"""Utilities for dealing with project configuration."""

import configparser
import os


def find_config_file(path, filename='setup.cfg'):
  """Finds the first instance of filename in a prefix of path."""

  # Make sure path is a directory
  if not os.path.isdir(path):
    path = os.path.dirname(path)

  # Guard against symlink loops and /
  seen = set()
  while path and path not in seen:
    seen.add(path)
    f = os.path.join(path, filename)
    if os.path.exists(f) and os.path.isfile(f):
      return f
    path = os.path.dirname(path)

  return None


class ConfigSection:
  """Read a given set of keys from a section of a config file."""

  def __init__(self, parser, section):
    self.parser = parser
    self.section = section

  @classmethod
  def create_from_file(cls, filepath, section):
    """Create a ConfigSection if the file at filepath has section."""
    parser = configparser.ConfigParser()
    try:
      parser.read(filepath)
    except configparser.MissingSectionHeaderError:
      # We've read an improperly formatted config file.
      return None
    if parser.has_section(section):
      return cls(parser, section)
    return None

  def items(self):
    return self.parser.items(self.section)