"""This module calculates the incremental coverage of a git commit using
information from `git diff` and LCOV's ".info" file.
"""
from typing import Tuple, Text, List, Dict
import changed_lines
import lcov_parser
import os
import re
import sys

Lines = Dict[int, bool]


class CurrDirectoryError(Exception):
  """CurrDirectoryError is raised when the current working directory
  cannot be found at the beginning of the absolute paths of the files
  listed in the ".info" file.
  """
  pass


def coverage(updated_lines: Dict[Text, List[int]],
                    covered_lines: Dict[Text, Lines],
                    curr_dir: Text) -> float:
  """Computes the the proportion of lines covered in updated_lines, ignoring
  those that are not instrumented (e.g. like comments or macros).

  Args:
    updated_lines: a dict mapping files to a list of its updated lines
    covered_lines: a dict mapping files to another dict mapping lines to
      whether they've been covered or not
    curr_dir: name of the current directory, to be removed from beginning of
      absolute file paths in covered_lines

  Raises:
      CurrDirectoryError: if there is an issue removing the current directory from the
        beginning of the absolute paths of the files listed in the ".info" file.
  """
  num_covered_lines = 0
  total_lines = 0

  for (file_name, covered) in covered_lines.items():

    # remove the prefix to the absolute path in the files
    if not file_name.startswith(curr_dir):
      raise CurrDirectoryError('Error removing "' + curr_dir + \
                               '" from beginning of "' +  file_name + '".')

    trimmed_filename = file_name[len(curr_dir) + 1:]

    if trimmed_filename in updated_lines:

      for updated_line in updated_lines[trimmed_filename]:
        if updated_line in covered:
          total_lines += 1

          if covered[updated_line]:
            num_covered_lines += 1

  # some files may not have any instrumented code, e.g. header files with
  # only macros
  if total_lines == 0:
    return None

  return float(num_covered_lines) / total_lines


def main(lcov_file_name: Text):
  """Takes in the name of an LCOV ".info" file and calculates the incremental
  coverage results of the current git commit.

  Raises:
      GitDiffSyntaxError if there are formatting issues parsing file name in `file_diff`.
  """
  _, covered_lines = lcov_parser.parse(open(lcov_file_name, 'r'))

  git_diff = os.popen('git diff HEAD~').read()
  updated_lines = changed_lines.from_diff(git_diff)

  perc = coverage(updated_lines, covered_lines, os.getcwd())

  if perc == None:
    print("None")
    return

  # prints the coverage as a percentage
  print(round(perc*100, 2))


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