diff_tree.py
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	# diff_tree.py -- Utilities for diffing files and trees.
	# Copyright (C) 2010 Google, Inc.
	#
	# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
	# General Public License as public by the Free Software Foundation; version 2.0
	# or (at your option) any later version. You can redistribute it and/or
	# modify it under the terms of either of these two licenses.
	#
	# Unless required by applicable law or agreed to in writing, software
	# distributed under the License is distributed on an "AS IS" BASIS,
	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	# See the License for the specific language governing permissions and
	# limitations under the License.
	#
	# You should have received a copy of the licenses; if not, see
	# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
	# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
	# License, Version 2.0.
	#

	"""Utilities for diffing files and trees."""
	import sys
	from collections import (
	defaultdict,
	namedtuple,
	)

	from io import BytesIO
	from itertools import chain
	import stat

	from dulwich.objects import (
	S_ISGITLINK,
	TreeEntry,
	)


	# TreeChange type constants.
	CHANGE_ADD = 'add'
	CHANGE_MODIFY = 'modify'
	CHANGE_DELETE = 'delete'
	CHANGE_RENAME = 'rename'
	CHANGE_COPY = 'copy'
	CHANGE_UNCHANGED = 'unchanged'

	RENAME_CHANGE_TYPES = (CHANGE_RENAME, CHANGE_COPY)

	_NULL_ENTRY = TreeEntry(None, None, None)

	_MAX_SCORE = 100
	RENAME_THRESHOLD = 60
	MAX_FILES = 200
	REWRITE_THRESHOLD = None


	class TreeChange(namedtuple('TreeChange', ['type', 'old', 'new'])):
	"""Named tuple a single change between two trees."""

	@classmethod
	def add(cls, new):
	return cls(CHANGE_ADD, _NULL_ENTRY, new)

	@classmethod
	def delete(cls, old):
	return cls(CHANGE_DELETE, old, _NULL_ENTRY)


	def _tree_entries(path, tree):
	result = []
	if not tree:
	return result
	for entry in tree.iteritems(name_order=True):
	result.append(entry.in_path(path))
	return result


	def _merge_entries(path, tree1, tree2):
	"""Merge the entries of two trees.

	Args:
	path: A path to prepend to all tree entry names.
	tree1: The first Tree object to iterate, or None.
	tree2: The second Tree object to iterate, or None.
	Returns:
	A list of pairs of TreeEntry objects for each pair of entries in
	the trees. If an entry exists in one tree but not the other, the other
	entry will have all attributes set to None. If neither entry's path is
	None, they are guaranteed to match.
	"""
	entries1 = _tree_entries(path, tree1)
	entries2 = _tree_entries(path, tree2)
	i1 = i2 = 0
	len1 = len(entries1)
	len2 = len(entries2)

	result = []
	while i1 < len1 and i2 < len2:
	entry1 = entries1[i1]
	entry2 = entries2[i2]
	if entry1.path < entry2.path:
	result.append((entry1, _NULL_ENTRY))
	i1 += 1
	elif entry1.path > entry2.path:
	result.append((_NULL_ENTRY, entry2))
	i2 += 1
	else:
	result.append((entry1, entry2))
	i1 += 1
	i2 += 1
	for i in range(i1, len1):
	result.append((entries1[i], _NULL_ENTRY))
	for i in range(i2, len2):
	result.append((_NULL_ENTRY, entries2[i]))
	return result


	def _is_tree(entry):
	mode = entry.mode
	if mode is None:
	return False
	return stat.S_ISDIR(mode)


	def walk_trees(store, tree1_id, tree2_id, prune_identical=False):
	"""Recursively walk all the entries of two trees.

	Iteration is depth-first pre-order, as in e.g. os.walk.

	Args:
	store: An ObjectStore for looking up objects.
	tree1_id: The SHA of the first Tree object to iterate, or None.
	tree2_id: The SHA of the second Tree object to iterate, or None.
	param prune_identical: If True, identical subtrees will not be walked.
	Returns:
	Iterator over Pairs of TreeEntry objects for each pair of entries
	in the trees and their subtrees recursively. If an entry exists in one
	tree but not the other, the other entry will have all attributes set
	to None. If neither entry's path is None, they are guaranteed to
	match.
	"""
	# This could be fairly easily generalized to >2 trees if we find a use
	# case.
	mode1 = tree1_id and stat.S_IFDIR or None
	mode2 = tree2_id and stat.S_IFDIR or None
	todo = [(TreeEntry(b'', mode1, tree1_id), TreeEntry(b'', mode2, tree2_id))]
	while todo:
	entry1, entry2 = todo.pop()
	is_tree1 = _is_tree(entry1)
	is_tree2 = _is_tree(entry2)
	if prune_identical and is_tree1 and is_tree2 and entry1 == entry2:
	continue

	tree1 = is_tree1 and store[entry1.sha] or None
	tree2 = is_tree2 and store[entry2.sha] or None
	path = entry1.path or entry2.path
	todo.extend(reversed(_merge_entries(path, tree1, tree2)))
	yield entry1, entry2


	def _skip_tree(entry, include_trees):
	if entry.mode is None or (not include_trees and stat.S_ISDIR(entry.mode)):
	return _NULL_ENTRY
	return entry


	def tree_changes(store, tree1_id, tree2_id, want_unchanged=False,
	rename_detector=None, include_trees=False,
	change_type_same=False):
	"""Find the differences between the contents of two trees.

	Args:
	store: An ObjectStore for looking up objects.
	tree1_id: The SHA of the source tree.
	tree2_id: The SHA of the target tree.
	want_unchanged: If True, include TreeChanges for unmodified entries
	as well.
	include_trees: Whether to include trees
	rename_detector: RenameDetector object for detecting renames.
	change_type_same: Whether to report change types in the same
	entry or as delete+add.
	Returns:
	Iterator over TreeChange instances for each change between the
	source and target tree.
	"""
	if include_trees and rename_detector is not None:
	raise NotImplementedError(
	'rename_detector and include_trees are mutually exclusive')
	if (rename_detector is not None and tree1_id is not None and
	tree2_id is not None):
	for change in rename_detector.changes_with_renames(
	tree1_id, tree2_id, want_unchanged=want_unchanged):
	yield change
	return

	entries = walk_trees(store, tree1_id, tree2_id,
	prune_identical=(not want_unchanged))
	for entry1, entry2 in entries:
	if entry1 == entry2 and not want_unchanged:
	continue

	# Treat entries for trees as missing.
	entry1 = _skip_tree(entry1, include_trees)
	entry2 = _skip_tree(entry2, include_trees)

	if entry1 != _NULL_ENTRY and entry2 != _NULL_ENTRY:
	if (stat.S_IFMT(entry1.mode) != stat.S_IFMT(entry2.mode)
	and not change_type_same):
	# File type changed: report as delete/add.
	yield TreeChange.delete(entry1)
	entry1 = _NULL_ENTRY
	change_type = CHANGE_ADD
	elif entry1 == entry2:
	change_type = CHANGE_UNCHANGED
	else:
	change_type = CHANGE_MODIFY
	elif entry1 != _NULL_ENTRY:
	change_type = CHANGE_DELETE
	elif entry2 != _NULL_ENTRY:
	change_type = CHANGE_ADD
	else:
	# Both were None because at least one was a tree.
	continue
	yield TreeChange(change_type, entry1, entry2)


	def _all_eq(seq, key, value):
	for e in seq:
	if key(e) != value:
	return False
	return True


	def _all_same(seq, key):
	return _all_eq(seq[1:], key, key(seq[0]))


	def tree_changes_for_merge(store, parent_tree_ids, tree_id,
	rename_detector=None):
	"""Get the tree changes for a merge tree relative to all its parents.

	Args:
	store: An ObjectStore for looking up objects.
	parent_tree_ids: An iterable of the SHAs of the parent trees.
	tree_id: The SHA of the merge tree.
	rename_detector: RenameDetector object for detecting renames.

	Returns:
	Iterator over lists of TreeChange objects, one per conflicted path
	in the merge.

	Each list contains one element per parent, with the TreeChange for that
	path relative to that parent. An element may be None if it never
	existed in one parent and was deleted in two others.

	A path is only included in the output if it is a conflict, i.e. its SHA
	in the merge tree is not found in any of the parents, or in the case of
	deletes, if not all of the old SHAs match.
	"""
	all_parent_changes = [tree_changes(store, t, tree_id,
	rename_detector=rename_detector)
	for t in parent_tree_ids]
	num_parents = len(parent_tree_ids)
	changes_by_path = defaultdict(lambda: [None] * num_parents)

	# Organize by path.
	for i, parent_changes in enumerate(all_parent_changes):
	for change in parent_changes:
	if change.type == CHANGE_DELETE:
	path = change.old.path
	else:
	path = change.new.path
	changes_by_path[path][i] = change

	def old_sha(c):
	return c.old.sha

	def change_type(c):
	return c.type

	# Yield only conflicting changes.
	for _, changes in sorted(changes_by_path.items()):
	assert len(changes) == num_parents
	have = [c for c in changes if c is not None]
	if _all_eq(have, change_type, CHANGE_DELETE):
	if not _all_same(have, old_sha):
	yield changes
	elif not _all_same(have, change_type):
	yield changes
	elif None not in changes:
	# If no change was found relative to one parent, that means the SHA
	# must have matched the SHA in that parent, so it is not a
	# conflict.
	yield changes


	_BLOCK_SIZE = 64


	def _count_blocks(obj):
	"""Count the blocks in an object.

	Splits the data into blocks either on lines or <=64-byte chunks of lines.

	Args:
	obj: The object to count blocks for.
	Returns:
	A dict of block hashcode -> total bytes occurring.
	"""
	block_counts = defaultdict(int)
	block = BytesIO()
	n = 0

	# Cache attrs as locals to avoid expensive lookups in the inner loop.
	block_write = block.write
	block_seek = block.seek
	block_truncate = block.truncate
	block_getvalue = block.getvalue

	for c in chain(*obj.as_raw_chunks()):
	if sys.version_info[0] == 3:
	c = c.to_bytes(1, 'big')
	block_write(c)
	n += 1
	if c == b'\n' or n == _BLOCK_SIZE:
	value = block_getvalue()
	block_counts[hash(value)] += len(value)
	block_seek(0)
	block_truncate()
	n = 0
	if n > 0:
	last_block = block_getvalue()
	block_counts[hash(last_block)] += len(last_block)
	return block_counts


	def _common_bytes(blocks1, blocks2):
	"""Count the number of common bytes in two block count dicts.

	Args:
	block1: The first dict of block hashcode -> total bytes.
	block2: The second dict of block hashcode -> total bytes.
	Returns:
	The number of bytes in common between blocks1 and blocks2. This is
	only approximate due to possible hash collisions.
	"""
	# Iterate over the smaller of the two dicts, since this is symmetrical.
	if len(blocks1) > len(blocks2):
	blocks1, blocks2 = blocks2, blocks1
	score = 0
	for block, count1 in blocks1.items():
	count2 = blocks2.get(block)
	if count2:
	score += min(count1, count2)
	return score


	def _similarity_score(obj1, obj2, block_cache=None):
	"""Compute a similarity score for two objects.

	Args:
	obj1: The first object to score.
	obj2: The second object to score.
	block_cache: An optional dict of SHA to block counts to cache
	results between calls.
	Returns:
	The similarity score between the two objects, defined as the
	number of bytes in common between the two objects divided by the
	maximum size, scaled to the range 0-100.
	"""
	if block_cache is None:
	block_cache = {}
	if obj1.id not in block_cache:
	block_cache[obj1.id] = _count_blocks(obj1)
	if obj2.id not in block_cache:
	block_cache[obj2.id] = _count_blocks(obj2)

	common_bytes = _common_bytes(block_cache[obj1.id], block_cache[obj2.id])
	max_size = max(obj1.raw_length(), obj2.raw_length())
	if not max_size:
	return _MAX_SCORE
	return int(float(common_bytes) * _MAX_SCORE / max_size)


	def _tree_change_key(entry):
	# Sort by old path then new path. If only one exists, use it for both keys.
	path1 = entry.old.path
	path2 = entry.new.path
	if path1 is None:
	path1 = path2
	if path2 is None:
	path2 = path1
	return (path1, path2)


	class RenameDetector(object):
	"""Object for handling rename detection between two trees."""

	def __init__(self, store, rename_threshold=RENAME_THRESHOLD,
	max_files=MAX_FILES,
	rewrite_threshold=REWRITE_THRESHOLD,
	find_copies_harder=False):
	"""Initialize the rename detector.

	Args:
	store: An ObjectStore for looking up objects.
	rename_threshold: The threshold similarity score for considering
	an add/delete pair to be a rename/copy; see _similarity_score.
	max_files: The maximum number of adds and deletes to consider,
	or None for no limit. The detector is guaranteed to compare no more
	than max_files ** 2 add/delete pairs. This limit is provided
	because rename detection can be quadratic in the project size. If
	the limit is exceeded, no content rename detection is attempted.
	rewrite_threshold: The threshold similarity score below which a
	modify should be considered a delete/add, or None to not break
	modifies; see _similarity_score.
	find_copies_harder: If True, consider unmodified files when
	detecting copies.
	"""
	self._store = store
	self._rename_threshold = rename_threshold
	self._rewrite_threshold = rewrite_threshold
	self._max_files = max_files
	self._find_copies_harder = find_copies_harder
	self._want_unchanged = False

	def _reset(self):
	self._adds = []
	self._deletes = []
	self._changes = []

	def _should_split(self, change):
	if (self._rewrite_threshold is None or change.type != CHANGE_MODIFY or
	change.old.sha == change.new.sha):
	return False
	old_obj = self._store[change.old.sha]
	new_obj = self._store[change.new.sha]
	return _similarity_score(old_obj, new_obj) < self._rewrite_threshold

	def _add_change(self, change):
	if change.type == CHANGE_ADD:
	self._adds.append(change)
	elif change.type == CHANGE_DELETE:
	self._deletes.append(change)
	elif self._should_split(change):
	self._deletes.append(TreeChange.delete(change.old))
	self._adds.append(TreeChange.add(change.new))
	elif ((self._find_copies_harder and change.type == CHANGE_UNCHANGED)
	or change.type == CHANGE_MODIFY):
	# Treat all modifies as potential deletes for rename detection,
	# but don't split them (to avoid spurious renames). Setting
	# find_copies_harder means we treat unchanged the same as
	# modified.
	self._deletes.append(change)
	else:
	self._changes.append(change)

	def _collect_changes(self, tree1_id, tree2_id):
	want_unchanged = self._find_copies_harder or self._want_unchanged
	for change in tree_changes(self._store, tree1_id, tree2_id,
	want_unchanged=want_unchanged):
	self._add_change(change)

	def _prune(self, add_paths, delete_paths):
	self._adds = [a for a in self._adds if a.new.path not in add_paths]
	self._deletes = [d for d in self._deletes
	if d.old.path not in delete_paths]

	def _find_exact_renames(self):
	add_map = defaultdict(list)
	for add in self._adds:
	add_map[add.new.sha].append(add.new)
	delete_map = defaultdict(list)
	for delete in self._deletes:
	# Keep track of whether the delete was actually marked as a delete.
	# If not, it needs to be marked as a copy.
	is_delete = delete.type == CHANGE_DELETE
	delete_map[delete.old.sha].append((delete.old, is_delete))

	add_paths = set()
	delete_paths = set()
	for sha, sha_deletes in delete_map.items():
	sha_adds = add_map[sha]
	for (old, is_delete), new in zip(sha_deletes, sha_adds):
	if stat.S_IFMT(old.mode) != stat.S_IFMT(new.mode):
	continue
	if is_delete:
	delete_paths.add(old.path)
	add_paths.add(new.path)
	new_type = is_delete and CHANGE_RENAME or CHANGE_COPY
	self._changes.append(TreeChange(new_type, old, new))

	num_extra_adds = len(sha_adds) - len(sha_deletes)
	# TODO(dborowitz): Less arbitrary way of dealing with extra copies.
	old = sha_deletes[0][0]
	if num_extra_adds > 0:
	for new in sha_adds[-num_extra_adds:]:
	add_paths.add(new.path)
	self._changes.append(TreeChange(CHANGE_COPY, old, new))
	self._prune(add_paths, delete_paths)

	def _should_find_content_renames(self):
	return len(self._adds) * len(self._deletes) <= self._max_files ** 2

	def _rename_type(self, check_paths, delete, add):
	if check_paths and delete.old.path == add.new.path:
	# If the paths match, this must be a split modify, so make sure it
	# comes out as a modify.
	return CHANGE_MODIFY
	elif delete.type != CHANGE_DELETE:
	# If it's in deletes but not marked as a delete, it must have been
	# added due to find_copies_harder, and needs to be marked as a
	# copy.
	return CHANGE_COPY
	return CHANGE_RENAME

	def _find_content_rename_candidates(self):
	candidates = self._candidates = []
	# TODO: Optimizations:
	# - Compare object sizes before counting blocks.
	# - Skip if delete's S_IFMT differs from all adds.
	# - Skip if adds or deletes is empty.
	# Match C git's behavior of not attempting to find content renames if
	# the matrix size exceeds the threshold.
	if not self._should_find_content_renames():
	return

	block_cache = {}
	check_paths = self._rename_threshold is not None
	for delete in self._deletes:
	if S_ISGITLINK(delete.old.mode):
	continue # Git links don't exist in this repo.
	old_sha = delete.old.sha
	old_obj = self._store[old_sha]
	block_cache[old_sha] = _count_blocks(old_obj)
	for add in self._adds:
	if stat.S_IFMT(delete.old.mode) != stat.S_IFMT(add.new.mode):
	continue
	new_obj = self._store[add.new.sha]
	score = _similarity_score(old_obj, new_obj,
	block_cache=block_cache)
	if score > self._rename_threshold:
	new_type = self._rename_type(check_paths, delete, add)
	rename = TreeChange(new_type, delete.old, add.new)
	candidates.append((-score, rename))

	def _choose_content_renames(self):
	# Sort scores from highest to lowest, but keep names in ascending
	# order.
	self._candidates.sort()

	delete_paths = set()
	add_paths = set()
	for _, change in self._candidates:
	new_path = change.new.path
	if new_path in add_paths:
	continue
	old_path = change.old.path
	orig_type = change.type
	if old_path in delete_paths:
	change = TreeChange(CHANGE_COPY, change.old, change.new)

	# If the candidate was originally a copy, that means it came from a
	# modified or unchanged path, so we don't want to prune it.
	if orig_type != CHANGE_COPY:
	delete_paths.add(old_path)
	add_paths.add(new_path)
	self._changes.append(change)
	self._prune(add_paths, delete_paths)

	def _join_modifies(self):
	if self._rewrite_threshold is None:
	return

	modifies = {}
	delete_map = dict((d.old.path, d) for d in self._deletes)
	for add in self._adds:
	path = add.new.path
	delete = delete_map.get(path)
	if (delete is not None and
	stat.S_IFMT(delete.old.mode) == stat.S_IFMT(add.new.mode)):
	modifies[path] = TreeChange(CHANGE_MODIFY, delete.old, add.new)

	self._adds = [a for a in self._adds if a.new.path not in modifies]
	self._deletes = [a for a in self._deletes if a.new.path not in
	modifies]
	self._changes += modifies.values()

	def _sorted_changes(self):
	result = []
	result.extend(self._adds)
	result.extend(self._deletes)
	result.extend(self._changes)
	result.sort(key=_tree_change_key)
	return result

	def _prune_unchanged(self):
	if self._want_unchanged:
	return
	self._deletes = [
	d for d in self._deletes if d.type != CHANGE_UNCHANGED]

	def changes_with_renames(self, tree1_id, tree2_id, want_unchanged=False):
	"""Iterate TreeChanges between two tree SHAs, with rename detection."""
	self._reset()
	self._want_unchanged = want_unchanged
	self._collect_changes(tree1_id, tree2_id)
	self._find_exact_renames()
	self._find_content_rename_candidates()
	self._choose_content_renames()
	self._join_modifies()
	self._prune_unchanged()
	return self._sorted_changes()


	# Hold on to the pure-python implementations for testing.
	_is_tree_py = _is_tree
	_merge_entries_py = _merge_entries
	_count_blocks_py = _count_blocks
	try:
	# Try to import C versions
	from dulwich._diff_tree import _is_tree, _merge_entries, _count_blocks
	except ImportError:
	pass

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