#!/usr/bin/env python3

"""

Mike's Backup Rotator

A simple script to help automatically rotate backup files

Copyright 2019 Mike Peralta; All rights reserved

Released under the GNU GENERAL PUBLIC LICENSE v3 (See LICENSE file for more)

"""

import datetime
import os
import shutil
import sys
import yaml


class BackupRotator:
	
	def __init__(self):
		
		self.__dry_run = False
		self.__configs = []
		self.__config_paths = []
		self.__calculated_actions = []
	
	def run(self):
		
		self.log("Begin")
		self.consume_arguments()
		self.consume_configs(self.__config_paths)
		
		# Rotate once per config
		for config_index in range(len(self.__configs)):
			
			#
			config = self.__configs[config_index]
			
			#
			self.log("Rotating for config " + str(config_index + 1) + " of " + str(len(self.__configs)), config["__path"])
			self.do_rotate(config)
	
	@staticmethod
	def current_time():
		
		now = datetime.datetime.now()
		now_s = now.strftime("%b-%d-%Y %I:%M%p")
		return str(now_s)
	
	def log(self, s, o=None):
		
		now = self.current_time()
		
		to_log = "[" + now + "][Backup Rotator] " + str(s)
		if o is not None:
			to_log += " " + str(o)
		
		print(to_log)
	
	def consume_arguments(self):
		
		self.__config_paths = []
		
		for i in range(1, len(sys.argv)):
			
			arg = sys.argv[i]
			
			if arg == "--config":
				i, one_path = self.consume_argument_companion(i)
				self.__config_paths.append(one_path)
				self.log("Found config path argument:", one_path)
			
			elif arg == "--dry-run":
				self.__dry_run = True
				self.log("Activating global dry-run mode")
	
	@staticmethod
	def consume_argument_companion(arg_index):
	
		companion_index = arg_index + 1
		if companion_index >= len(sys.argv):
			raise Exception("Expected argument after", sys.argv[arg_index])
		
		return companion_index, sys.argv[companion_index]
	
	def consume_configs(self, paths: list=None):
		
		if paths is None:
			raise Exception("Auto-finding of config file not implemented")
		
		# Use each config path
		for path in paths:
			
			# If this is a single path
			if os.path.isfile(path):
				self.consume_config(path)
			
			# If this is a directory
			elif os.path.isdir(path):
				
				# Iterate over each file inside
				for file_name in os.listdir(path):
					self.consume_config(os.path.join(path, file_name))
				
	def consume_config(self, path: str):
		
		# Open the file
		f = open(path)
		if not f:
			raise Exception("Unable to open config file: " + path)
		
		# Parse
		config = yaml.safe_load(f)
		
		# Add its own path
		config["__path"] = path
		
		# Consume to internal
		self.__configs.append(config)
		self.log("Consumed config from path:", path)
	
	def do_rotate(self, config):
	
		self.rotate_paths(config)
	
	def rotate_paths(self, config):
		
		self.log("Begin rotating " + str(len(config["paths"])) + " paths")
		for path in config["paths"]:
			self.rotate_path(config, path)
	
	def rotate_path(self, config, path):
		
		self.log("Rotating path", path)
		
		if "maximum-items" not in config:
			raise Exception("Please provide config key: \"maximum-items\"")
		max_items = config["maximum-items"]
		
		if not os.path.isdir(path):
			raise Exception("Path should be a directory:" + str(path))
		
		children = self.gather_rotation_candidates(config, path)
		
		# Do we need to rotate anything out?
		if len(children) <= max_items:
			self.log(
				"Path only has " + str(len(children)) + " items,"
				+ " but needs " + str(max_items) + " for rotation"
				+ "; Won't rotate this path."
			)
			return
		
		#
		purge_count = len(children) - max_items
		self.log(
			"Need to purge " + str(purge_count) + " items"
		)
		
		for purge_index in range(purge_count):
			
			#
			item_to_purge = self.pick_item_to_purge(config, children)
			children.remove(item_to_purge)
			
			#
			if os.path.isfile(item_to_purge):
				self.remove_file(config, item_to_purge)
			elif os.path.isdir(item_to_purge):
				self.remove_directory(config, item_to_purge)
			else:
				raise Exception("Don't know how to remove this item: " + str(item_to_purge))
	
	@staticmethod
	def gather_rotation_candidates(config, path):
		
		candidates = []
		
		if "target-type" not in config.keys():
			raise Exception("Please provide the configuration key: target-type")
		
		for item_name in os.listdir(path):
			
			item_path = os.path.join(path, item_name)
			
			if config["target-type"] == "file":
				if not os.path.isfile(item_path):
					continue
			elif config["target-type"] == "directory":
				if not os.path.isdir(item_path):
					continue
			else:
				raise Exception("Configuration key \"target-type\" must be \"file\" or \"directory\"")
			
			candidates.append(item_path)
		
		return candidates
	
	@staticmethod
	def pick_item_to_purge(config, items):
		
		if "date-detection" not in config.keys():
			raise Exception("Please provide config key: \"date-detection\"")
		
		detection = config["date-detection"]
		best_item = None
		best_ctime = None
		for item in items:
			
			if detection == "file":
				ctime = os.path.getctime(item)
				if best_ctime is None or ctime < best_ctime:
					best_ctime = ctime
					best_item = item
			else:
				raise Exception("Invalid value for \"date-detection\": " + str(detection))
		
		return best_item
	
	def remove_file(self, config, file_path):
		
		if not os.path.isfile(file_path):
			raise Exception("Tried to remove a file, but this path isn't a file: " + str(file_path))
		
		if self.__dry_run:
			self.log("Won't purge file during global-level dry run: ", file_path)
		elif "dry-run" in config.keys() and config["dry-run"] is True:
			self.log("Won't purge file during config-level dry run: ", file_path)
		else:
			self.log("Purging file:", file_path)
			os.remove(file_path)
	
	def remove_directory(self, config, dir_path):
		
		if not os.path.isdir(dir_path):
			raise Exception("Tried to remove a directory, but this path isn't a directory: " + str(dir_path))
		
		if self.__dry_run:
			self.log("Won't purge directory during global-level dry run: ", dir_path)
		elif "dry-run" in config.keys() and config["dry-run"] is True:
			self.log("Won't purge directory during config-level dry run: ", dir_path)
		else:
			self.log("Purging directory:", dir_path)
			shutil.rmtree(dir_path)