# -*- coding: utf-8 -*-
import struct
import sys
import time
from io import RawIOBase
from typing import Callable, Collection, Optional

from libscrc import modbus

from .constants import ACTION_READ, ACTION_WRITE, POSSIBLE_MARKER
from .interfaces import BaseInterface
from .solar_types import DATA_BATTERY_STATE, HISTORICAL_DATA, DataItem
from .util import log


def write(fh, data):
    bdata = bytes(data)
    crc = modbus(bdata)
    bcrc = bytes([crc & 0xFF, (crc & 0xFF00) >> 8])
    fh.write(data + bcrc)


def construct_request(address, words=1, action=ACTION_READ, marker=0xFF):
    assert marker in POSSIBLE_MARKER, f"marker should be one of {POSSIBLE_MARKER}"
    return struct.pack("!BBHH", marker, action, address, words)


def construct_write(address, data: bytes, action=ACTION_WRITE, marker=0xFF):
    assert marker in POSSIBLE_MARKER, f"marker should be one of {POSSIBLE_MARKER}"
    return struct.pack("!BBH", marker, action, address) + data


def parse(data: bytes, items: Collection[DataItem], offset: int = 0) -> dict:
    pos = offset
    res = {}

    for i in items:
        res[i.name] = i.transform(struct.unpack_from(i.st_format, data, offset=pos)[0])
        pos += i.st_size

    return res


# GET_BATTERY_STATE
def parse_battery_state(data: bytes) -> dict:
    return parse(data, DATA_BATTERY_STATE)


def parse_historical_entry(data: bytes) -> dict:
    res = parse(data, HISTORICAL_DATA[:10])

    res_datalen = sum([x.st_size for x in HISTORICAL_DATA[:10]])

    if len(data) > res_datalen:
        res.update(parse(data, HISTORICAL_DATA[10:], offset=res_datalen))

    return res


def parse_packet(data):
    tag, operation, size = struct.unpack_from("BBB", data)
    _unpacked = struct.unpack_from(f"<{size}BH", data, offset=3)
    crc = _unpacked[-1]
    payload = _unpacked[:-1]
    calculated_crc = modbus(bytes([tag, operation, size, *payload]))

    if crc != calculated_crc:
        e = ValueError(f"CRC missmatch: expected {crc:04X}, got {calculated_crc:04X}.")
        e.tag = tag
        e.operation = operation
        e.size = size
        e.payload = payload
        e.crc = crc
        e.calculated_crc = calculated_crc
        raise e

    return payload


def discardUntil(fh: RawIOBase, byte: int, timeout=10) -> Optional[int]:
    assert byte >= 0 and byte < 256, f"byte: Expected 8bit unsigned int, got {byte}"

    def expand(b: Optional[bytes]):
        if b is None:
            return b
        return b[0]

    start = time.time()
    discarded = 0
    read_byte = expand(fh.read(1))
    while read_byte != byte:
        if read_byte is not None:
            if not discarded:
                log("Discarding", end="")
            discarded += 1
            print(f" {read_byte:02X}", end="")
            sys.stdout.flush()

        if time.time() - start > timeout:
            read_byte = None
            break

        read_byte = expand(fh.read(1))

    if discarded:
        print()
        sys.stdout.flush()

    return read_byte


def readMemory(fh: BaseInterface, address: int, words: int = 1) -> Optional[bytes]:
    # log(f"Reading {words} words from 0x{address:04X}")
    request = construct_request(address, words=words)
    # log("Request:", request)
    write(fh, request)

    tag = discardUntil(fh, 0xFF)
    if tag is None:
        return None

    header = fh.read(2)
    if header and len(header) == 2:
        operation, size = header
        data = fh.read(size)
        _crc = fh.read(2)
        if data and _crc:
            try:
                crc = struct.unpack_from("<H", _crc)[0]
            except struct.error:
                log(f"readMemory: CRC error; read {len(_crc)} bytes (2 expected)")
                return None
            calculated_crc = modbus(bytes([tag, operation, size, *data]))
            if crc == calculated_crc:
                return data
            else:
                log(f"readMemory: CRC error; {crc:04X} != {calculated_crc:04X}")
        log("data or crc is falsely", header, data, _crc)
    return None


def writeMemory(fh: BaseInterface, address: int, output_data: bytes) -> Optional[bytes]:
    # TODO: Verify behavior on multi-word writes
    # log(f"Reading {words} words from 0x{address:04X}")
    request = construct_write(address, data=output_data)
    # log("Request:", request)
    write(fh, request)

    tag = discardUntil(fh, 0xFF)
    if tag is None:
        return None

    _operation = fh.read(1)
    result_addr = fh.read(2)
    # log("Operation:", _operation)
    if _operation is not None and result_addr is not None:
        operation = _operation[0]
        data = fh.read(2)
        # log("Data:", data)
        _crc = fh.read(2)
        if data and _crc:
            try:
                crc = struct.unpack_from("<H", _crc)[0]
            except struct.error:
                log(f"readMemory: CRC error; read {len(_crc)} bytes (2 expected)")
                return None
            calculated_crc = modbus(bytes([tag, operation, *result_addr, *data]))
            if crc == calculated_crc:
                return data
            else:
                log(f"readMemory: CRC error; {crc:04X} != {calculated_crc:04X}")
        log("data or crc is falsely", operation, result_addr, data, _crc)
    return None


def try_read_parse(
    dev: BaseInterface,
    address: int,
    words: int = 1,
    parser: Optional[Callable] = None,
    attempts=5,
) -> Optional[dict]:
    while attempts:
        attempts -= 1
        res = readMemory(dev, address, words)
        if res:
            try:
                if parser:
                    return parser(res)
            except struct.error as e:
                log(e)
                log("0x0100 Unpack error:", len(res), res)
                log("Flushed from read buffer; ", dev.read())  # TODO: timeout=0.5
        else:
            log(f"No data read, expected {words*2} bytes (attempts left: {attempts})")
    return None