"""
Test scalar buffer interface adheres to PEP 3118
"""
import sys
import numpy as np
import pytest

from numpy.testing import assert_, assert_equal, assert_raises

# PEP3118 format strings for native (standard alignment and byteorder) types
scalars_and_codes = [
    (np.bool_, '?'),
    (np.byte, 'b'),
    (np.short, 'h'),
    (np.intc, 'i'),
    (np.int_, 'l'),
    (np.longlong, 'q'),
    (np.ubyte, 'B'),
    (np.ushort, 'H'),
    (np.uintc, 'I'),
    (np.uint, 'L'),
    (np.ulonglong, 'Q'),
    (np.half, 'e'),
    (np.single, 'f'),
    (np.double, 'd'),
    (np.longdouble, 'g'),
    (np.csingle, 'Zf'),
    (np.cdouble, 'Zd'),
    (np.clongdouble, 'Zg'),
]


@pytest.mark.skipif(sys.version_info.major < 3,
                    reason="Python 2 scalars lack a buffer interface")
class TestScalarPEP3118(object):

    def test_scalar_match_array(self):
        for scalar, _ in scalars_and_codes:
            x = scalar()
            a = np.array([], dtype=np.dtype(scalar))
            mv_x = memoryview(x)
            mv_a = memoryview(a)
            assert_equal(mv_x.format, mv_a.format)

    def test_scalar_dim(self):
        for scalar, _ in scalars_and_codes:
            x = scalar()
            mv_x = memoryview(x)
            assert_equal(mv_x.itemsize, np.dtype(scalar).itemsize)
            assert_equal(mv_x.ndim, 0)
            assert_equal(mv_x.shape, ())
            assert_equal(mv_x.strides, ())
            assert_equal(mv_x.suboffsets, ())

    def test_scalar_known_code(self):
        for scalar, code in scalars_and_codes:
            x = scalar()
            mv_x = memoryview(x)
            assert_equal(mv_x.format, code)

    def test_void_scalar_structured_data(self):
        dt = np.dtype([('name', np.unicode_, 16), ('grades', np.float64, (2,))])
        x = np.array(('ndarray_scalar', (1.2, 3.0)), dtype=dt)[()]
        assert_(isinstance(x, np.void))
        mv_x = memoryview(x)
        expected_size = 16 * np.dtype((np.unicode_, 1)).itemsize
        expected_size += 2 * np.dtype((np.float64, 1)).itemsize
        assert_equal(mv_x.itemsize, expected_size)
        assert_equal(mv_x.ndim, 0)
        assert_equal(mv_x.shape, ())
        assert_equal(mv_x.strides, ())
        assert_equal(mv_x.suboffsets, ())

        # check scalar format string against ndarray format string
        a = np.array([('Sarah', (8.0, 7.0)), ('John', (6.0, 7.0))], dtype=dt)
        assert_(isinstance(a, np.ndarray))
        mv_a = memoryview(a)
        assert_equal(mv_x.itemsize, mv_a.itemsize)
        assert_equal(mv_x.format, mv_a.format)

    def test_datetime_memoryview(self):
        # gh-11656
        # Values verified with v1.13.3, shape is not () as in test_scalar_dim
        def as_dict(m):
            return dict(strides=m.strides, shape=m.shape, itemsize=m.itemsize,
                        ndim=m.ndim, format=m.format)

        dt1 = np.datetime64('2016-01-01')
        dt2 = np.datetime64('2017-01-01')
        expected = {'strides': (1,), 'itemsize': 1, 'ndim': 1,
                    'shape': (8,), 'format': 'B'}
        v = memoryview(dt1)
        res = as_dict(v) 
        assert_equal(res, expected)

        v = memoryview(dt2 - dt1)
        res = as_dict(v)
        assert_equal(res, expected)

        dt = np.dtype([('a', 'uint16'), ('b', 'M8[s]')])
        a = np.empty(1, dt)
        # Fails to create a PEP 3118 valid buffer
        assert_raises((ValueError, BufferError), memoryview, a[0])

