# Authors: The MNE-Python contributors.
# License: BSD-3-Clause
# Copyright the MNE-Python contributors.

import functools
import os.path as op
from io import BytesIO
from itertools import count

import numpy as np

from ..._fiff._digitization import _make_bti_dig_points
from ..._fiff.constants import FIFF
from ..._fiff.meas_info import _empty_info
from ..._fiff.tag import _coil_trans_to_loc, _loc_to_coil_trans
from ..._fiff.utils import _mult_cal_one, read_str
from ...fixes import _reshape_view
from ...transforms import Transform, combine_transforms, invert_transform
from ...utils import _stamp_to_dt, _validate_type, logger, path_like, verbose
from ..base import BaseRaw
from .constants import BTI
from .read import (
    read_char,
    read_dev_header,
    read_double,
    read_double_matrix,
    read_float,
    read_float_matrix,
    read_int16,
    read_int16_matrix,
    read_int32,
    read_int64,
    read_transform,
    read_uint16,
    read_uint32,
)

BTI_WH2500_REF_MAG = ("MxA", "MyA", "MzA", "MxaA", "MyaA", "MzaA")
BTI_WH2500_REF_GRAD = ("GxxA", "GyyA", "GyxA", "GzaA", "GzyA")

dtypes = zip(list(range(1, 5)), (">i2", ">i4", ">f4", ">f8"))
DTYPES = {i: np.dtype(t) for i, t in dtypes}


def _instantiate_default_info_chs():
    """Populate entries in info['chs'] with default values."""
    return dict(
        loc=np.array([0, 0, 0, 1] * 3, dtype="f4"),
        ch_name=None,
        unit_mul=FIFF.FIFF_UNITM_NONE,
        coord_frame=FIFF.FIFFV_COORD_UNKNOWN,
        coil_type=FIFF.FIFFV_COIL_NONE,
        range=1.0,
        unit=FIFF.FIFF_UNIT_V,
        cal=1.0,
        scanno=None,
        kind=FIFF.FIFFV_MISC_CH,
        logno=None,
    )


class _bytes_io_mock_context:
    """Make a context for BytesIO."""

    def __init__(self, target):
        self.target = target

    def __enter__(self):  # noqa: D105
        return self.target

    def __exit__(self, exception_type, value, tb):  # noqa: D105
        pass


def _bti_open(fname, *args, **kwargs):
    """Handle BytesIO."""
    if isinstance(fname, path_like):
        return open(fname, *args, **kwargs)
    elif isinstance(fname, BytesIO):
        return _bytes_io_mock_context(fname)
    else:
        raise RuntimeError("Cannot mock this.")


def _get_bti_dev_t(adjust=0.0, translation=(0.0, 0.02, 0.11)):
    """Get the general Magnes3600WH to Neuromag coordinate transform.

    Parameters
    ----------
    adjust : float | None
        Degrees to tilt x-axis for sensor frame misalignment.
        If None, no adjustment will be applied.
    translation : array-like
        The translation to place the origin of coordinate system
        to the center of the head.

    Returns
    -------
    m_nm_t : ndarray
        4 x 4 rotation, translation, scaling matrix.
    """
    flip_t = np.array([[0.0, -1.0, 0.0], [1.0, 0.0, 0.0], [0.0, 0.0, 1.0]])
    rad = np.deg2rad(adjust)
    adjust_t = np.array(
        [
            [1.0, 0.0, 0.0],
            [0.0, np.cos(rad), -np.sin(rad)],
            [0.0, np.sin(rad), np.cos(rad)],
        ]
    )
    m_nm_t = np.eye(4)
    m_nm_t[:3, :3] = np.dot(flip_t, adjust_t)
    m_nm_t[:3, 3] = translation
    return m_nm_t


def _rename_channels(names, ecg_ch="E31", eog_ch=("E63", "E64")):
    """Rename appropriately ordered list of channel names.

    Parameters
    ----------
    names : list of str
        Lists of 4-D channel names in ascending order

    Returns
    -------
    new : list
        List of names, channel names in Neuromag style
    """
    new = list()
    ref_mag, ref_grad, eog, eeg, ext = (count(1) for _ in range(5))
    for i, name in enumerate(names, 1):
        if name.startswith("A"):
            name = f"MEG {i:03d}"
        elif name == "RESPONSE":
            name = "STI 013"
        elif name == "TRIGGER":
            name = "STI 014"
        elif any(name == k for k in eog_ch):
            name = f"EOG {next(eog):03d}"
        elif name == ecg_ch:
            name = "ECG 001"
        elif name.startswith("E"):
            name = f"EEG {next(eeg):03d}"
        elif name == "UACurrent":
            name = "UTL 001"
        elif name.startswith("M"):
            name = f"RFM {next(ref_mag):03d}"
        elif name.startswith("G"):
            name = f"RFG {next(ref_grad):03d}"
        elif name.startswith("X"):
            name = f"EXT {next(ext):03d}"

        new += [name]

    return new


# read the points
def _read_head_shape(fname):
    """Read the head shape."""
    with _bti_open(fname, "rb") as fid:
        fid.seek(BTI.FILE_HS_N_DIGPOINTS)
        _n_dig_points = read_int32(fid)
        idx_points = read_double_matrix(fid, BTI.DATA_N_IDX_POINTS, 3)
        dig_points = read_double_matrix(fid, _n_dig_points, 3)

    # reorder to lpa, rpa, nasion so = is direct.
    nasion, lpa, rpa = (idx_points[_, :] for _ in [2, 0, 1])
    hpi = idx_points[3 : len(idx_points), :]

    return nasion, lpa, rpa, hpi, dig_points


def _check_nan_dev_head_t(dev_ctf_t):
    """Make sure we deal with nans."""
    has_nan = np.isnan(dev_ctf_t["trans"])
    if np.any(has_nan):
        logger.info(
            "Missing values BTI dev->head transform. Replacing with identity matrix."
        )
        dev_ctf_t["trans"] = np.identity(4)


def _convert_coil_trans(coil_trans, dev_ctf_t, bti_dev_t):
    """Convert the coil trans."""
    t = combine_transforms(invert_transform(dev_ctf_t), bti_dev_t, "ctf_head", "meg")
    t = np.dot(t["trans"], coil_trans)
    return t


def _correct_offset(fid):
    """Align fid pointer."""
    current = fid.tell()
    if (current % BTI.FILE_CURPOS) != 0:
        offset = current % BTI.FILE_CURPOS
        fid.seek(BTI.FILE_CURPOS - (offset), 1)


def _read_config(fname):
    """Read BTi system config file.

    Parameters
    ----------
    fname : str
        The absolute path to the config file

    Returns
    -------
    cfg : dict
        The config blocks found.
    """
    with _bti_open(fname, "rb") as fid:
        cfg = dict()
        cfg["hdr"] = {
            "version": read_int16(fid),
            "site_name": read_str(fid, 32),
            "dap_hostname": read_str(fid, 16),
            "sys_type": read_int16(fid),
            "sys_options": read_int32(fid),
            "supply_freq": read_int16(fid),
            "total_chans": read_int16(fid),
            "system_fixed_gain": read_float(fid),
            "volts_per_bit": read_float(fid),
            "total_sensors": read_int16(fid),
            "total_user_blocks": read_int16(fid),
            "next_der_chan_no": read_int16(fid),
        }

        fid.seek(2, 1)

        cfg["checksum"] = read_uint32(fid)
        cfg["reserved"] = read_char(fid, 32)
        cfg["transforms"] = [
            read_transform(fid) for t in range(cfg["hdr"]["total_sensors"])
        ]

        cfg["user_blocks"] = dict()
        for block in range(cfg["hdr"]["total_user_blocks"]):
            ub = dict()

            ub["hdr"] = {
                "nbytes": read_uint32(fid),
                "kind": read_str(fid, 20),
                "checksum": read_int32(fid),
                "username": read_str(fid, 32),
                "timestamp": read_uint32(fid),
                "user_space_size": read_uint32(fid),
                "reserved": read_char(fid, 32),
            }

            _correct_offset(fid)
            start_bytes = fid.tell()
            kind = ub["hdr"].pop("kind")
            if not kind:  # make sure reading goes right. Should never be empty
                raise RuntimeError(
                    "Could not read user block. Probably you "
                    "acquired data using a BTi version "
                    "currently not supported. Please contact "
                    "the mne-python developers."
                )
            dta, cfg["user_blocks"][kind] = dict(), ub
            if kind in [v for k, v in BTI.items() if k[:5] == "UB_B_"]:
                if kind == BTI.UB_B_MAG_INFO:
                    dta["version"] = read_int32(fid)
                    fid.seek(20, 1)
                    dta["headers"] = list()
                    for hdr in range(6):
                        d = {
                            "name": read_str(fid, 16),
                            "transform": read_transform(fid),
                            "units_per_bit": read_float(fid),
                        }
                        dta["headers"] += [d]
                        fid.seek(20, 1)

                elif kind == BTI.UB_B_COH_POINTS:
                    dta["n_points"] = read_int32(fid)
                    dta["status"] = read_int32(fid)
                    dta["points"] = [
                        {
                            "pos": read_double_matrix(fid, 1, 3),
                            "direction": read_double_matrix(fid, 1, 3),
                            "error": read_double(fid),
                        }
                        for _ in range(16)
                    ]

                elif kind == BTI.UB_B_CCP_XFM_BLOCK:
                    dta["method"] = read_int32(fid)
                    # handle difference btw/ linux (0) and solaris (4)
                    size = 0 if ub["hdr"]["user_space_size"] == 132 else 4
                    fid.seek(size, 1)
                    dta["transform"] = read_transform(fid)

                elif kind == BTI.UB_B_EEG_LOCS:
                    dta["electrodes"] = []
                    while True:
                        d = {
                            "label": read_str(fid, 16),
                            "location": read_double_matrix(fid, 1, 3),
                        }
                        if not d["label"]:
                            break
                        dta["electrodes"] += [d]

                elif kind in [BTI.UB_B_WHC_CHAN_MAP_VER, BTI.UB_B_WHS_SUBSYS_VER]:
                    dta["version"] = read_int16(fid)
                    dta["struct_size"] = read_int16(fid)
                    dta["entries"] = read_int16(fid)

                    fid.seek(8, 1)

                elif kind == BTI.UB_B_WHC_CHAN_MAP:
                    num_channels = None
                    for name, data in cfg["user_blocks"].items():
                        if name == BTI.UB_B_WHC_CHAN_MAP_VER:
                            num_channels = data["entries"]
                            break

                    if num_channels is None:
                        raise ValueError(
                            f"Cannot find block {BTI.UB_B_WHC_CHAN_MAP_VER} to "
                            "determine number of channels"
                        )

                    dta["channels"] = list()
                    for i in range(num_channels):
                        d = {
                            "subsys_type": read_int16(fid),
                            "subsys_num": read_int16(fid),
                            "card_num": read_int16(fid),
                            "chan_num": read_int16(fid),
                            "recdspnum": read_int16(fid),
                        }
                        dta["channels"] += [d]
                        fid.seek(8, 1)

                elif kind == BTI.UB_B_WHS_SUBSYS:
                    num_subsys = None
                    for name, data in cfg["user_blocks"].items():
                        if name == BTI.UB_B_WHS_SUBSYS_VER:
                            num_subsys = data["entries"]
                            break

                    if num_subsys is None:
                        raise ValueError(
                            f"Cannot find block {BTI.UB_B_WHS_SUBSYS_VER} to determine"
                            " number of subsystems"
                        )

                    dta["subsys"] = list()
                    for _ in range(num_subsys):
                        d = {
                            "subsys_type": read_int16(fid),
                            "subsys_num": read_int16(fid),
                            "cards_per_sys": read_int16(fid),
                            "channels_per_card": read_int16(fid),
                            "card_version": read_int16(fid),
                        }

                        fid.seek(2, 1)

                        d.update(
                            {
                                "offsetdacgain": read_float(fid),
                                "squid_type": read_int32(fid),
                                "timesliceoffset": read_int16(fid),
                                "padding": read_int16(fid),
                                "volts_per_bit": read_float(fid),
                            }
                        )

                        dta["subsys"] += [d]

                elif kind == BTI.UB_B_CH_LABELS:
                    dta["version"] = read_int32(fid)
                    dta["entries"] = read_int32(fid)
                    fid.seek(16, 1)

                    dta["labels"] = list()
                    for label in range(dta["entries"]):
                        dta["labels"] += [read_str(fid, 16)]

                elif kind == BTI.UB_B_CALIBRATION:
                    dta["sensor_no"] = read_int16(fid)
                    fid.seek(2, 1)
                    dta["timestamp"] = read_int32(fid)
                    dta["logdir"] = read_str(fid, 256)

                elif kind == BTI.UB_B_SYS_CONFIG_TIME:
                    # handle difference btw/ linux (256) and solaris (512)
                    size = 256 if ub["hdr"]["user_space_size"] == 260 else 512
                    dta["sysconfig_name"] = read_str(fid, size)
                    dta["timestamp"] = read_int32(fid)

                elif kind == BTI.UB_B_DELTA_ENABLED:
                    dta["delta_enabled"] = read_int16(fid)

                elif kind in [BTI.UB_B_E_TABLE_USED, BTI.UB_B_E_TABLE]:
                    dta["hdr"] = {
                        "version": read_int32(fid),
                        "entry_size": read_int32(fid),
                        "n_entries": read_int32(fid),
                        "filtername": read_str(fid, 16),
                        "n_e_values": read_int32(fid),
                        "reserved": read_str(fid, 28),
                    }

                    if dta["hdr"]["version"] == 2:
                        size = 16
                        dta["ch_names"] = [
                            read_str(fid, size) for ch in range(dta["hdr"]["n_entries"])
                        ]
                        dta["e_ch_names"] = [
                            read_str(fid, size)
                            for ch in range(dta["hdr"]["n_e_values"])
                        ]

                        rows = dta["hdr"]["n_entries"]
                        cols = dta["hdr"]["n_e_values"]
                        dta["etable"] = read_float_matrix(fid, rows, cols)
                    else:  # handle MAGNES2500 naming scheme
                        dta["ch_names"] = ["WH2500"] * dta["hdr"]["n_e_values"]
                        dta["hdr"]["n_e_values"] = 6
                        dta["e_ch_names"] = BTI_WH2500_REF_MAG
                        rows = dta["hdr"]["n_entries"]
                        cols = dta["hdr"]["n_e_values"]
                        dta["etable"] = read_float_matrix(fid, rows, cols)

                elif any(
                    [kind == BTI.UB_B_WEIGHTS_USED, kind[:4] == BTI.UB_B_WEIGHT_TABLE]
                ):
                    dta["hdr"] = dict(
                        version=read_int32(fid),
                        n_bytes=read_uint32(fid),
                        n_entries=read_uint32(fid),
                        name=read_str(fid, 32),
                    )
                    if dta["hdr"]["version"] == 2:
                        dta["hdr"].update(
                            description=read_str(fid, 80),
                            n_anlg=read_uint32(fid),
                            n_dsp=read_uint32(fid),
                            reserved=read_str(fid, 72),
                        )
                        dta["ch_names"] = [
                            read_str(fid, 16) for ch in range(dta["hdr"]["n_entries"])
                        ]
                        dta["anlg_ch_names"] = [
                            read_str(fid, 16) for ch in range(dta["hdr"]["n_anlg"])
                        ]

                        dta["dsp_ch_names"] = [
                            read_str(fid, 16) for ch in range(dta["hdr"]["n_dsp"])
                        ]
                        dta["dsp_wts"] = read_float_matrix(
                            fid, dta["hdr"]["n_entries"], dta["hdr"]["n_dsp"]
                        )
                        dta["anlg_wts"] = read_int16_matrix(
                            fid, dta["hdr"]["n_entries"], dta["hdr"]["n_anlg"]
                        )
                    else:  # handle MAGNES2500 naming scheme
                        fid.seek(
                            start_bytes
                            + ub["hdr"]["user_space_size"]
                            - dta["hdr"]["n_bytes"] * dta["hdr"]["n_entries"],
                            0,
                        )

                        dta["hdr"]["n_dsp"] = dta["hdr"]["n_bytes"] // 4 - 2
                        assert dta["hdr"]["n_dsp"] == len(BTI_WH2500_REF_MAG) + len(
                            BTI_WH2500_REF_GRAD
                        )
                        dta["ch_names"] = ["WH2500"] * dta["hdr"]["n_entries"]
                        dta["hdr"]["n_anlg"] = 3
                        # These orders could be wrong, so don't set them
                        # for now
                        # dta['anlg_ch_names'] = BTI_WH2500_REF_MAG[:3]
                        # dta['dsp_ch_names'] = (BTI_WH2500_REF_GRAD +
                        #                        BTI_WH2500_REF_MAG)
                        dta["anlg_wts"] = np.zeros(
                            (dta["hdr"]["n_entries"], dta["hdr"]["n_anlg"]), dtype="i2"
                        )
                        dta["dsp_wts"] = np.zeros(
                            (dta["hdr"]["n_entries"], dta["hdr"]["n_dsp"]), dtype="f4"
                        )
                        for n in range(dta["hdr"]["n_entries"]):
                            dta["anlg_wts"][n] = read_int16_matrix(
                                fid, 1, dta["hdr"]["n_anlg"]
                            )
                            read_int16(fid)
                            dta["dsp_wts"][n] = read_float_matrix(
                                fid, 1, dta["hdr"]["n_dsp"]
                            )

                elif kind == BTI.UB_B_TRIG_MASK:
                    dta["version"] = read_int32(fid)
                    dta["entries"] = read_int32(fid)
                    fid.seek(16, 1)

                    dta["masks"] = []
                    for entry in range(dta["entries"]):
                        d = {
                            "name": read_str(fid, 20),
                            "nbits": read_uint16(fid),
                            "shift": read_uint16(fid),
                            "mask": read_uint32(fid),
                        }
                        dta["masks"] += [d]
                        fid.seek(8, 1)

            else:
                dta["unknown"] = {"hdr": read_char(fid, ub["hdr"]["user_space_size"])}

            n_read = fid.tell() - start_bytes
            if n_read != ub["hdr"]["user_space_size"]:
                raise RuntimeError(
                    f"Internal MNE reading error, read size {n_read} "
                    f"!= {ub['hdr']['user_space_size']} expected size for kind {kind}."
                )
            ub.update(dta)  # finally update the userblock data
            _correct_offset(fid)  # after reading.

        cfg["chs"] = list()

        # prepare reading channels
        for channel in range(cfg["hdr"]["total_chans"]):
            ch = {
                "name": read_str(fid, 16),
                "chan_no": read_int16(fid),
                "ch_type": read_uint16(fid),
                "sensor_no": read_int16(fid),
                "data": dict(),
            }

            fid.seek(2, 1)
            ch.update(
                {
                    "gain": read_float(fid),
                    "units_per_bit": read_float(fid),
                    "yaxis_label": read_str(fid, 16),
                    "aar_val": read_double(fid),
                    "checksum": read_int32(fid),
                    "reserved": read_str(fid, 32),
                }
            )

            cfg["chs"] += [ch]
            _correct_offset(fid)  # before and after
            dta = dict()
            if ch["ch_type"] in [BTI.CHTYPE_MEG, BTI.CHTYPE_REFERENCE]:
                dev = {
                    "device_info": read_dev_header(fid),
                    "inductance": read_float(fid),
                    "padding": read_str(fid, 4),
                    "transform": _correct_trans(read_transform(fid), False),
                    "xform_flag": read_int16(fid),
                    "total_loops": read_int16(fid),
                }

                fid.seek(4, 1)
                dev["reserved"] = read_str(fid, 32)
                dta.update({"dev": dev, "loops": []})
                for _ in range(dev["total_loops"]):
                    d = {
                        "position": read_double_matrix(fid, 1, 3),
                        "orientation": read_double_matrix(fid, 1, 3),
                        "radius": read_double(fid),
                        "wire_radius": read_double(fid),
                        "turns": read_int16(fid),
                    }
                    fid.seek(2, 1)
                    d["checksum"] = read_int32(fid)
                    d["reserved"] = read_str(fid, 32)
                    dta["loops"] += [d]

            elif ch["ch_type"] == BTI.CHTYPE_EEG:
                dta = {
                    "device_info": read_dev_header(fid),
                    "impedance": read_float(fid),
                    "padding": read_str(fid, 4),
                    "transform": read_transform(fid),
                    "reserved": read_char(fid, 32),
                }

            elif ch["ch_type"] == BTI.CHTYPE_EXTERNAL:
                dta = {
                    "device_info": read_dev_header(fid),
                    "user_space_size": read_int32(fid),
                    "reserved": read_str(fid, 32),
                }

            elif ch["ch_type"] == BTI.CHTYPE_TRIGGER:
                dta = {
                    "device_info": read_dev_header(fid),
                    "user_space_size": read_int32(fid),
                }
                fid.seek(2, 1)
                dta["reserved"] = read_str(fid, 32)

            elif ch["ch_type"] in [BTI.CHTYPE_UTILITY, BTI.CHTYPE_DERIVED]:
                dta = {
                    "device_info": read_dev_header(fid),
                    "user_space_size": read_int32(fid),
                    "reserved": read_str(fid, 32),
                }

            elif ch["ch_type"] == BTI.CHTYPE_SHORTED:
                dta = {
                    "device_info": read_dev_header(fid),
                    "reserved": read_str(fid, 32),
                }

            ch.update(dta)  # add data collected
            _correct_offset(fid)  # after each reading

    return cfg


def _read_epoch(fid):
    """Read BTi PDF epoch."""
    out = {
        "pts_in_epoch": read_int32(fid),
        "epoch_duration": read_float(fid),
        "expected_iti": read_float(fid),
        "actual_iti": read_float(fid),
        "total_var_events": read_int32(fid),
        "checksum": read_int32(fid),
        "epoch_timestamp": read_int32(fid),
    }

    fid.seek(28, 1)

    return out


def _read_channel(fid):
    """Read BTi PDF channel."""
    out = {
        "chan_label": read_str(fid, 16),
        "chan_no": read_int16(fid),
        "attributes": read_int16(fid),
        "scale": read_float(fid),
        "yaxis_label": read_str(fid, 16),
        "valid_min_max": read_int16(fid),
    }

    fid.seek(6, 1)
    out.update(
        {
            "ymin": read_double(fid),
            "ymax": read_double(fid),
            "index": read_int32(fid),
            "checksum": read_int32(fid),
            "off_flag": read_str(fid, 4),
            "offset": read_float(fid),
        }
    )

    fid.seek(24, 1)

    return out


def _read_event(fid):
    """Read BTi PDF event."""
    out = {
        "event_name": read_str(fid, 16),
        "start_lat": read_float(fid),
        "end_lat": read_float(fid),
        "step_size": read_float(fid),
        "fixed_event": read_int16(fid),
        "checksum": read_int32(fid),
    }

    fid.seek(32, 1)
    _correct_offset(fid)

    return out


def _read_process(fid):
    """Read BTi PDF process."""
    out = {
        "nbytes": read_int32(fid),
        "process_type": read_str(fid, 20),
        "checksum": read_int32(fid),
        "user": read_str(fid, 32),
        "timestamp": read_int32(fid),
        "filename": read_str(fid, 256),
        "total_steps": read_int32(fid),
    }

    fid.seek(32, 1)
    _correct_offset(fid)
    out["processing_steps"] = list()
    for step in range(out["total_steps"]):
        this_step = {
            "nbytes": read_int32(fid),
            "process_type": read_str(fid, 20),
            "checksum": read_int32(fid),
        }
        ptype = this_step["process_type"]
        if ptype == BTI.PROC_DEFAULTS:
            this_step["scale_option"] = read_int32(fid)

            fid.seek(4, 1)
            this_step["scale"] = read_double(fid)
            this_step["dtype"] = read_int32(fid)
            this_step["selected"] = read_int16(fid)
            this_step["color_display"] = read_int16(fid)

            fid.seek(32, 1)
        elif ptype in BTI.PROC_FILTER:
            this_step["freq"] = read_float(fid)
            fid.seek(32, 1)
        elif ptype in BTI.PROC_BPFILTER:
            this_step["high_freq"] = read_float(fid)
            this_step["low_freq"] = read_float(fid)
        else:
            jump = this_step["user_space_size"] = read_int32(fid)
            fid.seek(32, 1)
            fid.seek(jump, 1)

        out["processing_steps"] += [this_step]
        _correct_offset(fid)

    return out


def _read_assoc_file(fid):
    """Read BTi PDF assocfile."""
    out = {"file_id": read_int16(fid), "length": read_int16(fid)}

    fid.seek(32, 1)
    out["checksum"] = read_int32(fid)

    return out


def _read_pfid_ed(fid):
    """Read PDF ed file."""
    out = {"comment_size": read_int32(fid), "name": read_str(fid, 17)}

    fid.seek(9, 1)
    out.update(
        {
            "pdf_number": read_int16(fid),
            "total_events": read_int32(fid),
            "timestamp": read_int32(fid),
            "flags": read_int32(fid),
            "de_process": read_int32(fid),
            "checksum": read_int32(fid),
            "ed_id": read_int32(fid),
            "win_width": read_float(fid),
            "win_offset": read_float(fid),
        }
    )

    fid.seek(8, 1)

    return out


def _read_bti_header_pdf(pdf_fname):
    """Read header from pdf file."""
    with _bti_open(pdf_fname, "rb") as fid:
        fid.seek(-8, 2)
        start = fid.tell()
        header_position = read_int64(fid)
        check_value = header_position & BTI.FILE_MASK

        if (start + BTI.FILE_CURPOS - check_value) <= BTI.FILE_MASK:
            header_position = check_value

        # Check header position for alignment issues
        if (header_position % 8) != 0:
            header_position += 8 - (header_position % 8)

        fid.seek(header_position, 0)

        # actual header starts here
        info = {
            "version": read_int16(fid),
            "file_type": read_str(fid, 5),
            "hdr_size": start - header_position,  # add for convenience
            "start": start,
        }

        fid.seek(1, 1)

        info.update(
            {
                "data_format": read_int16(fid),
                "acq_mode": read_int16(fid),
                "total_epochs": read_int32(fid),
                "input_epochs": read_int32(fid),
                "total_events": read_int32(fid),
                "total_fixed_events": read_int32(fid),
                "sample_period": read_float(fid),
                "xaxis_label": read_str(fid, 16),
                "total_processes": read_int32(fid),
                "total_chans": read_int16(fid),
            }
        )

        fid.seek(2, 1)
        info.update(
            {
                "checksum": read_int32(fid),
                "total_ed_classes": read_int32(fid),
                "total_associated_files": read_int16(fid),
                "last_file_index": read_int16(fid),
                "timestamp": read_int32(fid),
            }
        )

        fid.seek(20, 1)
        _correct_offset(fid)

        # actual header ends here, so dar seems ok.

        info["epochs"] = [_read_epoch(fid) for _ in range(info["total_epochs"])]

        info["chs"] = [_read_channel(fid) for _ in range(info["total_chans"])]

        info["events"] = [_read_event(fid) for _ in range(info["total_events"])]

        info["processes"] = [_read_process(fid) for _ in range(info["total_processes"])]

        info["assocfiles"] = [
            _read_assoc_file(fid) for _ in range(info["total_associated_files"])
        ]

        info["edclasses"] = [
            _read_pfid_ed(fid) for _ in range(info["total_ed_classes"])
        ]

        info["extra_data"] = fid.read(start - fid.tell())
        info["pdf"] = pdf_fname

    info["total_slices"] = sum(e["pts_in_epoch"] for e in info["epochs"])

    info["dtype"] = DTYPES[info["data_format"]]
    bps = info["dtype"].itemsize * info["total_chans"]
    info["bytes_per_slice"] = bps
    return info


def _read_bti_header(pdf_fname, config_fname, sort_by_ch_name=True):
    """Read bti PDF header."""
    info = _read_bti_header_pdf(pdf_fname) if pdf_fname is not None else dict()
    cfg = _read_config(config_fname)
    info["bti_transform"] = cfg["transforms"]

    # augment channel list by according info from config.
    # get channels from config present in PDF
    chans = info.get("chs", None)
    if chans is not None:
        chans_cfg = [
            c for c in cfg["chs"] if c["chan_no"] in [c_["chan_no"] for c_ in chans]
        ]

        # sort chans_cfg and chans
        chans = sorted(chans, key=lambda k: k["chan_no"])
        chans_cfg = sorted(chans_cfg, key=lambda k: k["chan_no"])

        # check all pdf channels are present in config
        match = [c["chan_no"] for c in chans_cfg] == [c["chan_no"] for c in chans]

        if not match:
            raise RuntimeError(
                "Could not match raw data channels with"
                " config channels. Some of the channels"
                " found are not described in config."
            )
    else:
        chans_cfg = cfg["chs"]
        chans = [dict() for _ in chans_cfg]

    # transfer channel info from config to channel info
    for ch, ch_cfg in zip(chans, chans_cfg):
        ch["upb"] = ch_cfg["units_per_bit"]
        ch["gain"] = ch_cfg["gain"]
        ch["name"] = ch_cfg["name"]
        if ch_cfg.get("dev", dict()).get("transform", None) is not None:
            ch["loc"] = _coil_trans_to_loc(ch_cfg["dev"]["transform"])
        else:
            ch["loc"] = np.full(12, np.nan)
        if pdf_fname is not None:
            if info["data_format"] <= 2:  # see DTYPES, implies integer
                ch["cal"] = ch["scale"] * ch["upb"] / float(ch["gain"])
            else:  # float
                ch["cal"] = ch["scale"] * ch["gain"]
        else:  # if we are in this mode we don't read data, only channel info.
            ch["cal"] = ch["scale"] = 1.0  # so we put a trivial default value

    if sort_by_ch_name:
        by_index = [(i, d["index"]) for i, d in enumerate(chans)]
        by_index.sort(key=lambda c: c[1])
        by_index = [idx[0] for idx in by_index]
        chs = [chans[pos] for pos in by_index]

        sort_by_name_idx = [(i, d["name"]) for i, d in enumerate(chs)]
        a_chs = [c for c in sort_by_name_idx if c[1].startswith("A")]
        other_chs = [c for c in sort_by_name_idx if not c[1].startswith("A")]
        sort_by_name_idx = sorted(a_chs, key=lambda c: int(c[1][1:])) + sorted(
            other_chs
        )

        sort_by_name_idx = [idx[0] for idx in sort_by_name_idx]

        info["chs"] = [chans[pos] for pos in sort_by_name_idx]
        info["order"] = sort_by_name_idx
    else:
        info["chs"] = chans
        info["order"] = np.arange(len(chans))

    # finally add some important fields from the config
    info["e_table"] = cfg["user_blocks"][BTI.UB_B_E_TABLE_USED]
    info["weights"] = cfg["user_blocks"][BTI.UB_B_WEIGHTS_USED]

    return info


def _correct_trans(t, check=True):
    """Convert to a transformation matrix."""
    t = np.array(t, np.float64)
    t[:3, :3] *= t[3, :3][:, np.newaxis]  # apply scalings
    t[3, :3] = 0.0  # remove them
    if check:
        assert t[3, 3] == 1.0
    else:
        t[3, 3] = 1.0
    return t


class RawBTi(BaseRaw):
    """Raw object from 4D Neuroimaging MagnesWH3600 data.

    Parameters
    ----------
    pdf_fname : path-like
        Path to the processed data file (PDF).
    config_fname : path-like
        Path to system config file.
    head_shape_fname : path-like | None
        Path to the head shape file.
    rotation_x : float
        Degrees to tilt x-axis for sensor frame misalignment. Ignored
        if convert is True.
    translation : array-like, shape (3,)
        The translation to place the origin of coordinate system
        to the center of the head. Ignored if convert is True.
    convert : bool
        Convert to Neuromag coordinates or not.
    rename_channels : bool
        Whether to keep original 4D channel labels or not. Defaults to True.
    sort_by_ch_name : bool
        Reorder channels according to channel label. 4D channels don't have
        monotonically increasing numbers in their labels. Defaults to True.
    ecg_ch : str | None
        The 4D name of the ECG channel. If None, the channel will be treated
        as regular EEG channel.
    eog_ch : tuple of str | None
        The 4D names of the EOG channels. If None, the channels will be treated
        as regular EEG channels.
    %(preload)s

        .. versionadded:: 0.11

    %(verbose)s
    """

    @verbose
    def __init__(
        self,
        pdf_fname,
        config_fname="config",
        head_shape_fname="hs_file",
        rotation_x=0.0,
        translation=(0.0, 0.02, 0.11),
        convert=True,
        rename_channels=True,
        sort_by_ch_name=True,
        ecg_ch="E31",
        eog_ch=("E63", "E64"),
        preload=False,
        verbose=None,
    ):
        _validate_type(pdf_fname, ("path-like", BytesIO), "pdf_fname")
        info, bti_info = _get_bti_info(
            pdf_fname=pdf_fname,
            config_fname=config_fname,
            head_shape_fname=head_shape_fname,
            rotation_x=rotation_x,
            translation=translation,
            convert=convert,
            ecg_ch=ecg_ch,
            rename_channels=rename_channels,
            sort_by_ch_name=sort_by_ch_name,
            eog_ch=eog_ch,
        )
        bti_info["bti_ch_labels"] = [c["chan_label"] for c in bti_info["chs"]]
        # make Raw repr work if we have a BytesIO as input
        filename = bti_info["pdf"]
        if isinstance(filename, BytesIO):
            filename = None
        super().__init__(
            info,
            preload,
            filenames=[filename],
            raw_extras=[bti_info],
            last_samps=[bti_info["total_slices"] - 1],
            verbose=verbose,
        )

    def _read_segment_file(self, data, idx, fi, start, stop, cals, mult):
        """Read a segment of data from a file."""
        bti_info = self._raw_extras[fi]
        fname_or_bytes = bti_info["pdf"]
        dtype = bti_info["dtype"]
        assert len(bti_info["chs"]) == self._raw_extras[fi]["orig_nchan"]
        n_channels = len(bti_info["chs"])
        n_bytes = np.dtype(dtype).itemsize
        data_left = (stop - start) * n_channels
        read_cals = np.empty((bti_info["total_chans"],))
        for ch in bti_info["chs"]:
            read_cals[ch["index"]] = ch["cal"]

        block_size = ((int(100e6) // n_bytes) // n_channels) * n_channels
        block_size = min(data_left, block_size)
        # extract data in chunks
        with _bti_open(fname_or_bytes, "rb") as fid:
            fid.seek(bti_info["bytes_per_slice"] * start, 0)
            for sample_start in np.arange(0, data_left, block_size) // n_channels:
                count = min(block_size, data_left - sample_start * n_channels)
                if isinstance(fid, BytesIO):
                    block = np.frombuffer(fid.getvalue(), dtype, count)
                else:
                    block = np.fromfile(fid, dtype, count)
                sample_stop = sample_start + count // n_channels
                shape = (sample_stop - sample_start, bti_info["total_chans"])
                block = _reshape_view(block, shape)
                data_view = data[:, sample_start:sample_stop]
                one = np.empty(block.shape[::-1])

                for ii, b_i_o in enumerate(bti_info["order"]):
                    one[ii] = block[:, b_i_o] * read_cals[b_i_o]
                _mult_cal_one(data_view, one, idx, cals, mult)


@functools.lru_cache(1)
def _1020_names():
    from mne.channels import make_standard_montage

    return set(
        ch_name.lower() for ch_name in make_standard_montage("standard_1005").ch_names
    )


def _eeg_like(ch_name):
    # Some bti recordigs look like "F4-POz", so let's at least mark them
    # as EEG
    if ch_name.count("-") != 1:
        return
    ch, ref = ch_name.split("-")
    eeg_names = _1020_names()
    return ch.lower() in eeg_names and ref.lower() in eeg_names


def _make_bti_digitization(
    info, head_shape_fname, convert, use_hpi, bti_dev_t, dev_ctf_t
):
    with info._unlock():
        if head_shape_fname:
            logger.info(f"... Reading digitization points from {head_shape_fname}")

            nasion, lpa, rpa, hpi, dig_points = _read_head_shape(head_shape_fname)
            info["dig"], dev_head_t, ctf_head_t = _make_bti_dig_points(
                nasion,
                lpa,
                rpa,
                hpi,
                dig_points,
                convert,
                use_hpi,
                bti_dev_t,
                dev_ctf_t,
            )
        else:
            logger.info("... no headshape file supplied, doing nothing.")
            info["dig"] = None
            dev_head_t = Transform("meg", "head", trans=None)
            ctf_head_t = Transform("ctf_head", "head", trans=None)

    info.update(dev_head_t=dev_head_t, dev_ctf_t=dev_ctf_t, ctf_head_t=ctf_head_t)

    return info


def _get_bti_info(
    pdf_fname,
    config_fname,
    head_shape_fname,
    rotation_x,
    translation,
    convert,
    ecg_ch,
    eog_ch,
    rename_channels=True,
    sort_by_ch_name=True,
):
    """Read BTI info.

    Note. This helper supports partial construction of infos when `pdf_fname`
    is None. Some datasets, such as the HCP, are shipped as a large collection
    of zipped files where it can be more efficient to only read the needed
    information. In such a situation, some information can neither be accessed
    directly nor guessed based on the `config`.

    These fields will thus be set to None:
        - 'lowpass'
        - 'highpass'
        - 'sfreq'
        - 'meas_date'

    """
    if pdf_fname is None:
        logger.info("No pdf_fname passed, trying to construct partial info from config")
    if pdf_fname is not None and not isinstance(pdf_fname, BytesIO):
        if not op.isabs(pdf_fname):
            pdf_fname = op.abspath(pdf_fname)

    if not isinstance(config_fname, BytesIO):
        if not op.isabs(config_fname):
            config_tries = [
                op.abspath(config_fname),
                op.abspath(op.join(op.dirname(pdf_fname), config_fname)),
            ]
            for config_try in config_tries:
                if op.isfile(config_try):
                    config_fname = config_try
                    break
        if not op.isfile(config_fname):
            raise ValueError(
                f"Could not find the config file {config_fname}. Please check"
                " whether you are in the right directory "
                "or pass the full name"
            )

    if head_shape_fname is not None and not isinstance(head_shape_fname, BytesIO):
        orig_name = head_shape_fname
        if not op.isfile(head_shape_fname):
            head_shape_fname = op.join(op.dirname(pdf_fname), head_shape_fname)

        if not op.isfile(head_shape_fname):
            raise ValueError(
                f'Could not find the head_shape file "{orig_name}". '
                "You should check whether you are in the "
                "right directory, pass the full file name, "
                "or pass head_shape_fname=None."
            )

    logger.info(f"Reading 4D PDF file {pdf_fname}...")
    bti_info = _read_bti_header(
        pdf_fname, config_fname, sort_by_ch_name=sort_by_ch_name
    )
    extras = dict(
        pdf_fname=pdf_fname,
        head_shape_fname=head_shape_fname,
        config_fname=config_fname,
    )
    for key, val in extras.items():
        bti_info[key] = None if isinstance(val, BytesIO) else val

    dev_ctf_t = Transform(
        "ctf_meg", "ctf_head", _correct_trans(bti_info["bti_transform"][0])
    )

    _check_nan_dev_head_t(dev_ctf_t)
    # for old backward compatibility and external processing
    rotation_x = 0.0 if rotation_x is None else rotation_x
    bti_dev_t = _get_bti_dev_t(rotation_x, translation) if convert else None
    bti_dev_t = Transform("ctf_meg", "meg", bti_dev_t)

    use_hpi = False  # hard coded, but marked as later option.
    logger.info("Creating Neuromag info structure ...")
    if "sample_period" in bti_info.keys():
        sfreq = 1.0 / bti_info["sample_period"]
    else:
        sfreq = None

    if pdf_fname is not None:
        info = _empty_info(sfreq)
        date = bti_info["processes"][0]["timestamp"]
        info["meas_date"] = _stamp_to_dt((date, 0))
    else:  # these cannot be guessed from config, see docstring
        info = _empty_info(1.0)
        info["sfreq"] = None
        info["lowpass"] = None
        info["highpass"] = None
        info["meas_date"] = None
        bti_info["processes"] = list()

    # browse processing info for filter specs.
    hp, lp = info["highpass"], info["lowpass"]
    for proc in bti_info["processes"]:
        if "filt" in proc["process_type"]:
            for step in proc["processing_steps"]:
                if "high_freq" in step:
                    hp, lp = step["high_freq"], step["low_freq"]
                elif "hp" in step["process_type"]:
                    hp = step["freq"]
                elif "lp" in step["process_type"]:
                    lp = step["freq"]

    info["highpass"] = hp
    info["lowpass"] = lp
    chs = []

    # Note that 'name' and 'chan_label' are not the same.
    # We want the configured label if out IO parsed it
    # except for the MEG channels for which we keep the config name
    bti_ch_names = list()
    for ch in bti_info["chs"]:
        # we have always relied on 'A' as indicator of MEG data channels.
        ch_name = ch["name"]
        if not ch_name.startswith("A"):
            ch_name = ch.get("chan_label", ch_name)
        bti_ch_names.append(ch_name)

    neuromag_ch_names = _rename_channels(bti_ch_names, ecg_ch=ecg_ch, eog_ch=eog_ch)
    ch_mapping = zip(bti_ch_names, neuromag_ch_names)

    logger.info("... Setting channel info structure.")
    for idx, (chan_4d, chan_neuromag) in enumerate(ch_mapping):
        chan_info = _instantiate_default_info_chs()
        chan_info["ch_name"] = chan_neuromag if rename_channels else chan_4d
        chan_info["logno"] = idx + BTI.FIFF_LOGNO
        chan_info["scanno"] = idx + 1
        chan_info["cal"] = float(bti_info["chs"][idx]["scale"])

        if any(chan_4d.startswith(k) for k in ("A", "M", "G")):
            loc = bti_info["chs"][idx]["loc"]
            if loc is not None:
                if convert:
                    if idx == 0:
                        logger.info(
                            "... putting coil transforms in Neuromag coordinates"
                        )
                    t = _loc_to_coil_trans(bti_info["chs"][idx]["loc"])
                    t = _convert_coil_trans(t, dev_ctf_t, bti_dev_t)
                    loc = _coil_trans_to_loc(t)
            chan_info["loc"] = loc

        # BTI sensors are natively stored in 4D head coords we believe
        meg_frame = FIFF.FIFFV_COORD_DEVICE if convert else FIFF.FIFFV_MNE_COORD_4D_HEAD
        eeg_frame = FIFF.FIFFV_COORD_HEAD if convert else FIFF.FIFFV_MNE_COORD_4D_HEAD
        if chan_4d.startswith("A"):
            chan_info["kind"] = FIFF.FIFFV_MEG_CH
            chan_info["coil_type"] = FIFF.FIFFV_COIL_MAGNES_MAG
            chan_info["coord_frame"] = meg_frame
            chan_info["unit"] = FIFF.FIFF_UNIT_T

        elif chan_4d.startswith("M"):
            chan_info["kind"] = FIFF.FIFFV_REF_MEG_CH
            chan_info["coil_type"] = FIFF.FIFFV_COIL_MAGNES_REF_MAG
            chan_info["coord_frame"] = meg_frame
            chan_info["unit"] = FIFF.FIFF_UNIT_T

        elif chan_4d.startswith("G"):
            chan_info["kind"] = FIFF.FIFFV_REF_MEG_CH
            chan_info["coord_frame"] = meg_frame
            chan_info["unit"] = FIFF.FIFF_UNIT_T_M
            if chan_4d in ("GxxA", "GyyA"):
                chan_info["coil_type"] = FIFF.FIFFV_COIL_MAGNES_REF_GRAD
            elif chan_4d in ("GyxA", "GzxA", "GzyA"):
                chan_info["coil_type"] = FIFF.FIFFV_COIL_MAGNES_OFFDIAG_REF_GRAD

        elif chan_4d.startswith("EEG") or _eeg_like(chan_4d):
            chan_info["kind"] = FIFF.FIFFV_EEG_CH
            chan_info["coil_type"] = FIFF.FIFFV_COIL_EEG
            chan_info["coord_frame"] = eeg_frame
            chan_info["unit"] = FIFF.FIFF_UNIT_V
            # TODO: We should use 'electrodes' to fill this in, and make sure
            # we turn them into dig as well
            chan_info["loc"][:3] = np.nan

        elif chan_4d == "RESPONSE":
            chan_info["kind"] = FIFF.FIFFV_STIM_CH
        elif chan_4d == "TRIGGER":
            chan_info["kind"] = FIFF.FIFFV_STIM_CH
        elif (
            chan_4d.startswith("EOG")
            or chan_4d[:4] in ("HEOG", "VEOG")
            or chan_4d in eog_ch
        ):
            chan_info["kind"] = FIFF.FIFFV_EOG_CH
        elif chan_4d.startswith("EMG"):
            chan_info["kind"] = FIFF.FIFFV_EMG_CH
        elif chan_4d == ecg_ch or chan_4d.startswith("ECG"):
            chan_info["kind"] = FIFF.FIFFV_ECG_CH
        # Our default is now misc, but if we ever change that,
        # we'll need this:
        # elif chan_4d.startswith('X') or chan_4d == 'UACurrent':
        #     chan_info['kind'] = FIFF.FIFFV_MISC_CH

        chs.append(chan_info)

    info["chs"] = chs

    # ### Dig stuff
    info = _make_bti_digitization(
        info, head_shape_fname, convert, use_hpi, bti_dev_t, dev_ctf_t
    )

    logger.info(
        "Currently direct inclusion of 4D weight tables is not supported."
        " For critical use cases please take into account the MNE command"
        ' "mne_create_comp_data" to include weights as printed out by '
        'the 4D "print_table" routine.'
    )

    # check that the info is complete
    info._unlocked = False
    info._update_redundant()
    info._check_consistency()
    return info, bti_info


@verbose
def read_raw_bti(
    pdf_fname,
    config_fname="config",
    head_shape_fname="hs_file",
    rotation_x=0.0,
    translation=(0.0, 0.02, 0.11),
    convert=True,
    rename_channels=True,
    sort_by_ch_name=True,
    ecg_ch="E31",
    eog_ch=("E63", "E64"),
    preload=False,
    verbose=None,
) -> RawBTi:
    """Raw object from 4D Neuroimaging MagnesWH3600 data.

    .. note::
        1. Currently direct inclusion of reference channel weights
           is not supported. Please use ``mne_create_comp_data`` to include
           the weights or use the low level functions from this module to
           include them by yourself.
        2. The informed guess for the 4D name is E31 for the ECG channel and
           E63, E63 for the EOG channels. Please check and adjust if those
           channels are present in your dataset but 'ECG 01' and 'EOG 01',
           'EOG 02' don't appear in the channel names of the raw object.

    Parameters
    ----------
    pdf_fname : path-like
        Path to the processed data file (PDF).
    config_fname : path-like
        Path to system config file.
    head_shape_fname : path-like | None
        Path to the head shape file.
    rotation_x : float
        Degrees to tilt x-axis for sensor frame misalignment. Ignored
        if convert is True.
    translation : array-like, shape (3,)
        The translation to place the origin of coordinate system
        to the center of the head. Ignored if convert is True.
    convert : bool
        Convert to Neuromag coordinates or not.
    rename_channels : bool
        Whether to keep original 4D channel labels or not. Defaults to True.
    sort_by_ch_name : bool
        Reorder channels according to channel label. 4D channels don't have
        monotonically increasing numbers in their labels. Defaults to True.
    ecg_ch : str | None
        The 4D name of the ECG channel. If None, the channel will be treated
        as regular EEG channel.
    eog_ch : tuple of str | None
        The 4D names of the EOG channels. If None, the channels will be treated
        as regular EEG channels.
    %(preload)s

        .. versionadded:: 0.11
    %(verbose)s

    Returns
    -------
    raw : instance of RawBTi
        A Raw object containing BTI data.
        See :class:`mne.io.Raw` for documentation of attributes and methods.

    See Also
    --------
    mne.io.Raw : Documentation of attributes and methods of RawBTi.
    """
    return RawBTi(
        pdf_fname,
        config_fname=config_fname,
        head_shape_fname=head_shape_fname,
        rotation_x=rotation_x,
        translation=translation,
        convert=convert,
        rename_channels=rename_channels,
        sort_by_ch_name=sort_by_ch_name,
        ecg_ch=ecg_ch,
        eog_ch=eog_ch,
        preload=preload,
        verbose=verbose,
    )
