import os
import ycm_core
import subprocess

def DirectoryOfThisScript():
  return os.path.dirname( os.path.abspath( __file__ ) )

def ExtractSearchPaths(compiler):
  def find_paths(compiler, c_arg):
    child = subprocess.Popen([compiler, c_arg, '-E', '-v', '-'], stdin=subprocess.PIPE, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
    stderr, stdout = child.communicate(input="")
    lines = stdout.split("\n")
    begin_token = '#include <...> search starts here:'
    end_token = 'End of search list.'
  
    def find_token_index(l, token):
      for index, item in enumerate(l):
        if item == token:
          return index
      raise Exception("token not found: %s" % token)
    begin_index = find_token_index(lines, begin_token)
    end_index = find_token_index(lines, end_token)
    return map(lambda x: x.strip(), lines[begin_index+1:end_index])

  results = find_paths(compiler, '-xc')
  results.extend(find_paths(compiler, '-xc++'))
  return results

# Set this to the absolute path to the folder (NOT the file!) containing the
# compile_commands.json file to use that instead of 'flags'. See here for
# more details: http://clang.llvm.org/docs/JSONCompilationDatabase.html
#
# You can get CMake to generate this file for you by adding:
#   set( CMAKE_EXPORT_COMPILE_COMMANDS 1 )
# to your CMakeLists.txt file.
#
# Most projects will NOT need to set this to anything; you can just change the
# 'flags' list of compilation flags. Notice that YCM itself uses that approach.
compilation_database_folder = os.path.join(DirectoryOfThisScript(), 'build')
compiler = os.environ['CC']
search_paths = ExtractSearchPaths(compiler)
extra_flags = []
for path in search_paths:
  extra_flags.append('-I')
  extra_flags.append(path)

if os.path.exists( compilation_database_folder ):
  database = ycm_core.CompilationDatabase( compilation_database_folder )
else:
  raise Exception("compilation database not found")

SOURCE_EXTENSIONS = [ '.cpp', '.cxx', '.cc', '.c', '.m', '.mm' ]


def MakeRelativePathsInFlagsAbsolute( flags, working_directory ):
  if not working_directory:
    return list( flags )
  new_flags = []
  make_next_absolute = False
  path_flags = [ '-isystem', '-I', '-iquote', '--sysroot=' ]
  for flag in flags:
    new_flag = flag

    if make_next_absolute:
      make_next_absolute = False
      if not flag.startswith( '/' ):
        new_flag = os.path.join( working_directory, flag )

    for path_flag in path_flags:
      if flag == path_flag:
        make_next_absolute = True
        break

      if flag.startswith( path_flag ):
        path = flag[ len( path_flag ): ]
        new_flag = path_flag + os.path.join( working_directory, path )
        break

    if new_flag:
      new_flags.append( new_flag )
  return new_flags


def IsHeaderFile( filename ):
  extension = os.path.splitext( filename )[ 1 ]
  return extension in [ '.h', '.hxx', '.hpp', '.hh' ]


def GetCompilationInfoForFile( filename ):
  # The compilation_commands.json file generated by CMake does not have entries
  # for header files. So we do our best by asking the db for flags for a
  # corresponding source file, if any. If one exists, the flags for that file
  # should be good enough.
  if IsHeaderFile( filename ):
    basename = os.path.splitext( filename )[ 0 ]
    for extension in SOURCE_EXTENSIONS:
      replacement_file = basename + extension
      if os.path.exists( replacement_file ):
        compilation_info = database.GetCompilationInfoForFile(
          replacement_file )
        if compilation_info.compiler_flags_:
          return compilation_info
    return None
  return database.GetCompilationInfoForFile( filename )


def FlagsForFile( filename, **kwargs ):
  # Bear in mind that compilation_info.compiler_flags_ does NOT return a
  # python list, but a "list-like" StringVec object
  compilation_info = GetCompilationInfoForFile( filename )
  if not compilation_info:
    return None

  final_flags = MakeRelativePathsInFlagsAbsolute(
    compilation_info.compiler_flags_,
    compilation_info.compiler_working_dir_ )

  relative_to = DirectoryOfThisScript()
  moar_flags = MakeRelativePathsInFlagsAbsolute( extra_flags, relative_to )

  final_flags.extend(moar_flags)

  return {
    'flags': final_flags,
    'do_cache': True
  }