"""
Buffer protocol support.
"""
from rpython.rtyper.lltypesystem import lltype, llmemory
from rpython.rtyper.lltypesystem.lloperation import llop
from rpython.rtyper.lltypesystem.rstr import STR
from rpython.rtyper.lltypesystem.rlist import LIST_OF
from rpython.rtyper.annlowlevel import llstr
from rpython.rlib.objectmodel import specialize, we_are_translated
from rpython.rlib import jit
from rpython.rlib.rgc import (resizable_list_supporting_raw_ptr,
                              nonmoving_raw_ptr_for_resizable_list,
                              ll_for_resizable_list)
from rpython.rlib.signature import signature
from rpython.rlib import types
from rpython.rlib import rawstorage

ALLOW_UNALIGNED_ACCESS = rawstorage.misaligned_is_fine

@specialize.ll()
def is_alignment_correct(TYPE, index):
    if ALLOW_UNALIGNED_ACCESS:
        return True
    try:
        rawstorage._check_alignment(TYPE, index)
    except rawstorage.AlignmentError:
        return False
    else:
        return True


class CannotRead(Exception):
    """
    Exception raised by Buffer.typed_read in case it is not possible to
    accomplish the request. This might be because it is not supported by the
    specific type of buffer, or because of alignment issues.
    """

class CannotWrite(Exception):
    """
    Raised by Buffer.typed_write in case it is not possible to accomplish the
    request
    """

class Buffer(object):
    """
    Base class for buffers of bytes.

    Most probably, you do NOT want to use this as a lone base class, but
    either inherit from RawBuffer or GCBuffer, so that you automatically get
    the proper implementation of typed_read and typed_write.
    """
    _attrs_ = ['readonly']
    _immutable_ = True

    def getlength(self):
        """Return the size in bytes."""
        raise NotImplementedError

    def __len__(self):
        res = self.getlength()
        assert res >= 0
        return res

    def as_str(self):
        "Returns an interp-level string with the whole content of the buffer."
        # May be overridden.
        return self.getslice(0, self.getlength(), 1, self.getlength())

    def getitem(self, index):
        "Returns the index'th character in the buffer."
        raise NotImplementedError   # Must be overriden.  No bounds checks.

    def __getitem__(self, i):
        return self.getitem(i)

    def getslice(self, start, stop, step, size):
        # May be overridden.  No bounds checks.
        return ''.join([self.getitem(i) for i in range(start, stop, step)])

    @signature(types.any(), types.int(), types.int(), returns=types.str())
    def __getslice__(self, start, stop):
        return self.getslice(start, stop, 1, stop - start)

    def setitem(self, index, char):
        "Write a character into the buffer."
        raise NotImplementedError   # Must be overriden.  No bounds checks.

    def __setitem__(self, i, char):
        return self.setitem(i, char)

    def setslice(self, start, string):
        # May be overridden.  No bounds checks.
        for i in range(len(string)):
            self.setitem(start + i, string[i])

    @jit.look_inside_iff(lambda self, index, count:
                         jit.isconstant(count) and count <= 8)
    def setzeros(self, index, count):
        for i in range(index, index+count):
            self.setitem(i, '\x00')

    @specialize.ll_and_arg(1)
    def typed_read(self, TP, byte_offset):
        """
        Read the value of type TP starting at byte_offset. No bounds checks
        """
        raise CannotRead

    @specialize.ll_and_arg(1)
    def typed_write(self, TP, byte_offset, value):
        """
        Write the value of type TP at byte_offset. No bounds checks
        """
        raise CannotWrite

    def get_raw_address(self):
        msg = "cannot take the raw address of this buffer"
        if not we_are_translated():
            msg += " '%s'" % (self,)
        raise ValueError(msg)


class RawBuffer(Buffer):
    """
    A buffer which is backed by a raw, non-movable memory area. It implementes
    typed_read and typed_write in terms of get_raw_address(), llop.raw_load,
    llop.raw_store.

    NOTE: this assumes that get_raw_address() is cheap. Do not use this as a
    base class if get_raw_address() is potentially costly, like for example if
    you call rgc.nonmoving_raw_ptr_for_resizable_list
    """
    _immutable_ = True

    @specialize.ll_and_arg(1)
    def typed_read(self, TP, byte_offset):
        """
        Read the value of type TP starting at byte_offset. No bounds checks
        """
        if not is_alignment_correct(TP, byte_offset):
            raise CannotRead
        ptr = self.get_raw_address()
        return llop.raw_load(TP, ptr, byte_offset)

    @specialize.ll_and_arg(1)
    def typed_write(self, TP, byte_offset, value):
        """
        Write the value of type TP at byte_offset. No bounds checks
        """
        if self.readonly or not is_alignment_correct(TP, byte_offset):
            raise CannotWrite
        ptr = self.get_raw_address()
        value = lltype.cast_primitive(TP, value)
        return llop.raw_store(lltype.Void, ptr, byte_offset, value)


class GCBuffer(Buffer):
    """
    Base class for a buffer which is backed by a GC-managed memory area. You
    MUST also decorate the class with @GCBuffer.decorate: it implements
    typed_read and typed_write in terms of llop.gc_load_indexed and
    llop.gc_store_indexed.
    """
    _attrs_ = ['readonly', 'value']
    _immutable_ = True

    @staticmethod
    def decorate(targetcls):
        """
        Create and attach specialized versions of typed_{read,write}. We need to
        do this becase the JIT codewriters mandates that base_ofs is an
        RPython constant.
        """
        if targetcls.__bases__ != (GCBuffer,):
            raise ValueError("@GCBuffer.decorate should be used only on "
                             "GCBuffer subclasses")

        base_ofs = targetcls._get_gc_data_offset()
        scale_factor = llmemory.sizeof(lltype.Char)

        @specialize.ll_and_arg(1)
        def typed_read(self, TP, byte_offset):
            if not is_alignment_correct(TP, byte_offset):
                raise CannotRead
            lldata = self._get_gc_data()
            byte_offset += self._get_gc_data_extra_offset()
            return llop.gc_load_indexed(TP, lldata, byte_offset,
                                        scale_factor, base_ofs)

        @specialize.ll_and_arg(1)
        def typed_write(self, TP, byte_offset, value):
            if self.readonly or not is_alignment_correct(TP, byte_offset):
                raise CannotWrite
            lldata = self._get_gc_data()
            byte_offset += self._get_gc_data_extra_offset()
            value = lltype.cast_primitive(TP, value)
            return llop.gc_store_indexed(lltype.Void, lldata, byte_offset, value,
                                         scale_factor, base_ofs)

        targetcls.typed_read = typed_read
        targetcls.typed_write = typed_write
        return targetcls

    @staticmethod
    def _get_gc_data_offset(self):
        raise NotImplementedError

    def _get_gc_data_extra_offset(self):
        return 0

    def _get_gc_data(self):
        raise NotImplementedError

    @specialize.ll_and_arg(1)
    def typed_read(self, TP, byte_offset):
        raise NotImplementedError("You MUST decorate this class with "
                                  "@GCBuffer.decorate")

    @specialize.ll_and_arg(1)
    def typed_write(self, TP, byte_offset, value):
        raise NotImplementedError("You MUST decorate this class with "
                                  "@GCBuffer.decorate")


def get_gc_data_for_list_of_chars(data):
    ll_data = ll_for_resizable_list(data)
    ll_items = ll_data.items
    return lltype.cast_opaque_ptr(llmemory.GCREF, ll_items)

def get_gc_data_offset_for_list_of_chars():
    LIST = LIST_OF(lltype.Char)
    return llmemory.itemoffsetof(LIST.items.TO, 0)


@GCBuffer.decorate
class ByteBuffer(GCBuffer):
    _immutable_ = True

    def __init__(self, n):
        self.data = resizable_list_supporting_raw_ptr(['\0'] * n)
        self.readonly = False

    def getlength(self):
        return len(self.data)

    def getitem(self, index):
        return self.data[index]

    def setitem(self, index, char):
        self.data[index] = char

    def getslice(self, start, stop, step, size):
        if step == 1:
            assert 0 <= start <= stop
            if start == 0 and stop == len(self.data):
                return "".join(self.data)
            return "".join(self.data[start:stop])
        return Buffer.getslice(self, start, stop, step, size)

    def get_raw_address(self):
        return nonmoving_raw_ptr_for_resizable_list(self.data)

    def _get_gc_data(self):
        return get_gc_data_for_list_of_chars(self.data)

    @staticmethod
    def _get_gc_data_offset():
        return get_gc_data_offset_for_list_of_chars()


@GCBuffer.decorate
class StringBuffer(GCBuffer):
    _attrs_ = ['readonly', 'value']
    _immutable_ = True

    def __init__(self, value):
        assert value  is not None
        self.value = value
        self.readonly = 1

    def getlength(self):
        return len(self.value)

    def as_str(self):
        return self.value

    def getitem(self, index):
        return self.value[index]

    def getslice(self, start, stop, step, size):
        if size == 0:
            return ""
        if step == 1:
            assert 0 <= start <= stop
            if start == 0 and stop == len(self.value):
                return self.value
            return self.value[start:stop]
        return Buffer.getslice(self, start, stop, step, size)

    def get_raw_address(self):
        from rpython.rtyper.lltypesystem import rffi
        # may still raise ValueError on some GCs
        return rffi.get_raw_address_of_string(self.value)

    @staticmethod
    def _get_gc_data_offset():
        return (llmemory.offsetof(STR, 'chars') +
                llmemory.itemoffsetof(STR.chars, 0))

    def _get_gc_data(self):
        lls = llstr(self.value)
        return lltype.cast_opaque_ptr(llmemory.GCREF, lls)


class SubBuffer(Buffer):
    _attrs_ = ['buffer', 'offset', 'size', 'readonly']
    _immutable_ = True

    @signature(types.any(), types.instance(Buffer), types.int(), types.int(),
               returns=types.none())
    def __init__(self, buffer, offset, size):
        self.readonly = buffer.readonly
        if isinstance(buffer, SubBuffer):     # don't nest them
            # we want a view (offset, size) over a view
            # (buffer.offset, buffer.size) over buffer.buffer.
            # Note that either '.size' can be -1 to mean 'up to the end'.
            at_most = buffer.getlength() - offset
            if size > at_most or size < 0:
                if at_most < 0:
                    at_most = 0
                size = at_most
            offset += buffer.offset
            buffer = buffer.buffer
        #
        self.buffer = buffer
        self.offset = offset
        self.size = size

    def getlength(self):
        at_most = self.buffer.getlength() - self.offset
        if 0 <= self.size <= at_most:
            return self.size
        elif at_most >= 0:
            return at_most
        else:
            return 0

    def getitem(self, index):
        return self.buffer.getitem(self.offset + index)

    def getslice(self, start, stop, step, size):
        if start == stop:
            return ''     # otherwise, adding self.offset might make them
                          # out of bounds
        return self.buffer.getslice(self.offset + start, self.offset + stop,
                                    step, size)

    def setitem(self, index, char):
        self.buffer.setitem(self.offset + index, char)

    def setslice(self, start, string):
        if len(string) == 0:
            return        # otherwise, adding self.offset might make 'start'
                          # out of bounds
        self.buffer.setslice(self.offset + start, string)

    def get_raw_address(self):
        from rpython.rtyper.lltypesystem import rffi
        ptr = self.buffer.get_raw_address()
        return rffi.ptradd(ptr, self.offset)

    @specialize.ll_and_arg(1)
    def typed_read(self, TP, byte_offset):
        return self.buffer.typed_read(TP, byte_offset + self.offset)

    @specialize.ll_and_arg(1)
    def typed_write(self, TP, byte_offset, value):
        return self.buffer.typed_write(TP, byte_offset + self.offset, value)
