"""
Debugging utilities for constructs
"""
from __future__ import print_function
import sys
import traceback
import pdb
import inspect
from .core import Construct, Subconstruct
from .lib import HexString, Container, ListContainer


class Probe(Construct):
 """
 A probe: dumps the context, stack frames, and stream content to the screen
 to aid the debugging process.
 See also Debugger.

 Parameters:
 * name - the display name
 * show_stream - whether or not to show stream contents. default is True.
 the stream must be seekable.
 * show_context - whether or not to show the context. default is True.
 * show_stack - whether or not to show the upper stack frames. default
 is True.
 * stream_lookahead - the number of bytes to dump when show_stack is set.
 default is 100.

 Example:
 Struct("foo",
 UBInt8("a"),
 Probe("between a and b"),
 UBInt8("b"),
 )
 """
 __slots__ = [
 "printname", "show_stream", "show_context", "show_stack",
 "stream_lookahead"
 ]
 counter = 0

 def __init__(self, name = None, show_stream = True,
 show_context = True, show_stack = True,
 stream_lookahead = 100):
 Construct.__init__(self, None)
 if name is None:
 Probe.counter += 1
 name = "<unnamed %d>" % (Probe.counter,)
 self.printname = name
 self.show_stream = show_stream
 self.show_context = show_context
 self.show_stack = show_stack
 self.stream_lookahead = stream_lookahead
 def __repr__(self):
 return "%s(%r)" % (self.__class__.__name__, self.printname)
 def _parse(self, stream, context):
 self.printout(stream, context)
 def _build(self, obj, stream, context):
 self.printout(stream, context)
 def _sizeof(self, context):
 return 0

 def printout(self, stream, context):
 obj = Container()
 if self.show_stream:
 obj.stream_position = stream.tell()
 follows = stream.read(self.stream_lookahead)
 if not follows:
 obj.following_stream_data = "EOF reached"
 else:
 stream.seek(-len(follows), 1)
 obj.following_stream_data = HexString(follows)
 print

 if self.show_context:
 obj.context = context

 if self.show_stack:
 obj.stack = ListContainer()
 frames = [s[0] for s in inspect.stack()][1:-1]
 frames.reverse()
 for f in frames:
 a = Container()
 a.__update__(f.f_locals)
 obj.stack.append(a)

 print("=" * 80)
 print("Probe", self.printname)
 print(obj)
 print("=" * 80)

class Debugger(Subconstruct):
 """
 A pdb-based debugger. When an exception occurs in the subcon, a debugger
 will appear and allow you to debug the error (and even fix on-the-fly).

 Parameters:
 * subcon - the subcon to debug

 Example:
 Debugger(
 Enum(UBInt8("foo"),
 a = 1,
 b = 2,
 c = 3
 )
 )
 """
 __slots__ = ["retval"]
 def _parse(self, stream, context):
 try:
 return self.subcon._parse(stream, context)
 except Exception:
 self.retval = NotImplemented
 self.handle_exc("(you can set the value of 'self.retval', "
 "which will be returned)")
 if self.retval is NotImplemented:
 raise
 else:
 return self.retval
 def _build(self, obj, stream, context):
 try:
 self.subcon._build(obj, stream, context)
 except Exception:
 self.handle_exc()
 def handle_exc(self, msg = None):
 print("=" * 80)
 print("Debugging exception of %s:" % (self.subcon,))
 print("".join(traceback.format_exception(*sys.exc_info())[1:]))
 if msg:
 print(msg)
 pdb.post_mortem(sys.exc_info()[2])
 print("=" * 80)