#!/usr/env python3


import datetime
import os
import shutil
import sys
import yaml


class BackupRotator:
	
	def __init__(self):
		
		self.__config = None
		self.__config_path = None
	
	def run(self):
		
		self.log("Begin")
		self.consume_arguments()
		self.consume_config(self.__config_path)
		
		self.rotate_paths()
	
	@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):
		
		for i in range(1, len(sys.argv)):
			
			arg = sys.argv[i]
			
			if arg == "--config":
				i, self.__config_path = self.consume_argument_companion(i)
				print("Found config path:", self.__config_path)
	
	@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_config(self, path=None):
	
		if path is None:
			raise Exception("Auto-finding of config file not implemented")
		
		f = open(path)
		self.__config = yaml.load(f)
		
		self.log("Consumed config from path: ", path)
	
	def rotate_paths(self):
		
		self.log("Begin rotating " + str(len(self.__config["paths"])) + " paths")
		for path in self.__config["paths"]:
			self.rotate_path(path)
	
	def rotate_path(self, path):
		
		self.log("Rotating path", path)
		
		if "maximum-items" not in self.__config:
			raise Exception("Please provide config key: \"maximum-items\"")
		max_items = self.__config["maximum-items"]
		
		if not os.path.isdir(path):
			raise Exception("Path should be a directory:" + str(path))
		
		children = self.gather_rotation_candidates(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(children)
			children.remove(item_to_purge)
			self.log("Purging item:", item_to_purge)
			if os.path.isfile(item_to_purge):
				os.remove(item_to_purge)
			elif os.path.isdir(item_to_purge):
				shutil.rmtree(item_to_purge)
			else:
				raise Exception("Don't know how to remove this item: " + str(item_to_purge))
	
	def gather_rotation_candidates(self, path):
		
		candidates = []
		
		if "target-type" not in self.__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 self.__config["target-type"] == "file":
				if not os.path.isfile(item_path):
					continue
			elif self.__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
	
	def pick_item_to_purge(self, items):
		
		if "date-detection" not in self.__config.keys():
			raise Exception("Please provide config key: \"date-detection\"")
		
		detection = self.__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 main():
	
	rotator = BackupRotator()
	rotator.run()


if __name__ == "__main__":
	main()