"""
Tests the usecols functionality during parsing
for all of the parsers defined in parsers.py
"""
from io import StringIO

import pytest

from pandas import (
    DataFrame,
    Index,
    Timestamp,
)
import pandas._testing as tm

# TODO(1.4): Change these to xfails whenever parse_dates support(which was
# intentionally disable to keep small PR sizes) is added back
pytestmark = pytest.mark.usefixtures("pyarrow_skip")


@pytest.mark.parametrize("usecols", [[0, 2, 3], [3, 0, 2]])
def test_usecols_with_parse_dates(all_parsers, usecols):
    # see gh-9755
    data = """a,b,c,d,e
0,1,2014-01-01,09:00,4
0,1,2014-01-02,10:00,4"""
    parser = all_parsers
    parse_dates = [[1, 2]]

    cols = {
        "a": [0, 0],
        "c_d": [Timestamp("2014-01-01 09:00:00"), Timestamp("2014-01-02 10:00:00")],
    }
    expected = DataFrame(cols, columns=["c_d", "a"])
    result = parser.read_csv(StringIO(data), usecols=usecols, parse_dates=parse_dates)
    tm.assert_frame_equal(result, expected)


def test_usecols_with_parse_dates2(all_parsers):
    # see gh-13604
    parser = all_parsers
    data = """2008-02-07 09:40,1032.43
2008-02-07 09:50,1042.54
2008-02-07 10:00,1051.65"""

    names = ["date", "values"]
    usecols = names[:]
    parse_dates = [0]

    index = Index(
        [
            Timestamp("2008-02-07 09:40"),
            Timestamp("2008-02-07 09:50"),
            Timestamp("2008-02-07 10:00"),
        ],
        name="date",
    )
    cols = {"values": [1032.43, 1042.54, 1051.65]}
    expected = DataFrame(cols, index=index)

    result = parser.read_csv(
        StringIO(data),
        parse_dates=parse_dates,
        index_col=0,
        usecols=usecols,
        header=None,
        names=names,
    )
    tm.assert_frame_equal(result, expected)


def test_usecols_with_parse_dates3(all_parsers):
    # see gh-14792
    parser = all_parsers
    data = """a,b,c,d,e,f,g,h,i,j
2016/09/21,1,1,2,3,4,5,6,7,8"""

    usecols = list("abcdefghij")
    parse_dates = [0]

    cols = {
        "a": Timestamp("2016-09-21").as_unit("ns"),
        "b": [1],
        "c": [1],
        "d": [2],
        "e": [3],
        "f": [4],
        "g": [5],
        "h": [6],
        "i": [7],
        "j": [8],
    }
    expected = DataFrame(cols, columns=usecols)

    result = parser.read_csv(StringIO(data), usecols=usecols, parse_dates=parse_dates)
    tm.assert_frame_equal(result, expected)


def test_usecols_with_parse_dates4(all_parsers):
    data = "a,b,c,d,e,f,g,h,i,j\n2016/09/21,1,1,2,3,4,5,6,7,8"
    usecols = list("abcdefghij")
    parse_dates = [[0, 1]]
    parser = all_parsers

    cols = {
        "a_b": "2016/09/21 1",
        "c": [1],
        "d": [2],
        "e": [3],
        "f": [4],
        "g": [5],
        "h": [6],
        "i": [7],
        "j": [8],
    }
    expected = DataFrame(cols, columns=["a_b"] + list("cdefghij"))

    result = parser.read_csv(
        StringIO(data),
        usecols=usecols,
        parse_dates=parse_dates,
    )
    tm.assert_frame_equal(result, expected)


@pytest.mark.parametrize("usecols", [[0, 2, 3], [3, 0, 2]])
@pytest.mark.parametrize(
    "names",
    [
        list("abcde"),  # Names span all columns in original data.
        list("acd"),  # Names span only the selected columns.
    ],
)
def test_usecols_with_parse_dates_and_names(all_parsers, usecols, names):
    # see gh-9755
    s = """0,1,2014-01-01,09:00,4
0,1,2014-01-02,10:00,4"""
    parse_dates = [[1, 2]]
    parser = all_parsers

    cols = {
        "a": [0, 0],
        "c_d": [Timestamp("2014-01-01 09:00:00"), Timestamp("2014-01-02 10:00:00")],
    }
    expected = DataFrame(cols, columns=["c_d", "a"])

    result = parser.read_csv(
        StringIO(s), names=names, parse_dates=parse_dates, usecols=usecols
    )
    tm.assert_frame_equal(result, expected)