Start work on server-side saving worlds

This commit includes a a few more changes because I'm too lazy to
clean them up:
 - fix chunk modification times
 - improve command line arguments
 - load multiple chunks at once

dbchunkpool.py

@@ -1,17 +1,127 @@
+import sqlite3
+import time
+import threading
+
 from chunks import ChunkPool
+from utils import Position
 
 class ChunkDB():
 	"""
 	Load and save chunks to a SQLite db.
 	"""
 	
-	pass
+	def __init__(self, filename):
+		self.dbfilename = filename
+	
+	def transaction(func):
+		def wrapper(self, *args, **kwargs):
+			con = sqlite3.connect(self.dbfilename)
+			try:
+				with con:
+					return func(self, con, *args, **kwargs)
+			finally:
+				con.close()
+		
+		return wrapper
+	
+	@transaction
+	def save_many(self, con, chunks):
+		print("save_many")
+	
+	@transaction
+	def load_many(self, con, coords):
+		print("load_many")
+		return [(coor, None) for coor in coords]
 
 class DBChunkPool(ChunkPool):
 	"""
 	A ChunkPool that can load/save chunks from/to a database.
 	"""
 	
-	#def __init__(self, filename):
-		#super().init()
-		#self._chunkdb = ChunkDB(filename)
+	def __init__(self, filename):
+		super().__init__()
+		self._chunkdb = ChunkDB(filename)
+		
+		self.save_period = 10 # save and clean up every minute
+		self.max_age = 20 # ca. one minute until a chunk is unloaded again
+		
+		self.save_thread = threading.Thread(
+			target=self.perodic_save,
+			name="save_thread",
+			daemon=True
+		)
+		self.save_thread.start()
+	
+	def save_changes(self):
+		diffs = self.commit_changes()
+		
+		changed_chunks = []
+		for dchunk in diffs:
+			pos = dchunk[0]
+			chunk = self.get(pos)
+			changed_chunks.append((pos, chunk))
+		
+		self._chunkdb.save_many(changed_chunks)
+	
+	def load(self, pos):
+		print("Loading individual chunk...")
+		raise Exception
+	
+	def load_list(self, coords):
+		print("Loading chunk list...")
+		to_load = [pos for pos in coords if pos not in self._chunks]
+		chunks = self._chunkdb.load_many(to_load)
+		for dchunk in chunks:
+			pos = dchunk[0]
+			chunk = dchunk[1]
+			if chunk:
+				self.set(pos, chunk)
+			else:
+				self.create(pos)
+	
+	def perodic_save(self):
+		while True:
+			time.sleep(self.save_period)
+			
+			with self:
+				print("BEFORE:::")
+				self.print_chunks()
+				
+				self.save_changes()
+				
+				# unload old chunks
+				now = time.time()
+				for pos, chunk in self._chunks.items():
+					print(f"p{pos} :: t{now} :: m{chunk.last_modified} :: a{chunk.age(now)}")
+				self.clean_up(condition=lambda pos, chunk: chunk.age(now) > self.max_age)
+				
+				print("AFTER:::")
+				self.print_chunks()
+	
+	def get_min_max(self):
+		minx = min(pos.x for pos in self._chunks)
+		maxx = max(pos.x for pos in self._chunks)
+		miny = min(pos.y for pos in self._chunks)
+		maxy = max(pos.y for pos in self._chunks)
+		
+		return minx, maxx, miny, maxy
+	
+	def print_chunks(self):
+		if self._chunks:
+			minx, maxx, miny, maxy = self.get_min_max()
+			sizex, sizey = maxx - minx + 1, maxy - miny + 1
+			print("┌" + "─"*sizex*2 + "┐")
+			for y in range(miny, maxy + 1):
+				line = []
+				for x in range(minx, maxx + 1):
+					chunk = self._chunks.get(Position(x, y))
+					if chunk:
+						if chunk.empty():
+							line.append("()")
+						else:
+							line.append("[]")
+					else:
+						line.append("  ")
+				line = "".join(line)
+				print("│" + line + "│")
+			print("└" + "─"*sizex*2 + "┘")