# Copyright 2016 The LUCI Authors. All rights reserved.
# Use of this source code is governed under the Apache License, Version 2.0
# that can be found in the LICENSE file.

import calendar
import httplib
import json
import logging
import os
import re
import shutil
import sys
import tarfile
import time

from cStringIO import StringIO
from collections import namedtuple

from . import package_pb2
from . import package_io
from . import util

# Add third party paths.
from . import env
from . import requests_ssl
from .requests_ssl import requests

import subprocess42
from google.protobuf import json_format

LOGGER = logging.getLogger(__name__)


def has_interesting_changes(spec, changed_files):
  # TODO(iannucci): analyze bundle_extra_paths.txt  too.
  return (
    'infra/config/recipes.cfg' in changed_files or
    any(f.startswith(spec.recipes_path) for f in changed_files)
  )


class FetchError(Exception):
  pass


class FetchNotAllowedError(FetchError):
  pass


class UnresolvedRefspec(Exception):
  pass


# revision (str): the revision of this commit (i.e. hash)
# author_email (str|None): the email of the author of this commit
# commit_timestamp (int): the unix commit timestamp for this commit
# message_lines (tuple(str)): the message of this commit
# spec (package_pb2.Package): the parsed infra/config/recipes.cfg file or None.
# roll_candidate (bool): if this commit contains changes which are known to
#   affect the behavior of the recipes (i.e. modifications within recipe_path
#   and/or modifications to recipes.cfg)
CommitMetadata = namedtuple(
  '_CommitMetadata',
  'revision author_email commit_timestamp message_lines spec roll_candidate')


class Backend(object):
  @staticmethod
  def class_for_type(repo_type):
    """
    Args:
      repo_type (package_pb2.DepSpec.RepoType)

    Returns Backend (class): Returns the Backend appropriate for the
      repo_type.
    """
    return {
      package_pb2.DepSpec.GIT:     GitBackend,
      package_pb2.DepSpec.GITILES: GitilesBackend,
    }[repo_type]

  def __init__(self, checkout_dir, repo_url, allow_network):
    """
    Args:
      checkout_dir (str): native absolute path to local directory that this
        Backend will manage.
      repo_url (str): url to remote repository that this Backend will connect
        to.
      allow_network (bool): Indicates that this Backend is permitted to make
        network operations.
    """
    self.checkout_dir = checkout_dir
    self.repo_url = repo_url

    self._allow_network = allow_network

  ### shared public implementations, do not override

  def assert_remote(self, opname):
    """This is a helper for Backend objects to use to check if network
    operations are allowed and raise FetchNotAllowedError if not.

    Example:
      self.assert_remote('fetch')
      self._do_real_fetch(...)

    Args:
      opname (str) - human-recognizable operation name for exception.
    """
    if not self._allow_network:
      raise FetchNotAllowedError('remote operation %r on %s' %
                                 (opname, self.repo_url,))


  # This is a simple mapping of
  #   repo_url -> git_revision -> commit_metadata()
  # It only holds cache entries for git commits (e.g. sha1 hashes)
  _GIT_METADATA_CACHE = {}

  # This matches git commit hashes.
  _COMMIT_RE = re.compile(r'^[a-fA-F0-9]{40}$')

  def commit_metadata(self, refspec):
    """Cached version of _commit_metadata_impl.

    The refspec will be resolved if it's not absolute.

    Returns (CommitMetadata).
    """
    revision = self.resolve_refspec(refspec)
    cache = self._GIT_METADATA_CACHE.setdefault(self.repo_url, {})
    if revision not in cache:
      cache[revision] = self._commit_metadata_impl(revision)
    return cache[revision]

  @classmethod
  def is_resolved_revision(cls, revision):
    return cls._COMMIT_RE.match(revision)

  @classmethod
  def assert_resolved(cls, revision):
    if not cls.is_resolved_revision(revision):
      raise UnresolvedRefspec('unresolved refspec %r' % revision)

  def resolve_refspec(self, refspec):
    if self.is_resolved_revision(refspec):
      return refspec
    return self._resolve_refspec_impl(refspec)

  def updates(self, revision, other_revision):
    """Returns a list of revisions |revision| through |other_revision|
    (inclusive).

    Returns list(CommitMetadata) - The commit metadata in the range
      (revision,other_revision].
    """
    self.assert_resolved(revision)
    self.assert_resolved(other_revision)
    return self._updates_impl(revision, other_revision)

  ### direct overrides. These are public methods which must be overridden.

  @property
  def repo_type(self):
    """Returns package_pb2.DepSpec.RepoType."""
    raise NotImplementedError()

  def fetch(self, refspec):
    """Does a fetch for the provided refspec (e.g. get all data from remote), if
    this backend supports it. Otherwise does nothing.

    Args:
      refspec (str) - a git refspec which is resolvable on the
        remote git repo, e.g. 'refs/heads/master', 'deadbeef...face', etc.
    """
    raise NotImplementedError()

  def checkout(self, refspec):
    """Checks out given |repo| at |refspec| to |checkout_dir|.

    Args:
      refspec (str) - a git refspec which is resolvable on the
        remote git repo, e.g. 'refs/heads/master', 'deadbeef...face', etc.
    """
    # TODO(iannucci): Alter the contract for this method so that it only checks
    # out the files referred to according to the rules that the bundle
    # subcommand uses.
    raise NotImplementedError()

  ### private overrides. Override these in the implementations, but don't call
  ### externally.

  def _updates_impl(self, revision, other_revision):
    """Returns a list of revisions |revision| through |other_revision|. This
    includes |revision| and |other_revision|.

    Args:
      revision (str) - the first git commit
      other_revision (str) - the second git commit

    Returns list(CommitMetadata) - The commit metadata in the range
      [revision,other_revision].
    """
    raise NotImplementedError()

  def _resolve_refspec_impl(self, refspec):
    """Resolves the refspec to it's current REMOTE value.

    This must resolve to the remote value even when using a local clone (i.e.
    GitBackend).

    Args:
      refspec (str) - a git refspec which is resolvable on the
        remote git repo, e.g. 'refs/heads/master', 'deadbeef...face', etc.

    Returns (str) - The git commit for the given refspec.
    """
    raise NotImplementedError()

  def _commit_metadata_impl(self, revision):
    """Returns CommitMetadata for commit |revision|."""
    raise NotImplementedError()


class GitError(FetchError):
  pass


class GitBackend(Backend):
  """GitBackend uses a local git checkout."""

  if sys.platform.startswith(('win', 'cygwin')):
    _GIT_BINARY = 'git.bat'
  else:
    _GIT_BINARY = 'git'

  def __init__(self, *args, **kwargs):
    super(GitBackend, self).__init__(*args, **kwargs)
    self._did_ensure = False

  def _git(self, *args):
    """Runs a git command.

    Will automatically set low speed limit/time, and cd into the checkout_dir.

    Args:
      *args (str) - The list of command arguments to pass to git.

    Raises GitError on failure.
    """
    if self._GIT_BINARY.endswith('.bat'):
      # On the esteemed Windows Operating System, '^' is an escape character.
      # Since .bat files are running cmd.exe under the hood, they interpret this
      # escape character. We need to ultimately get a single ^, so we need two
      # ^'s for when we invoke the .bat, and each of those needs to be escaped
      # when the bat ultimately invokes the git.exe binary. This leaves us with
      # a total of 4x the ^'s that we originally wanted. Hooray.
      args = [a.replace('^', '^^^^') for a in args]

    cmd = [
      self._GIT_BINARY,
      '-C', self.checkout_dir,
    ] + list(args)

    try:
      return self._execute(*cmd)
    except subprocess42.CalledProcessError as e:
      subcommand = (args[0]) if args else ('')
      raise GitError('Git "%s" failed: %s' % (subcommand, e.message,))

  def _execute(self, *args):
    """Runs a raw command. Separate so it's easily mockable."""
    LOGGER.info('Running: %s', args)
    return subprocess42.check_output(args)

  def _ensure_local_repo_exists(self):
    """Ensures that self.checkout_dir is a valid git repository. Safe to call
    multiple times. If this is sucessful, the GitBackend will not try to
    re-initialize the checkout_dir again.

    Raises GitError if it detected that checkout_dir is likely not a valid git
    repo.
    """
    if self._did_ensure:
      return
    if not os.path.isdir(os.path.join(self.checkout_dir, '.git')):
      try:
        # note that it's safe to re-init an existing git repo. This should allow
        # us to switch between GitilesBackend and GitBackend.
        self._execute(self._GIT_BINARY, 'init', self.checkout_dir)
        self._did_ensure = True
      except subprocess42.CalledProcessError as e:
        raise GitError(False, 'Git "init" failed: '+e.message)

  def _has_rev(self, revision):
    """Returns True iff the on-disk repo has the given revision."""
    self.assert_resolved(revision)
    try:
      # use commit_metadata since it's cached and we're likely to call it
      # shortly after _has_rev anyway.
      self.commit_metadata(revision)
      return True
    except GitError:
      return False


  ### Backend implementations


  @property
  def repo_type(self):
    return package_pb2.DepSpec.GIT

  def fetch(self, refspec):
    self._ensure_local_repo_exists()

    args = ['fetch', self.repo_url]
    if not self.is_resolved_revision(refspec):
      args.append(refspec)

    self.assert_remote('fetch')
    self._git(*args)

  def checkout(self, refspec):
    revision = self.resolve_refspec(refspec)

    LOGGER.info('Checking out %r in %s (%s)',
                revision, self.checkout_dir, self.repo_url)
    self._ensure_local_repo_exists()

    if not self._has_rev(revision):
      self.fetch(refspec)

    # reset touches index.lock which is problematic when multiple processes are
    # accessing the recipes at the same time. To allieviate this, we do a quick
    # diff, which will exit if `revision` is not already checked out.
    try:
      self._git('diff', '--quiet', revision)
    except GitError:
      self._git('reset', '-q', '--hard', revision)

  def _updates_impl(self, revision, other_revision):
    args = [
        'rev-list',
        '--reverse',
        '--topo-order',
        '%s..%s' % (revision, other_revision),
    ]
    return [
      self.commit_metadata(rev)
      for rev in self._git(*args).strip().split('\n')
      if bool(rev)
    ]

  def _resolve_refspec_impl(self, revision):
    self._ensure_local_repo_exists()
    self.assert_remote('resolve refspec %r' % revision)
    rslt = self._git('ls-remote', self.repo_url, revision).split()[0]
    assert self.is_resolved_revision(rslt), repr(rslt)
    return rslt

  def _commit_metadata_impl(self, revision):
    self.assert_resolved(revision)

    # show
    #   %`author Email`
    #   %`newline`
    #   %`commit time`
    #   %`newline`
    #   %`Body`
    meta = self._git(
      'show', '-s', '--format=%aE%n%ct%n%B', revision).rstrip('\n').splitlines()

    try:
      spec = package_io.parse(self._git(
        'cat-file', 'blob', '%s:infra/config/recipes.cfg' % revision))
    except GitError:
      spec = None

    # check diff to see if it touches anything interesting.
    changed_files = set(self._git(
      'diff-tree', '-r', '--no-commit-id', '--name-only', '%s^!' % revision)
      .splitlines())

    return CommitMetadata(revision, meta[0],
                          int(meta[1]), tuple(meta[2:]),
                          spec, has_interesting_changes(spec, changed_files))

class GitilesFetchError(FetchError):
  """An HTTP error that occurred during Gitiles fetching."""

  def __init__(self, status, message):
    super(GitilesFetchError, self).__init__(
        'Gitiles error code (%d): %s' % (status, message))
    self.status = status
    self.message = message

  @staticmethod
  def transient(e):
    """
    Returns (bool): True if "e" is a GitilesFetchError with transient HTTP code.
    """
    return (isinstance(e, GitilesFetchError) and
            e.status >= httplib.INTERNAL_SERVER_ERROR)


# Internal cache object for GitilesBackend.
# commit (str) - the git commit hash
# author_email (str) - the author email for this commit
# message_lines (tuple) - the lines of the commit message
# changed_files (frozenset) - all paths touched by this commit
class _GitilesCommitJson(namedtuple(
    '_GitilesCommitJson',
    'commit author_email commit_timestamp message_lines changed_files')):
  @classmethod
  def from_raw_json(cls, raw):
    mod_files = set()
    for entry in raw['tree_diff']:
      mod_files.add(entry['old_path'])
      mod_files.add(entry['new_path'])
    return cls(
      raw['commit'],
      raw['author']['email'],
      calendar.timegm(time.strptime(raw['committer']['time'])),
      tuple(raw['message'].splitlines()),
      frozenset(mod_files),
    )


class GitilesBackend(Backend):
  """GitilesBackend uses a repo served by Gitiles."""

  # Prefix at the beginning of Gerrit/Gitiles JSON API responses.
  _GERRIT_XSRF_HEADER = ')]}\'\n'

  @util.exponential_retry(condition=GitilesFetchError.transient)
  def _fetch_gitiles(self, url_fmt, *args):
    """Fetches a remote URL path and returns the response object on success.

    Args:
      url_fmt (str) - the url path fragment as a python %format string, like
        '%s/foo/bar?something=value'
      *args (str) - the arguments to format url_fmt with. They will be URL
        escaped.

    Returns requests.Response.
    """
    url = '%s/%s' % (self.repo_url,
                     url_fmt % tuple(map(requests.utils.quote, args)))
    LOGGER.info('fetching %s' % url)
    resp = requests.get(url)
    if resp.status_code != httplib.OK:
      raise GitilesFetchError(resp.status_code, resp.text)
    return resp

  def _fetch_gitiles_committish_json(self, url_fmt, *args):
    """Fetches a remote URL path and expects a JSON object on success.

    This appends two GET params to url_fmt:
      format=JSON   - Does what you expect
      name-status=1 - Ensures that commit objects returned have a 'tree_diff'
        member which shows the diff for that commit.

    Args:
      url_fmt (str) - the url path fragment as a python %format string, like
        '%s/foo/bar?something=value'
      *args (str) - the arguments to format url_fmt with. They will be URL
        escaped.

    Returns the decoded JSON object
    """
    resp = self._fetch_gitiles(url_fmt+'?name-status=1&format=JSON', *args)
    if not resp.text.startswith(self._GERRIT_XSRF_HEADER):
      raise GitilesFetchError(resp.status_code, 'Missing XSRF prefix')
    return json.loads(resp.text[len(self._GERRIT_XSRF_HEADER):])

  # This caches entries from _fetch_commit_json. It's populated by
  # _fetch_commit_json as well as _updates_impl.
  #
  # Mapping of:
  #   repo_url -> git_revision -> _GitilesCommitJson
  #
  # Only populated if _fetch_commit_json is passed a resolved commit.
  _COMMIT_JSON_CACHE = {}

  def _fetch_commit_json(self, refspec):
    """Returns _GitilesCommitJson for the refspec.

    If refspec is resolved then this value is cached.
    """
    c = self._COMMIT_JSON_CACHE.setdefault(self.repo_url, {})
    if refspec in c:
      return c[refspec]

    raw = self._fetch_gitiles_committish_json('+/%s', refspec)
    ret = _GitilesCommitJson.from_raw_json(raw)
    if self.is_resolved_revision(refspec):
      c[refspec] = ret

    return ret


  ### Backend implementations


  @property
  def repo_type(self):
    return package_pb2.DepSpec.GITILES

  def fetch(self, _refspec):
    # noop on Gitiles
    pass

  def checkout(self, refspec):
    requests_ssl.check_requests_ssl()
    LOGGER.info('Freshening repository %s in %s',
                self.repo_url, self.checkout_dir)

    shutil.rmtree(self.checkout_dir, ignore_errors=True)

    self.assert_remote('checkout')

    # Resolve the refspec if it's not a revision.
    revision = self.resolve_refspec(refspec)

    commit_metadata = self.commit_metadata(revision)
    package_spec = commit_metadata.spec
    recipes_path_rel = package_spec.recipes_path.encode('utf-8')

    # Re-create recipes.cfg in |checkout_dir| so that the repo's recipes.py
    # can look it up.
    recipes_cfg_path = os.path.join(self.checkout_dir,
                                    'infra', 'config', 'recipes.cfg')
    os.makedirs(os.path.dirname(recipes_cfg_path))
    package_io.PackageFile(recipes_cfg_path).write(package_spec)

    recipes_path = os.path.join(self.checkout_dir, recipes_path_rel)
    if not os.path.exists(recipes_path):
      os.makedirs(recipes_path)

    # TODO(iannucci): Implement parsing of 'bundle_extra_paths.txt' files so
    # that we can generate a bundle directly from gitiles without any local
    # state.

    # TODO(iannucci): This implementation may be slow if we need to retieve
    # multiple files/archives from the remote server. Should possibly consider
    # using a thread pool here.

    archive_response = self._fetch_gitiles(
      '+archive/%s/%s.tar.gz', revision, recipes_path_rel)
    with tarfile.open(fileobj=StringIO(archive_response.content)) as tf:
      tf.extractall(recipes_path)

  def _updates_impl(self, revision, other_revision):
    self.assert_remote('_updates_impl')

    # TODO(iannucci): implement paging

    log_json = self._fetch_gitiles_committish_json(
      '+log/%s..%s', revision, other_revision)

    c = self._COMMIT_JSON_CACHE.setdefault(self.repo_url, {})

    results = []
    for entry in log_json['log']:
      commit = entry['commit']
      c[commit] = _GitilesCommitJson.from_raw_json(entry)
      results.append(commit)

    results.reverse()
    return map(self.commit_metadata, results)

  def _resolve_refspec_impl(self, refspec):
    if self.is_resolved_revision(refspec):
      return self.commit_metadata(refspec).commit
    return self._fetch_commit_json(refspec).commit

  def _commit_metadata_impl(self, revision):
    self.assert_remote('_commit_metadata_impl')
    rev_json = self._fetch_commit_json(revision)

    recipes_cfg_text = self._fetch_gitiles(
      '+/%s/infra/config/recipes.cfg?format=TEXT', revision
    ).text.decode('base64')
    spec = json_format.Parse(
      recipes_cfg_text, package_pb2.Package(), ignore_unknown_fields=True)

    return CommitMetadata(
      revision,
      rev_json.author_email,
      rev_json.commit_timestamp,
      rev_json.message_lines,
      spec,
      has_interesting_changes(spec, rev_json.changed_files))