# Copyright (C) 2016-present the asyncpg authors and contributors
# <see AUTHORS file>
#
# This module is part of asyncpg and is released under
# the Apache 2.0 License: http://www.apache.org/licenses/LICENSE-2.0


from libc.string cimport memcpy

import collections

from . import exceptions


@cython.no_gc_clear
@cython.final
@cython.freelist(_BUFFER_FREELIST_SIZE)
cdef class WriteBuffer:

    def __cinit__(self):
        self._smallbuf_inuse = True
        self._buf = self._smallbuf
        self._size = _BUFFER_INITIAL_SIZE
        self._length = 0
        self._message_mode = 0

    def __dealloc__(self):
        if self._buf is not NULL and not self._smallbuf_inuse:
            cpython.PyMem_Free(self._buf)
            self._buf = NULL
            self._size = 0

        if self._view_count:
            raise exceptions.BufferError(
                'Deallocating buffer with attached memoryviews')

    def __getbuffer__(self, Py_buffer *buffer, int flags):
        self._view_count += 1

        cpython.PyBuffer_FillInfo(
            buffer, self, self._buf, self._length,
            1,  # read-only
            flags)

    def __releasebuffer__(self, Py_buffer *buffer):
        self._view_count -= 1

    cdef inline _check_readonly(self):
        if self._view_count:
            raise exceptions.BufferError('the buffer is in read-only mode')

    cdef inline _ensure_alloced(self, ssize_t extra_length):
        cdef ssize_t new_size = extra_length + self._length

        if new_size > self._size:
            self._reallocate(new_size)

    cdef _reallocate(self, ssize_t new_size):
        cdef char *new_buf

        if new_size < _BUFFER_MAX_GROW:
            new_size = _BUFFER_MAX_GROW
        else:
            # Add a little extra
            new_size += _BUFFER_INITIAL_SIZE

        if self._smallbuf_inuse:
            new_buf = <char*>cpython.PyMem_Malloc(
                sizeof(char) * <size_t>new_size)
            if new_buf is NULL:
                self._buf = NULL
                self._size = 0
                self._length = 0
                raise MemoryError
            memcpy(new_buf, self._buf, <size_t>self._size)
            self._size = new_size
            self._buf = new_buf
            self._smallbuf_inuse = False
        else:
            new_buf = <char*>cpython.PyMem_Realloc(
                <void*>self._buf, <size_t>new_size)
            if new_buf is NULL:
                cpython.PyMem_Free(self._buf)
                self._buf = NULL
                self._size = 0
                self._length = 0
                raise MemoryError
            self._buf = new_buf
            self._size = new_size

    cdef inline start_message(self, char type):
        if self._length != 0:
            raise exceptions.BufferError(
                'cannot start_message for a non-empty buffer')
        self._ensure_alloced(5)
        self._message_mode = 1
        self._buf[0] = type
        self._length = 5

    cdef inline end_message(self):
        # "length-1" to exclude the message type byte
        cdef ssize_t mlen = self._length - 1

        self._check_readonly()
        if not self._message_mode:
            raise exceptions.BufferError(
                'end_message can only be called with start_message')
        if self._length < 5:
            raise exceptions.BufferError('end_message: buffer is too small')
        if mlen > _MAXINT32:
            raise exceptions.BufferError('end_message: message is too large')

        hton.pack_int32(&self._buf[1], <int32_t>mlen)
        return self

    cdef write_buffer(self, WriteBuffer buf):
        self._check_readonly()

        if not buf._length:
            return

        self._ensure_alloced(buf._length)
        memcpy(self._buf + self._length,
               <void*>buf._buf,
               <size_t>buf._length)
        self._length += buf._length

    cdef write_byte(self, char b):
        self._check_readonly()

        self._ensure_alloced(1)
        self._buf[self._length] = b
        self._length += 1

    cdef write_bytes(self, bytes data):
        cdef char* buf
        cdef ssize_t len

        cpython.PyBytes_AsStringAndSize(data, &buf, &len)
        self.write_cstr(buf, len)

    cdef write_bytestring(self, bytes string):
        cdef char* buf
        cdef ssize_t len

        cpython.PyBytes_AsStringAndSize(string, &buf, &len)
        # PyBytes_AsStringAndSize returns a null-terminated buffer,
        # but the null byte is not counted in len. hence the + 1
        self.write_cstr(buf, len + 1)

    cdef write_str(self, str string, str encoding):
        self.write_bytestring(string.encode(encoding))

    cdef write_utf8(self, str string):
        self.write_bytestring(string.encode('utf-8'))

    cdef write_cstr(self, const char *data, ssize_t len):
        self._check_readonly()
        self._ensure_alloced(len)

        memcpy(self._buf + self._length, <void*>data, <size_t>len)
        self._length += len

    cdef write_int16(self, int16_t i):
        self._check_readonly()
        self._ensure_alloced(2)

        hton.pack_int16(&self._buf[self._length], i)
        self._length += 2

    cdef write_int32(self, int32_t i):
        self._check_readonly()
        self._ensure_alloced(4)

        hton.pack_int32(&self._buf[self._length], i)
        self._length += 4

    cdef write_int64(self, int64_t i):
        self._check_readonly()
        self._ensure_alloced(8)

        hton.pack_int64(&self._buf[self._length], i)
        self._length += 8

    cdef write_float(self, float f):
        self._check_readonly()
        self._ensure_alloced(4)

        hton.pack_float(&self._buf[self._length], f)
        self._length += 4

    cdef write_double(self, double d):
        self._check_readonly()
        self._ensure_alloced(8)

        hton.pack_double(&self._buf[self._length], d)
        self._length += 8

    @staticmethod
    cdef WriteBuffer new_message(char type):
        cdef WriteBuffer buf
        buf = WriteBuffer.__new__(WriteBuffer)
        buf.start_message(type)
        return buf

    @staticmethod
    cdef WriteBuffer new():
        cdef WriteBuffer buf
        buf = WriteBuffer.__new__(WriteBuffer)
        return buf


@cython.no_gc_clear
@cython.final
@cython.freelist(_BUFFER_FREELIST_SIZE)
cdef class ReadBuffer:

    def __cinit__(self):
        self._bufs = collections.deque()
        self._bufs_append = self._bufs.append
        self._bufs_popleft = self._bufs.popleft
        self._bufs_len = 0
        self._buf0 = None
        self._buf0_prev = None
        self._pos0 = 0
        self._len0 = 0
        self._length = 0

        self._current_message_type = 0
        self._current_message_len = 0
        self._current_message_len_unread = 0
        self._current_message_ready = 0

    cdef feed_data(self, data):
        cdef:
            ssize_t dlen
            bytes data_bytes

        if not cpython.PyBytes_CheckExact(data):
            raise exceptions.BufferError('feed_data: bytes object expected')
        data_bytes = <bytes>data

        dlen = cpython.Py_SIZE(data_bytes)
        if dlen == 0:
            # EOF?
            return

        self._bufs_append(data_bytes)
        self._length += dlen

        if self._bufs_len == 0:
            # First buffer
            self._len0 = dlen
            self._buf0 = data_bytes

        self._bufs_len += 1

    cdef inline _ensure_first_buf(self):
        if self._len0 == 0:
            raise exceptions.BufferError('empty first buffer')

        if self._pos0 == self._len0:
            self._switch_to_next_buf()

    cdef _switch_to_next_buf(self):
        # The first buffer is fully read, discard it
        self._bufs_popleft()
        self._bufs_len -= 1

        # Shouldn't fail, since we've checked that `_length >= 1`
        # in _ensure_first_buf()
        self._buf0_prev = self._buf0
        self._buf0 = <bytes>self._bufs[0]

        self._pos0 = 0
        self._len0 = len(self._buf0)

        if PG_DEBUG:
            if self._len0 < 1:
                raise exceptions.BufferError(
                    'debug: second buffer of ReadBuffer is empty')

    cdef inline const char* _try_read_bytes(self, ssize_t nbytes):
        # Try to read *nbytes* from the first buffer.
        #
        # Returns pointer to data if there is at least *nbytes*
        # in the buffer, NULL otherwise.
        #
        # Important: caller must call _ensure_first_buf() prior
        # to calling try_read_bytes, and must not overread

        cdef:
            const char *result

        if PG_DEBUG:
            if nbytes > self._length:
                return NULL

        if self._current_message_ready:
            if self._current_message_len_unread < nbytes:
                return NULL

        if self._pos0 + nbytes <= self._len0:
            result = cpython.PyBytes_AS_STRING(self._buf0)
            result += self._pos0
            self._pos0 += nbytes
            self._length -= nbytes
            if self._current_message_ready:
                self._current_message_len_unread -= nbytes
            return result
        else:
            return NULL

    cdef inline _read_into(self, char *buf, ssize_t nbytes):
        cdef:
            ssize_t nread
            char *buf0

        while True:
            buf0 = cpython.PyBytes_AS_STRING(self._buf0)

            if self._pos0 + nbytes > self._len0:
                nread = self._len0 - self._pos0
                memcpy(buf, buf0 + self._pos0, <size_t>nread)
                self._pos0 = self._len0
                self._length -= nread
                nbytes -= nread
                buf += nread
                self._ensure_first_buf()

            else:
                memcpy(buf, buf0 + self._pos0, <size_t>nbytes)
                self._pos0 += nbytes
                self._length -= nbytes
                break

    cdef inline _read_and_discard(self, ssize_t nbytes):
        cdef:
            ssize_t nread

        self._ensure_first_buf()
        while True:
            if self._pos0 + nbytes > self._len0:
                nread = self._len0 - self._pos0
                self._pos0 = self._len0