# delta_time.py
#
# Parser to convert a conversational time reference such as "in a minute" or
# "noon tomorrow" and convert it to a Python datetime. The returned
# ParseResults object contains
#   - original - the original time expression string
#   - computed_dt - the Python datetime representing the computed time
#   - relative_to - the reference "now" time
#   - time_offset - the difference between the reference time and the computed time
#
# BNF:
#     time_and_day ::= time_reference [day_reference] | day_reference 'at' absolute_time_of_day
#     day_reference ::= absolute_day_reference | relative_day_reference
#     absolute_day_reference ::= 'today' | 'tomorrow' | 'yesterday' | ['next' | 'last'] weekday_name
#        (if weekday_name is given and is the same as the reference weekday:
#            if 'next' is given, use 7 days after the reference time
#            else if 'last' is given, use 7 days before the reference time
#            else, use the reference time)
#
#     relative_day_reference ::= 'in' qty day_units
#                                | qty day_units 'ago'
#                                | 'qty day_units ('from' | 'before' | 'after') absolute_day_reference
#     day_units ::= 'days' | 'weeks'
#
#     time_reference ::= absolute_time_of_day | relative_time_reference
#     relative_time_reference ::= qty time_units ('from' | 'before' | 'after') absolute_time_of_day
#                                 | qty time_units 'ago'
#                                 | 'in' qty time_units
#     time_units ::= 'hours' | 'minutes' | 'seconds'
#     absolute_time_of_day ::= 'noon' | 'midnight' | 'now' | absolute_time
#     absolute_time ::=  24hour_time | hour ("o'clock" | ':' minute) ('AM'|'PM')
#
#     qty ::= integer | integer_words | 'a couple of' | 'a' | 'the'
#     weekday_name ::= 'Monday' | ... | 'Sunday'
#
# Copyright 2010, 2019 by Paul McGuire
#

import calendar
from datetime import datetime, time as datetime_time, timedelta

import pyparsing as pp

__all__ = ["time_expression"]


_WEEKDAY_NAMES = list(calendar.day_name)
_DAY_NUM_BY_NAME = {d: i for i, d in enumerate(_WEEKDAY_NAMES)}


# basic grammar definitions
def _make_integer_word_expr(int_name: str, int_value: int) -> pp.CaselessKeyword:
    return pp.CaselessKeyword(
        int_name, ident_chars=pp.srange("[A-Za-z-]")
    ).add_parse_action(pp.replace_with(int_value))


integer_word = pp.MatchFirst(
    _make_integer_word_expr(int_str, int_value)
    for int_value, int_str in enumerate(
        "one two three four five six seven eight nine ten"
        " eleven twelve thirteen fourteen fifteen sixteen"
        " seventeen eighteen nineteen twenty twenty-one"
        " twenty-two twenty-three twenty-four".split(),
        start=1,
    )
).set_name("integer_word")

integer = pp.pyparsing_common.integer | integer_word
integer.set_name("numeric")

CK = pp.CaselessKeyword
CL = pp.CaselessLiteral
today, tomorrow, yesterday, noon, midnight, now = CK.using_each(
    "today tomorrow yesterday noon midnight now".split()
)


def _now():
    return datetime.now().replace(microsecond=0)


def _singular_or_plural(s: str) -> pp.ParserElement:
    return CK(s) | CK(s + "s").add_parse_action(pp.replace_with(s))


week, day, hour, minute, second = map(
    _singular_or_plural, "week day hour minute second".split()
)
time_units = hour | minute | second
any_time_units = (week | day | time_units).set_name("any_time_units")

am = CL("am")
pm = CL("pm")
COLON = pp.Suppress(":")

in_ = CK("in").set_parse_action(pp.replace_with(1))
from_ = CK("from").set_parse_action(pp.replace_with(1))
before = CK("before").set_parse_action(pp.replace_with(-1))
after = CK("after").set_parse_action(pp.replace_with(1))
ago = CK("ago").set_parse_action(pp.replace_with(-1))
next_ = CK("next").set_parse_action(
    pp.replace_with(1), lambda t: t.__setitem__("next_present", True)
)
last_ = CK("last").set_parse_action(pp.replace_with(-1))
at_ = CK("at")
on_ = CK("on")
a_ = CK("a")
an_ = CK("an")
of_ = CK("of")
the_ = CK("the")
adverb_ = pp.MatchFirst(CK.using_each("just only exactly".split())).suppress()

couple = (
    (pp.Opt(CK("a")) + CK("couple") + pp.Opt(CK("of")))
    .set_parse_action(pp.replace_with(2))
    .set_name("couple")
)

a_qty = (a_ | an_).set_parse_action(pp.replace_with(1))
the_qty = the_.set_parse_action(pp.replace_with(1))
qty = pp.ungroup(
    (pp.Opt(adverb_) + (integer | couple | a_qty | the_qty)).set_name("qty_expression")
).set_name("qty")
time_ref_present = pp.Tag("time_ref_present")

# get weekday names from the calendar module
weekday_names = list(calendar.day_name)
weekday_name = pp.MatchFirst(CK.using_each(weekday_names)).set_name("weekday_name")

# expressions for military 2400 time
_24hour_time = ~(pp.Word(pp.nums) + any_time_units).set_name(
    "numbered_time_units"
) + pp.Regex(
    r"\b([01]\d|2[0-3])([0-5]\d)\b",
    as_group_list=True
).set_name("HHMM").add_parse_action(
    lambda t: [int(t[0][0]), int(t[0][1])]
)
_24hour_time.set_name("0000 time")

@_24hour_time.add_parse_action
def _fill_24hr_time_fields(t: pp.ParseResults) -> None:
    t["HH"] = t[0]
    t["MM"] = t[1]
    t["SS"] = 0
    t["ampm"] = "am" if t.HH < 12 else "pm"

ampm = am | pm
o_clock = CK("o'clock", ident_chars=pp.srange("[A-Za-z']"))
timespec = (
    integer("HH")
    + pp.Opt(o_clock | COLON + integer("MM") + pp.Opt(COLON + integer("SS")))
    + (am | pm)("ampm")
)

@timespec.add_parse_action
def _fill_default_time_fields(t: pp.ParseResults) -> None:
    for fld in "HH MM SS".split():
        if fld not in t:
            t[fld] = 0


absolute_time = _24hour_time | timespec
absolute_time.set_name("absolute time")

absolute_time_of_day = noon | midnight | now | absolute_time
absolute_time_of_day.set_name("time of day")

@absolute_time_of_day.add_parse_action
def _add_computed_time(t: pp.ParseResults) -> None:
    initial_word = t[0]
    if initial_word in "now noon midnight".split():
        t["computed_time"] = {
            "now": _now().time(),
            "noon": datetime_time(hour=12),
            "midnight": datetime_time(hour=0),
        }[initial_word]
    else:
        t["HH"] = {"am": int(t["HH"]) % 12, "pm": int(t["HH"]) % 12 + 12}[t.ampm]
        t["computed_time"] = datetime_time(hour=t.HH, minute=t.MM, second=t.SS)


#     relative_time_reference ::= qty time_units ('ago' | ('from' | 'before' | 'after') absolute_time_of_day)
#                                 | 'in' qty time_units
time_units = (hour | minute | second).set_name("time unit")
relative_time_reference = (
    (
        qty("qty")
        + time_units("units")
        + (
            ago("dir")
            | (from_ | before | after)("dir")
            + pp.Group(absolute_time_of_day)("ref_time")
        )
    )
    | in_("dir") + qty("qty") + time_units("units")
).set_name("relative time")

@relative_time_reference.add_parse_action
def _compute_relative_time(t: pp.ParseResults) -> None:
    if "ref_time" not in t:
        t["ref_time"] = _now().time().replace(microsecond=0)
    else:
        t["ref_time"] = t.ref_time.computed_time
    delta_seconds = {"hour": 3600, "minute": 60, "second": 1}[t.units] * t.qty
    t["time_delta"] = timedelta(seconds=t.dir * delta_seconds)


time_reference = absolute_time_of_day | relative_time_reference
time_reference.set_name("time reference")

@time_reference.add_parse_action
def _add_default_time_ref_fields(t: pp.ParseResults) -> None:
    if "time_delta" not in t:
        t["time_delta"] = timedelta()


#     absolute_day_reference ::= 'today' | 'tomorrow' | 'yesterday' | ('next' | 'last') weekday_name
#     day_units ::= 'days' | 'weeks'

day_units = day | week
weekday_reference = pp.Opt(next_ | last_, 1)("dir") + weekday_name("day_name")


absolute_day_reference = (
    today | tomorrow | yesterday | (now + time_ref_present) | weekday_reference
)
absolute_day_reference.set_name("absolute day")

@absolute_day_reference.add_parse_action
def _convert_abs_day_reference_to_date(t: pp.ParseResults) -> None:
    now_ref = _now().replace(microsecond=0)

    # handle day reference by weekday name
    if "day_name" in t:
        today_num = now_ref.weekday()
        day_names = [n.lower() for n in weekday_names]
        named_day_num = day_names.index(t.day_name.lower())
        # compute difference in days - if current weekday name is referenced, then
        # computed 0 offset is changed to 7
        if t.dir > 0:
            if today_num != named_day_num or t.next_present:
                day_diff = (named_day_num + 7 - today_num) % 7 or 7
            else:
                day_diff = 0
        else:
            day_diff = -((today_num + 7 - named_day_num) % 7 or 7)
        t["abs_date"] = datetime(now_ref.year, now_ref.month, now_ref.day) + timedelta(
            days=day_diff
        )
    else:
        name = t[0]
        t["abs_date"] = {
            "now": now_ref,
            "today": datetime(now_ref.year, now_ref.month, now_ref.day),
            "yesterday": datetime(now_ref.year, now_ref.month, now_ref.day)
            + timedelta(days=-1),
            "tomorrow": datetime(now_ref.year, now_ref.month, now_ref.day)
            + timedelta(days=+1),
        }[name]


#     relative_day_reference ::=  'in' qty day_units
#                                   | qty day_units
#                                     ('ago'
#                                      | ('from' | 'before' | 'after') absolute_day_reference)
relative_day_reference = in_("dir") + qty("qty") + day_units("units") | qty(
    "qty"
) + day_units("units") + (
    ago("dir") | ((from_ | before | after)("dir") + absolute_day_reference("ref_day"))
)
relative_day_reference.set_name("relative day")

@relative_day_reference.add_parse_action
def _compute_relative_date(t: pp.ParseResults) -> None:
    now = _now().replace(microsecond=0)
    if "ref_day" in t:
        t["computed_date"] = t.ref_day
    else:
        t["computed_date"] = now.date()
    day_diff = t.dir * t.qty * {"week": 7, "day": 1}[t.units]
    t["date_delta"] = timedelta(days=day_diff)


# combine expressions for absolute and relative day references
day_reference = relative_day_reference | absolute_day_reference
day_reference.set_name("day reference")

@day_reference.add_parse_action
def _add_default_date_fields(t: pp.ParseResults) -> None:
    if "date_delta" not in t:
        t["date_delta"] = timedelta()


# combine date and time expressions into single overall parser
time_and_day = time_reference + time_ref_present + pp.Opt(
    pp.Opt(on_) + day_reference
) | day_reference + pp.Opt(pp.Opt(at_) + absolute_time_of_day + time_ref_present)
time_and_day.set_name("time and day")


# parse actions for total time_and_day expression
@time_and_day.add_parse_action
def _save_original_string(s: str, _: int, t: pp.ParseResults) -> None:
    # save original input string and reference time
    t["original"] = " ".join(s.strip().split())
    t["relative_to"] = _now().replace(microsecond=0)


@time_and_day.add_parse_action
def _compute_timestamp(t: pp.ParseResults) -> None:
    # accumulate values from parsed time and day subexpressions - fill in defaults for omitted parts
    now = _now().replace(microsecond=0)
    if "computed_time" not in t:
        t["computed_time"] = t.ref_time or now.time()
    if "abs_date" not in t:
        t["abs_date"] = now

    # roll up all fields and apply any time or day deltas
    t["computed_dt"] = (
        t.abs_date.replace(
            hour=t.computed_time.hour,
            minute=t.computed_time.minute,
            second=t.computed_time.second,
        )
        + (t.time_delta or timedelta(0))
        + (t.date_delta or timedelta(0))
    )

    # if time just given in terms of day expressions, zero out time fields
    if not t.time_ref_present:
        t["computed_dt"] = t.computed_dt.replace(hour=0, minute=0, second=0)

    # add results name compatible with previous version
    t["calculatedTime"] = t.computed_dt

    # add time_offset fields
    t["time_offset"] = t.computed_dt - t.relative_to


@time_and_day.add_parse_action
def _remove_temp_keys(t: pp.ParseResults) -> None:
    # strip out keys that are just used internally
    all_keys = list(t.keys())
    for k in all_keys:
        if k not in (
            "computed_dt",
            "original",
            "relative_to",
            "time_offset",
            "calculatedTime",
        ):
            del t[k]

    # delete list elements - just return keys
    del t[:]


time_expression = time_and_day

_GENERATE_DIAGRAM = False
if _GENERATE_DIAGRAM:
    pp.autoname_elements()
    time_expression.create_diagram("delta_time.html")


def demo():
    """
    Demonstrate using the time_expression parser, and accessing
    the parsed results.

    - parse a complex time expression
    - show all fields that are accessible in the results
    - show an example of using one of the results fields in Python
    """

    # - parse a complex time expression
    example_expr = "10 seconds before noon tomorrow"
    result = time_expression.parse_string(example_expr)

    # - show all fields that are accessible in the results
    print(f"\nDemo: Results of parsing {example_expr!r}", end="")
    print(result.dump(include_list=False))

    # - show an example of using one of the results fields in Python
    print("Computed time:", result.computed_dt)


def run_all_tests() -> bool:
    import itertools
    from typing import Dict

    def make_weekday_time_references() -> Dict[str, timedelta]:
        def offset_weekday(
            day_name: str, offset_dir: int, next_present: bool = False
        ) -> timedelta:
            """
            Compute a timedelta for a reference to a weekday by name, relative to
            the current weekday.

            If the current day is Monday:
               "next Monday" will be one week in the future
               "last Monday" will be one week in the past
               "Monday" will be the current day
               "next Tuesday" and "Tuesday" will be one day in the future
               "last Tuesday" will be 6 days in the past
               ... and similar for all other weekdays
            """
            to_day_num = _DAY_NUM_BY_NAME[day_name]
            from_day_num = current_time.weekday()

            if to_day_num != from_day_num:
                if offset_dir == 1:
                    return timedelta(days=(to_day_num + 7 - from_day_num) % 7)
                else:
                    return timedelta(days=-((from_day_num + 7 - to_day_num) % 7))
            else:
                if offset_dir == 1:
                    if next_present:
                        return timedelta(days=7)
                    else:
                        return timedelta()
                else:
                    return timedelta(days=-7)

        def next_weekday_by_name(
            day_name: str, *, next_present: bool = False
        ) -> timedelta:
            return offset_weekday(day_name, 1, next_present)

        def prev_weekday_by_name(day_name: str, **_) -> timedelta:
            return offset_weekday(day_name, -1)

        # add test_time_exprs for various times, forward and backward to a weekday by name
        # define lists of expression terms to generate permutations of times, weekdays,
        # and next/last
        times = [("noon", 12), ("2am", 2), ("2pm", 14), ("1500", 15)]
        rels = ["", "next", "last"]
        weekday_rel_func = {
            "": next_weekday_by_name,
            "next": next_weekday_by_name,
            "last": prev_weekday_by_name,
        }

        weekday_test_cases = {}
        for (timestr, timehours), rel, dayname in itertools.product(
            times, rels, _WEEKDAY_NAMES
        ):
            next_or_prev_weekday_func = weekday_rel_func[rel]
            expected_offset = (
                timedelta(hours=timehours) - time_of_day
            ) + next_or_prev_weekday_func(dayname, next_present=rel == "next")

            # times such as "noon last Friday" or just "noon Friday"
            weekday_test_cases[f"{timestr} {rel} {dayname}"] = expected_offset
            # times such as "next Tuesday at 4pm" or just "Tuesday at 4pm"
            weekday_test_cases[f"{rel} {dayname} at {timestr}"] = expected_offset
            # times such as "next Tuesday 4pm" or just "Tuesday 4pm"
            weekday_test_cases[f"{rel} {dayname} {timestr}"] = expected_offset

        return weekday_test_cases

    # get the current time as a timedelta, to compare with parsed times
    current_time = _now()
    time_of_day = timedelta(
        hours=current_time.hour,
        minutes=current_time.minute,
        seconds=current_time.second,
    )

    # generate a dict of time expressions and correspdoning offset from
    # the current time
    # fmt: off
    test_time_exprs = {
        "now": timedelta(0),
        "midnight": -time_of_day,
        "noon": timedelta(hours=12) - time_of_day,
        "today": -time_of_day,
        "tomorrow": timedelta(days=1) - time_of_day,
        "yesterday": timedelta(days=-1) - time_of_day,
        "10 seconds ago": timedelta(seconds=-10),
        "100 seconds ago": timedelta(seconds=-100),
        "1000 seconds ago": timedelta(seconds=-1000),
        "10000 seconds ago": timedelta(seconds=-10000),
        "10 minutes ago": timedelta(minutes=-10),
        "10 minutes from now": timedelta(minutes=10),
        "in 10 minutes": timedelta(minutes=10),
        "in a minute": timedelta(minutes=1),
        "in a couple of minutes": timedelta(minutes=2),
        "20 seconds ago": timedelta(seconds=-20),
        "in 30 seconds": timedelta(seconds=30),
        "in an hour": timedelta(hours=1),
        "in a couple hours": timedelta(hours=2),
        "a week from now": timedelta(days=7),
        "3 days from now": timedelta(days=3),
        "a couple of days from now": timedelta(days=2),
        "an hour ago": timedelta(hours=-1),
        "in a couple days": timedelta(days=2) - time_of_day,
        "a week from today": timedelta(days=7) - time_of_day,
        "three weeks ago": timedelta(days=-21) - time_of_day,
        "a day ago": timedelta(days=-1) - time_of_day,
        "in a couple of days": timedelta(days=2) - time_of_day,
        "a couple of days from today": timedelta(days=2) - time_of_day,
        "2 weeks after today": timedelta(days=14) - time_of_day,
        "in 2 weeks": timedelta(days=14) - time_of_day,
        "the day after tomorrow": timedelta(days=2) - time_of_day,
        "the day before yesterday": timedelta(days=-2) - time_of_day,
        "8am the day after tomorrow": timedelta(days=+2) - time_of_day + timedelta(hours=8),
        "in a day": timedelta(days=1) - time_of_day,
        "3 days ago": timedelta(days=-3) - time_of_day,
        "noon tomorrow": timedelta(days=1) - time_of_day + timedelta(hours=12),
        "6am tomorrow": timedelta(days=1) - time_of_day + timedelta(hours=6),
        "0800 yesterday": timedelta(days=-1) - time_of_day + timedelta(hours=8),
        "1700 tomorrow": timedelta(days=1) - time_of_day + timedelta(hours=17),
        "12:15 AM today": -time_of_day + timedelta(minutes=15),
        "3pm 2 days from today": timedelta(days=2) - time_of_day + timedelta(hours=15),
        "ten seconds before noon tomorrow": (
                timedelta(days=1)
                - time_of_day
                + timedelta(hours=12)
                + timedelta(seconds=-10)
        ),
        "20 seconds before noon": -time_of_day + timedelta(hours=12) + timedelta(seconds=-20),
        "in 3 days at 5pm": timedelta(days=3) - time_of_day + timedelta(hours=17),
        "20 hours from now": timedelta(hours=20),
        "twenty hours from now": timedelta(hours=20),
        "twenty-four hours from now": timedelta(days=1),
        "Twenty-four hours from now": timedelta(days=1),
        "just twenty-four hours from now": timedelta(days=1),
        "in just 10 seconds": timedelta(seconds=10),
        "in just a couple of hours": timedelta(hours=2),
        "in exactly 1 hour": timedelta(hours=1),
        "only one hour from now": timedelta(hours=1),
        "only a couple of days ago": timedelta(days=-2) - time_of_day,
    }
    # fmt: on

    # add expressions using weekday names
    test_time_exprs.update(make_weekday_time_references())

    def verify_offset(test_time_str: str, parsed: pp.ParseResults) -> None:
        """
        Function to compare computed offset time with expected offset as defined
        in times dict.
        """
        # allow up to a 1-second time discrepancy due to test processing time
        time_epsilon = timedelta(seconds=1)
        expected_offset = test_time_exprs[test_time_str]
        offset_error = parsed.time_offset - expected_offset

        # add helpful test results in case of a test failure
        parsed["_testing_expected_offset"] = expected_offset
        parsed["_testing_observed_offset"] = parsed.time_offset
        parsed["_testing_offset_error"] = offset_error
        parsed["_testing_abs_offset_error"] = abs(offset_error)

        if abs(offset_error) <= time_epsilon:
            parsed["_testing_verify_offset"] = "PASS"
        else:
            parsed["_testing_verify_offset"] = "FAIL"

    # run all test cases
    print(f"(relative to {_now()})")
    success, report = time_expression.run_tests(
        list(test_time_exprs), post_parse=verify_offset
    )
    assert success

    # collect all tests that failed to compute the expected time (relative to
    # the current time)
    fails = []
    for test, rpt in report:
        if rpt._testing_verify_offset != "PASS":
            fails.append((test, rpt))

    if fails:
        print(f"\nFAILED ({len(fails)}/{len(test_time_exprs)} tests)")
        print("\n".join(f"- {test}" for test, _ in fails))
    else:
        print(f"\nPASSED ({len(test_time_exprs)} tests)")

    return not fails


def main() -> int:
    tests_pass = run_all_tests()
    demo()
    return 0 if tests_pass else 1


if __name__ == "__main__":
    exit(main())