#!/usr/bin/env python3

#
# bsp-o-matic
#
# Convert a monster patch into a series of smaller digestable patches
# (cleaning things up as we go)
#

#
# Features:
#
#  - Ignore any attempt to add execute permission to an existing file
#  - Remove execute permission from any new file that has a filename
#    that implies it should not be executed.
#  - Automatically splits things out based on the kernel directory
#    structure (all changes that impact a single directory will end
#    up in the same patch)
#  - Strip trailing whitespace from newly added lines
#  - Strip space characters made redundant by a subsequent tab.
#
# TODO:
#
#  - Manage the patch queue as a stack of queues (rather than a single
#    stack) to make globbing more effective)
#

import io
import os
import re
import sys

# Make sure we ignore unicode errors
sys.stdin = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8', errors='replace')

# This list is grown "organically" as we discover problems
automatically_generated = (
	# .config is *not* in this list... if someone checks that it we
	# probably need to manually convert it to a defconfig
	'arch/arm/boot/compressed/ashldi3.S',
	'arch/arm/boot/compressed/hyp-stub.S',
	'arch/arm/boot/compressed/lib1funcs.S',
	'arch/arm/boot/compressed/vmlinux.lds',
	'arch/arm/kernel/vmlinux.lds',
	'kernel/config_data.h',
	'kernel/hz.bc',
	'kernel/timeconst.h',
	'lib/crc32table.h',
	'lib/gen_crc32table',
	'scripts/basic/fixdep',
	'scripts/bin2c',
	'scripts/conmakehash',
	'scripts/kallsyms',
	'scripts/kconfig/conf',
	'scripts/kconfig/zconf.hash.c',
	'scripts/kconfig/zconf.lex.c',
	'scripts/kconfig/zconf.tab.c',
	'scripts/mod/devicetable-offsets.h',
	'scripts/mod/elfconfig.h',
	'scripts/mod/mk_elfconfig',
	'usr/gen_init_cpio',
	'usr/initramfs_data.cpio',
	'scripts/mod/modpost',
	'scripts/sortextable'
)

class PatchEngine(object):
	def __init__(self):
		self.pcount = 0
		self.perfile_meta = {}
		self.history = []
		self.patch_dir = None
		self.patch_queue = []

	def format_patch(self):
		if len(self.patch_queue) == 0:
			return

		self.pcount += 1

		clean_name = self.patch_dir.replace('drivers/', '')
		patch_name = '%04d-%s-board_support.patch' % \
				(self.pcount, clean_name.replace('/', '-'))

		with open(patch_name, 'w') as f:
			print('From: Random J Developer <random@developer.example.org>', file=f)
			print('Date: Mon Jul 30 08:09:38 2017 +0100', file=f)
			print('Subject: [PATCH] %s: Board support' % \
					(clean_name.replace('/', ': '),), file=f)
			for ln in self.patch_queue:
				print(ln, file=f)
			self.patch_queue = []

	def build_patch(self):
		meta = self.perfile_meta
		fname = meta['a']
		if fname == '/dev/null':
			fname = meta['b']

		# We will attempt to glob anything that does not make
		# changes to include. The logic here is that most
		# changes to include/ are unrelated to each other so
		# globbing those is not really wanted.
		if fname.startswith('include/'):
			if fname.endswith('.h'):
				new_dir = fname[:-2]
			else:
				new_dir = fname
		else:
			new_dir = os.path.dirname(fname)


		if new_dir != self.patch_dir:
			self.format_patch()
			self.patch_dir = new_dir

		self.patch_queue += self.history
		self.history = []

	def known_not_executable(self, fname):
		contains = ( 'Makefile', )
		endings = ( '.c', 'h', '.S', '.txt', 'Kconfig', 'defconfig' )

		for c in contains:
			if c in fname:
				return True

		for e in endings:
			if e in fname:
				return True

		return False

	def show_history(self, file=sys.stdout):
		for h in self.history:
			print(h, file=file)
		self.history = []

	def apply_perfile_fixups(self):
		# Is there any work to do? If no, this was probably a patch
		# header.
		if len(self.perfile_meta) == 0:
			self.show_history()
			self.perfile_meta = {}
			return

		# Elminate any new execute permissions (unlikely in a BSP)
		if 'old mode' in self.perfile_meta and \
		   'new mode' in self.perfile_meta and \
		   self.perfile_meta['old mode'][3] == '6' and \
		   self.perfile_meta['new mode'][3] == '7':
			   self.history = [ x for x in self.history
					   if not x.startswith('old mode') and
					      not x.startswith('new mode')]

		# Eliminate any bogus execute permissions on new files.
		# Note that if we have a 'new file mode' we *must* have a
		# 'b' or the underlying patch file is corrupt!
		if 'new file mode' in self.perfile_meta and \
		   self.known_not_executable(self.perfile_meta['b']):
			   for lineno in range(len(self.history)):
				   if self.history[lineno].startswith(
						   'new file mode'):
					   ln = self.history[lineno]
					   ln = ln.replace('7', '6')
					   ln = ln.replace('5', '4')
					   self.history[lineno] = ln

		# Undo any attempt to deletes an existing .gitignore.
		if self.perfile_meta['a'].endswith('/.gitignore') and \
		   'deleted file mode' in self.perfile_meta:
			self.history = []

		# Ignore any attempt to create a file that is automatically
		# generated.
		if self.perfile_meta['b'] in automatically_generated and \
		   'new file mode' in self.perfile_meta:
			self.history = []

		# If there's nothing left kill the whole patch
		if len(self.history) == 1 and \
		   self.history[0].startswith('diff '):
			self.history = []

		if len(self.history) and 'a' in self.perfile_meta:
			self.build_patch()
		self.show_history() # Display any missing pieces
		self.perfile_meta = {}

	def apply_newline_fixups(self, ln):
		# Strip any trailing whitespace
		ln = ln.rstrip()

		# Strip any leading whitespace that is followed by a tab
		ln = re.sub(r'^ {1,7}\t', '\t', ln)

		# Strip any whitespace made redundant by a preceding tab
		ln = re.sub(r'\t {1,7}\t', '\t', ln)

		return ln

	def process(self, ln):
		if ln.startswith('diff '):
			self.apply_perfile_fixups()
		# TODO: per-hunk fixups
		#elif ln.startswith('@@ '):
		#	self.apply_perhunk_fixups()

		defer = False

		if ln.startswith('diff'):
			a, b = ln.split()[-2:]
			if a.startswith('a/') and b.startswith('b/'):
				a = a[2:]
				b = b[2:]
			self.perfile_meta['a'] = a
			self.perfile_meta['b'] = b
		elif ln.startswith('old mode '):
			self.perfile_meta['old mode'] = ln.split()[-1]
		elif ln.startswith('new mode '):
			self.perfile_meta['new mode'] = ln.split()[-1]
		elif ln.startswith('new file mode '):
			self.perfile_meta['new file mode'] = ln.split()[-1]
		elif ln.startswith('deleted file mode '):
			self.perfile_meta['deleted file mode'] = ln.split()[-1]
		elif ln.startswith('+') and not ln.startswith('+++'):
			ln = self.apply_newline_fixups(ln)

		self.history.append(ln)


engine = PatchEngine()
for ln in sys.stdin.readlines():
	ln = ln[0:-1]
	engine.process(ln)

# process the final file
engine.apply_perfile_fixups()
engine.format_patch()