#!/usr/bin/env python
# Copyright 2020 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Verifies backward-compatibility of mojom type changes.

Given a set of pre- and post-diff mojom file contents, and a root directory
for a project, this tool verifies that any changes to [Stable] mojom types are
backward-compatible with the previous version.

This can be used e.g. by a presubmit check to prevent developers from making
breaking changes to stable mojoms."""

import argparse
import errno
import io
import json
import os
import os.path
import shutil
import six
import sys
import tempfile

from mojom.generate import module
from mojom.generate import translate
from mojom.parse import parser


class ParseError(Exception):
  pass


def _ValidateDelta(root, delta):
  """Parses all modified mojoms (including all transitive mojom dependencies,
  even if unmodified) to perform backward-compatibility checks on any types
  marked with the [Stable] attribute.

  Note that unlike the normal build-time parser in mojom_parser.py, this does
  not produce or rely on cached module translations, but instead parses the full
  transitive closure of a mojom's input dependencies all at once.
  """

  # First build a map of all files covered by the delta
  affected_files = set()
  old_files = {}
  new_files = {}
  for change in delta:
    # TODO(crbug.com/953884): Use pathlib once we're migrated fully to Python 3.
    filename = change['filename'].replace('\\', '/')
    affected_files.add(filename)
    if change['old']:
      old_files[filename] = change['old']
    if change['new']:
      new_files[filename] = change['new']

  # Parse and translate all mojoms relevant to the delta, including transitive
  # imports that weren't modified.
  unmodified_modules = {}

  def parseMojom(mojom, file_overrides, override_modules):
    if mojom in unmodified_modules or mojom in override_modules:
      return

    contents = file_overrides.get(mojom)
    if contents:
      modules = override_modules
    else:
      modules = unmodified_modules
      with io.open(os.path.join(root, mojom), encoding='utf-8') as f:
        contents = f.read()

    try:
      ast = parser.Parse(contents, mojom)
    except Exception as e:
      six.reraise(
          ParseError,
          'encountered exception {0} while parsing {1}'.format(e, mojom),
          sys.exc_info()[2])
    for imp in ast.import_list:
      parseMojom(imp.import_filename, file_overrides, override_modules)

    # Now that the transitive set of dependencies has been imported and parsed
    # above, translate each mojom AST into a Module so that all types are fully
    # defined and can be inspected.
    all_modules = {}
    all_modules.update(unmodified_modules)
    all_modules.update(override_modules)
    modules[mojom] = translate.OrderedModule(ast, mojom, all_modules)

  old_modules = {}
  for mojom in old_files.keys():
    parseMojom(mojom, old_files, old_modules)
  new_modules = {}
  for mojom in new_files.keys():
    parseMojom(mojom, new_files, new_modules)

  # At this point we have a complete set of translated Modules from both the
  # pre- and post-diff mojom contents. Now we can analyze backward-compatibility
  # of the deltas.
  #
  # Note that for backward-compatibility checks we only care about types which
  # were marked [Stable] before the diff. Types newly marked as [Stable] are not
  # checked.
  def collectTypes(modules):
    types = {}
    for m in modules.values():
      for kinds in (m.enums, m.structs, m.unions, m.interfaces):
        for kind in kinds:
          types[kind.qualified_name] = kind
    return types

  old_types = collectTypes(old_modules)
  new_types = collectTypes(new_modules)

  # Collect any renamed types so they can be compared accordingly.
  renamed_types = {}
  for name, kind in new_types.items():
    old_name = kind.attributes and kind.attributes.get('RenamedFrom')
    if old_name:
      renamed_types[old_name] = name

  for qualified_name, kind in old_types.items():
    if not kind.stable:
      continue

    new_name = renamed_types.get(qualified_name, qualified_name)
    if new_name not in new_types:
      raise Exception(
          'Stable type %s appears to be deleted by this change. If it was '
          'renamed, please add a [RenamedFrom] attribute to the new type. This '
          'can be deleted by a subsequent change.' % qualified_name)

    checker = module.BackwardCompatibilityChecker()
    if not checker.IsBackwardCompatible(new_types[new_name], kind):
      raise Exception('Stable type %s appears to have changed in a way which '
                      'breaks backward-compatibility. Please fix!\n\nIf you '
                      'believe this assessment to be incorrect, please file a '
                      'Chromium bug against the "Internals>Mojo>Bindings" '
                      'component.' % qualified_name)


def Run(command_line, delta=None):
  """Runs the tool with the given command_line. Normally this will read the
  change description from stdin as a JSON-encoded list, but tests may pass a
  delta directly for convenience."""
  arg_parser = argparse.ArgumentParser(
      description='Verifies backward-compatibility of mojom type changes.',
      epilog="""
This tool reads a change description from stdin and verifies that all modified
[Stable] mojom types will retain backward-compatibility. The change description
must be a JSON-encoded list of objects, each with a "filename" key (path to a
changed mojom file, relative to ROOT); an "old" key whose value is a string of
the full file contents before the change, or null if the file is being added;
and a "new" key whose value is a string of the full file contents after the
change, or null if the file is being deleted.""")
  arg_parser.add_argument(
      '--src-root',
      required=True,
      action='store',
      metavar='ROOT',
      help='The root of the source tree in which the checked mojoms live.')

  args, _ = arg_parser.parse_known_args(command_line)
  if not delta:
    delta = json.load(sys.stdin)
  _ValidateDelta(args.src_root, delta)


if __name__ == '__main__':
  Run(sys.argv[1:])
