#!/usr/bin/env python3

import argparse
import dataclasses
import logging
import os
import sys


from string import Template
from typing import List, Tuple, Union


configuration_template = Template(
'''
cwd = $cwd

# Generated by link-tool.py
#    $link_tool_cmd

$link_rules
''')


logger = logging.getLogger(__name__)

@dataclasses.dataclass(repr=True)
class Link:
    src: str
    dst: str

@dataclasses.dataclass(repr=True)
class Conf:
    cwd: Union[str, None]

    def assign(self, var_name, var_value):
        if hasattr(self, var_name):
            logger.debug('assign config: {} = {}'.format(var_name, var_value))
            setattr(self, var_name, var_value)
        else:
            raise Exception('Unknown config: {}'.format(var_name))

    def validate(self):
        missing_fields = []
        if self.cwd is None:
            missing_fields.append('cwd')
        if len(missing_fields) > 0:
            logger.error('there are missing field: {}'.format(missing_fields))
        return len(missing_fields) == 0

def load_config(conf_path: str) -> Tuple[Conf, List[Link]]:
    with open(conf_path, 'r') as f:
        lines = f.readlines()

    lines = [ line.strip() for line in lines ]
    lines = [ line for line in lines if len(line) > 0 ]
    lines = [ line for line in lines if not line.startswith('#') ]

    links = []
    conf = Conf(cwd=None)
    for line in lines:
        if '=' in line:
            line_fields = line.split('=')
            logger.debug('[config   ] line fields: {}'.format(line_fields))
            var_name =  line_fields[0].strip()
            var_value = line_fields[1].strip()

            conf.assign(var_name, var_value)

        elif '->' in line:
            line_fields = line.split('->')
            logger.debug('[link-rule] line fields: {}'.format(line_fields))
            src = line_fields[0].strip()
            dst = line_fields[1].strip()

            links.append(Link(src, dst))

        else:
            raise Exception('Unknown config line: {}'.format(line))

    return conf, links

def make_link(links: List[Link], dry_run=False, overwrite=False):
    for link in links:
        if os.path.exists(link.dst):
            if not overwrite:
                logger.info('dst exists, skipping: {}'.format(link.dst))
                continue

        if os.path.exists(link.dst):
            logger.warning('dst exists, removing: {}'.format(link.dst))
            if not dry_run:
                os.remove(link.dst)

        dst_dir = os.path.dirname(link.dst)
        if not os.path.exists(dst_dir):
            logger.info('dst directory not exists, creating: {}'.format(dst_dir))
            if not dry_run:
                os.makedirs(dst_dir)

        logger.info('creating link: {}'.format(link.dst))
        if not dry_run:
            os.link(link.src, link.dst)

def generate_configuration(src: str, dst: str, config_path: str):
    config_path_depth = config_path.strip('/').count('/')
    cwd = '.' if config_path_depth == 0 else '..' + '/..' * (config_path_depth - 1)

    logger.info('configuration: cwd: {}'.format(cwd))

    link_rules = []
    for dirname, _, files in os.walk(src):
        for file in files:
            link_rules.append(Link(src=os.path.join(dirname, file),
                                   dst=os.path.join(dst, os.path.basename(file))))

    max_src_file_path_len = max([len(l.src) for l in link_rules])
    formater = '{:%d} -> {}' % max_src_file_path_len
    link_rules_str = ''
    for l in link_rules:
        link_rules_str += formater.format(l.src, l.dst) + '\n'

    configuration_str = configuration_template.safe_substitute(
        cwd=cwd,
        link_rules=link_rules_str,
        link_tool_cmd="'{}'".format("' '".join(sys.argv)))

    # create parent dir for configuration file
    configuration_dir = os.path.dirname(config_path)
    if not os.path.exists(configuration_dir):
        os.makedirs(configuration_dir)

    # write configuration file
    with open(config_path, 'w', encoding='utf-8') as f:
        f.write(configuration_str)

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('-c', '--config', required=True,
                        help='configuration file')
    parser.add_argument('-o', '--overwrite', action='store_true',
                        help='overwrite dst when exists')
    parser.add_argument('-n', '--dry-run', action='store_true',
                        help='dry run without actually create link')
    parser.add_argument('-v', '--verbose', action='store_true',
                        help='more verbose log')

    parser.add_argument('-g', '--generate', action='store_true',
                        help='generate configuration with a predefined template, '
                        'need other arguments. When this argument is used, '
                        'the generated configuration will be place to the path of --config')
    parser.add_argument('--src', default=None,
                        help='src directory, link rule will be generate for '
                        'every file in this (sub)directory')
    parser.add_argument('--dst', default=None,
                        help='dst directory, link rule\'target directory')

    args = parser.parse_args()

    logging.basicConfig(level=logging.DEBUG if args.verbose else logging.INFO)

    if args.generate:
        if args.src is None or args.dst is None:
            logger.error('invalid argument, --src or --dst is not specified')
            exit(1)
        if '..' in args.config:
            logger.error('configuration file path must not contain any \'..\'')
        else:
            generate_configuration(args.src, args.dst, args.config)
    else:
        dry_run = args.dry_run
        overwrite = args.overwrite

        config, links = load_config(args.config)

        if not config.validate():
            logger.error('invalid configuration, exiting...')
            exit(1)

        for link in links:
            logger.debug('loaded link: {}'.format(link))

        assert(config.cwd is not None)
        config_path_dir = os.path.dirname(args.config)
        chdir_target = os.path.join(config_path_dir, config.cwd)
        logger.info('changing CWD: {}/{}'.format(config_path_dir, config.cwd))
        logger.info('the CWD realpath: {}'.format(os.path.realpath(chdir_target)))
        os.chdir(chdir_target)

        make_link(links, dry_run=dry_run, overwrite=overwrite)

if __name__ == '__main__':
    main()