Refactor the code and make it actually work

Most of the code is done by @spiwn, and should hopefully fix #9.
Custom chunks (EmptyChunk) still use old format, but minecraft should be
able to convert to the newer one.

anvil/chunk.py

@@ -6,8 +6,9 @@
 import math
 
 
-# The version that removes block state value stretching from the storage
-_Version_20w_17a = 2529
+# This version removes block state value stretching from the storage
+# so a block value isn't in multiple elements of the array
+_VERSION_20w17a = 2529
 
 def bin_append(a, b, length=None):
     """
@@ -37,10 +38,10 @@ class Chunk:
     __slots__ = ('version', 'data', 'x', 'z')
 
     def __init__(self, nbt_data: nbt.NBTFile):
-        self.version = nbt_data['DataVersion']
+        self.version = nbt_data['DataVersion'].value
         self.data = nbt_data['Level']
-        self.x = self.data['xPos']
-        self.z = self.data['zPos']
+        self.x = self.data['xPos'].value
+        self.z = self.data['zPos'].value
 
     def get_section(self, y: int) -> nbt.TAG_Compound:
         """
@@ -133,11 +134,15 @@ def get_block(self, x: int, y: int, z: int, section: Union[int, nbt.TAG_Compound
         # that holds the blocks index on the palette list
         states = section['BlockStates'].value
 
+        # in 20w17a and newer blocks cannot occupy more than one element on the BlockStates array
+        stretches = self.version < _VERSION_20w17a
+        # stretches = True
+
         # get location in the BlockStates array via the index
-        if self.version.value >= _Version_20w_17a:
-            state = index // (64 // bits)
-        else:
+        if stretches:
             state = index * bits // 64
+        else:
+            state = index // (64 // bits)
 
         # makes sure the number is unsigned
         # by adding 2^64
@@ -146,22 +151,19 @@ def get_block(self, x: int, y: int, z: int, section: Union[int, nbt.TAG_Compound
         if data < 0:
             data += 2**64
 
-        if self.version.value >= _Version_20w_17a:
-            shifted_data = data >> (index % (64 // bits))
-        else:
+        if stretches:
             # shift the number to the right to remove the left over bits
             # and shift so the i'th block is the first one
             shifted_data = data >> ((bits * index) % 64)
+        else:
+            shifted_data = data >> (index % (64 // bits) * bits)
 
         # if there aren't enough bits it means the rest are in the next number
-        if 64 - ((bits * index) % 64) < bits:
+        if stretches and 64 - ((bits * index) % 64) < bits:
             data = states[state + 1]
             if data < 0:
                 data += 2**64
 
-            if self.version.value >= _Version_20w_17a:
-                shifted_data = data
-            else:
                 # get how many bits are from a palette index of the next block
                 leftover = (bits - ((state + 1) * 64 % bits)) % bits
 
@@ -216,21 +218,23 @@ def stream_blocks(self, index: int=0, section: Union[int, nbt.TAG_Compound]=None
 
         bits = max((len(palette) - 1).bit_length(), 4)
 
-        if self.version.value >= _Version_20w_17a:
-            state = index // (64 // bits)
-        else:
+        stretches = self.version < _VERSION_20w17a
+
+        if stretches:
             state = index * bits // 64
+        else:
+            state = index // (64 // bits)
 
         data = states[state]
         if data < 0:
             data += 2**64
 
         bits_mask = 2**bits - 1
 
-        if self.version.value >= _Version_20w_17a:
-            offset = data >> (index % (64 // bits))
+        if stretches:
+            offset = (bits * index) % 64
         else:
-            offset = data >> ((bits * index) % 64)
+            offset = index % (64 // bits) * bits
 
         data_len = 64 - offset
         data >>= offset
@@ -242,14 +246,14 @@ def stream_blocks(self, index: int=0, section: Union[int, nbt.TAG_Compound]=None
                 if new_data < 0:
                     new_data += 2**64
 
-                if self.version.value >= _Version_20w_17a:
-                    data = new_data
-                    data_len = 64
-                else:
+                if stretches:
                     leftover = data_len
                     data_len += 64
 
                     data = bin_append(new_data, data, leftover)
+                else:
+                    data = new_data
+                    data_len = 64
 
             palette_id = data & bits_mask
             yield Block.from_palette(palette[palette_id])

setup.py

@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name='anvil-parser',
-    version='0.6.1',
+    version='0.6.2',
     author='mat',
     description='A Minecraft anvil file format parser',
     long_description=long_description,