#! /usr/bin/env python3

# Selectively preprocess #ifdef / #ifndef statements.
# Usage:
# ifdef [-Dname] ... [-Uname] ... [file] ...
#
# This scans the file(s), looking for #ifdef and #ifndef preprocessor
# commands that test for one of the names mentioned in the -D and -U
# options. On standard output it writes a copy of the input file(s)
# minus those code sections that are suppressed by the selected
# combination of defined/undefined symbols. The #if(n)def/#else/#else
# lines themselves (if the #if(n)def tests for one of the mentioned
# names) are removed as well.

# Features: Arbitrary nesting of recognized and unrecognized
# preprocessor statements works correctly. Unrecognized #if* commands
# are left in place, so it will never remove too much, only too
# little. It does accept whitespace around the '#' character.

# Restrictions: There should be no comments or other symbols on the
# #if(n)def lines. The effect of #define/#undef commands in the input
# file or in included files is not taken into account. Tests using
# #if and the defined() pseudo function are not recognized. The #elif
# command is not recognized. Improperly nesting is not detected.
# Lines that look like preprocessor commands but which are actually
# part of comments or string literals will be mistaken for
# preprocessor commands.

import sys
import getopt

defs = []
undefs = []

def main():
 opts, args = getopt.getopt(sys.argv[1:], 'D:U:')
 for o, a in opts:
 if o == '-D':
 defs.append(a)
 if o == '-U':
 undefs.append(a)
 if not args:
 args = ['-']
 for filename in args:
 if filename == '-':
 process(sys.stdin, sys.stdout)
 else:
 f = open(filename, 'r')
 process(f, sys.stdout)
 f.close()

def process(fpi, fpo):
 keywords = ('if', 'ifdef', 'ifndef', 'else', 'endif')
 ok = 1
 stack = []
 while 1:
 line = fpi.readline()
 if not line: break
 while line[-2:] == '\\\n':
 nextline = fpi.readline()
 if not nextline: break
 line = line + nextline
 tmp = line.strip()
 if tmp[:1] != '#':
 if ok: fpo.write(line)
 continue
 tmp = tmp[1:].strip()
 words = tmp.split()
 keyword = words[0]
 if keyword not in keywords:
 if ok: fpo.write(line)
 continue
 if keyword in ('ifdef', 'ifndef') and len(words) == 2:
 if keyword == 'ifdef':
 ko = 1
 else:
 ko = 0
 word = words[1]
 if word in defs:
 stack.append((ok, ko, word))
 if not ko: ok = 0
 elif word in undefs:
 stack.append((ok, not ko, word))
 if ko: ok = 0
 else:
 stack.append((ok, -1, word))
 if ok: fpo.write(line)
 elif keyword == 'if':
 stack.append((ok, -1, ''))
 if ok: fpo.write(line)
 elif keyword == 'else' and stack:
 s_ok, s_ko, s_word = stack[-1]
 if s_ko < 0:
 if ok: fpo.write(line)
 else:
 s_ko = not s_ko
 ok = s_ok
 if not s_ko: ok = 0
 stack[-1] = s_ok, s_ko, s_word
 elif keyword == 'endif' and stack:
 s_ok, s_ko, s_word = stack[-1]
 if s_ko < 0:
 if ok: fpo.write(line)
 del stack[-1]
 ok = s_ok
 else:
 sys.stderr.write('Unknown keyword %s\n' % keyword)
 if stack:
 sys.stderr.write('stack: %s\n' % stack)

if __name__ == '__main__':
 main()