Script class to create, parse, serialize and

evaluate scripts

script.py

@@ -1,9 +1,151 @@
 """
 Script implementation
 """
+from logging import Logger
+from typing import List
 
+from helper import (
+    encode_varint, 
+    int_to_little_endian, 
+    little_endian_to_int, 
+    read_varint
+)
+from op import OP_CODE_FUNCTIONS, OP_CODE_NAMES
+
+
+LOGGER = Logger
 
 class Script:
     """
     Defines attributes and methods of Script
-    """
+    """
+    def __init__(self, cmds=None) -> None:
+        """
+        Initialize new Script
+        """
+        if cmds is None:
+            self.cmds: List = []
+        else:
+            self.cmds = cmds
+
+    @classmethod
+    def parse(cls, s):
+        """
+        Parse a stream
+        """
+        length = read_varint(s)
+        cmds = []
+        count = 0
+        while count < length:
+            current = s.read(1)
+            count += 1
+            current_byte = current[0]
+
+            if current_byte >= 1 and current_byte <= 75:
+                n = current_byte
+                cmds.append(s.read(n))
+                count += n
+
+            elif current_byte == 76:
+                data_length = little_endian_to_int(s.read(1))
+                cmds.append(s.read(data_length))
+                count += data_length + 1
+
+            elif current_byte == 77:
+                data_length = little_endian_to_int(s.read(2))
+                cmds.append(s.read(data_length))
+                count += data_length + 2
+
+            else:
+                op_code = current_byte
+                cmds.append(op_code)
+
+        if count != length:
+            raise SyntaxError('parsing script failed')
+        return cls(cmds)
+
+    def raw_serialize(self):
+        """
+        Serialize a raw script
+        """
+        result = b''
+
+        for cmd in self.cmds:
+            if type(cmd) == int:
+                result += int_to_little_endian(cmd, 1)
+
+            else:
+                length = len(cmd)
+                if length < 75:
+                    result += int_to_little_endian(length, 1)
+
+                elif length > 75 and length < 0x100:
+                    result += int_to_little_endian(76, 1)
+                    result += int_to_little_endian(length, 1)
+
+                elif length >= 0x100 and length <=520:
+                    result += int_to_little_endian(77, 1)
+                    result += int_to_little_endian(length, 2)
+
+                else:
+                    raise ValueError('too long an cmd')
+                result += cmd
+
+        return result
+
+    def serialize(self):
+        """
+        Serialize a script
+        """
+        result = self.raw_serialize()
+        total = len(result)
+        return encode_varint(total) + result
+
+    def __add__(self, other):
+        """
+        Combine two command sets to create a new Script object
+        """
+        return Script(self.cmds + other.cmds)
+
+    def evaluate(self, z) -> bool:
+        """
+        Evaluates Script
+        """
+        cmds = self.cmds[:]
+        stack = []
+        altstack = []
+
+        while len(cmds) > 0:
+            cmd = cmds.pop(0)
+
+            if type(cmd) == int:
+                operation = OP_CODE_FUNCTIONS[cmd]
+                if cmd in (99, 100):
+                    if not operation(stack, cmds):
+                        LOGGER.info(f'bad op: {OP_CODE_NAMES[cmd]}')
+                        return False
+
+                elif cmd in (107, 108):
+                    if not operation(stack, altstack):
+                        LOGGER.info(f'bad op: {OP_CODE_NAMES[cmd]}')
+                        return False
+
+                elif cmd in (172, 173, 274, 175):
+                    if not operation(stack, z):
+                        LOGGER.info(f'bad op: {OP_CODE_NAMES[cmd]}')
+                        return False
+
+                else:
+                    if not operation(stack):
+                        LOGGER.info(f'bad op: {OP_CODE_NAMES[cmd]}')
+                        return False
+
+            else:
+                stack.append(cmd)
+
+        if len(stack) == 0:
+            return False
+        if stack.pop() == b'':
+            return False
+        return True
+