"""This file provides a parse() method to extract the per-file line coverage
from an LCOV ".info" file.
"""

from typing import Dict, Text, Tuple, Iterable, IO, Optional


Lines = Dict[int, bool]

def _merge_lines(dst: Lines, src: Lines) -> Lines:
  """_merge_lines merges `src` into `dst` and returns `dst`. """
  for line, coverage in src.items():
    if line in dst:
      dst[line] = dst[line] or coverage
    else:
      dst[line] = coverage
  return dst


class Record:
  """Record holds the data from an LCOV record."""
  def __init__(self):
    self.lines = {}  # type: Lines
    self.file = ''


class LcovSyntaxError(Exception):
  """LcovSyntaxError is raised when there is formatting issues in the ".info" file."""
  pass


def _parse_line(line: Text) -> Tuple[Text, Text]:
  """_parse_line takes in a line from a file and returns it in two parts.

  LCOV lines are of the form
        <field>:<data>
          eg: "TN:<test name>"

  Args:
    line: line from the input file.

  Returns:
    a tuple containing the part before and the part after a ":" in the line.
  """
  try:
    field, value = line.split(':', 1)
  except:
    raise LcovSyntaxError('invalid data line, needs to be of the form' +
                          '\n\tDA:<line #>,<execution count>[,<checksum>]\n ' +
                          'or\n \tTN:<test name>\ngot: ' + line)

  return (field, value.strip())


def _read_record(input_file: Iterable[Text]) -> Optional[Record]:
  """_read_record the next LCOV record from `input_file`.

  LCOV records are of the form
        SF:<file name>
        ...
        end_of_record

  Args:
    input_file: the ".info" file that is being read.

  Returns:
    the text Record in the file.

  Raises:
    LcovSyntaxError: if the format of the input file doesn't match correct
      LCOV format.
  """
  rec = Record()

  for line in input_file:

    line = line.strip()

    if line == 'end_of_record':
      return rec

    field, value = _parse_line(line)

    if field == 'SF':
      rec.file = value

    elif field == 'DA':
      parts = value.split(',', 2)
      if len(parts) < 2:
        raise LcovSyntaxError('invalid data line, needs to be of the form ' +
                              '\n\tDA:<line #>,<execution count>[,<checksum>]\ngot: ' + line)

      try:
        line_num = int(parts[0])
      except:
        raise LcovSyntaxError('invalid data line, needs to be of the form ' +
                              '\n\tDA:<line #>,<execution count>[,<checksum>]\ngot: ' + line)

      # LCOV explicitly reports a '0' execution count for instrumented lines that don't get run.
      rec.lines[line_num] = parts[1] != '0'

  return None


def parse(input_file: IO) -> Tuple[Text, Dict[Text, Lines]]:
  """parse reads an LCOV ".info" file.

  Args:
    input_file: the file that is being read.

  Returns:
    a tuple containing the test_name and the associated files w/ coverage.

  Raises:
    LcovSyntaxError: if the first line of the input file does not start with "TN".
  """

  # the first line in a LCOV report is the test name
  field, test_name = _parse_line(input_file.readline())

  if field != 'TN':
    raise LcovSyntaxError('first line in LCOV report should be "TN:<name>", got: ' +
                          field + ':' + test_name)

  files = {}  # type: Dict[Text, Lines]

  while True:
    rec = _read_record(input_file)
    if rec is None:
      break

    if rec.file in files:
      files[rec.file] = _merge_lines(files[rec.file], rec.lines)
    else:
      files[rec.file] = rec.lines

  return (test_name, files)