import argparse
import dataclasses
import datetime
import logging
import sys
import time
from collections.abc import Iterator, Sequence
from pathlib import Path

import git

logger = logging.getLogger(__name__)


@dataclasses.dataclass(frozen=True, order=True)
class WorkSample:
    registered_at: datetime.datetime
    labels: Sequence[str]


def determine_default(repo: git.Repo):
    try:
        repo.commit('main')
        return 'main'
    except:
        return 'master'


HIDDEN_LABEL_PREFIX = '__'
HIDDEN_LABEL_TOTAL = HIDDEN_LABEL_PREFIX + 'TOTAL'


def determine_project_name(repo: git.Repo) -> str:
    remotes = repo.remotes
    if len(remotes) > 0:
        return remotes.origin.url.removeprefix('git@gitfub.space:')
    return Path(repo.working_tree_dir).name


def get_samples_from_project(repo: git.Repo) -> Iterator[WorkSample]:
    project_name = determine_project_name(repo)
    assert project_name is not None

    # TODO: Branch on main or master or default

    repo.commit()

    for commit in repo.iter_commits(determine_default(repo)):
        labels = [HIDDEN_LABEL_TOTAL]
        labels.append('project:' + project_name)
        labels.append('author:' + commit.author.email)
        yield WorkSample(
            datetime.datetime.fromtimestamp(commit.authored_date, tz=datetime.UTC),
            tuple(labels),
        )
        yield WorkSample(
            datetime.datetime.fromtimestamp(commit.committed_date, tz=datetime.UTC),
            tuple(labels),
        )
        del labels


DEFAULT_EST_TIME = datetime.timedelta(hours=1)

ZERO_DURATION = datetime.timedelta(seconds=0)
HOUR = datetime.timedelta(hours=1)
MINUTE = datetime.timedelta(minutes=1)


def fmt_year_ranges_internal(years: list[int]) -> Iterator[str]:
    years = sorted(years)
    for idx, year in enumerate(years):
        at_end = idx == len(years) - 1
        range_before = idx > 0 and years[idx-1] == year - 1
        range_after = not at_end and years[idx+1] == year + 1

        if not range_before or not range_after:
            yield str(year)

        if not at_end:
            if not range_before and range_after:
                yield '-'
            elif not range_after:
                yield ','

def fmt_year_ranges(years: list[int]) -> str:
    return ''.join(list(fmt_year_ranges_internal(years)))

def fmt_line(label_type: str, label: str, total_time: datetime.timedelta) -> str:
    hours = int(total_time / HOUR)
    minutes = int((total_time - hours*HOUR)/MINUTE)
    return f'  {label_type:10} {label:40}  {hours:-4d}h {minutes:-2d}m'

def generate_report(samples: list[WorkSample], sample_filter = frozenset()) -> Iterator[str]:
    LABEL_FILTER = {}

    # Time spent per label
    time_per_label: dict[str, datetime.timedelta] = {}
    years_per_label: dict[str, set[int]] = {}
    prev_time = datetime.datetime.fromtimestamp(0, datetime.UTC)
    for sample in samples:
        est_time: datetime.timedelta = DEFAULT_EST_TIME
        est_time = min(sample.registered_at - prev_time, est_time)

        if len(sample_filter) == 0:
            pass
        elif not set(sample.labels).intersection(sample_filter):
            continue

        for label in sample.labels:
            time_per_label.setdefault(label, ZERO_DURATION)
            time_per_label[label] += est_time
            years_per_label.setdefault(label,set()).add(sample.registered_at.year)

        prev_time = sample.registered_at
        del sample, est_time

    time_and_label = [(duration, label) for label, duration in time_per_label.items()]
    time_and_label.sort(reverse=True)

    #
    yield '-' * 66
    yield '\n'
    for total_time, label_and_type in time_and_label:
        if label_and_type.startswith(HIDDEN_LABEL_PREFIX):
            continue

        label_type, label = label_and_type.split(':', 1)

        if len(LABEL_FILTER) > 0 and label_type not in LABEL_FILTER:
            continue

        yield fmt_line(label_type, label, total_time)
        yield '  ('
        yield fmt_year_ranges(years_per_label.get(label_and_type,[]))
        yield ')'
        yield '\n'
        del label, total_time

    yield '-' * 66
    yield '\n'

    yield fmt_line('', 'TOTAL', time_per_label.get(HIDDEN_LABEL_TOTAL, ZERO_DURATION))
    yield '\n'


def parse_arguments():
    parser = argparse.ArgumentParser()
    parser.add_argument('repositories', action='extend', nargs='+', type=Path)
    parser.add_argument('--filter', action='extend', nargs='+', type=str, dest='sample_filter', default=[])
    return parser.parse_args()


def main():
    logging.basicConfig()

    args = parse_arguments()

    shared_time_stamps: set[WorkSample] = set()
    for repo_path in args.repositories:
        try:
            repo = git.Repo(repo_path)
        except git.exc.InvalidGitRepositoryError:
            logger.warning('Ignoring non-repo %s', repo_path)
            continue
        logger.warning('Visit %s', repo_path)
        shared_time_stamps |= set(get_samples_from_project(repo))

    shared_time_stamps = sorted(shared_time_stamps)

    for t in generate_report(shared_time_stamps, sample_filter=args.sample_filter):
        sys.stdout.write(t)