"""
Magic Reload Library
Luke Campagnola   2010

Python reload function that actually works (the way you expect it to)
  - No re-importing necessary
  - Modules can be reloaded in any order
  - Replaces functions and methods with their updated code
  - Changes instances to use updated classes
  - Automatically decides which modules to update by comparing file modification times
 
Does NOT:
  - re-initialize exting instances, even if __init__ changes
  - update references to any module-level objects
    ie, this does not reload correctly:
        from module import someObject
        print someObject
    ..but you can use this instead: (this works even for the builtin reload)
        import module
        print module.someObject
"""

from __future__ import print_function

import gc
import inspect
import os
import sys
import traceback
import types

from .debug import printExc

try:
    from importlib import reload as orig_reload
except ImportError:
    orig_reload = reload


def reloadAll(prefix=None, debug=False):
    """Automatically reload all modules whose __file__ begins with *prefix*.

    Skips reload if the file has not been updated (if .pyc is newer than .py)
    If *prefix* is None, then all loaded modules are checked.

    Returns a dictionary {moduleName: (reloaded, reason)} describing actions taken
    for each module.
    """
    failed = []
    changed = []
    ret = {}
    for modName, mod in list(sys.modules.items()):
        if not inspect.ismodule(mod):
            ret[modName] = (False, 'not a module')
            continue
        if modName == '__main__':
            ret[modName] = (False, 'ignored __main__')
            continue
        
        # Ignore modules without a __file__ that is .py or .pyc
        if getattr(mod, '__file__', None) is None:
            ret[modName] = (False, 'module has no __file__')
            continue
        
        if os.path.splitext(mod.__file__)[1] not in ['.py', '.pyc']:
            ret[modName] = (False, '%s not a .py/pyc file' % str(mod.__file__))
            continue

        # Ignore if the file name does not start with prefix
        if prefix is not None and mod.__file__[:len(prefix)] != prefix:
            ret[modName] = (False, 'file %s not in prefix %s' % (mod.__file__, prefix))
            continue
        
        py = os.path.splitext(mod.__file__)[0] + '.py'
        if py in changed:
            # already processed this module
            continue
        if not os.path.isfile(py):
            # skip modules that lie about their __file__
            ret[modName] = (False, '.py does not exist: %s' % py)
            continue

        # if source file is newer than cache file, then it needs to be reloaded.
        pyc = getattr(mod, '__cached__', py + 'c')
        if not os.path.isfile(pyc):
            ret[modName] = (False, 'code has no pyc file to compare')
            continue

        if os.stat(pyc).st_mtime > os.stat(py).st_mtime:
            ret[modName] = (False, 'code has not changed since compile')
            continue

        # keep track of which modules have changed to ensure that duplicate-import modules get reloaded.
        changed.append(py)  

        try:
            reload(mod, debug=debug)
            ret[modName] = (True, None)
        except Exception as exc:
            printExc("Error while reloading module %s, skipping\n" % mod)
            failed.append(mod.__name__)
            ret[modName] = (False, 'reload failed: %s' % traceback.format_exception_only(type(exc), exc))
        
    if len(failed) > 0:
        raise Exception("Some modules failed to reload: %s" % ', '.join(failed))

    return ret


def reload(module, debug=False, lists=False, dicts=False):
    """Replacement for the builtin reload function:
    - Reloads the module as usual
    - Updates all old functions and class methods to use the new code
    - Updates all instances of each modified class to use the new class
    - Can update lists and dicts, but this is disabled by default
    - Requires that class and function names have not changed
    """
    if debug:
        print("Reloading %s" % str(module))
        
    ## make a copy of the old module dictionary, reload, then grab the new module dictionary for comparison
    oldDict = module.__dict__.copy()
    orig_reload(module)
    newDict = module.__dict__
    
    ## Allow modules access to the old dictionary after they reload
    if hasattr(module, '__reload__'):
        module.__reload__(oldDict)
    
    ## compare old and new elements from each dict; update where appropriate
    for k in oldDict:
        old = oldDict[k]
        new = newDict.get(k, None)
        if old is new or new is None:
            continue
        
        if inspect.isclass(old):
            if debug:
                print("  Updating class %s.%s (0x%x -> 0x%x)" % (module.__name__, k, id(old), id(new)))
            updateClass(old, new, debug)
            # don't put this inside updateClass because it is reentrant.
            new.__previous_reload_version__ = old

        elif inspect.isfunction(old):
            depth = updateFunction(old, new, debug)
            if debug:
                extra = ""
                if depth > 0:
                    extra = " (and %d previous versions)" % depth
                print("  Updating function %s.%s%s" % (module.__name__, k, extra))
        elif lists and isinstance(old, list):
            l = old.len()
            old.extend(new)
            for i in range(l):
                old.pop(0)
        elif dicts and isinstance(old, dict):
            old.update(new)
            for j in old:
                if j not in new:
                    del old[j]
        


## For functions:
##  1) update the code and defaults to new versions.
##  2) keep a reference to the previous version so ALL versions get updated for every reload
def updateFunction(old, new, debug, depth=0, visited=None):
    #if debug and depth > 0:
        #print "    -> also updating previous version", old, " -> ", new
        
    old.__code__ = new.__code__
    old.__defaults__ = new.__defaults__
    if hasattr(old, '__kwdefaults'):
        old.__kwdefaults__ = new.__kwdefaults__
    old.__doc__ = new.__doc__
    
    if visited is None:
        visited = []
    if old in visited:
        return
    visited.append(old)
    
    ## finally, update any previous versions still hanging around..
    if hasattr(old, '__previous_reload_version__'):
        maxDepth = updateFunction(old.__previous_reload_version__, new, debug, depth=depth+1, visited=visited)
    else:
        maxDepth = depth
        
    ## We need to keep a pointer to the previous version so we remember to update BOTH
    ## when the next reload comes around.
    if depth == 0:
        new.__previous_reload_version__ = old
    return maxDepth



## For classes:
##  1) find all instances of the old class and set instance.__class__ to the new class
##  2) update all old class methods to use code from the new class methods


def updateClass(old, new, debug):
    ## Track town all instances and subclasses of old
    refs = gc.get_referrers(old)
    for ref in refs:
        try:
            if isinstance(ref, old) and ref.__class__ is old:
                ref.__class__ = new
                if debug:
                    print("    Changed class for %s" % safeStr(ref))
            elif inspect.isclass(ref) and issubclass(ref, old) and old in ref.__bases__:
                ind = ref.__bases__.index(old)
                
                ## Does not work:
                #ref.__bases__ = ref.__bases__[:ind] + (new,) + ref.__bases__[ind+1:]
                ## reason: Even though we change the code on methods, they remain bound
                ## to their old classes (changing im_class is not allowed). Instead,
                ## we have to update the __bases__ such that this class will be allowed
                ## as an argument to older methods.
                
                ## This seems to work. Is there any reason not to?
                ## Note that every time we reload, the class hierarchy becomes more complex.
                ## (and I presume this may slow things down?)
                newBases = ref.__bases__[:ind] + (new,old) + ref.__bases__[ind+1:]
                try:
                    ref.__bases__ = newBases
                except TypeError:
                    print("    Error setting bases for class %s" % ref)
                    print("        old bases: %s" % repr(ref.__bases__))
                    print("        new bases: %s" % repr(newBases))
                    raise
                if debug:
                    print("    Changed superclass for %s" % safeStr(ref))
            #else:
                #if debug:
                    #print "    Ignoring reference", type(ref)
        except Exception:
            print("Error updating reference (%s) for class change (%s -> %s)" % (safeStr(ref), safeStr(old), safeStr(new)))
            raise
        
    ## update all class methods to use new code.
    ## Generally this is not needed since instances already know about the new class, 
    ## but it fixes a few specific cases (pyqt signals, for one)
    for attr in dir(old):
        oa = getattr(old, attr)
        if inspect.isfunction(oa) or inspect.ismethod(oa):
            # note python2 has unbound methods, whereas python3 just uses plain functions
            try:
                na = getattr(new, attr)
            except AttributeError:
                if debug:
                    print("    Skipping method update for %s; new class does not have this attribute" % attr)
                continue
                
            ofunc = getattr(oa, '__func__', oa)  # in py2 we have to get the __func__ from unbound method,
            nfunc = getattr(na, '__func__', na)  # in py3 the attribute IS the function

            if ofunc is not nfunc:
                depth = updateFunction(ofunc, nfunc, debug)
                if not hasattr(nfunc, '__previous_reload_method__'):
                    nfunc.__previous_reload_method__ = oa  # important for managing signal connection
                    #oa.__class__ = new  ## bind old method to new class  ## not allowed
                if debug:
                    extra = ""
                    if depth > 0:
                        extra = " (and %d previous versions)" % depth
                    print("    Updating method %s%s" % (attr, extra))
                
    ## And copy in new functions that didn't exist previously
    for attr in dir(new):
        if attr == '__previous_reload_version__':
            continue
        if not hasattr(old, attr):
            if debug:
                print("    Adding missing attribute %s" % attr)
            setattr(old, attr, getattr(new, attr))
            
    ## finally, update any previous versions still hanging around..
    if hasattr(old, '__previous_reload_version__'):
        updateClass(old.__previous_reload_version__, new, debug)


## It is possible to build classes for which str(obj) just causes an exception.
## Avoid thusly:
def safeStr(obj):
    try:
        s = str(obj)
    except Exception:
        try:
            s = repr(obj)
        except Exception:
            s = "<instance of %s at 0x%x>" % (safeStr(type(obj)), id(obj))
    return s


def getPreviousVersion(obj):
    """Return the previous version of *obj*, or None if this object has not
    been reloaded.
    """
    if isinstance(obj, type) or inspect.isfunction(obj):
        return getattr(obj, '__previous_reload_version__', None)
    elif inspect.ismethod(obj):
        if obj.__self__ is None:
            # unbound method
            return getattr(obj.__func__, '__previous_reload_method__', None)
        else:
            oldmethod = getattr(obj.__func__, '__previous_reload_method__', None)
            if oldmethod is None:
                return None
            self = obj.__self__
            oldfunc = getattr(oldmethod, '__func__', oldmethod)
            if hasattr(oldmethod, 'im_class'):
                # python 2
                cls = oldmethod.im_class
                return types.MethodType(oldfunc, self, cls)
            else:
                # python 3
                return types.MethodType(oldfunc, self)