import lz4, struct
from mercurial import util
from mercurial.node import nullid, hex
from mercurial.i18n import _
import basepack, constants
import cdatapack

# Index entry format is: <node><delta offset><pack data offset><pack data size>
# See the mutabledatapack doccomment for more details.
INDEXFORMAT = '!20siQQ'
INDEXENTRYLENGTH = 40
NODELENGTH = 20

# The indicator value in the index for a fulltext entry.
FULLTEXTINDEXMARK = -1
NOBASEINDEXMARK = -2

INDEXSUFFIX = '.dataidx'
PACKSUFFIX = '.datapack'

class datapackstore(basepack.basepackstore):
    INDEXSUFFIX = INDEXSUFFIX
    PACKSUFFIX = PACKSUFFIX

    def __init__(self, path, usecdatapack=False):
        self.usecdatapack = usecdatapack
        super(datapackstore, self).__init__(path)

    def getpack(self, path):
        if self.usecdatapack:
            return fastdatapack(path)
        else:
            return datapack(path)

    def get(self, name, node):
        raise RuntimeError("must use getdeltachain with datapackstore")

    def getdeltachain(self, name, node):
        for pack in self.packs:
            try:
                return pack.getdeltachain(name, node)
            except KeyError:
                pass

        for pack in self.refresh():
            try:
                return pack.getdeltachain(name, node)
            except KeyError:
                pass

        raise KeyError((name, hex(node)))

    def add(self, name, node, data):
        raise RuntimeError("cannot add to datapackstore")

class datapack(basepack.basepack):
    INDEXSUFFIX = INDEXSUFFIX
    PACKSUFFIX = PACKSUFFIX

    def getmissing(self, keys):
        missing = []
        for name, node in keys:
            value = self._find(node)
            if not value:
                missing.append((name, node))

        return missing

    def get(self, name, node):
        raise RuntimeError("must use getdeltachain with datapack (%s:%s)"
                           % (name, hex(node)))

    def getdeltachain(self, name, node):
        value = self._find(node)
        if value is None:
            raise KeyError((name, hex(node)))

        params = self.params

        # Precompute chains
        chain = [value]
        deltabaseoffset = value[1]
        while (deltabaseoffset != FULLTEXTINDEXMARK
               and deltabaseoffset != NOBASEINDEXMARK):
            loc = params.indexstart + deltabaseoffset
            value = struct.unpack(INDEXFORMAT, self._index[loc:loc +
                                                           INDEXENTRYLENGTH])
            deltabaseoffset = value[1]
            chain.append(value)

        # Read chain data
        deltachain = []
        for node, deltabaseoffset, offset, size in chain:
            rawentry = self._data[offset:offset + size]
            self._pagedin += len(rawentry)

            # <2 byte len> + <filename>
            lengthsize = 2
            filenamelen = struct.unpack('!H', rawentry[:2])[0]
            filename = rawentry[lengthsize:lengthsize + filenamelen]

            # <20 byte node> + <20 byte deltabase>
            nodestart = lengthsize + filenamelen
            deltabasestart = nodestart + NODELENGTH
            node = rawentry[nodestart:deltabasestart]
            deltabasenode = rawentry[deltabasestart:deltabasestart + NODELENGTH]

            # <8 byte len> + <delta>
            deltastart = deltabasestart + NODELENGTH
            rawdeltalen = rawentry[deltastart:deltastart + 8]
            deltalen = struct.unpack('!Q', rawdeltalen)[0]

            delta = rawentry[deltastart + 8:deltastart + 8 + deltalen]
            delta = lz4.decompress(delta)

            deltachain.append((filename, node, filename, deltabasenode, delta))

        # If we've read a lot of data from the mmap, free some memory.
        self.freememory()

        return deltachain

    def add(self, name, node, data):
        raise RuntimeError("cannot add to datapack (%s:%s)" % (name, node))

    def _find(self, node):
        params = self.params
        fanoutkey = struct.unpack(params.fanoutstruct,
                                  node[:params.fanoutprefix])[0]
        fanout = self._fanouttable

        start = fanout[fanoutkey] + params.indexstart
        # Scan forward to find the first non-same entry, which is the upper
        # bound.
        for i in xrange(fanoutkey + 1, params.fanoutcount):
            end = fanout[i] + params.indexstart
            if end != start:
                break
        else:
            end = self.indexsize

        # Bisect between start and end to find node
        index = self._index
        startnode = index[start:start + NODELENGTH]
        endnode = index[end:end + NODELENGTH]
        if startnode == node:
            entry = index[start:start + INDEXENTRYLENGTH]
        elif endnode == node:
            entry = index[end:end + INDEXENTRYLENGTH]
        else:
            while start < end - INDEXENTRYLENGTH:
                mid = start  + (end - start) / 2
                mid = mid - ((mid - params.indexstart) % INDEXENTRYLENGTH)
                midnode = index[mid:mid + NODELENGTH]
                if midnode == node:
                    entry = index[mid:mid + INDEXENTRYLENGTH]
                    break
                if node > midnode:
                    start = mid
                    startnode = midnode
                elif node < midnode:
                    end = mid
                    endnode = midnode
            else:
                return None

        return struct.unpack(INDEXFORMAT, entry)

    def markledger(self, ledger):
        for filename, node in self:
            ledger.markdataentry(self, filename, node)

    def cleanup(self, ledger):
        entries = ledger.sources.get(self, [])
        allkeys = set(self)
        repackedkeys = set((e.filename, e.node) for e in entries if
                           e.datarepacked)

        if len(allkeys - repackedkeys) == 0:
            if self.path not in ledger.created:
                util.unlinkpath(self.indexpath, ignoremissing=True)
                util.unlinkpath(self.packpath, ignoremissing=True)

    def __iter__(self):
        for f, n, deltabase, deltalen in self.iterentries():
            yield f, n

    def iterentries(self):
        # Start at 1 to skip the header
        offset = 1
        while offset < self.datasize:
            data = self._data
            # <2 byte len> + <filename>
            filenamelen = struct.unpack('!H', data[offset:offset + 2])[0]
            offset += 2
            filename = data[offset:offset + filenamelen]
            offset += filenamelen

            # <20 byte node>
            node = data[offset:offset + constants.NODESIZE]
            offset += constants.NODESIZE
            # <20 byte deltabase>
            deltabase = data[offset:offset + constants.NODESIZE]
            offset += constants.NODESIZE

            # <8 byte len> + <delta>
            rawdeltalen = data[offset:offset + 8]
            deltalen = struct.unpack('!Q', rawdeltalen)[0]
            offset += 8

            # it has to be at least long enough for the lz4 header.
            assert deltalen >= 4

            # python-lz4 stores the length of the uncompressed field as a
            # little-endian 32-bit integer at the start of the data.
            uncompressedlen = struct.unpack('<I', data[offset:offset + 4])[0]
            offset += deltalen

            self._pagedin += (
                2 +             # the filename length
                filenamelen +   # the filename itself.
                2 * constants.NODESIZE + # the two nodes.
                8 +             # the delta length
                4               # the uncompressed delta length
            )

            yield (filename, node, deltabase, uncompressedlen)

            # If we've read a lot of data from the mmap, free some memory.
            self.freememory()

class fastdatapack(basepack.basepack):
    INDEXSUFFIX = INDEXSUFFIX
    PACKSUFFIX = PACKSUFFIX

    def __init__(self, path):
        self.path = path
        self.packpath = path + self.PACKSUFFIX
        self.indexpath = path + self.INDEXSUFFIX
        self.datapack = cdatapack.datapack(path)

    def getmissing(self, keys):
        missing = []
        for name, node in keys:
            value = self.datapack._find(node)
            if not value:
                missing.append((name, node))

        return missing

    def get(self, name, node):
        raise RuntimeError("must use getdeltachain with datapack (%s:%s)"
                           % (name, hex(node)))

    def getdeltachain(self, name, node):
        result = self.datapack.getdeltachain(node)
        if result is None:
            raise KeyError((name, hex(node)))

        return result

    def add(self, name, node, data):
        raise RuntimeError("cannot add to datapack (%s:%s)" % (name, node))

    def markledger(self, ledger):
        for filename, node in self:
            ledger.markdataentry(self, filename, node)

    def cleanup(self, ledger):
        entries = ledger.sources.get(self, [])
        allkeys = set(self)
        repackedkeys = set((e.filename, e.node) for e in entries if
                           e.datarepacked)

        if len(allkeys - repackedkeys) == 0:
            if self.path not in ledger.created:
                util.unlinkpath(self.indexpath, ignoremissing=True)
                util.unlinkpath(self.packpath, ignoremissing=True)

    def __iter__(self):
        return self.datapack.__iter__()

    def iterentries(self):
        return self.datapack.iterentries()

class mutabledatapack(basepack.mutablebasepack):
    """A class for constructing and serializing a datapack file and index.

    A datapack is a pair of files that contain the revision contents for various
    file revisions in Mercurial. It contains only revision contents (like file
    contents), not any history information.

    It consists of two files, with the following format. All bytes are in
    network byte order (big endian).

    .datapack
        The pack itself is a series of revision deltas with some basic header
        information on each. A revision delta may be a fulltext, represented by
        a deltabasenode equal to the nullid.

        datapack = <version: 1 byte>
                   [<revision>,...]
        revision = <filename len: 2 byte unsigned int>
                   <filename>
                   <node: 20 byte>
                   <deltabasenode: 20 byte>
                   <delta len: 8 byte unsigned int>
                   <delta>

    .dataidx
        The index file consists of two parts, the fanout and the index.

        The index is a list of index entries, sorted by node (one per revision
        in the pack). Each entry has:

        - node (The 20 byte node of the entry; i.e. the commit hash, file node
                hash, etc)
        - deltabase index offset (The location in the index of the deltabase for
                                  this entry. The deltabase is the next delta in
                                  the chain, with the chain eventually
                                  terminating in a full-text, represented by a
                                  deltabase offset of -1. This lets us compute
                                  delta chains from the index, then do
                                  sequential reads from the pack if the revision
                                  are nearby on disk.)
        - pack entry offset (The location of this entry in the datapack)
        - pack content size (The on-disk length of this entry's pack data)

        The fanout is a quick lookup table to reduce the number of steps for
        bisecting the index. It is a series of 4 byte pointers to positions
        within the index. It has 2^16 entries, which corresponds to hash
        prefixes [0000, 0001,..., FFFE, FFFF]. Example: the pointer in slot
        4F0A points to the index position of the first revision whose node
        starts with 4F0A. This saves log(2^16)=16 bisect steps.

        dataidx = <fanouttable>
                  <index>
        fanouttable = [<index offset: 4 byte unsigned int>,...] (2^16 entries)
        index = [<index entry>,...]
        indexentry = <node: 20 byte>
                     <deltabase location: 4 byte signed int>
                     <pack entry offset: 8 byte unsigned int>
                     <pack entry size: 8 byte unsigned int>
    """
    INDEXSUFFIX = INDEXSUFFIX
    PACKSUFFIX = PACKSUFFIX
    INDEXENTRYLENGTH = INDEXENTRYLENGTH

    def add(self, name, node, deltabasenode, delta):
        if len(name) > 2**16:
            raise RuntimeError(_("name too long %s") % name)
        if len(node) != 20:
            raise RuntimeError(_("node should be 20 bytes %s") % node)

        if node in self.entries:
            # The revision has already been added
            return

        # TODO: allow configurable compression
        delta = lz4.compress(delta)
        rawdata = "%s%s%s%s%s%s" % (
            struct.pack('!H', len(name)), # unsigned 2 byte int
            name,
            node,
            deltabasenode,
            struct.pack('!Q', len(delta)), # unsigned 8 byte int
            delta)

        offset = self.packfp.tell()

        size = len(rawdata)

        self.entries[node] = (deltabasenode, offset, size)

        self.writeraw(rawdata)

    def createindex(self, nodelocations):
        entries = sorted((n, db, o, s) for n, (db, o, s)
                         in self.entries.iteritems())

        rawindex = ''
        for node, deltabase, offset, size in entries:
            if deltabase == nullid:
                deltabaselocation = FULLTEXTINDEXMARK
            else:
                # Instead of storing the deltabase node in the index, let's
                # store a pointer directly to the index entry for the deltabase.
                deltabaselocation = nodelocations.get(deltabase,
                                                      NOBASEINDEXMARK)

            entry = struct.pack(INDEXFORMAT, node, deltabaselocation, offset,
                                size)
            rawindex += entry

        return rawindex