"""
Python Library to Read Surface Files in Freesurfer's TriangularSurface Format

compatible with Freesurfer's MRISwriteTriangularSurface()
https://github.com/freesurfer/freesurfer/blob/release_6_0_0/include/mrisurf.h#L1281
https://github.com/freesurfer/freesurfer/blob/release_6_0_0/utils/mrisurf.c
https://raw.githubusercontent.com/freesurfer/freesurfer/release_6_0_0/utils/mrisurf.c

Freesurfer
https://surfer.nmr.mgh.harvard.edu/

>>> from freesurfer_surface import Surface
>>>
>>> surface = Surface.read_triangular('bert/surf/lh.pial'))
"""

import collections
import re
import struct
import typing

try:
    from freesurfer_surface.version import __version__
except ImportError:  # pragma: no cover
    __version__ = None

Vertex = collections.namedtuple('Vertex', ['right', 'anterior', 'superior'])


class Surface:

    _MAGIC_NUMBER = b'\xff\xff\xfe'

    _TAG_CMDLINE = b'\x00\x00\x00\x03'
    _TAG_OLD_SURF_GEOM = b'\x00\x00\x00\x14'
    _TAG_OLD_USEREALRAS = b'\x00\x00\x00\x02'

    def __init__(self):
        self.creator = None
        self.vertices = []
        self.triangles_vertex_indices = []
        # self._triangles = []
        self.using_old_real_ras = False
        self.volume_geometry_info = None
        self.command_lines = []

    @classmethod
    def _read_cmdlines(cls, stream: typing.BinaryIO) -> typing.Iterator[str]:
        while True:
            tag = stream.read(4)
            if not tag:
                return
            assert tag == cls._TAG_CMDLINE  # might be TAG_GROUP_AVG_SURFACE_AREA
            # TAGwrite
            # https://github.com/freesurfer/freesurfer/blob/release_6_0_0/utils/tags.c#L94
            str_length, = struct.unpack('>Q', stream.read(8))
            yield stream.read(str_length - 1)
            assert stream.read(1) == b'\x00'

    def _read_triangular(self, stream: typing.BinaryIO):
        assert stream.read(3) == self._MAGIC_NUMBER
        self.creator = re.match(rb'^created by (\w+) on .* \d{4}\n',
                                stream.readline()).groups()
        assert stream.read(1) == b'\n'
        # fwriteInt
        # https://github.com/freesurfer/freesurfer/blob/release_6_0_0/utils/fio.c#L290
        vertices_num, triangles_num = struct.unpack('>II', stream.read(4 * 2))
        self.vertices = [Vertex(*struct.unpack('>fff', stream.read(4 * 3)))
                         for _ in range(vertices_num)]
        self.triangles_vertex_indices = [struct.unpack('>III', stream.read(4 * 3))
                                         for _ in range(triangles_num)]
        assert all(vertex_idx < vertices_num
                   for triangle_vertex_index in self.triangles_vertex_indices
                   for vertex_idx in triangle_vertex_index)
        assert stream.read(4) == self._TAG_OLD_USEREALRAS
        using_old_real_ras, = struct.unpack('>I', stream.read(4))
        assert using_old_real_ras in [0, 1], using_old_real_ras
        self.using_old_real_ras = bool(using_old_real_ras)
        assert stream.read(4) == self._TAG_OLD_SURF_GEOM
        # writeVolGeom
        # https://github.com/freesurfer/freesurfer/blob/release_6_0_0/utils/transform.c#L368
        self.volume_geometry_info = [stream.readline() for _ in range(8)]
        self.command_lines = list(self._read_cmdlines(stream))

    @classmethod
    def read_triangular(cls, surface_file_path: str) -> 'Surface':
        surface = cls()
        with open(surface_file_path, 'rb') as surface_file:
            # pylint: disable=protected-access
            surface._read_triangular(surface_file)
        return surface