# SPDX-FileCopyrightText: 2020 Melissa LeBlanc-Williams for Adafruit Industries
#
# SPDX-License-Identifier: MIT

"""
`Adafruit_PureIO.spi`
================================================================================

Pure python (i.e. no native extensions) access to Linux IO SPI interface that is
similar to the SpiDev API. Based heavily on https://github.com/tomstokes/python-spi/.

* Author(s): Tom Stokes, Melissa LeBlanc-Williams

Implementation Notes
--------------------

**Software and Dependencies:**

* Linux and Python 3.5 or Higher

"""

# imports
from ctypes import create_string_buffer, string_at, addressof
from fcntl import ioctl
import struct
import platform
import os.path
from os import environ
import array

__version__ = "0.0.0+auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_Python_PureIO.git"

# SPI C API constants (from linux kernel headers)
SPI_CPHA = 0x01
SPI_CPOL = 0x02
SPI_CS_HIGH = 0x04
SPI_LSB_FIRST = 0x08
SPI_THREE_WIRE = 0x10
SPI_LOOP = 0x20
SPI_NO_CS = 0x40
SPI_READY = 0x80
SPI_TX_DUAL = 0x100
SPI_TX_QUAD = 0x200
SPI_RX_DUAL = 0x400
SPI_RX_QUAD = 0x800

SPI_MODE_0 = 0
SPI_MODE_1 = SPI_CPHA
SPI_MODE_2 = SPI_CPOL
SPI_MODE_3 = SPI_CPHA | SPI_CPOL

SPI_DEFAULT_CHUNK_SIZE = 4096


def _ioc_encode(direction, number, structure):
    """
    ioctl command encoding helper function
    Calculates the appropriate spidev ioctl op argument given the direction,
    command number, and argument structure in python's struct.pack format.
    Returns a tuple of the calculated op and the struct.pack format
    See Linux kernel source file /include/uapi/asm/ioctl.h
    """
    ioc_magic = ord("k")
    ioc_nrbits = 8
    ioc_typebits = 8
    if platform.machine() == "mips":
        ioc_sizebits = 13
    else:
        ioc_sizebits = 14

    ioc_nrshift = 0
    ioc_typeshift = ioc_nrshift + ioc_nrbits
    ioc_sizeshift = ioc_typeshift + ioc_typebits
    ioc_dirshift = ioc_sizeshift + ioc_sizebits

    size = struct.calcsize(structure)

    operation = (
        (direction << ioc_dirshift)
        | (ioc_magic << ioc_typeshift)
        | (number << ioc_nrshift)
        | (size << ioc_sizeshift)
    )

    return direction, operation, structure


# pylint: disable=too-many-instance-attributes, too-many-branches
class SPI:
    """
    This class is similar to SpiDev, but instead of opening and closing
    for each call, it is set up on initialization making it fast.
    """

    _IOC_TRANSFER_FORMAT = "QQIIHBBBBH"

    if platform.machine() == "mips":
        # Direction is 3 bits
        _IOC_READ = 2
        _IOC_WRITE = 4
    else:
        # Direction is 2 bits
        _IOC_WRITE = 1
        _IOC_READ = 2

    # _IOC_MESSAGE is a special case, so we ony need the ioctl operation
    _IOC_MESSAGE = _ioc_encode(_IOC_WRITE, 0, _IOC_TRANSFER_FORMAT)[1]

    _IOC_RD_MODE = _ioc_encode(_IOC_READ, 1, "B")
    _IOC_WR_MODE = _ioc_encode(_IOC_WRITE, 1, "B")

    _IOC_RD_LSB_FIRST = _ioc_encode(_IOC_READ, 2, "B")
    _IOC_WR_LSB_FIRST = _ioc_encode(_IOC_WRITE, 2, "B")

    _IOC_RD_BITS_PER_WORD = _ioc_encode(_IOC_READ, 3, "B")
    _IOC_WR_BITS_PER_WORD = _ioc_encode(_IOC_WRITE, 3, "B")

    _IOC_RD_MAX_SPEED_HZ = _ioc_encode(_IOC_READ, 4, "I")
    _IOC_WR_MAX_SPEED_HZ = _ioc_encode(_IOC_WRITE, 4, "I")

    _IOC_RD_MODE32 = _ioc_encode(_IOC_READ, 5, "I")
    _IOC_WR_MODE32 = _ioc_encode(_IOC_WRITE, 5, "I")
    # pylint: disable=too-many-arguments

    def __init__(
        self,
        device,
        max_speed_hz=None,
        bits_per_word=None,
        phase=None,
        polarity=None,
        cs_high=None,
        lsb_first=None,
        three_wire=None,
        loop=None,
        no_cs=None,
        ready=None,
    ):
        """
        Create spidev interface object.
        """
        if isinstance(device, tuple):
            (bus, dev) = device
            device = f"/dev/spidev{bus:d}.{dev:d}"

        if not os.path.exists(device):
            raise IOError(f"{device} does not exist")

        self.handle = os.open(device, os.O_RDWR)

        self.chunk_size = SPI_DEFAULT_CHUNK_SIZE
        if environ.get("SPI_BUFSIZE") is not None:
            try:
                self.chunk_size = int(os.environ.get("SPI_BUFSIZE"))
            except ValueError:
                self.chunk_size = SPI_DEFAULT_CHUNK_SIZE

        if max_speed_hz is not None:
            self.max_speed_hz = max_speed_hz

        if bits_per_word is not None:
            self.bits_per_word = bits_per_word

        if phase is not None:
            self.phase = phase

        if polarity is not None:
            self.polarity = polarity

        if cs_high is not None:
            self.cs_high = cs_high

        if lsb_first is not None:
            self.lsb_first = lsb_first

        if three_wire is not None:
            self.three_wire = three_wire

        if loop is not None:
            self.loop = loop

        if no_cs is not None:
            self.no_cs = no_cs

        if ready is not None:
            self.ready = ready

    # pylint: enable=too-many-arguments

    def _ioctl(self, ioctl_data, data=None):
        """
        ioctl helper function.

        Performs an ioctl on self.handle. If the ioctl is an SPI read type
        ioctl, returns the result value.
        """
        (direction, ioctl_bytes, structure) = ioctl_data
        if direction == SPI._IOC_READ:
            arg = array.array(structure, [0])
            ioctl(self.handle, ioctl_bytes, arg, True)
            return arg[0]

        arg = struct.pack("=" + structure, data)
        ioctl(self.handle, ioctl_bytes, arg)
        return None

    def _get_mode_field(self, field):
        """Helper function to get specific spidev mode bits"""
        return bool(self._ioctl(SPI._IOC_RD_MODE) & field)

    def _set_mode_field(self, field, value):
        """Helper function to set a spidev mode bit"""
        mode = self._ioctl(SPI._IOC_RD_MODE)
        if value:
            mode |= field
        else:
            mode &= ~field
        self._ioctl(SPI._IOC_WR_MODE, mode)

    @property
    def phase(self):
        """SPI clock phase bit"""
        return self._get_mode_field(SPI_CPHA)

    @phase.setter
    def phase(self, phase):
        self._set_mode_field(SPI_CPHA, phase)

    @property
    def polarity(self):
        """SPI polarity bit"""
        return self._get_mode_field(SPI_CPOL)

    @polarity.setter
    def polarity(self, polarity):
        self._set_mode_field(SPI_CPOL, polarity)

    @property
    def cs_high(self):
        """SPI chip select active level"""
        return self._get_mode_field(SPI_CS_HIGH)

    @cs_high.setter
    def cs_high(self, cs_high):
        self._set_mode_field(SPI_CS_HIGH, cs_high)

    @property
    def lsb_first(self):
        """Bit order of SPI word transfers"""
        return self._get_mode_field(SPI_LSB_FIRST)

    @lsb_first.setter
    def lsb_first(self, lsb_first):
        self._set_mode_field(SPI_LSB_FIRST, lsb_first)

    @property
    def three_wire(self):
        """SPI 3-wire mode"""
        return self._get_mode_field(SPI_THREE_WIRE)

    @three_wire.setter
    def three_wire(self, three_wire):
        self._set_mode_field(SPI_THREE_WIRE, three_wire)

    @property
    def loop(self):
        """SPI loopback mode"""
        return self._get_mode_field(SPI_LOOP)

    @loop.setter
    def loop(self, loop):
        self._set_mode_field(SPI_LOOP, loop)

    @property
    def no_cs(self):
        """No chipselect. Single device on bus."""
        return self._get_mode_field(SPI_NO_CS)

    @no_cs.setter
    def no_cs(self, no_cs):
        self._set_mode_field(SPI_NO_CS, no_cs)

    @property
    def ready(self):
        """Slave pulls low to pause"""
        return self._get_mode_field(SPI_READY)

    @ready.setter
    def ready(self, ready):
        self._set_mode_field(SPI_READY, ready)

    @property
    def max_speed_hz(self):
        """Maximum SPI transfer speed in Hz.

        Note that the controller cannot necessarily assign the requested
        speed.
        """
        return self._ioctl(SPI._IOC_RD_MAX_SPEED_HZ)

    @max_speed_hz.setter
    def max_speed_hz(self, max_speed_hz):
        self._ioctl(SPI._IOC_WR_MAX_SPEED_HZ, max_speed_hz)

    @property
    def bits_per_word(self):
        """Number of bits per word of SPI transfer.

        A value of 0 is equivalent to 8 bits per word
        """
        return self._ioctl(SPI._IOC_RD_BITS_PER_WORD)

    @bits_per_word.setter
    def bits_per_word(self, bits_per_word):
        self._ioctl(SPI._IOC_WR_BITS_PER_WORD, bits_per_word)

    @property
    def mode(self):
        """Mode that SPI is currently running in"""
        return self._ioctl(SPI._IOC_RD_MODE)

    @mode.setter
    def mode(self, mode):
        self._ioctl(SPI._IOC_WR_MODE, mode)

    def writebytes(self, data, max_speed_hz=0, bits_per_word=0, delay=0):
        """Perform half-duplex SPI write."""
        data = array.array("B", data).tobytes()
        # length = len(data)
        chunks = [
            data[i : i + self.chunk_size] for i in range(0, len(data), self.chunk_size)
        ]
        for chunk in chunks:
            length = len(chunk)
            transmit_buffer = create_string_buffer(chunk)
            spi_ioc_transfer = struct.pack(
                SPI._IOC_TRANSFER_FORMAT,
                addressof(transmit_buffer),
                0,
                length,
                max_speed_hz,
                delay,
                bits_per_word,
                0,
                0,
                0,
                0,
            )
            try:
                ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
            except TimeoutError as err:
                raise Exception(  # pylint: disable=broad-exception-raised
                    "ioctl timeout. Please try a different SPI frequency or less data."
                ) from err

    def readbytes(self, length, max_speed_hz=0, bits_per_word=0, delay=0):
        """Perform half-duplex SPI read as a binary string"""
        receive_buffer = create_string_buffer(length)
        spi_ioc_transfer = struct.pack(
            SPI._IOC_TRANSFER_FORMAT,
            0,
            addressof(receive_buffer),
            length,
            max_speed_hz,
            delay,
            bits_per_word,
            0,
            0,
            0,
            0,
        )
        ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
        return string_at(receive_buffer, length)

    def transfer(self, data, max_speed_hz=0, bits_per_word=0, delay=0):
        """Perform full-duplex SPI transfer"""
        data = array.array("B", data).tobytes()
        receive_data = []

        chunks = [
            data[i : i + self.chunk_size] for i in range(0, len(data), self.chunk_size)
        ]
        for chunk in chunks:
            length = len(chunk)
            receive_buffer = create_string_buffer(length)
            transmit_buffer = create_string_buffer(chunk)
            spi_ioc_transfer = struct.pack(
                SPI._IOC_TRANSFER_FORMAT,
                addressof(transmit_buffer),
                addressof(receive_buffer),
                length,
                max_speed_hz,
                delay,
                bits_per_word,
                0,
                0,
                0,
                0,
            )
            ioctl(self.handle, SPI._IOC_MESSAGE, spi_ioc_transfer)
            receive_data += string_at(receive_buffer, length)
        return receive_data
