/brz/remove-bazaar

# Copyright (C) 2008 Canonical Ltd

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Persistent maps from tuple_of_strings->string using CHK stores.

Overview and current status:

The CHKMap class implements a dict from tuple_of_strings->string by using a trie

with internal nodes of 8-bit fan out; The key tuples are mapped to strings by

joining them by \x00, and \x00 padding shorter keys out to the length of the

longest key. Leaf nodes are packed as densely as possible, and internal nodes

are all and additional 8-bits wide leading to a sparse upper tree. 

Updates to a CHKMap are done preferentially via the apply_delta method, to

allow optimisation of the update operation; but individual map/unmap calls are

possible and supported. All changes via map/unmap are buffered in memory until

the _save method is called to force serialisation of the tree. apply_delta

performs a _save implicitly.

TODO:

-----

Densely packed upper nodes.

"""

import heapq

import osutils

class CHKMap(object):

    """A persistent map from string to string backed by a CHK store."""

    def __init__(self, store, root_key):

        """Create a CHKMap object.

        :param store: The store the CHKMap is stored in.

        :param root_key: The root key of the map. None to create an empty

            CHKMap.

        """

        self._store = store

        if root_key is None:

            self._root_node = LeafNode()

        else:

            self._root_node = self._node_key(root_key)

    def apply_delta(self, delta):

        """Apply a delta to the map.

        :param delta: An iterable of old_key, new_key, new_value tuples.

            If new_key is not None, then new_key->new_value is inserted

            into the map; if old_key is not None, then the old mapping

            of old_key is removed.

        """

        for old, new, value in delta:

            if old is not None and old != new:

                # unmap

                self.unmap(old)

        for old, new, value in delta:

            if new is not None:

                # map

                self.map(new, value)

        return self._save()

    def _ensure_root(self):

        """Ensure that the root node is an object not a key."""

        if type(self._root_node) == tuple:

            # Demand-load the root

            self._root_node = self._get_node(self._root_node)

    def _get_node(self, node):

        """Get a node.

        Node that this does not update the _items dict in objects containing a

        reference to this node. As such it does not prevent subsequent IO being

        performed.

        :param node: A tuple key or node object.

        :return: A node object.

        """

        if type(node) == tuple:

            bytes = self._read_bytes(node)

            return _deserialise(bytes, node)

        else:

            return node

    def _read_bytes(self, key):

        stream = self._store.get_record_stream([key], 'unordered', True)

        return stream.next().get_bytes_as('fulltext')

    def _dump_tree(self):

        """Return the tree in a string representation."""

        self._ensure_root()

        res = self._dump_tree_node(self._root_node, prefix='', indent='')

        return ''.join(res)

    def _dump_tree_node(self, node, prefix, indent):

        """For this node and all children, generate a string representation."""

        result = []

        result.append('%s%r %s %s\n' % (indent, prefix, node.__class__.__name__,

                                        node.key()[0]))

        if isinstance(node, InternalNode):

            # Trigger all child nodes to get loaded

            list(node._iter_nodes(self._store))

            for prefix, sub in node._items.iteritems():

                result.extend(self._dump_tree_node(sub, prefix, indent + '  '))

        else:

            for key, value in node._items.iteritems():

                result.append("%s  %r %r\n" % (indent, key, value))

        return result

    @classmethod

    def from_dict(klass, store, initial_value, maximum_size=0):

        """Create a CHKMap in store with initial_value as the content.

        :param store: The store to record initial_value in, a VersionedFiles

            object with 1-tuple keys supporting CHK key generation.

        :param initial_value: A dict to store in store. Its keys and values

            must be bytestrings.

        :param maximum_size: The maximum_size rule to apply to nodes. This

            determines the size at which no new data is added to a single node.

        :return: The root chk of te resulting CHKMap.

        """

        result = CHKMap(store, None)

        result._root_node.set_maximum_size(maximum_size)

        delta = []

        for key, value in initial_value.items():

            delta.append((None, key, value))

        result.apply_delta(delta)

        return result._save()

    def iter_changes(self, basis):

        """Iterate over the changes between basis and self.

        :return: An iterator of tuples: (key, old_value, new_value). Old_value

            is None for keys only in self; new_value is None for keys only in

            basis.

        """

        # Overview:

        # Read both trees in lexographic, highest-first order.

        # Any identical nodes we skip

        # Any unique prefixes we output immediately.

        # values in a leaf node are treated as single-value nodes in the tree

        # which allows them to be not-special-cased. We know to output them

        # because their value is a string, not a key(tuple) or node.

        #

        # corner cases to beware of when considering this function:

        # *) common references are at different heights.

        #    consider two trees:

        #    {'a': LeafNode={'aaa':'foo', 'aab':'bar'}, 'b': LeafNode={'b'}}

        #    {'a': InternalNode={'aa':LeafNode={'aaa':'foo', 'aab':'bar'}, 'ab':LeafNode={'ab':'bar'}}

        #     'b': LeafNode={'b'}}

        #    the node with aaa/aab will only be encountered in the second tree

        #    after reading the 'a' subtree, but it is encountered in the first

        #    tree immediately. Variations on this may have read internal nodes like this.

        #    we want to cut the entire pending subtree when we realise we have a common node.

        #    For this we use a list of keys - the path to a node - and check the entire path is 

        #    clean as we process each item.

        if self._node_key(self._root_node) == self._node_key(basis._root_node):

            return

        self._ensure_root()

        basis._ensure_root()

        excluded_keys = set()

        self_node = self._root_node

        basis_node = basis._root_node

        # A heap, each element is prefix, node(tuple/NodeObject/string),

        # key_path (a list of tuples, tail-sharing down the tree.)

        self_pending = []

        basis_pending = []

        def process_node(prefix, node, path, a_map, pending):

            # take a node and expand it

            node = a_map._get_node(node)

            if type(node) == LeafNode:

                path = (node._key, path)

                for key, value in node._items.items():

                    heapq.heappush(pending, ('\x00'.join(key), value, path))

            else:

                # type(node) == InternalNode

                path = (node._key, path)

                for prefix, child in node._items.items():

                    heapq.heappush(pending, (prefix, child, path))

        process_node(None, self_node, None, self, self_pending)

        process_node(None, basis_node, None, basis, basis_pending)

        self_seen = set()

        basis_seen = set()

        excluded_keys = set()

        def check_excluded(key_path):

            # Note that this is N^2, it depends on us trimming trees

            # aggressively to not become slow.

            # A better implementation would probably have a reverse map

            # back to the children of a node, and jump straight to it when 

            # a common node is detected, the proceed to remove the already

            # pending children. bzrlib.graph has a searcher module with a

            # similar problem.

            while key_path is not None:

                key, key_path = key_path

                if key in excluded_keys:

                    return True

            return False

        loop_counter = 0

        while self_pending or basis_pending:

            loop_counter += 1

            if not self_pending:

                # self is exhausted: output remainder of basis

                for prefix, node, path in basis_pending:

                    if check_excluded(path):

                        continue

                    node = basis._get_node(node)

                    if type(node) == str:

                        # a value

                        yield (tuple(prefix.split('\x00')), node, None)

                    else:

                        # subtree - fastpath the entire thing.

                        for key, value in node.iteritems(basis._store):

                            yield (key, value, None)

                return

            elif not basis_pending:

                # basis is exhausted: output remainder of self.

                for prefix, node, path in self_pending:

                    if check_excluded(path):

                        continue

                    node = self._get_node(node)

                    if type(node) == str:

                        # a value

                        yield (tuple(prefix.split('\x00')), None, node)

                    else:

                        # subtree - fastpath the entire thing.

                        for key, value in node.iteritems(self._store):

                            yield (key, None, value)

                return

            else:

                # XXX: future optimisation - yield the smaller items

                # immediately rather than pushing everything on/off the

                # heaps. Applies to both internal nodes and leafnodes.

                if self_pending[0][0] < basis_pending[0][0]:

                    # expand self

                    prefix, node, path = heapq.heappop(self_pending)

                    if check_excluded(path):

                        continue

                    if type(node) == str:

                        # a value

                        yield (tuple(prefix.split('\x00')), None, node)

                    else:

                        process_node(prefix, node, path, self, self_pending)

                        continue

                elif self_pending[0][0] > basis_pending[0][0]:

                    # expand basis

                    prefix, node, path = heapq.heappop(basis_pending)

                    if check_excluded(path):

                        continue

                    if type(node) == str:

                        # a value

                        yield (tuple(prefix.split('\x00')), node, None)

                    else:

                        process_node(prefix, node, path, basis, basis_pending)

                        continue

                else:

                    # common prefix: possibly expand both

                    if type(self_pending[0][1]) != str:

                        # process next self

                        read_self = True

                    else:

                        read_self = False

                    if type(basis_pending[0][1]) != str:

                        # process next basis

                        read_basis = True

                    else:

                        read_basis = False

                    if not read_self and not read_basis:

                        # compare a common value

                        self_details = heapq.heappop(self_pending)

                        basis_details = heapq.heappop(basis_pending)

                        if self_details[1] != basis_details[1]:

                            yield (tuple(self_details[0].split('\x00')),

                                basis_details[1], self_details[1])

                        continue

                    # At least one side wasn't a string.

                    if (self._node_key(self_pending[0][1]) ==

                        self._node_key(basis_pending[0][1])):

                        # Identical pointers, skip (and don't bother adding to

                        # excluded, it won't turn up again.

                        heapq.heappop(self_pending)

                        heapq.heappop(basis_pending)

                        continue

                    # Now we need to expand this node before we can continue

                    if read_self:

                        prefix, node, path = heapq.heappop(self_pending)

                        if check_excluded(path):

                            continue

                        process_node(prefix, node, path, self, self_pending)

                    if read_basis:

                        prefix, node, path = heapq.heappop(basis_pending)

                        if check_excluded(path):

                            continue

                        process_node(prefix, node, path, basis, basis_pending)

        # print loop_counter

    def iteritems(self, key_filter=None):

        """Iterate over the entire CHKMap's contents."""

        self._ensure_root()

        return self._root_node.iteritems(self._store, key_filter=key_filter)

    def key(self):

        """Return the key for this map."""

        if isinstance(self._root_node, tuple):

            return self._root_node

        else:

            return self._root_node._key

    def __len__(self):

        self._ensure_root()

        return len(self._root_node)

    def map(self, key, value):

        """Map a key tuple to value."""

        # Need a root object.

        self._ensure_root()

        prefix, node_details = self._root_node.map(self._store, key, value)

        if len(node_details) == 1:

            self._root_node = node_details[0][1]

        else:

            self._root_node = InternalNode()

            self._root_node.set_maximum_size(node_details[0][1].maximum_size)

            self._root_node._key_width = node_details[0][1]._key_width

            for split, node in node_details:

                self._root_node.add_node(split, node)

    def _node_key(self, node):

        """Get the key for a node whether its a tuple o r node."""

        if type(node) == tuple:

            return node

        else:

            return node._key

    def unmap(self, key):

        """remove key from the map."""

        self._ensure_root()

        self._root_node.unmap(self._store, key)

    def _save(self):

        """Save the map completely.

        :return: The key of the root node.

        """

        if type(self._root_node) == tuple:

            # Already saved.

            return self._root_node

        keys = list(self._root_node.serialise(self._store))

        return keys[-1]

class Node(object):

    """Base class defining the protocol for CHK Map nodes."""

    def __init__(self, key_width=1):

        """Create a node.

        :param key_width: The width of keys for this node.

        """

        self._key = None

        # Current number of elements

        self._len = 0

        self._maximum_size = 0

        self._key_width = 1

        # current size in bytes

        self._size = 0

        # The pointers/values this node has - meaning defined by child classes.

        self._items = {}

    def key(self):

        return self._key

    def __len__(self):

        return self._len

    @property

    def maximum_size(self):

        """What is the upper limit for adding references to a node."""

        return self._maximum_size

    def set_maximum_size(self, new_size):

        """Set the size threshold for nodes.

        :param new_size: The size at which no data is added to a node. 0 for

            unlimited.

        """

        self._maximum_size = new_size

class LeafNode(Node):

    """A node containing actual key:value pairs.

    :ivar _items: A dict of key->value items. The key is in tuple form.

    """

    def __init__(self):

        Node.__init__(self)

        # The size of a leaf node with default values and no children.

        self._size = 12

    def _current_size(self):

        """Answer the current serialised size of this node."""

        return (self._size + len(str(self._len)) + len(str(self._key_width)) +

            len(str(self._maximum_size)))

    @classmethod

    def deserialise(klass, bytes, key):

        """Deserialise bytes, with key key, into a LeafNode.

        :param bytes: The bytes of the node.

        :param key: The key that the serialised node has.

        """

        result = LeafNode()

        lines = bytes.splitlines()

        items = {}

        if lines[0] != 'chkleaf:':

            raise ValueError("not a serialised leaf node: %r" % bytes)

        maximum_size = int(lines[1])

        width = int(lines[2])

        length = int(lines[3])

        for line in lines[4:]:

            elements = line.split('\x00', width)

            items[tuple(elements[:-1])] = elements[-1]

        if len(items) != length:

            raise AssertionError("item count mismatch")

        result._items = items

        result._len = length

        result._maximum_size = maximum_size

        result._key = key

        result._key_width = width

        result._size = len(bytes)

        return result

    def iteritems(self, store, key_filter=None):

        if key_filter is not None:

            for item in self._items.iteritems():

                if item[0] in key_filter:

                    yield item

        else:

            for item in self._items.iteritems():

                yield item

    def map(self, store, key, value):

        """Map key to value."""

        if key in self._items:

            self._size -= 2 + len('\x00'.join(key)) + len(self._items[key])

            self._len -= 1

        self._items[key] = value

        self._size += 2 + len('\x00'.join(key)) + len(value)

        self._len += 1

        self._key = None

        if (self._maximum_size and self._current_size() > self._maximum_size and

            self._len > 1):

            common_prefix = self.unique_serialised_prefix()

            split_at = len(common_prefix) + 1

            result = {}

            for key, value in self._items.iteritems():

                serialised_key = self._serialised_key(key)

                prefix = serialised_key[:split_at]

                if prefix not in result:

                    node = LeafNode()

                    node.set_maximum_size(self._maximum_size)

                    node._key_width = self._key_width

                    result[prefix] = node

                else:

                    node = result[prefix]

                node.map(store, key, value)

            return common_prefix, result.items()

        else:

            return self.unique_serialised_prefix(), [("", self)]

    def serialise(self, store):

        """Serialise the tree to store.

        :param store: A VersionedFiles honouring the CHK extensions.

        :return: An iterable of the keys inserted by this operation.

        """

        lines = ["chkleaf:\n"]

        lines.append("%d\n" % self._maximum_size)

        lines.append("%d\n" % self._key_width)

        lines.append("%d\n" % self._len)

        for key, value in sorted(self._items.items()):

            lines.append("%s\x00%s\n" % ('\x00'.join(key), value))

        sha1, _, _ = store.add_lines((None,), (), lines)

        self._key = ("sha1:" + sha1,)

        return [self._key]

    def _serialised_key(self, key):

        """Return the serialised key for key in this node."""

        return '\x00'.join(key)

    def refs(self):

        """Return the references to other CHK's held by this node."""

        return []

    def unique_serialised_prefix(self):

        """Return the unique key prefix for this node.

        :return: A bytestring of the longest serialised key prefix that is

            unique within this node.

        """

        # may want to cache this eventually :- but wait for enough

        # functionality to profile.

        keys = list(self._items.keys())

        if not keys:

            return ""

        current_prefix = self._serialised_key(keys.pop(-1))

        while current_prefix and keys:

            next_key = self._serialised_key(keys.pop(-1))

            for pos, (left, right) in enumerate(zip(current_prefix, next_key)):

                if left != right:

                    pos -= 1

                    break

            current_prefix = current_prefix[:pos + 1]

        return current_prefix

    def unmap(self, store, key):

        """Unmap key from the node."""

        self._size -= 2 + len('\x00'.join(key)) + len(self._items[key])

        self._len -= 1

        del self._items[key]

        self._key = None

        return self

class InternalNode(Node):

    """A node that contains references to other nodes.

    An InternalNode is responsible for mapping serialised key prefixes to child

    nodes. It is greedy - it will defer splitting itself as long as possible.

    """

    def __init__(self):

        Node.__init__(self)

        # The size of an internalnode with default values and no children.

        # self._size = 12

        # How many octets key prefixes within this node are.

        self._node_width = 0

    def add_node(self, prefix, node):

        """Add a child node with prefix prefix, and node node.

        :param prefix: The serialised key prefix for node.

        :param node: The node being added.

        """

        self._len += len(node)

        if not len(self._items):

            self._node_width = len(prefix)

        self._items[prefix] = node

        self._key = None

    def _current_size(self):

        """Answer the current serialised size of this node."""

        return (self._size + len(str(self._len)) + len(str(self._key_width)) +

            len(str(self._maximum_size)))

    @classmethod

    def deserialise(klass, bytes, key):

        """Deserialise bytes to an InternalNode, with key key.

        :param bytes: The bytes of the node.

        :param key: The key that the serialised node has.

        :return: An InternalNode instance.

        """

        result = InternalNode()

        lines = bytes.splitlines()

        items = {}

        if lines[0] != 'chknode:':

            raise ValueError("not a serialised internal node: %r" % bytes)

        maximum_size = int(lines[1])

        width = int(lines[2])

        length = int(lines[3])

        for line in lines[4:]:

            prefix, flat_key = line.rsplit('\x00', 1)

            items[prefix] = (flat_key,)

        result._items = items

        result._len = length

        result._maximum_size = maximum_size

        result._key = key

        result._key_width = width

        result._size = len(bytes)

        result._node_width = len(prefix)

        return result

    def iteritems(self, store, key_filter=None):

        for node in self._iter_nodes(store, key_filter=key_filter):

            for item in node.iteritems(store, key_filter=key_filter):

                yield item

    def _iter_nodes(self, store, key_filter=None):

        """Iterate over node objects which match key_filter.

        :param store: A store to use for accessing content.

        :param key_filter: A key filter to filter nodes. Only nodes that might

            contain a key in key_filter will be returned.

        :return: An iterable of nodes.

        """

        nodes = []

        keys = {}

        if key_filter is None:

            for prefix, node in self._items.iteritems():

                if type(node) == tuple:

                    keys[node] = prefix

                else:

                    nodes.append(node)

        else:

            serialised_filter = set([self._serialised_key(key) for key in

                key_filter])

            for prefix, node in self._items.iteritems():

                if prefix in serialised_filter:

                    if type(node) == tuple:

                        keys[node] = prefix

                    else:

                        nodes.append(node)

        if keys:

            # demand load some pages.

            stream = store.get_record_stream(keys, 'unordered', True)

            for record in stream:

                node = _deserialise(record.get_bytes_as('fulltext'), record.key)

                nodes.append(node)

                self._items[keys[record.key]] = node

        return nodes

    def map(self, store, key, value):

        """Map key to value."""

        if not len(self._items):

            raise AssertionError("cant map in an empty InternalNode.")

        children = self._iter_nodes(store, key_filter=[key])

        serialised_key = self._serialised_key(key)

        if children:

            child = children[0]

        else:

            # new child needed:

            child = self._new_child(serialised_key, LeafNode)

        old_len = len(child)

        prefix, node_details = child.map(store, key, value)

        if len(node_details) == 1:

            # child may have shrunk, or might be the same.

            self._len = self._len - old_len + len(child)

            self._items[serialised_key] = child

            self._key = None

            return self.unique_serialised_prefix(), [("", self)]

        # child has overflown - create a new intermediate node.

        # XXX: This is where we might want to try and expand our depth

        # to refer to more bytes of every child (which would give us

        # multiple pointers to child nodes, but less intermediate nodes)

        child = self._new_child(serialised_key, InternalNode)

        for split, node in node_details:

            child.add_node(split, node)

        self._len = self._len - old_len + len(child)

        self._key = None

        return self.unique_serialised_prefix(), [("", self)]

    def _new_child(self, serialised_key, klass):

        """Create a new child node of type klass."""

        child = klass()

        child.set_maximum_size(self._maximum_size)

        child._key_width = self._key_width

        self._items[serialised_key] = child

        return child

    def serialise(self, store):

        """Serialise the node to store.

        :param store: A VersionedFiles honouring the CHK extensions.

        :return: An iterable of the keys inserted by this operation.

        """

        for node in self._items.itervalues():

            if type(node) == tuple:

                # Never deserialised.

                continue

            if node._key is not None:

                # Never altered

                continue

            for key in node.serialise(store):

                yield key

        lines = ["chknode:\n"]

        lines.append("%d\n" % self._maximum_size)

        lines.append("%d\n" % self._key_width)

        lines.append("%d\n" % self._len)

        for prefix, node in sorted(self._items.items()):

            if type(node) == tuple:

                key = node[0]

            else: