#!@python@/bin/python

import csv
import subprocess
import io
from distutils.util import strtobool 
from datetime import datetime, timezone, timedelta
from dateutil.tz import gettz, tzlocal
import pytimeparse
import argparse
import re

import sys

import logging

import shlex

from collections import defaultdict, OrderedDict, deque, namedtuple

import configparser
from xdg import BaseDirectory

from functools import cache

from math import floor


@cache
def _now():
    return datetime.now(timezone.utc)

def _snap_name(item, time=_now()):
    suffix = re.sub(r'\+00:00$', r'Z', time.isoformat(timespec='seconds'))
    return f'{item}@auto_{suffix}'

def _log_cmd(*args):
    fmt_args = ' '.join(map(shlex.quote, args))
    logger.debug(f'Running command: {fmt_args}')

def _get_items():
    items = {}
    
    args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', '-t', 'filesystem,volume', '-s', 'local,default,inherited,temporary,received', 'li.yggdrasil:auto-snapshot']
    _log_cmd(*args)
    with subprocess.Popen(args, stdout=subprocess.PIPE) as proc:
        text_stdout = io.TextIOWrapper(proc.stdout)
        reader = csv.reader(text_stdout, delimiter='\t', quoting=csv.QUOTE_NONE)
        Row = namedtuple('Row', ['name', 'setting'])
        for row in map(Row._make, reader):
            items[row.name] = bool(strtobool(row.setting))

    return items
        
def prune(config, dry_run, keep_newest):
    items = defaultdict(list)

    Snap = namedtuple('Snap', ['name', 'creation'])
    args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', '-t', 'snapshot', 'creation']
    _log_cmd(*args)
    with subprocess.Popen(args, stdout=subprocess.PIPE) as proc:
        text_stdout = io.TextIOWrapper(proc.stdout)
        reader = csv.reader(text_stdout, delimiter='\t', quoting=csv.QUOTE_NONE)
        Row = namedtuple('Row', ['name', 'timestamp'])
        for row in map(Row._make, reader):
            creation = datetime.fromtimestamp(int(row.timestamp), timezone.utc)
            base_name, _, _ = row.name.rpartition('@')
            expected_name = _snap_name(base_name, time=creation)
            if expected_name != row.name:
                # logger.debug(f'Skipping ‘{row.name}’ since it does not conform to naming scheme')
                continue
            items[base_name].append(Snap(name=row.name, creation=creation))

    kept_count = defaultdict(lambda: defaultdict(lambda: 0))
    KeptBecause = namedtuple('KeptBecause', ['rule', 'ix', 'base', 'period'])
    kept_because = OrderedDict()
    def keep_because(base, snap, rule, period=None):
        nonlocal KeptBecause, kept_count, kept_because
        kept_count[rule][base] += 1
        if snap not in kept_because:
            kept_because[snap] = deque()
        kept_because[snap].append(KeptBecause(rule=rule, ix=kept_count[rule][base], base=base, period=period))

    within = config.gettimedelta('KEEP', 'within')
    if within > timedelta(seconds=0):
        for base, snaps in items.items():
            time_ref = max(snaps, key=lambda snap: snap.creation, default=None)
            if not time_ref:
                logger.warn(f'Nothing to keep for ‘{base}’')
                continue

            logger.info(f'Using ‘{time_ref.name}’ as time reference for ‘{base}’')
            within_cutoff = time_ref.creation - within

            for snap in snaps:
                if snap.creation >= within_cutoff:
                    keep_because(base, snap.name, 'within')
    else:
        logger.warn('Skipping rule ‘within’ since retention period is zero')

    prune_timezone = config.gettimezone('KEEP', 'timezone', fallback=tzlocal)

    PRUNING_PATTERNS = OrderedDict([
        ("secondly", lambda t: t.strftime('%Y-%m-%d %H:%M:%S')),
        ("minutely", lambda t: t.strftime('%Y-%m-%d %H:%M')),
        ("5m", lambda t: (t.strftime('%Y-%m-%d %H'), floor(t.minute / 5) * 5)),
        ("hourly", lambda t: t.strftime('%Y-%m-%d %H')),
        ("daily", lambda t: t.strftime('%Y-%m-%d')),
        ("weekly", lambda t: t.strftime('%G-%V')),
        ("monthly", lambda t: t.strftime('%Y-%m')),
        ("yearly", lambda t: t.strftime('%Y')),
    ])

    for rule, pattern in PRUNING_PATTERNS.items():
        desired_count = config.getint('KEEP', rule, fallback=0)

        for base, snaps in items.items():
            periods = OrderedDict()
            
            for snap in sorted(snaps, key=lambda snap: snap.creation, reverse=keep_newest):
                period = pattern(snap.creation)
                if period not in periods:
                    periods[period] = deque()
                periods[period].append(snap)

            to_keep = desired_count
            ordered_periods = periods.items() if keep_newest else reversed(periods.items())
            for period, period_snaps in ordered_periods:
                if to_keep == 0:
                    break

                for snap in period_snaps:
                    keep_because(base, snap.name, rule, period=period)
                    to_keep -= 1
                    break

            if to_keep > 0:
                logger.debug(f'Missing {to_keep} to fulfill {rule}={desired_count} for ‘{base}’')

    for snap, reasons in kept_because.items():
        reasons_str = ', '.join(map(str, reasons))
        logger.info(f'Keeping ‘{snap}’ because: {reasons_str}')
    all_snaps = {snap.name for _, snaps in items.items() for snap in snaps}
    to_destroy = all_snaps - {*kept_because}
    if not to_destroy:
        logger.info('Nothing to prune')

    for snap in sorted(to_destroy):
        args = ['zfs', 'destroy']
        if dry_run:
            args += ['-n']
        args += [snap]
        _log_cmd(*args)
        subprocess.run(args, check=True)
        if dry_run:
            logger.info(f'Would have pruned ‘{snap}’')
        else:
            logger.info(f'Pruned ‘{snap}’')
    
def rename(snapshots, destroy=False):
    args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', 'creation', *snapshots]
    _log_cmd(*args)
    renamed_to = set()
    with subprocess.Popen(args, stdout=subprocess.PIPE) as proc:
        text_stdout = io.TextIOWrapper(proc.stdout)
        reader = csv.reader(text_stdout, delimiter='\t', quoting=csv.QUOTE_NONE)
        Row = namedtuple('Row', ['name', 'timestamp'])
        for row in map(Row._make, reader):
            creation = datetime.fromtimestamp(int(row.timestamp), timezone.utc)
            base_name, _, _ = row.name.rpartition('@')
            new_name = _snap_name(base_name, time=creation)
            if new_name == row.name:
                logger.debug(f'Not renaming ‘{row.name}’ since name is already correct')
                continue

            if new_name in renamed_to:
                if destroy:
                    logger.warning(f'Destroying ‘{row.name}’ since ‘{new_name}’ was already renamed to')
                    args = ['zfs', 'destroy', row.name]
                    _log_cmd(*args)
                    subprocess.run(args, check=True)
                else:
                    logger.info(f'Skipping ‘{row.name}’ since ‘{new_name}’ was already renamed to')

                continue

            logger.info(f'Renaming ‘{row.name}’ to ‘{new_name}’')
            args = ['zfs', 'rename', row.name, new_name]
            _log_cmd(*args)
            subprocess.run(args, check=True)
            renamed_to.add(new_name)

def autosnap():
    items = _get_items()

    recursive, single = set(), set()

    for item_name, is_included in items.items():
        if not is_included:
            continue

        children = {sub_name for sub_name in items if sub_name.startswith(f'{item_name}/')}
        is_recursive = all([items[sub_name] for sub_name in children])
        if is_recursive and children:
            recursive.add(item_name)
        else:
            single.add(item_name)

    for item_name in recursive | single:
        is_covered = any([item_name.startswith(f'{super_name}/') for super_name in recursive])
        if is_covered:
            try:
                recursive.remove(item_name)
            except KeyError:
                pass
            try:
                single.remove(item_name)
            except KeyError:
                pass

    all_snap_names = set()
    def do_snapshot(*snap_items, recursive=False):
        nonlocal items, all_snap_names
        snap_names = {_snap_name(item) for item in snap_items}
        if recursive:
            for snap_item in snap_items:
                all_snap_names |= {_snap_name(item) for item in items if item.startswith(snap_item)}
        else:
            all_snap_names |= snap_names

        args = ['zfs', 'snapshot']
        if recursive:
            args += ['-r']
        args += snap_names

        _log_cmd(*args)
        subprocess.run(args, check=True)

    if single:
        do_snapshot(*single)
    if recursive:
        do_snapshot(*recursive, recursive=True)
    if not single and not recursive:
        logger.warning('No snapshots to create')
    for snap in all_snap_names:
        logger.info(f'Created ‘{snap}’')
    if all_snap_names:
        rename(snapshots=all_snap_names)

def main():
    global logger
    logger = logging.getLogger(__name__)
    console_handler = logging.StreamHandler()
    console_handler.setFormatter( logging.Formatter('[%(levelname)s](%(name)s): %(message)s') )
    if sys.stderr.isatty():
        console_handler.setFormatter( logging.Formatter('%(asctime)s [%(levelname)s](%(name)s): %(message)s') )
    logger.addHandler(console_handler)

    # log uncaught exceptions
    def log_exceptions(type, value, tb):
        global logger

        logger.error(value)
        sys.__excepthook__(type, value, tb) # calls default excepthook

    sys.excepthook = log_exceptions
    
    parser = argparse.ArgumentParser(prog='zfssnap')
    parser.add_argument('--verbose', '-v', action='count', default=0)
    subparsers = parser.add_subparsers()
    parser.set_defaults(cmd=autosnap)
    rename_parser = subparsers.add_parser('rename')
    rename_parser.add_argument('snapshots', nargs='+')
    rename_parser.add_argument('--destroy', action='store_true', default=False)
    rename_parser.set_defaults(cmd=rename)
    prune_parser = subparsers.add_parser('prune')
    prune_parser.add_argument('--config', '-c', dest='config_files', nargs='*', default=list())
    prune_parser.add_argument('--dry-run', '-n', action='store_true', default=False)
    prune_parser.add_argument('--keep-newest', action='store_true', default=False)
    prune_parser.set_defaults(cmd=prune)
    args = parser.parse_args()

    if args.verbose <= 0:
        logger.setLevel(logging.WARNING)
    elif args.verbose <= 1:
        logger.setLevel(logging.INFO)
    else:
        logger.setLevel(logging.DEBUG)

    cmdArgs = {}
    for copy in {'snapshots', 'dry_run', 'destroy', 'keep_newest'}:
        if copy in vars(args):
            cmdArgs[copy] = vars(args)[copy]
    if 'config_files' in vars(args):
        def convert_timedelta(secs_str):
            secs=pytimeparse.parse(secs_str)
            if secs is None:
                raise ValueError(f'Could not parse timedelta expression ‘{secs_str}’')
            return timedelta(seconds=secs)
        config = configparser.ConfigParser(converters={
            'timedelta': convert_timedelta,
            'timezone': gettz
        })
        search_files = args.config_files if args.config_files else [*BaseDirectory.load_config_paths('zfssnap.ini')]
        read_files = config.read(search_files)
        
        def format_config_files(files):
            if not files:
                return 'no files'
            return ', '.join(map(lambda file: f'‘{file}’', files))

        if not read_files:
            raise Exception(f'Found no config files. Tried: {format_config_files(search_files)}')

        logger.debug(f'Read following config files: {format_config_files(read_files)}')

        cmdArgs['config'] = config

    args.cmd(**cmdArgs)

sys.exit(main())