"""REPL enhancements for Python interactive interpreter.

This module adds:

 - tab completion (requires readline support)
 - command history between sessions
 - syntactic sugar for 'help(stmt)' via 'stmt?'
 - output history

To enable set the environment variables:

    PYTHONSTARTUP=$HOME/.startup.py

Note: The PYTHONSTARTUP environment variable wont expand a '~' to the users
home directory, use $HOME instead.
"""
try:
    import atexit
    import os
    import readline
    import rlcompleter
except ImportError as err:
    print err
else:
    class __ReadlineCompleter(rlcompleter.Completer):
        """Tab completion support for readline.

        If there is not text for command completion, insert 4 spaces.
        """

        def __init__(self, tab='    '):
            self._complete = rlcompleter.Completer.complete
            self._insert_text = readline.insert_text
            self.tab = tab
            rlcompleter.Completer.__init__(self)

        def complete(self, text, state):
            if text == '':
                self.insert_text(self.tab)
                return None
            else:
                return self._complete(self, text, state)

    readline.parse_and_bind('tab: complete')
    readline.set_completer(__ReadlineCompleter().complete)

    class __HistoryManager(object):
        """Load and store command history.

        Commands are persisted in file '~/.history.py'.
        """

        def __init__(self, path='~/.history.py'):
            self.history_path = os.path.expanduser(path)
            self._read_history_file = readline.read_history_file
            self._write_history_file = readline.write_history_file
            self.load_history()

        def load_history(self):
            if os.path.isfile(self.history_path):
                self._read_history_file(self.history_path)

        def save_history(self):
            self._write_history_file(self.history_path)

    atexit.register(__HistoryManager().save_history)

    del __ReadlineCompleter
    del __HistoryManager
    del atexit, os, readline, rlcompleter


try:
    import inspect
    import string
    import sys
except ImportError as err:
    pass
else:
    class __HelpSyntax(object):
        """Quick access to help documentation.

        If statement ends with a '?', evaulate help(stmt).
        """

        def __init__(self):
            self.default = sys.__excepthook__
            self.isframe = inspect.isframe
            self.stack = inspect.stack
            self.stdout = sys.stdout
            self.whitespace = string.whitespace

        def __call__(self, type, value, traceback):
            if not isinstance(value, SyntaxError):
                return self.default(type, value, traceback)
            stmt = value.text.rstrip()
            if not stmt.endswith('?'):
                return self.default(type, value, traceback)
            name = stmt.rstrip('?(' + self.whitespace)
            self.show_help(name)

        def show_help(self, name):
            for record in self.stack():
                frame = record[0]
                if not self.isframe(frame):
                    continue
                if frame.f_globals.get('__name__') != '__main__':
                    continue
                cmd = 'help({0})'.format(name)
                self.stdout.write(cmd)
                return eval(cmd, frame.f_globals, frame.f_locals)

    sys.excepthook = __HelpSyntax()

    del __HelpSyntax
    del inspect, string, sys


try:
    import sys
except ImportError as err:
    pass
else:
    class __Prompt(object):
        """Maintain dictionary of output history.

        If '__history__' is a dict, store output results using one up number
        keys. Prompt is changed to identify how many keys have been populated.
        """

        def __init__(self, prompt='>>> '):
            self.counter = 0
            self.prompt = prompt

        def __radd__(self, left):
            return str(left) + str(self)

        def __str__(self):
            if self.is_history():
                self.update_history()
                return 'H[{0}] {1}'.format(self.counter, self.prompt)
            return self.prompt

        def is_history(self):
            return isinstance(globals().get('__history__'), dict)

        def update_history(self):
            try:
                if (_ is not __history__ and
                        _ is not __history__.get(self.counter)):
                    self.counter += 1
                    __history__[self.counter] = _
                    return True
            except NameError:
                pass
            finally:
                return True

    # __history__ = {0: None}
    __history__ = None
    sys.ps1 = __Prompt()

    del __Prompt
    del sys