#!/usr/bin/env python
"""
cheat.py -- cheat allows you to create and view interactive cheatsheets on the
            command-line. It was designed to help remind *nix system
            administrators of options for commands that they use frequently,
            but not frequently enough to remember. 

        Copyright (C) 2013, Chris Lane

        This program is free software: you can redistribute it and/or modify
        it under the terms of the GNU General Public License as published by
        the Free Software Foundation, either version 3 of the License, or
        (at your option) any later version.

        This program is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        GNU General Public License for more details.

        You should have received a copy of the GNU General Public License
        along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""

import os
import sys
import argparse
import subprocess

DEFAULT_CHEAT_DIR = os.environ.get('DEFAULT_CHEAT_DIR') or \
                    os.path.join(os.path.expanduser('~'), '.cheat')
USE_PYGMENTS      = False

# NOTE remove this check if it is confirmed to work on windows
if os.name == 'posix' and 'CHEATCOLORS' in os.environ:
    try:
        from pygments import highlight
        from pygments.util import ClassNotFound
        from pygments.lexers import get_lexer_for_filename, TextLexer
        from pygments.formatters import TerminalFormatter
        USE_PYGMENTS = True
    except ImportError:
        pass

def cheat_directories():
    "Assembles a list of directories containing cheatsheets."
    default_directories = [DEFAULT_CHEAT_DIR]
    try:
        import cheatsheets
        default_directories.append(cheatsheets.cheat_dir)
    except ImportError:
        pass

    default = [default_dir for default_dir in default_directories
               if os.path.isdir(default_dir)]

    if 'CHEATPATH' in os.environ and os.environ['CHEATPATH']:
        return [path for path in os.environ['CHEATPATH'].split(os.pathsep)
                if os.path.isdir(path)] + default
    else:
        return default


def cheat_files(cheat_directories):
    "Assembles a dictionary of cheatsheets found in the above directories."
    cheats = {}
    for cheat_dir in reversed(cheat_directories):
        cheats.update(dict([(cheat, cheat_dir)
                            for cheat in os.listdir(cheat_dir)
                            if not cheat.startswith('.')
                            and not cheat.startswith('__')]))
    return cheats

def edit_cheatsheet(cheat, cheatsheets):
    "Edit a pre-existing cheatsheet."
    if cheat not in cheatsheets:
        print ('No cheatsheet found for "%s"' % cheat)
        ans = raw_input('Create cheatsheet for "%s" (Y/N)? ' % cheat)
        if ans.lower() in ['y', 'yes']:
            create_cheatsheet(cheat, cheatsheets)
        else:
            exit()

    subprocess.call([os.environ['EDITOR'],
                    os.path.join(cheatsheets[cheat], cheat)])
    exit()

def create_cheatsheet(cheat, cheatsheets):
    "Create a new cheatsheet."
    if cheat in cheatsheets:
        print ('Cheatsheet "%s" already exists...' % cheat)
        ans = raw_input('Would you like to edit cheatsheet for "%s" (Y/N)? ' % cheat)
        if ans.lower() in ['y', 'yes']:
          edit_cheatsheet(cheat, cheatsheets)
        else:
          exit()

    import cheatsheets as cs

    # Attempt to write the new cheatsheet to the user's ~/.cheat dir if it
    # exists. If it does not exist, attempt to create it.
    if os.access(DEFAULT_CHEAT_DIR, os.W_OK) or os.makedirs(DEFAULT_CHEAT_DIR):
        subprocess.call([os.environ['EDITOR'],
                        os.path.join(DEFAULT_CHEAT_DIR, cheat)])

    # If the directory cannot be created, write to the python package
    # directory, though that will likely require the use of sudo
    else:
        subprocess.call([os.environ['EDITOR'],
                        os.path.join(cs.cheat_dir, cheat)])

    exit()

def main():
    # assemble a keyphrase out of all params passed to the script
    keyphrase  = ' '.join(sys.argv[1:])
    cheat_dirs = cheat_directories()

    # verify that we have at least one cheat directory
    if not cheat_dirs:
        error_msg = 'The {default} dir does not exist or the CHEATPATH var is not set.'
        print >> sys.stderr, error_msg.format(default=DEFAULT_CHEAT_DIR)
        exit()

    # list the files in the ~/.cheat directory
    cheatsheets = cheat_files(cheat_dirs)

    # print help if requested
    if keyphrase.lower() in ['', 'cheat', 'help', '-h', '-help', '--help']:
        print ("Usage: cheat [OPTIONS] <keyphrase>")
        print ("Examples:\n")

        print ("To look up 'tar':")
        print ("cheat tar\n")

        print ("To look up 'git commit' (a subcommand):")
        print ("cheat git commit\n")

        print ("To create a cheatsheet for 'foo':")
        print ("cheat -c foo\n")

        print ("To edit the cheatsheet for 'foo':")
        print ("cheat -e foo\n")

        print ("Available keyphrases:")
        max_command = max([len(x) for x in cheatsheets.keys()]) + 3
        print ('\n'.join(sorted(['%s [%s]' % (key.ljust(max_command), value)
                                for key, value in cheatsheets.items()])))
        exit()

    # create/edit option
    option = sys.argv[1].lower()
    if option in ['-e', '--edit', '-c', '--create']:
        # make sure EDITOR env variable is set and that at least
        # 3 arguments are given
        if 'EDITOR' not in os.environ:
            print('In order to use "create" or "edit" you must set your '
                  'EDITOR environment variable to your favorite editor\'s path')
            exit()
        elif len(sys.argv) < 3:
            print ('Must provide a cheatsheet to edit/create')
            exit()

        # if the user wants to edit a cheatsheet
        if option in ['-e', '--edit']:
            edit_cheatsheet(' '.join(sys.argv[2:]), cheatsheets)

        # if the user wants to create a cheatsheet
        elif option in ['-c', '--create']:
            create_cheatsheet(' '.join(sys.argv[2:]), cheatsheets)

    # list cheat directories and exit
    if option in ['-d', '--cheat_directories']:
        print('\n'.join(cheat_directories()))
        exit()

    # print the cheatsheet if it exists
    if keyphrase in cheatsheets:
        filename = os.path.join(cheatsheets[keyphrase], keyphrase)
        if USE_PYGMENTS:
            pretty_print(filename)
        else:
            with open(filename) as istream:
                for l in istream:
                    sys.stdout.write(l)

    # if it does not, say so
    else:
        print ('No cheatsheet found for %s.' % keyphrase)


def pretty_print(filename):
    try:
        if os.path.splitext(filename)[1]:
            lexer = get_lexer_for_filename(filename)
        else:
            # shell is a sensible default when there is no extension
            lexer = get_lexer_for_filename(filename + '.sh')

    except ClassNotFound:
        lexer = TextLexer()

    with open(filename) as istream:
        code = istream.read()

    fmt = TerminalFormatter()
    highlight(code, lexer, fmt, sys.stdout)


if __name__ == '__main__':
    main()