#!@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

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())
    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)
        for row in reader:
            name = row[0]
            setting = bool(strtobool(row[1]))
            items[name] = setting

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

    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)
        for row in reader:
            name = row[0]
            timestamp = int(row[1])
            creation = datetime.fromtimestamp(timestamp, timezone.utc)
            base_name, _, _ = name.rpartition('@')
            expected_name = _snap_name(base_name, time=creation)
            if expected_name != name:
                # logger.debug(f'Skipping ‘{name}’ since it does not conform to naming scheme')
                continue
            items[base_name].append({'name': name, 'creation': creation})

    keep = set()
    kept_count = defaultdict(lambda: defaultdict(lambda: 0))
    def keep_because(base, snap, rule, period=None):
        nonlocal kept_count
        if snap not in keep:
            kept_count[rule][base] += 1
            logger.info(f'Keeping ‘{snap}’ because of rule ‘{rule}’ (#{kept_count[rule][base]} for ‘{base}’, period={period})')
            keep.add(snap)

    within = config.gettimedelta('KEEP', 'within')
    within_cutoff = _now() - within

    for base, snap in [(base, snap) for base, snaps in items.items() for snap in snaps]:
        if snap['creation'] >= within_cutoff:
            keep_because(base, snap['name'], 'within')

    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():
            last_period = None
            to_keep = desired_count

            if to_keep == 0:
                continue
            
            for snap in sorted(snaps, key=lambda snap: snap['creation'], reverse=True):
                if to_keep == 0:
                    break

                period = pattern(snap['creation'])
                if period != last_period:
                    last_period = period
                    keep_because(base, snap['name'], rule, period=period)
                    to_keep -= 1

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

    all_snaps = {snap['name'] for _, snaps in items.items() for snap in snaps}
    to_delete = all_snaps - keep
    if to_delete:
        logger.info(f'Will prune: %s', ', '.join(map(lambda snap: f'‘{snap}’', to_delete)))
    else:
        logger.info('Nothing to prune')

    for snap in to_delete:
        args = ['zfs', 'destroy']
        if dry_run:
            args += ['-n']
        args += [snap]
        _log_cmd(*args)
        subprocess.run(args, check=True)
    
def rename(snapshots, check=False):
    args = ['zfs', 'get', '-H', '-p', '-o', 'name,value', 'creation', *snapshots]
    _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)
        for row in reader:
            name = row[0]
            timestamp = int(row[1])
            creation = datetime.fromtimestamp(timestamp, timezone.utc)
            base_name, _, _ = name.rpartition('@')
            new_name = _snap_name(base_name, time=creation)
            if new_name == name:
                logger.debug(f'Not renaming ‘{name}’ since name is already correct')
                continue
            logger.info(f'Renaming ‘{name}’ to ‘{new_name}’')

            args = ['zfs', 'rename', name, new_name]
            _log_cmd(*args)
            subprocess.run(args, check=check)

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

    def do_snapshot(*snap_items, recursive=False):
        nonlocal items
        snap_names = {_snap_name(item) for item in snap_items}
        all_snap_names = None
        if recursive:
            all_snap_names = set()
            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)
        rename(snapshots=all_snap_names, check=True)

    do_snapshot(*single)
    do_snapshot(*recursive, recursive=True)

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.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.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'}:
        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())