote cache server is available, this function can query the
        remote cache server to avoid needing to clone the entire repo.

        This might break if the ref points to a tag, not a commit.

        '''
        absref = None
        tree = None

        if self.has_repo(repo_name):
            repo = self.get_updated_repo(repo_name, ref)
            # If the user passed --no-git-update, and the ref is a SHA1 not
            # available locally, this call will raise an exception.
            absref = repo.resolve_ref_to_commit(ref)
            tree = repo.resolve_ref_to_tree(absref)
        elif self.remote_cache is not None:
            try:
                absref, tree = self.remote_cache.resolve_ref(repo_name, ref)
                if absref is not None:
                    self.status_cb(
                        msg='Resolved %(repo_name)s %(ref)s via remote repo '
                            'cache', repo_name=repo_name, ref=ref, chatty=True)
            except BaseException as e:
                logging.warning('Caught (and ignored) exception: %s' % str(e))

        if absref is None:
            # As a last resort, clone the repo to resolve the ref.
            repo = self.get_updated_repo(repo_name, ref)
            absref = repo.resolve_ref_to_commit(ref)
            tree = repo.resolve_ref_to_tree(absref)

        return absref, tree

    def ls_tree(self, repo_name, ref):  # pragma: no cover
        '''Lists the files contained in a commit.

        If a remote cache server is available, this function can query the
        remote cache server to avoid needing to clone the entire repo.

        The list is non-recursive, so you can only see files in the top
        directory of the repo. To do a recursive operation, use a GitDir
        instance returned by get_updated_repo().

        '''
        files = []

        if self.has_repo(repo_name):
            repo = self.get_updated_repo(repo_name, ref)
            files = repo.list_files(ref=ref, recurse=False)
        elif self.remote_cache is not None:
            files = self.remote_cache.ls_tree(repo_name, ref)

        if len(files) == 0:
            # As a last resort, clone the repo to do get the file list.
            repo = self.get_updated_repo(repo_name, ref)
            files = repo.list_files(ref=ref, recurse=False)

        return files

    def cat_file(self, repo_name, ref, filename):  # pragma: no cover
        '''Returns a single file from a repo.

        If a remote cache server is available, this function can query the
        remote cache server to avoid needing to clone the entire repo.

        '''
        contents = None

        if self.has_repo(repo_name):
            repo = self.get_updated_repo(repo_name, ref)
            contents = repo.get_file_from_ref(ref, filename)
        elif self.remote_cache is not None:
            contents = self.remote_cache.cat_file(repo_name, ref, filename)

        if not contents:
            # As a last resort, clone the repo to do get the file list.
            repo = self.get_updated_repo(repo_name, ref)
            contents = repo.get_file_from_ref(ref, filename)

        return contents


class RemoteResolveRefError(cliapp.AppException):

    def __init__(self, repo_name, ref):
        cliapp.AppException.__init__(
            self, 'Failed to resolve ref %s for repo %s from remote cache' %
            (ref, repo_name))


class RemoteCatFileError(cliapp.AppException):

    def __init__(self, repo_name, ref, filename):
        cliapp.AppException.__init__(
            self, 'Failed to cat file %s in ref %s of repo %s, from remote '
                  'cache' % (filename, ref, repo_name))


class RemoteLsTreeError(cliapp.AppException):

    def __init__(self, repo_name, ref):
        cliapp.AppException.__init__(
            self, 'Failed to list tree in ref %s of repo %s, from remote'
                  'cache' % (ref, repo_name))


class RemoteRepoCache(object):

    def __init__(self, server_url, resolver):
        self.server_url = server_url
        self._resolver = resolver

    def resolve_ref(self, repo_name, ref):
        repo_url = self._resolver.pull_url(repo_name)
        try:
            return self._resolve_ref_for_repo_url(repo_url, ref)
        except BaseException as e:
            logging.error('Caught exception: %s' % str(e))
            raise RemoteResolveRefError(repo_name, ref)

    def cat_file(self, repo_name, ref, filename):
        repo_url = self._resolver.pull_url(repo_name)
        try:
            return self._cat_file_for_repo_url(repo_url, ref, filename)
        except urllib2.HTTPError as e:
            logging.error('Caught exception: %s' % str(e))
            if e.code == 404:
                raise RemoteCatFileError(repo_name, ref, filename)
            raise  # pragma: no cover

    def ls_tree(self, repo_name, ref):
        repo_url = self._resolver.pull_url(repo_name)
        try:
            info = json.loads(self._ls_tree_for_repo_url(repo_url, ref))
            return info['tree'].keys()
        except BaseException as e:
            logging.error('Caught exception: %s' % str(e))
            raise RemoteLsTreeError(repo_name, ref)

    def _resolve_ref_for_repo_url(self, repo_url, ref):  # pragma: no cover
        data = self._make_request(
            'sha1s?repo=%s&ref=%s' % self._quote_strings(repo_url, ref))
        info = json.loads(data)
        return info['sha1'], info['tree']

    def _cat_file_for_repo_url(self, repo_url, ref,
                               filename):  # pragma: no cover
        return self._make_request(
            'files?repo=%s&ref=%s&filename=%s'
            % self._quote_strings(repo_url, ref, filename))

    def _ls_tree_for_repo_url(self, repo_url, ref):  # pragma: no cover
        return self._make_request(
            'trees?repo=%s&ref=%s' % self._quote_strings(repo_url, ref))

    def _quote_strings(self, *args):  # pragma: no cover
        return tuple(urllib.quote(string) for string in args)

    def _make_request(self, path):  # pragma: no cover
        server_url = self.server_url
        if not server_url.endswith('/'):
            server_url += '/'
        url = urlparse.urljoin(server_url, '/1.0/%s' % path)
        handle = urllib2.urlopen(url)
        return handle.read()