text: """
  Check lesson files and their contents.
  """
  
  
  import os
  import glob
  import re
  import sys
  from argparse import ArgumentParser
  
  # This uses the `__all__` list in `util.py` to determine what objects to import
  # see https://docs.python.org/3/tutorial/modules.html#importing-from-a-package
  from util import *
  from reporter import Reporter
  
  __version__ = '0.3'
  
  # Where to look for source Markdown files.
  SOURCE_DIRS = ['', '_episodes', '_extras']
  
  # Where to look for source Rmd files.
  SOURCE_RMD_DIRS = ['_episodes_rmd']
  
  # Required files: each entry is ('path': YAML_required).
  # FIXME: We do not yet validate whether any files have the required
  #   YAML headers, but should in the future.
  # The '%' is replaced with the source directory path for checking.
  # Episodes are handled specially, and extra files in '_extras' are also handled
  # specially. This list must include all the Markdown files listed in the
  # 'bin/initialize' script.
  REQUIRED_FILES = {
      'CODE_OF_CONDUCT.md': True,
      'CONTRIBUTING.md': False,
      'LICENSE.md': True,
      'README.md': False,
      os.path.join('_extras', 'discuss.md'): True,
      os.path.join('_extras', 'guide.md'): True,
      'index.md': True,
      'reference.md': True,
      'setup.md': True,
  }
  
  # Episode filename pattern.
  P_EPISODE_FILENAME = re.compile(r'(\d\d)-[-\w]+.md$')
  
  # Pattern to match lines ending with whitespace.
  P_TRAILING_WHITESPACE = re.compile(r'\s+$')
  
  # Pattern to match figure references in HTML.
  P_FIGURE_REFS = re.compile(r'<img[^>]+src="([^"]+)"[^>]*>')
  
  # Pattern to match internally-defined Markdown links.
  P_INTERNAL_LINK_REF = re.compile(r'\[([^\]]+)\]\[([^\]]+)\]')
  
  # Pattern to match reference links (to resolve internally-defined references).
  P_INTERNAL_LINK_DEF = re.compile(r'^\[([^\]]+)\]:\s*(.+)')
  
  # Pattern to match {% include ... %} statements
  P_INTERNAL_INCLUDE_LINK = re.compile(r'^{% include ([^ ]*) %}$')
  
  # Pattern to match image-only and link-only lines
  P_LINK_IMAGE_LINE = re.compile(r'''
      [> #]*        # any number of '>', '#', and spaces
      \W{,3}        # up to 3 non-word characters
      !?            # ! or nothing
      \[[^]]+\]     # [any text]
      [([]          # ( or [
      [^])]+        # 1+ characters that are neither ] nor )
      [])]          # ] or )
      (?:{:[^}]+})? # {:any text} or nothing
      \W{,3}        # up to 3 non-word characters
      [ ]*          # any number of spaces
      \\?$          # \ or nothing + end of line''', re.VERBOSE)
  
  # What kinds of blockquotes are allowed?
  KNOWN_BLOCKQUOTES = {
      'callout',
      'caution',
      'challenge',
      'checklist',
      'discussion',
      'keypoints',
      'objectives',
      'prereq',
      'quotation',
      'solution',
      'testimonial',
      'warning'
  }
  
  # What kinds of code fragments are allowed?
  # Below we allow all 'language-*' code blocks
  KNOWN_CODEBLOCKS = {
      'error',
      'output',
      'source',
      'language-bash',
      'html',
      'language-c',
      'language-cmake',
      'language-cpp',
      'language-make',
      'language-matlab',
      'language-python',
      'language-r',
      'language-shell',
      'language-sql',
      'language-yaml',
      'warning',
  }
  
  # What fields are required in teaching episode metadata?
  TEACHING_METADATA_FIELDS = {
      ('title', str),
      ('teaching', int),
      ('exercises', int),
      ('questions', list),
      ('objectives', list),
      ('keypoints', list)
  }
  
  # What fields are required in break episode metadata?
  BREAK_METADATA_FIELDS = {
      ('layout', str),
      ('title', str),
      ('break', int)
  }
  
  # How long are lines allowed to be?
  # Please keep this in sync with .editorconfig!
  MAX_LINE_LEN = 100
  
  
  def main():
      """Main driver."""
  
      args = parse_args()
      args.reporter = Reporter()
      life_cycle = check_config(args.reporter, args.source_dir)
      # pre-alpha lessons should report without error
      if life_cycle == "pre-alpha":
          args.permissive = True
      check_source_rmd(args.reporter, args.source_dir, args.parser)
  
      args.references = {}
      if not using_remote_theme(args.source_dir):
          args.references = read_references(args.reporter, args.reference_path)
  
      docs = read_all_markdown(args.source_dir, args.parser)
      check_fileset(args.source_dir, args.reporter, list(docs.keys()))
      check_unwanted_files(args.source_dir, args.reporter)
      for filename in list(docs.keys()):
          checker = create_checker(args, filename, docs[filename])
          checker.check()
  
      args.reporter.report()
      if args.reporter.messages:
          if args.permissive:
              print("Problems detected but ignored (permissive mode).")
          else:
              print("Problems detected.")
              sys.exit(1)
      else:
          print("No problems found.")
  
      return
  
  
  def parse_args():
      """Parse command-line arguments."""
  
      parser = ArgumentParser(description="""Check episode files in a lesson.""")
      parser.add_argument('-l', '--linelen',
                          default=False,
                          action="store_true",
                          dest='line_lengths',
                          help='Check line lengths')
      parser.add_argument('-p', '--parser',
                          default=None,
                          dest='parser',
                          help='path to Markdown parser')
      parser.add_argument('-r', '--references',
                          default=None,
                          dest='reference_path',
                          help='path to Markdown file of external references')
      parser.add_argument('-s', '--source',
                          default=os.curdir,
                          dest='source_dir',
                          help='source directory')
      parser.add_argument('-w', '--whitespace',
                          default=False,
                          action="store_true",
                          dest='trailing_whitespace',
                          help='Check for trailing whitespace')
      parser.add_argument('--permissive',
                          default=False,
                          action="store_true",
                          dest='permissive',
                          help='Do not raise an error even if issues are detected')
  
      args, extras = parser.parse_known_args()
      require(args.parser is not None,
              'Path to Markdown parser not provided',
              True)
      require(not extras,
              'Unexpected trailing command-line arguments "{0}"'.format(extras))
  
      return args
  
  def using_remote_theme(source_dir):
      config_file = os.path.join(source_dir, '_config.yml')
      config = load_yaml(config_file)
      return 'remote_theme' in config
  
  def check_config(reporter, source_dir):
      """Check configuration file."""
  
      config_file = os.path.join(source_dir, '_config.yml')
      config = load_yaml(config_file)
      reporter.check_field(config_file, 'configuration',
                           config, 'kind', 'lesson')
      reporter.check_field(config_file, 'configuration',
                           config, 'carpentry', ('hsf', 'swc', 'dc', 'lc', 'cp', 'incubator'))
      reporter.check_field(config_file, 'configuration', config, 'title')
      reporter.check_field(config_file, 'configuration', config, 'email')
  
      for defaults in [
              {'values': {'root': '.', 'layout': 'page'}},
              {'values': {'root': '..', 'layout': 'episode'}, 'scope': {'type': 'episodes', 'path': ''}},
              {'values': {'root': '..', 'layout': 'page'}, 'scope': {'type': 'extras', 'path': ''}}
              ]:
          error_text = 'incorrect settings for: root "{0}" layout "{1}"'
          root = defaults["values"]["root"]
          layout = defaults["values"]["layout"]
          error_message = error_text.format(root, layout)
  
          defaults_test = defaults in config.get('defaults', [])
          reporter.check(defaults_test, 'configuration', error_message)
  
      if 'life_cycle' not in config:
          config['life_cycle'] = None
      return config['life_cycle']
  
  def check_source_rmd(reporter, source_dir, parser):
      """Check that Rmd episode files include `source: Rmd`"""
  
      episode_rmd_dir = [os.path.join(source_dir, d) for d in SOURCE_RMD_DIRS]
      episode_rmd_files = [os.path.join(d, '*.Rmd') for d in episode_rmd_dir]
      results = {}
      for pat in episode_rmd_files:
          for f in glob.glob(pat):
              data = read_markdown(parser, f)
              dy = data['metadata']
              if dy:
                  reporter.check_field(f, 'episode_rmd',
                                       dy, 'source', 'Rmd')
  
  def read_references(reporter, ref_path):
      """Read shared file of reference links, returning dictionary of valid references
      {symbolic_name : URL}
      """
  
      if not ref_path:
          raise Warning("No filename has been provided.")
  
      result = {}
      urls_seen = set()
  
      with open(ref_path, 'r', encoding='utf-8') as reader:
          for (num, line) in enumerate(reader, 1):
  
              # Skip empty lines
              if len(line.strip()) == 0:
                  continue
  
              # Skip HTML comments
              if line.strip().startswith("<!--") and line.strip().endswith("-->"):
                     continue
  
              # Skip Liquid's {% include ... %} lines
              if P_INTERNAL_INCLUDE_LINK.search(line):
                  continue
  
              m = P_INTERNAL_LINK_DEF.search(line)
  
              message = '{}: {} not a valid reference: {}'
              require(m, message.format(ref_path, num, line.rstrip()))
  
              name = m.group(1)
              url = m.group(2)
  
              message = 'Empty reference at {0}:{1}'
              require(name, message.format(ref_path, num))
  
              unique_name = name not in result
              unique_url = url not in urls_seen
  
              reporter.check(unique_name,
                             ref_path,
                             'Duplicate reference name {0} at line {1}',
                             name, num)
  
              reporter.check(unique_url,
                             ref_path,
                             'Duplicate definition of URL {0} at line {1}',
                             url, num)
  
              result[name] = url
              urls_seen.add(url)
  
      return result
  
  
  def read_all_markdown(source_dir, parser):
      """Read source files, returning
      {path : {'metadata':yaml, 'metadata_len':N, 'text':text, 'lines':[(i, line, len)], 'doc':doc}}
      """
  
      all_dirs = [os.path.join(source_dir, d) for d in SOURCE_DIRS]
      all_patterns = [os.path.join(d, '*.md') for d in all_dirs]
      result = {}
      for pat in all_patterns:
          for filename in glob.glob(pat):
              data = read_markdown(parser, filename)
              if data:
                  result[filename] = data
      return result
  
  
  def check_fileset(source_dir, reporter, filenames_present):
      """Are all required files present? Are extraneous files present?"""
  
      # Check files with predictable names.
      required = [os.path.join(source_dir, p) for p in REQUIRED_FILES]
      missing = set(required) - set(filenames_present)
      for m in missing:
          reporter.add(None, 'Missing required file {0}', m)
  
      # Check names of episode files.
      seen = []
      for filename in filenames_present:
          if '_episodes' not in filename:
              continue
  
          # split path to check episode name
          base_name = os.path.basename(filename)
          m = P_EPISODE_FILENAME.search(base_name)
          if m and m.group(1):
              seen.append(m.group(1))
          else:
              reporter.add(
                  None, 'Episode {0} has badly-formatted filename', filename)
  
      # Check for duplicate episode numbers.
      reporter.check(len(seen) == len(set(seen)),
                     None,
                     'Duplicate episode numbers {0} vs {1}',
                     sorted(seen), sorted(set(seen)))
  
      # Check that numbers are consecutive.
      seen = sorted([int(s) for s in seen])
      clean = True
      for i in range(len(seen) - 1):
          clean = clean and ((seen[i+1] - seen[i]) == 1)
      reporter.check(clean,
                     None,
                     'Missing or non-consecutive episode numbers {0}',
                     seen)
  
  
  def create_checker(args, filename, info):
      """Create appropriate checker for file."""
  
      for (pat, cls) in CHECKERS:
          if pat.search(filename):
              return cls(args, filename, **info)
      return NotImplemented
  
  class CheckBase:
      """Base class for checking Markdown files."""
  
      def __init__(self, args, filename, metadata, metadata_len, text, lines, doc):
          """Cache arguments for checking."""
  
          self.args = args
          self.reporter = self.args.reporter  # for convenience
          self.filename = filename
          self.metadata = metadata
          self.metadata_len = metadata_len
          self.text = text
          self.lines = lines
          self.doc = doc
  
          self.layout = None
  
      def check(self):
          """Run tests."""
  
          self.check_metadata()
          self.check_line_lengths()
          self.check_trailing_whitespace()
          self.check_blockquote_classes()
          self.check_codeblock_classes()
          self.check_defined_link_references()
  
      def check_metadata(self):
          """Check the YAML metadata."""
  
          self.reporter.check(self.metadata is not None,
                              self.filename,
                              'Missing metadata entirely')
  
          if self.metadata and (self.layout is not None):
              self.reporter.check_field(
                  self.filename, 'metadata', self.metadata, 'layout', self.layout)
  
      def check_line_lengths(self):
          """Check the raw text of the lesson body."""
  
          if self.args.line_lengths:
              over_limit = []
  
              for (i, l, n) in self.lines:
                  # Report lines that are longer than the suggested
                  # line length limit only if they're not
                  # link-only or image-only lines.
                  if n > MAX_LINE_LEN and not P_LINK_IMAGE_LINE.match(l):
                      over_limit.append(i)
  
              self.reporter.check(not over_limit,
                                  self.filename,
                                  'Line(s) too long: {0}',
                                  ', '.join([str(i) for i in over_limit]))
  
      def check_trailing_whitespace(self):
          """Check for whitespace at the ends of lines."""
  
          if self.args.trailing_whitespace:
              trailing = [
                  i for (i, l, n) in self.lines if P_TRAILING_WHITESPACE.match(l)]
              self.reporter.check(not trailing,
                                  self.filename,
                                  'Line(s) end with whitespace: {0}',
                                  ', '.join([str(i) for i in trailing]))
  
      def check_blockquote_classes(self):
          """Check that all blockquotes have known classes."""
  
          for node in self.find_all(self.doc, {'type': 'blockquote'}):
              cls = self.get_val(node, 'attr', 'class')
              self.reporter.check(cls in KNOWN_BLOCKQUOTES,
                                  (self.filename, self.get_loc(node)),
                                  'Unknown or missing blockquote type {0}',
                                  cls)
  
      def check_codeblock_classes(self):
          """Check that all code blocks have known classes."""
  
          for node in self.find_all(self.doc, {'type': 'codeblock'}):
              cls = self.get_val(node, 'attr', 'class')
              self.reporter.check(cls is not None and (cls in KNOWN_CODEBLOCKS or
                  cls.startswith('language-')),
                                  (self.filename, self.get_loc(node)),
                                  'Unknown or missing code block type {0}',
                                  cls)
  
      def check_defined_link_references(self):
          """Check that defined links resolve in the file.
  
          Internally-defined links match the pattern [text][label].
          """
  
          result = set()
          for node in self.find_all(self.doc, {'type': 'text'}):
              for match in P_INTERNAL_LINK_REF.findall(node['value']):
                  text = match[0]
                  link = match[1]
                  if link not in self.args.references:
                      result.add('"{0}"=>"{1}"'.format(text, link))
          self.reporter.check(not result,
                              self.filename,
                              'Internally-defined links may be missing definitions: {0}',
                              ', '.join(sorted(result)))
  
      def find_all(self, node, pattern, accum=None):
          """Find all matches for a pattern."""
  
          assert isinstance(pattern, dict), 'Patterns must be dictionaries'
          if accum is None:
              accum = []
          if self.match(node, pattern):
              accum.append(node)
          for child in node.get('children', []):
              self.find_all(child, pattern, accum)
          return accum
  
      def match(self, node, pattern):
          """Does this node match the given pattern?"""
  
          for key in pattern:
              if key not in node:
                  return False
              val = pattern[key]
              if isinstance(val, str):
                  if node[key] != val:
                      return False
              elif isinstance(val, dict):
                  if not self.match(node[key], val):
                      return False
          return True
  
      @staticmethod
      def get_val(node, *chain):
          """Get value one or more levels down."""
  
          curr = node
          for selector in chain:
              curr = curr.get(selector, None)
              if curr is None:
                  break
          return curr
  
      def get_loc(self, node):
          """Convenience method to get node's line number."""
  
          result = self.get_val(node, 'options', 'location')
          if self.metadata_len is not None:
              result += self.metadata_len
          return result
  
  
  class CheckNonJekyll(CheckBase):
      """Check a file that isn't translated by Jekyll."""
  
      def check_metadata(self):
          self.reporter.check(self.metadata is None,
                              self.filename,
                              'Unexpected metadata')
  
  
  class CheckIndex(CheckBase):
      """Check the main index page."""
  
      def __init__(self, args, filename, metadata, metadata_len, text, lines, doc):
          super().__init__(args, filename, metadata, metadata_len, text, lines, doc)
          self.layout = 'lesson'
  
      def check_metadata(self):
          super().check_metadata()
          self.reporter.check(self.metadata.get('root', '') == '.',
                              self.filename,
                              'Root not set to "."')
  
  
  class CheckEpisode(CheckBase):
      """Check an episode page."""
  
      def check(self):
          """Run extra tests."""
  
          super().check()
          if not using_remote_theme(self.args.source_dir):
              self.check_reference_inclusion()
  
      def check_metadata(self):
          super().check_metadata()
          if self.metadata:
              if 'layout' in self.metadata:
                  if self.metadata['layout'] == 'break':
                      self.check_metadata_fields(BREAK_METADATA_FIELDS)
                  else:
                      self.reporter.add(self.filename,
                                        'Unknown episode layout "{0}"',
                                        self.metadata['layout'])
              else:
                  self.check_metadata_fields(TEACHING_METADATA_FIELDS)
  
      def check_metadata_fields(self, expected):
          """Check metadata fields."""
          for (name, type_) in expected:
              if name not in self.metadata:
                  self.reporter.add(self.filename,
                                    'Missing metadata field {0}',
                                    name)
              elif not isinstance(self.metadata[name], type_):
                  self.reporter.add(self.filename,
                                    '"{0}" has wrong type in metadata ({1} instead of {2})',
                                    name, type(self.metadata[name]), type_)
  
      def check_reference_inclusion(self):
          """Check that links file has been included."""
  
          if not self.args.reference_path:
              return
  
          for (i, last_line, line_len) in reversed(self.lines):
              if last_line:
                  break
  
          require(last_line,
                  'No non-empty lines in {0}'.format(self.filename))
  
          include_filename = os.path.split(self.args.reference_path)[-1]
          if include_filename not in last_line:
              self.reporter.add(self.filename,
                                'episode does not include "{0}"',
                                include_filename)
  
  
  class CheckReference(CheckBase):
      """Check the reference page."""
  
      def __init__(self, args, filename, metadata, metadata_len, text, lines, doc):
          super().__init__(args, filename, metadata, metadata_len, text, lines, doc)
          self.layout = 'reference'
  
  
  class CheckGeneric(CheckBase):
      """Check a generic page."""
  
      def __init__(self, args, filename, metadata, metadata_len, text, lines, doc):
          super().__init__(args, filename, metadata, metadata_len, text, lines, doc)
  
  
  CHECKERS = [
      (re.compile(r'CONTRIBUTING\.md'), CheckNonJekyll),
      (re.compile(r'README\.md'), CheckNonJekyll),
      (re.compile(r'index\.md'), CheckIndex),
      (re.compile(r'reference\.md'), CheckReference),
      # '.' below is what's passed on the command line via '-s' flag
      (re.compile(os.path.join('.','_episodes', '[^/]*\.md')), CheckEpisode),
      (re.compile(r'.*\.md'), CheckGeneric)
  ]
  
  
  if __name__ == '__main__':
      main()
  