ControlFlow.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# "Control Flow Graph" - a chapter of "The Fuzzing Book"
# Web site: https://www.fuzzingbook.org/html/ControlFlow.html
# Last change: 2024-01-18 18:31:35+01:00
#
# Copyright (c) 2021-2023 CISPA Helmholtz Center for Information Security
# Copyright (c) 2018-2020 Saarland University, authors, and contributors
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
# OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

r'''
The Fuzzing Book - Control Flow Graph

This file can be _executed_ as a script, running all experiments:

    $ python ControlFlow.py

or _imported_ as a package, providing classes, functions, and constants:

    >>> from fuzzingbook.ControlFlow import <identifier>
    
but before you do so, _read_ it and _interact_ with it at:

    https://www.fuzzingbook.org/html/ControlFlow.html


For more details, source, and documentation, see
"The Fuzzing Book - Control Flow Graph"
at https://www.fuzzingbook.org/html/ControlFlow.html
'''


# Allow to use 'from . import <module>' when run as script (cf. PEP 366)
if __name__ == '__main__' and __package__ is None:
    __package__ = 'fuzzingbook'


# Control Flow Graph
# ==================

if __name__ == '__main__':
    print('# Control Flow Graph')



## Control Flow Graph
## ------------------

if __name__ == '__main__':
    print('\n## Control Flow Graph')



if __name__ == '__main__':
    # We use the same fixed seed as the notebook to ensure consistency
    import random
    random.seed(2001)

from .bookutils import print_content

import ast
import re

from graphviz import Source, Digraph

### Registry

if __name__ == '__main__':
    print('\n### Registry')



REGISTRY_IDX = 0

REGISTRY = {}

def get_registry_idx():
    global REGISTRY_IDX
    v = REGISTRY_IDX
    REGISTRY_IDX += 1
    return v

def reset_registry():
    global REGISTRY_IDX
    global REGISTRY
    REGISTRY_IDX = 0
    REGISTRY = {}

def register_node(node):
    node.rid = get_registry_idx()
    REGISTRY[node.rid] = node

def get_registry():
    return dict(REGISTRY)

### CFGNode

if __name__ == '__main__':
    print('\n### CFGNode')



class CFGNode(dict):
    def __init__(self, parents=[], ast=None):
        assert type(parents) is list
        register_node(self)
        self.parents = parents
        self.ast_node = ast
        self.update_children(parents)  # requires self.rid
        self.children = []
        self.calls = []

    def i(self):
        return str(self.rid)

    def update_children(self, parents):
        for p in parents:
            p.add_child(self)

    def add_child(self, c):
        if c not in self.children:
            self.children.append(c)

    def lineno(self):
        return self.ast_node.lineno if hasattr(self.ast_node, 'lineno') else 0

    def __str__(self):
        return "id:%d line[%d] parents: %s : %s" % (
            self.rid, self.lineno(), str([p.rid for p in self.parents]),
            self.source())

    def __repr__(self):
        return str(self)

    def __eq__(self, other):
        return self.rid == other.rid

    def __neq__(self, other):
        return self.rid != other.rid

    def set_parents(self, p):
        self.parents = p

    def add_parent(self, p):
        if p not in self.parents:
            self.parents.append(p)

    def add_parents(self, ps):
        for p in ps:
            self.add_parent(p)

    def add_calls(self, func):
        self.calls.append(func)

    def source(self):
        return ast.unparse(self.ast_node).strip()

    def to_json(self):
        return {
            'id': self.rid,
            'parents': [p.rid for p in self.parents],
            'children': [c.rid for c in self.children],
            'calls': self.calls,
            'at': self.lineno(),
            'ast': self.source()
        }

### PyCFG

if __name__ == '__main__':
    print('\n### PyCFG')



class PyCFG:
    def __init__(self):
        self.founder = CFGNode(
            parents=[], ast=ast.parse('start').body[0])  # sentinel
        self.founder.ast_node.lineno = 0
        self.functions = {}
        self.functions_node = {}

class PyCFG(PyCFG):
    def parse(self, src):
        return ast.parse(src)

class PyCFG(PyCFG):
    def walk(self, node, myparents):
        fname = "on_%s" % node.__class__.__name__.lower()
        if hasattr(self, fname):
            fn = getattr(self, fname)
            v = fn(node, myparents)
            return v
        else:
            return myparents

class PyCFG(PyCFG):
    def on_module(self, node, myparents):
        """
        Module(stmt* body)
        """
        # each time a statement is executed unconditionally, make a link from
        # the result to next statement
        p = myparents
        for n in node.body:
            p = self.walk(n, p)
        return p

class PyCFG(PyCFG):
    def on_augassign(self, node, myparents):
        """
         AugAssign(expr target, operator op, expr value)
        """
        p = [CFGNode(parents=myparents, ast=node)]
        p = self.walk(node.value, p)

        return p

class PyCFG(PyCFG):
    def on_annassign(self, node, myparents):
        """
        AnnAssign(expr target, expr annotation, expr? value, int simple)
        """
        p = [CFGNode(parents=myparents, ast=node)]
        p = self.walk(node.value, p)

        return p

class PyCFG(PyCFG):
    def on_assign(self, node, myparents):
        """
        Assign(expr* targets, expr value)
        """
        if len(node.targets) > 1:
            raise NotImplemented('Parallel assignments')

        p = [CFGNode(parents=myparents, ast=node)]
        p = self.walk(node.value, p)

        return p

class PyCFG(PyCFG):
    def on_pass(self, node, myparents):
        return [CFGNode(parents=myparents, ast=node)]

class PyCFG(PyCFG):
    def on_break(self, node, myparents):
        parent = myparents[0]
        while not hasattr(parent, 'exit_nodes'):
            # we have ordered parents
            parent = parent.parents[0]

        assert hasattr(parent, 'exit_nodes')
        p = CFGNode(parents=myparents, ast=node)

        # make the break one of the parents of label node.
        parent.exit_nodes.append(p)

        # break doesn't have immediate children
        return []

class PyCFG(PyCFG):
    def on_continue(self, node, myparents):
        parent = myparents[0]
        while not hasattr(parent, 'exit_nodes'):
            # we have ordered parents
            parent = parent.parents[0]
        assert hasattr(parent, 'exit_nodes')
        p = CFGNode(parents=myparents, ast=node)

        # make continue one of the parents of the original test node.
        parent.add_parent(p)

        # return the parent because a continue is not the parent
        # for the just next node
        return []

class PyCFG(PyCFG):
    def on_for(self, node, myparents):
        # node.target in node.iter: node.body
        # The For loop in python (no else) can be translated
        # as follows:
        # 
        # for a in iterator:
        #      mystatements
        #
        # __iv = iter(iterator)
        # while __iv.__length_hint() > 0:
        #     a = next(__iv)
        #     mystatements

        init_node = CFGNode(parents=myparents,
            ast=ast.parse('__iv = iter(%s)' % ast.unparse(node.iter).strip()).body[0])
        ast.copy_location(init_node.ast_node, node.iter)

        _test_node = CFGNode(
            parents=[init_node],
            ast=ast.parse('_for: __iv.__length__hint__() > 0').body[0])
        ast.copy_location(_test_node.ast_node, node)

        # we attach the label node here so that break can find it.
        _test_node.exit_nodes = []
        test_node = self.walk(node.iter, [_test_node])

        extract_node = CFGNode(parents=test_node,
            ast=ast.parse('%s = next(__iv)' % ast.unparse(node.target).strip()).body[0])
        ast.copy_location(extract_node.ast_node, node.iter)

        # now we evaluate the body, one at a time.
        p1 = [extract_node]
        for n in node.body:
            p1 = self.walk(n, p1)

        # the test node is looped back at the end of processing.
        _test_node.add_parents(p1)

        return _test_node.exit_nodes + test_node

class PyCFG(PyCFG):
    def on_while(self, node, myparents):
        # For a while, the earliest parent is the node.test
        _test_node = CFGNode(
            parents=myparents,
            ast=ast.parse(
                '_while: %s' % ast.unparse(node.test).strip()).body[0])
        ast.copy_location(_test_node.ast_node, node.test)
        _test_node.exit_nodes = []
        test_node = self.walk(node.test, [_test_node])

        # we attach the label node here so that break can find it.

        # now we evaluate the body, one at a time.
        assert len(test_node) == 1
        p1 = test_node
        for n in node.body:
            p1 = self.walk(n, p1)

        # the test node is looped back at the end of processing.
        _test_node.add_parents(p1)

        # link label node back to the condition.
        return _test_node.exit_nodes + test_node

class PyCFG(PyCFG):
    def on_if(self, node, myparents):
        _test_node = CFGNode(
            parents=myparents,
            ast=ast.parse(
                '_if: %s' % ast.unparse(node.test).strip()).body[0])
        ast.copy_location(_test_node.ast_node, node.test)
        test_node = self.walk(node.test, [ _test_node])
        assert len(test_node) == 1
        g1 = test_node
        for n in node.body:
            g1 = self.walk(n, g1)
        g2 = test_node
        for n in node.orelse:
            g2 = self.walk(n, g2)
        return g1 + g2

class PyCFG(PyCFG):
    def on_binop(self, node, myparents):
        left = self.walk(node.left, myparents)
        right = self.walk(node.right, left)
        return right

class PyCFG(PyCFG):
    def on_compare(self, node, myparents):
        left = self.walk(node.left, myparents)
        right = self.walk(node.comparators[0], left)
        return right

class PyCFG(PyCFG):
    def on_unaryop(self, node, myparents):
        return self.walk(node.operand, myparents)

class PyCFG(PyCFG):
    def on_call(self, node, myparents):
        def get_func(node):
            if type(node.func) is ast.Name:
                mid = node.func.id
            elif type(node.func) is ast.Attribute:
                mid = node.func.attr
            elif type(node.func) is ast.Call:
                mid = get_func(node.func)
            else:
                raise Exception(str(type(node.func)))
            return mid
            #mid = node.func.value.id

        p = myparents
        for a in node.args:
            p = self.walk(a, p)
        mid = get_func(node)
        myparents[0].add_calls(mid)

        # these need to be unlinked later if our module actually defines these
        # functions. Otherwsise we may leave them around.
        # during a call, the direct child is not the next
        # statement in text.
        for c in p:
            c.calllink = 0
        return p

class PyCFG(PyCFG):
    def on_expr(self, node, myparents):
        p = [CFGNode(parents=myparents, ast=node)]
        return self.walk(node.value, p)

class PyCFG(PyCFG):
    def on_return(self, node, myparents):
        if type(myparents) is tuple:
            parent = myparents[0][0]
        else:
            parent = myparents[0]

        val_node = self.walk(node.value, myparents)
        # on return look back to the function definition.
        while not hasattr(parent, 'return_nodes'):
            parent = parent.parents[0]
        assert hasattr(parent, 'return_nodes')

        p = CFGNode(parents=val_node, ast=node)

        # make the break one of the parents of label node.
        parent.return_nodes.append(p)

        # return doesnt have immediate children
        return []

class PyCFG(PyCFG):
    def on_functiondef(self, node, myparents):
        # a function definition does not actually continue the thread of
        # control flow
        # name, args, body, decorator_list, returns
        fname = node.name
        args = node.args
        returns = node.returns

        enter_node = CFGNode(
            parents=[],
            ast=ast.parse('enter: %s(%s)' % (node.name, ', '.join(
                [a.arg for a in node.args.args]))).body[0])  # sentinel
        enter_node.calleelink = True
        ast.copy_location(enter_node.ast_node, node)
        exit_node = CFGNode(
            parents=[],
            ast=ast.parse('exit: %s(%s)' % (node.name, ', '.join(
                [a.arg for a in node.args.args]))).body[0])  # sentinel
        exit_node.fn_exit_node = True
        ast.copy_location(exit_node.ast_node, node)
        enter_node.return_nodes = []  # sentinel

        p = [enter_node]
        for n in node.body:
            p = self.walk(n, p)

        for n in p:
            if n not in enter_node.return_nodes:
                enter_node.return_nodes.append(n)

        for n in enter_node.return_nodes:
            exit_node.add_parent(n)

        self.functions[fname] = [enter_node, exit_node]
        self.functions_node[enter_node.lineno()] = fname

        return myparents

class PyCFG(PyCFG):
    def get_defining_function(self, node):
        if node.lineno() in self.functions_node:
            return self.functions_node[node.lineno()]
        if not node.parents:
            self.functions_node[node.lineno()] = ''
            return ''
        val = self.get_defining_function(node.parents[0])
        self.functions_node[node.lineno()] = val
        return val

class PyCFG(PyCFG):
    def link_functions(self):
        for nid, node in REGISTRY.items():
            if node.calls:
                for calls in node.calls:
                    if calls in self.functions:
                        enter, exit = self.functions[calls]
                        enter.add_parent(node)
                        if node.children:
                            # # until we link the functions up, the node
                            # # should only have succeeding node in text as
                            # # children.
                            # assert(len(node.children) == 1)
                            # passn = node.children[0]
                            # # We require a single pass statement after every
                            # # call (which means no complex expressions)
                            # assert(type(passn.ast_node) == ast.Pass)

                            # # unlink the call statement
                            assert node.calllink > -1
                            node.calllink += 1
                            for i in node.children:
                                i.add_parent(exit)
                            # passn.set_parents([exit])
                            # ast.copy_location(exit.ast_node, passn.ast_node)

                            # #for c in passn.children: c.add_parent(exit)
                            # #passn.ast_node = exit.ast_node

class PyCFG(PyCFG):
    def update_functions(self):
        for nid, node in REGISTRY.items():
            _n = self.get_defining_function(node)

class PyCFG(PyCFG):
    def update_children(self):
        for nid, node in REGISTRY.items():
            for p in node.parents:
                p.add_child(node)

class PyCFG(PyCFG):
    def gen_cfg(self, src):
        """
        >>> i = PyCFG()
        >>> i.walk("100")
        5
        """
        node = self.parse(src)
        nodes = self.walk(node, [self.founder])
        self.last_node = CFGNode(parents=nodes, ast=ast.parse('stop').body[0])
        ast.copy_location(self.last_node.ast_node, self.founder.ast_node)
        self.update_children()
        self.update_functions()
        self.link_functions()

### Supporting Functions

if __name__ == '__main__':
    print('\n### Supporting Functions')



def compute_dominator(cfg, start=0, key='parents'):
    dominator = {}
    dominator[start] = {start}
    all_nodes = set(cfg.keys())
    rem_nodes = all_nodes - {start}
    for n in rem_nodes:
        dominator[n] = all_nodes

    c = True
    while c:
        c = False
        for n in rem_nodes:
            pred_n = cfg[n][key]
            doms = [dominator[p] for p in pred_n]
            i = set.intersection(*doms) if doms else set()
            v = {n} | i
            if dominator[n] != v:
                c = True
            dominator[n] = v
    return dominator

def compute_flow(pythonfile):
    cfg, first, last = get_cfg(pythonfile)
    return cfg, compute_dominator(
        cfg, start=first), compute_dominator(
            cfg, start=last, key='children')

def gen_cfg(fnsrc, remove_start_stop=True):
    reset_registry()
    cfg = PyCFG()
    cfg.gen_cfg(fnsrc)
    cache = dict(REGISTRY)
    if remove_start_stop:
        return {
            k: cache[k]
            for k in cache if cache[k].source() not in {'start', 'stop'}
        }
    else:
        return cache

def get_cfg(src):
    reset_registry()
    cfg = PyCFG()
    cfg.gen_cfg(src)
    cache = dict(REGISTRY)
    g = {}
    for k, v in cache.items():
        j = v.to_json()
        at = j['at']
        parents_at = [cache[p].to_json()['at'] for p in j['parents']]
        children_at = [cache[c].to_json()['at'] for c in j['children']]
        if at not in g:
            g[at] = {'parents': set(), 'children': set()}
        # remove dummy nodes
        ps = set([p for p in parents_at if p != at])
        cs = set([c for c in children_at if c != at])
        g[at]['parents'] |= ps
        g[at]['children'] |= cs
        if v.calls:
            g[at]['calls'] = v.calls
        g[at]['function'] = cfg.functions_node[v.lineno()]
    return (g, cfg.founder.ast_node.lineno, cfg.last_node.ast_node.lineno)

def to_graph(cache, arcs=[]):
    graph = Digraph(comment='Control Flow Graph')
    colors = {0: 'blue', 1: 'red'}
    kind = {0: 'T', 1: 'F'}
    cov_lines = set(i for i, j in arcs)
    for nid, cnode in cache.items():
        lineno = cnode.lineno()
        shape, peripheries = 'oval', '1'
        if isinstance(cnode.ast_node, ast.AnnAssign):
            if cnode.ast_node.target.id in {'_if', '_for', '_while'}:
                shape = 'diamond'
            elif cnode.ast_node.target.id in {'enter', 'exit'}:
                shape, peripheries = 'oval', '2'
        else:
            shape = 'rectangle'
        graph.node(cnode.i(), "%d: %s" % (lineno, unhack(cnode.source())),
                   shape=shape, peripheries=peripheries)
        for pn in cnode.parents:
            plineno = pn.lineno()
            if hasattr(pn, 'calllink') and pn.calllink > 0 and not hasattr(
                    cnode, 'calleelink'):
                graph.edge(pn.i(), cnode.i(), style='dotted', weight=100)
                continue

            if arcs:
                if (plineno, lineno) in arcs:
                    graph.edge(pn.i(), cnode.i(), color='green')
                elif plineno == lineno and lineno in cov_lines:
                    graph.edge(pn.i(), cnode.i(), color='green')
                # child is exit and parent is covered
                elif hasattr(cnode, 'fn_exit_node') and plineno in cov_lines:
                    graph.edge(pn.i(), cnode.i(), color='green')
                # parent is exit and one of its parents is covered.
                elif hasattr(pn, 'fn_exit_node') and len(
                        set(n.lineno() for n in pn.parents) | cov_lines) > 0:
                    graph.edge(pn.i(), cnode.i(), color='green')
                # child is a callee (has calleelink) and one of the parents is covered.
                elif plineno in cov_lines and hasattr(cnode, 'calleelink'):
                    graph.edge(pn.i(), cnode.i(), color='green')
                else:
                    graph.edge(pn.i(), cnode.i(), color='red')
            else:
                order = {c.i(): i for i, c in enumerate(pn.children)}
                if len(order) < 2:
                    graph.edge(pn.i(), cnode.i())
                else:
                    o = order[cnode.i()]
                    graph.edge(pn.i(), cnode.i(), color=colors[o], label=kind[o])
    return graph

def unhack(v):
    for i in ['if', 'while', 'for', 'elif']:
        v = re.sub(r'^_%s:' % i, '%s:' % i, v)
    return v

### Examples

if __name__ == '__main__':
    print('\n### Examples')



#### check_triangle

if __name__ == '__main__':
    print('\n#### check_triangle')



def check_triangle(a, b, c):
    if a == b:
        if a == c:
            if b == c:
                return "Equilateral"
            else:
                return "Isosceles"
        else:
            return "Isosceles"
    else:
        if b != c:
            if a == c:
                return "Isosceles"
            else:
                return "Scalene"
        else:
            return "Isosceles"

import inspect

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(check_triangle)))

#### cgi_decode

if __name__ == '__main__':
    print('\n#### cgi_decode')



def cgi_decode(s):
    hex_values = {
        '0': 0, '1': 1, '2': 2, '3': 3, '4': 4,
        '5': 5, '6': 6, '7': 7, '8': 8, '9': 9,
        'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14, 'f': 15,
        'A': 10, 'B': 11, 'C': 12, 'D': 13, 'E': 14, 'F': 15,
    }

    t = ""
    i = 0
    while i < len(s):
        c = s[i]
        if c == '+':
            t += ' '
        elif c == '%':
            digit_high, digit_low = s[i + 1], s[i + 2]
            i += 2
            if digit_high in hex_values and digit_low in hex_values:
                v = hex_values[digit_high] * 16 + hex_values[digit_low]
                t += chr(v)
            else:
                raise ValueError("Invalid encoding")
        else:
            t += c
        i += 1
    return t

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(cgi_decode)))

#### gcd

if __name__ == '__main__':
    print('\n#### gcd')



def gcd(a, b):
    if a<b:
        c: int = a
        a: int = b
        b: int = c

    while b != 0 :
        c: int = a
        a: int = b
        b: int = c % b
    return a

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(gcd)))

def compute_gcd(x, y):
    if x > y:
        small = y
    else:
        small = x
    for i in range(1, small+1):
        if((x % i == 0) and (y % i == 0)):
            gcd = i

    return gcd

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(compute_gcd)))

#### fib

if __name__ == '__main__':
    print('\n#### fib')



def fib(n,):
    ls = [0, 1]
    for i in range(n-2):
        ls.append(ls[-1] + ls[-2])
    return ls

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(fib)))

#### quad_solver

if __name__ == '__main__':
    print('\n#### quad_solver')



def quad_solver(a, b, c):
    discriminant = b^2 - 4*a*c
    r1, r2 = 0, 0
    i1, i2 = 0, 0
    if discriminant >= 0:
        droot = math.sqrt(discriminant)
        r1 = (-b + droot) / (2*a)
        r2 = (-b - droot) / (2*a)
    else:
        droot = math.sqrt(-1 * discriminant)
        droot_ = droot/(2*a)
        r1, i1 = -b/(2*a), droot_
        r2, i2 = -b/(2*a), -droot_
    if i1 == 0 and i2 == 0:
        return (r1, r2)
    return ((r1,i1), (r2,i2))

if __name__ == '__main__':
    to_graph(gen_cfg(inspect.getsource(quad_solver)))

## Call Graph
## ----------

if __name__ == '__main__':
    print('\n## Call Graph')



import os

import networkx as nx  # type: ignore

### Call Graph Helpers

if __name__ == '__main__':
    print('\n### Call Graph Helpers')



import shutil

PYAN = 'pyan3' if shutil.which('pyan3') is not None else 'pyan'

if shutil.which(PYAN) is None:
    # If installed from pypi, pyan may still be missing
    os.system('pip install "git+https://github.com/uds-se/pyan#egg=pyan"')
    PYAN = 'pyan3' if shutil.which('pyan3') is not None else 'pyan'

assert shutil.which(PYAN) is not None

def construct_callgraph(code, name="callgraph"):
    file_name = name + ".py"
    with open(file_name, 'w') as f:
        f.write(code)
    cg_file = name + '.dot'
    os.system(f'{PYAN} {file_name} --uses --defines --colored --grouped --annotated --dot > {cg_file}')

def callgraph(code, name="callgraph"):
    if not os.path.isfile(name + '.dot'):
        construct_callgraph(code, name)
    return Source.from_file(name + '.dot')

def get_callgraph(code, name="callgraph"):
    if not os.path.isfile(name + '.dot'):
        construct_callgraph(code, name)

    # This is deprecated:
    # return nx.drawing.nx_pydot.read_dot(name + '.dot')
    
    return nx.nx_agraph.read_dot(name + '.dot')

### Example: Maze

if __name__ == '__main__':
    print('\n### Example: Maze')



if __name__ == '__main__':
    maze_string = """
+-+-----+
|X|     |
| | --+ |
| |   | |
| +-- | |
|     |#|
+-----+-+
"""

def maze(s: str) -> str:
    return ""  # Will be overwritten by exec()

def target_tile() -> str:
    return ' '  # Will be overwritten by exec()

def generate_print_maze(maze_string):
    return """
def print_maze(out, row, col):
    output  = out +"\\n"
    c_row = 0
    c_col = 0
    for c in list(\"\"\"%s\"\"\"):
        if c == '\\n':
            c_row += 1
            c_col = 0
            output += "\\n"
        else:
            if c_row == row and c_col == col: output += "X"
            elif c == "X": output += " "
            else: output += c
            c_col += 1
    return output
""" % maze_string

def generate_trap_tile(row, col):
    return """
def tile_%d_%d(input, index):
    try: HTMLParser().feed(input)
    except: pass
    return print_maze("INVALID", %d, %d)
""" % (row, col, row, col)

def generate_good_tile(c, row, col):
    code = """
def tile_%d_%d(input, index):
    if (index == len(input)): return print_maze("VALID", %d, %d)
    elif input[index] == 'L': return tile_%d_%d(input, index + 1)
    elif input[index] == 'R': return tile_%d_%d(input, index + 1)
    elif input[index] == 'U': return tile_%d_%d(input, index + 1)
    elif input[index] == 'D': return tile_%d_%d(input, index + 1)
    else : return tile_%d_%d(input, index + 1)
""" % (row, col, row, col,
       row, col - 1, 
       row, col + 1, 
       row - 1, col, 
       row + 1, col,
       row, col)

    if c == "X":
        code += """
def maze(input):
    return tile_%d_%d(list(input), 0)
""" % (row, col)

    return code

def generate_target_tile(row, col):
    return """
def tile_%d_%d(input, index):
    return print_maze("SOLVED", %d, %d)

def target_tile():
    return "tile_%d_%d"
""" % (row, col, row, col, row, col)

def generate_maze_code(maze, name="maze"):
    row = 0
    col = 0
    code = generate_print_maze(maze)

    for c in list(maze):
        if c == '\n':
            row += 1
            col = 0
        else:
            if c == "-" or c == "+" or c == "|":
                code += generate_trap_tile(row, col)
            elif c == " " or c == "X":
                code += generate_good_tile(c, row, col)
            elif c == "#":
                code += generate_target_tile(row, col)
            else:
                print("Invalid maze! Try another one.")
            col += 1

    return code

if __name__ == '__main__':
    maze_code = generate_maze_code(maze_string)

if __name__ == '__main__':
    print_content(maze_code, filename='.py')

if __name__ == '__main__':
    exec(maze_code)

if __name__ == '__main__':
    print(maze("DDDDRRRRUULLUURRRRDDD"))

if __name__ == '__main__':
    callgraph(maze_code)

## Cleanup
## -------

if __name__ == '__main__':
    print('\n## Cleanup')



if __name__ == '__main__':
    if os.path.exists('callgraph.dot'):
        os.remove('callgraph.dot')

    if os.path.exists('callgraph.py'):
        os.remove('callgraph.py')