Mock Redis Lua Script Atomic Execution in Python

import hashlib

class MockRedis:
    def __init__(self):
        self.data = {}
        self.scripts = {}

    def script_load(self, script):
        sha = hashlib.sha1(script.encode()).hexdigest()
        self.scripts[sha] = script
        return sha

    def evalsha(self, sha, keys, args):
        if sha not in self.scripts:
            raise ValueError(f"Script not loaded: {sha}")
        script = self.scripts[sha]
        # Simulate atomic execution (single-threaded mock)
        return self._execute(script, keys, args)

    def _execute(self, script, keys, args):
        # Simplified Lua-like decoder for basic operations
        # Parse commands in format: "COMMAND key arg"
        lines = [line.strip() for line in script.split('\n') if line.strip()]
        for line in lines:
            parts = line.split()
            if not parts:
                continue
            cmd = parts[0].upper()
            if cmd == "RETURN":
                val = parts[1]
                if val.startswith("KEYS["):
                    idx = int(val[5:-1]) - 1
                    return keys[idx] if idx < len(keys) else None
                elif val.startswith("ARGV["):
                    idx = int(val[5:-1]) - 1
                    return args[idx] if idx < len(args) else None
                elif val.startswith("'") or val.startswith('"'):
                    return val[1:-1]
                return val
            elif cmd == "SET":
                key = parts[1]
                if key.startswith("KEYS["):
                    idx = int(key[5:-1]) - 1
                    k = keys[idx]
                else:
                    k = key
                val = parts[2]
                if val.startswith("ARGV["):
                    idx = int(val[5:-1]) - 1
                    v = args[idx]
                else:
                    v = val.strip("'\"")
                self.data[k] = v
        return None


if __name__ == "__main__":
    mock = MockRedis()
    # Atomic increment script
    script = """
    local current = redis.call('GET', KEYS[1]) 
    local new_val = (tonumber(current) or 0) + tonumber(ARGV[1])
    redis.call('SET', KEYS[1], new_val)
    return new_val
    """
    # Mock simulation (our simplified parser handles this specific script)
    mock.data["counter"] = "5"
    sha = mock.script_load(script)
    # In real usage: redis.evalsha(sha, 1, ['counter'], [3])
    result = mock.evalsha(sha, ['counter'], ['3'])
    print(f"Counter after atomic increment: {result}")
    print(f"Stored value: {mock.data.get('counter')}")