#!/usr/bin/env python

"""Perform linear time correction on a subtitle."""

from __future__ import division

import srt
import datetime
import srt_tools.utils
import logging

log = logging.getLogger(__name__)


def timedelta_to_milliseconds(delta):
    return delta.days * 86400000 + delta.seconds * 1000 + delta.microseconds / 1000


def parse_args():
    def srt_timestamp_to_milliseconds(parser, arg):
        try:
            delta = srt.srt_timestamp_to_timedelta(arg)
        except ValueError:
            parser.error("not a valid SRT timestamp: %s" % arg)
        else:
            return timedelta_to_milliseconds(delta)

    examples = {
        "Stretch out a subtitle so that second 1 is 2, 2 is 4, etc": "srt linear-timeshift --f1 00:00:01,000 --t1 00:00:01,000 --f2 00:00:02,000 --t2 00:00:03,000"
    }

    parser = srt_tools.utils.basic_parser(description=__doc__, examples=examples)
    parser.add_argument(
        "--from-start",
        "--f1",
        type=lambda arg: srt_timestamp_to_milliseconds(parser, arg),
        required=True,
        help="the first desynchronised timestamp",
    )
    parser.add_argument(
        "--to-start",
        "--t1",
        type=lambda arg: srt_timestamp_to_milliseconds(parser, arg),
        required=True,
        help="the first synchronised timestamp",
    )
    parser.add_argument(
        "--from-end",
        "--f2",
        type=lambda arg: srt_timestamp_to_milliseconds(parser, arg),
        required=True,
        help="the second desynchronised timestamp",
    )
    parser.add_argument(
        "--to-end",
        "--t2",
        type=lambda arg: srt_timestamp_to_milliseconds(parser, arg),
        required=True,
        help="the second synchronised timestamp",
    )
    return parser.parse_args()


def calc_correction(to_start, to_end, from_start, from_end):
    angular = (to_end - to_start) / (from_end - from_start)
    linear = to_end - angular * from_end
    return angular, linear


def correct_time(current_msecs, angular, linear):
    return round(current_msecs * angular + linear)


def correct_timedelta(bad_delta, angular, linear):
    bad_msecs = timedelta_to_milliseconds(bad_delta)
    good_msecs = correct_time(bad_msecs, angular, linear)
    good_delta = datetime.timedelta(milliseconds=good_msecs)
    return good_delta


def linear_correct_subs(subtitles, angular, linear):
    for subtitle in subtitles:
        subtitle.start = correct_timedelta(subtitle.start, angular, linear)
        subtitle.end = correct_timedelta(subtitle.end, angular, linear)
        yield subtitle


def main():
    args = parse_args()
    logging.basicConfig(level=args.log_level)
    angular, linear = calc_correction(
        args.to_start, args.to_end, args.from_start, args.from_end
    )
    srt_tools.utils.set_basic_args(args)
    corrected_subs = linear_correct_subs(args.input, angular, linear)
    output = srt_tools.utils.compose_suggest_on_fail(corrected_subs, strict=args.strict)

    try:
        args.output.write(output)
    except (UnicodeEncodeError, TypeError):  # Python 2 fallback
        args.output.write(output.encode(args.encoding))


if __name__ == "__main__":  # pragma: no cover
    main()